Journal of Neuro-Ophthalmology, December 1997, Volume 17, Issue 4

Neuro-Ophthalmology of the Pregeniculate Afferent Visual System

Journal of Neuro- Ophthalmology 17( 4): 267- 277, 1997. © 1997 Lippincott- Raven Publishers, Philadelphia Neuro- Ophthalmology of the Pregeniculate Afferent Visual System: Part I November 1996- April 1997 Laura J. Balcer, M. D. and Steven L. Galetta, M. D. In neuro- ophthalmology, as in other specialties, the volume and variety of published literature continues to increase with each passing year. This year has been no exception. This review, now published semi- annually, will discuss developments in neuro- ophthalmologic di­agnosis and therapy related to the pregeniculate afferent visual system. The following material covers the period of November 1996 through April 1997. EVALUATION OF THE AFFERENT VISUAL SYSTEM Advances in MR imaging have continued to enable neuro- ophthalmologists to examine, in a noninvasive manner, the characteristics of a variety of disease pro­cesses. Recent advances in the use of MRI, as applied to the optic nerve, chiasm, and lateral geniculate nuclei, will be discussed in upcoming sections of this review. However, as in the case of any technology, it is equally important to recognize its potential limitations. Borges and colleagues ( 1) demonstrated that failure of fre­quency- selective fat suppression ( FATSAT) in MR im­aging may produce artifacts which mimic orbital disease. To further characterize these artifacts, FATSAT images from two phantom simulators of orbital anatomy and one normal volunteer were compared with similar imaging studies of three patients. Two of the patients had no evidence of orbital disease clinically; the other had bi­opsy- confirmed orbital inflammatory disease and clinical signs of proptosis and optic neuropathy. Areas of asym­metric orbital signal hyperintensity, consistent with fail­ure of fat suppression, were seen following imaging of the two phantoms, the normal volunteer, and the two clinically unaffected patients. This artifact was localized Manuscript accepted July 11, 1997; accepted August 20, 1997. From the division of Neuro- Ophthalmology, Departments of Neu­rology and Ophthalmology, Hospital of the University of Pennsylvania, Scheie Eye Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA Address correspondence to: Dr. Steven L. Galetta, Department of Neurology, 3 West Gates, 3400 Spruce Street, Philadelphia, PA 19104, USA. This work was supported in part by grant EY00351- 01 from the National Eye Institute, Bethesda, Maryland ( Dr. Balcer). primarily at air- fat interfaces, demonstrating heteroge­neous signal. Underlying orbital structures were ob­scured but did not appear abnormal. In contrast, FAT­SAT imaging of the patient with biopsy- confirmed or­bital inflammatory disease showed diffuse hyperintensity of the orbital fat as well as abnormal enlargement of the ocular muscles. In the use of FATSAT MRI, the authors ( 1) recommend careful correlation of imaging abnor­malities with clinical findings. The use of additional fat suppression techniques and alternative head imaging angles may also be helpful for avoiding the misinterpre­tation of FATSAT signal abnormalities. While some imaging abnormalities may represent ar­tifact in otherwise normal individuals, subtle neuro-ophthalmologic examination findings may indicate nor­mal physiologic variation in the absence of underlying disease. Kawasaki et al. ( 2) used infrared pupillography to demonstrate that patients with normal visual function ( as measured by Snellen acuity, stereo testing, and auto­mated perimetry) may have a small but persistent affer­ent pupillary defect ( APD) of up to 0.3 log units in mag­nitude. Eight of 17 patients in the study had an APD in the same eye at each of four separate visits during a three- year period. Other patients demonstrated random fluctuations in the magnitude of the APD; the side of the APD changed between visits in nine patients. No corre­lation was detected between APD magnitude ( in log units) and interocular difference in automated perimetry mean deviation measured at the same visit. The results of this study ( 2) indicate that infrared pupillometry tech­niques may detect subtle abnormalities in patients with normal afferent visual examinations. In the absence of other clinical or historical indicators of visual dysfunc­tion, such findings likely represent benign physiologic variation. As indicated by Kawasaki and colleagues ( 2), further investigations using the infrared pupillometer may lead to the development of an automated alternating light (" swinging flashlight") test for use in neuro-ophthalmologic practice. The Farnsworth- Munsell 100- Hue test ( FM- 100) is a test of color vision for which practical clinical use has been limited due to the length of time required for its administration ( 3). To determine whether a subset of the FM- 100 test could be of practical use in the diagnosis 267 268 BALCER AND GALETTA and follow- up of patients with optic nerve disorders, Nichols et al. ( 3) performed both a prospective and ret­rospective investigation of patients with optic neuritis, Graves' ophthalmopathy, and pseudotumor cerebri. In addition to the 136 patients studied ( 106 retrospectively, 30 prospectively), 74 healthy volunteers were tested in order to calculate sensitivity and specificity of the FM- 100 for detection of optic neuropathy. For any given specificity, two possible 21- chip subtests ( chips num­bered 22- 42 and those numbered 70- 6) were found to have sensitivities nearly identical to that of the full FM- 100 test in this group of patients. Since the chips num­bered 22- 42 correspond fortuitously to the second box of four, the authors ( 3) concluded that the use of this second box alone may provide a sensitive and practical subtest for monitoring color vision in patients with optic neu­ropathy. Further prospective studies under controlled conditions similar to those used by Nichols and cowork­ers ( 3) may confirm these findings in patients with vari­ous forms of optic neuropathy. NEURO- OPHTHALMOLOGY AND THE RETINA Retinal dysfunction and optic neuropathy in patients with HIV infection are often associated with viral or other opportunistic infections. Iragui et al. ( 4) demon­strated that anterior visual pathway dysfunction may also be present at a subclinical level in HIV- infected patients, even in the absence of known infection or funduscopic abnormalities. Three groups of patients were studied us­ing transient and steady- state pattern electroretinograms ( PERG) and pattern- reversal visual evoked potentials ( PVEP). Group 1 consisted of 21 HIV- negative controls, group 2 had 16 HIV- positive patients with CD4 count 3= 200/ mL, and group 3 had 17 HIV- positive patients with CD4 count < 200/ mL. None of the patients had vi­sual symptoms; those with ophthalmologic findings sec­ondary to opportunistic infection were excluded. Tran­sient PERG amplitudes were reduced in each of the two HIV- positive groups compared with the control group ( by 26% and 18%, respectively), and the PVEP P100 latency was significantly delayed in the HIV- positive group with CD4 count < 200 compared with the high CD4 count and control groups. Within the two groups of HIV- positive patients, no significant differences were observed between a group of seven eyes with cotton­wool spots and a group of 23 eyes with no funduscopic abnormalities with respect to any PERG or PVEP mea­sure. This study, therefore, provided evidence of sub­clinical retinal dysfunction in HIV- infected patients with both high and low CD4 counts. Optic nerve and retro-chiasmal involvement were also demonstrated in the group with CD4 counts < 200/ mL, as indicated by pro­longation of the PVEP P100 latency. The authors ( 4) suggest that retinal microangiopathy and axonal loss as­sociated with HIV infection, although presently asymp­tomatic may, in the future, be associated with clinically apparent visual dysfunction as life spans continue to in­crease for patients with HIV. Similar findings were ob­tained by Latkany and coworkers ( 5) using electroretin-ography in three groups of patients with varying stages of HIV infection. The diagnosis and treatment of ocular disease caused by viral pathogens other than cytomegalovirus ( CMV) have been the topic of several reports and reviews ( 6- 8). To date, the second largest series of patients with vari­cella zoster virus ( VZV) retinitis and AIDS was pub­lished by Moorthy and colleagues ( 6). These investiga­tors performed a retrospective record review of 20 pa­tients from six centers, examining in detail the clinical features at presentation, the type of systemic antiviral therapy used, and visual acuities at the end of the follow-up period. Final visual acuities, after a median follow- up of six months ( range 1.3- 26 months), were significantly better in the groups of patients who received combina­tion ganciclovir and foscarnet therapy ( p = 0.0003) or ganciclovir alone ( p = 0.0054) when compared with those receiving either acyclovir or foscarnet mono­therapy. Importantly, baseline visual acuities among these treatment groups were not statistically significantly different. Based on these results, Moorthy and colleagues ( 6) suggest that patients with VZV retinitis and AIDS should receive aggressive treatment with systemic anti­viral therapy, and that acyclovir alone may not be as effective as other regimens in this group of patients. Friedlander et al. demonstrated that an optic neurop­athy secondary to VZV may precede the onset of retinitis in patients with AIDS ( 7). All three patients in this series presented with varicella zoster dermatitis and had been treated with acyclovir prior to the onset of optic nerve dysfunction and subsequent retinitis. The authors ( 7) suggest consideration of VZV optic neuropathy as a cause of unexplained visual loss in immunocompromised patients, emphasizing the importance of a thorough evaluation in this setting. The potential impacts of the varicella zoster vaccine and new antiviral therapies on ocular disease related to VZV was recently reviewed by Pepose ( 8). He discussed the incidence and demographics of VZV infection, uses of the VZV vaccine, and the effectiveness of newer an­tiviral agents, including valacyclovir, famciclovir, sorivudine, and brivudin. Pepose ( 8) stresses the need for further large, randomized trials to determine the effec­tiveness of new antivirals vs. acyclovir. He also cautions that thorough knowledge and judicious use of such an­tiviral therapies will be necessary for many years to come, even in the setting of widespread VZV vaccina­tion. An unusual case of a different sort of retinopathy was presented by Lang and Kuba ( 9). Their patient, a 30- year- old otherwise healthy man, developed visual loss and intraretinal hemorrhages after a two- week excursion to the Argentine Andes. High- altitude retinopathy, thought to result from hemoconcentration, hypoxia, and consequent impairment of retinal microcirculation, was diagnosed. The patient was treated with isovolemic he-modilution, pentoxifylline, and aspirin therapy. Accord­ing to the authors ( 9), the potential risks of high altitude complications may be reduced by maintaining adequate J Neuro- Ophthalmol, Vol. 17, No. 4, 1997 PREGENICULATE AFFERENT VISUAL SYSTEM: PART I 269 hydration and by gradual ascent and descent to and from one's destination. In their report of two patients with critical carotid artery stenosis, Levin and coworkers ( 10) remind us that the hazards of eating a large noon- time meal may extend beyond the risk of falling asleep during an afternoon conference. One of the patients, a 59- year- old woman with a history of diabetes, hypertension, and cigarette smoking experienced daily episodes of transient visual loss in the left eye. The visual symptoms occurred con­sistently one hour after lunch, and were often accompa­nied by weakness and numbness of the right arm. Carotid angiography confirmed a 90% left internal carotid artery stenosis; the episodes resolved following carotid endar-terectomy. Both patients described a " blotchy," scoto-matous pattern of visual loss. This was consistent, ac­cording to the authors ( 10), with retinal hypoperfusion as a rare manifestation of postprandial hypotension. Abnormalities of orbital circulation hemodynamics in the setting of carotid artery stenosis were examined by Mawn et al. ( 11) in a color doppler imaging study of 24 patients. All of the patients had signs of ocular ischemia or had experienced ipsilateral transient monocular blind­ness or visual loss. Compared with those of 53 healthy patients, mean systolic blood flow velocities in the pa­tients with carotid stenosis were significantly reduced in the central retinal artery ( p < 0.001), posterior ciliary artery ( p = 0.006), and ophthalmic artery ( p = 0.009). Mean systolic flow velocities improved in 12 patients following carotid endarterectomy, but were not signifi­cantly increased from those obtained preoperatively. In a similar study using color doppler imaging, Riihelainen and colleagues ( 12) found that carotid endarterectomy significantly increased the peak systolic and end diastolic flow velocities in the central retinal artery ( p = 0.027 and p = 0.023) and ophthalmic artery ( p = 0.034 and p = 0.047) compared with preoperative values in 17 con­secutive patients with 80- 90% internal carotid artery ste­nosis. In a study of repeatability and interobserver agreement by Quaranta et al. ( 13), color doppler imaging was dem­onstrated to be a reliable technique for evaluation of the orbital circulation. These are key issues in the evaluation of any diagnostic modality, particularly for its applica­tion to clinical settings and anatomic locations beyond current use. Doppler techniques have recently been used to investigate blood flow velocities in the orbital circu­lations of chronic smokers ( 14) and to demonstrate in­creased vascular resistance to venous outflow in patients with central retinal vein occlusion ( 15). THE OPTIC NERVE Since previous studies have suggested alterations in ocular blood vessel hemodynamics in patients with low tension glaucoma, Goh et al. ( 16) used color doppler imaging techniques to evaluate patients with non-gluacomatous, and non- ischemic optic neuropathies to determine whether optic atrophy itself could be associ­ated with such abnormalities. Ten patients ( 19 eyes) with compressive, inflammatory, toxic, or hereditary optic neuropathies were studied; the results of orbital color doppler imaging were compared with those of a control group ( 10 patients, 20 eyes). Mean peak systolic flow velocities and end diastolic velocities in the central reti­nal, short posterior ciliary, and ophthalmic arteries were not significantly different between the two groups. How­ever, the authors ( 16) emphasize that the small sample size in this study may have likely reduced the statistical power to detect such differences. Although limited con­clusions can be drawn from this investigation, the results suggest that optic atrophy of non- glaucomatous, non­ischemic origin may not alter ocular circulation hemo­dynamics. Larger studies are needed to address the pos­sibility of vascular abnormalities in patients with low tension glaucoma vs. those with other optic neuropathies of non- ischemic origin. Nonarteritic anterior ischemic optic neuropathy ( NAION) has been the subject of numerous recent in­vestigations. Hattenhauer and colleagues ( 17) reviewed medical records from the Rochester Epidemiology Proj­ect in Olmsted County, Minnesota, to determine the in­cidence of acute NAION in that area. Cases were defined as those patients, 50 years of age or older, who had unilateral sudden visual loss or a new optic nerve- type visual field defect ( or both), and optic disc edema. Data from 1981 through 1990 revealed 22 cases of acute NAION in 21 patients. The age- and sex- adjusted inci­dence rate was 10.2/ 100,000 individuals ( 95% CI = 6.0- 14.5). Characteristics of this group at the time of diag­nosis included a median age of 72 years ( range 50- 87), a male to female ratio of approximately 1: 1, and a mean visual acuity of 20/ 200 ( range 20/ 20 to light perception). Although the most frequently noted type of visual field defect was altitudinal ( 10/ 22 eyes examined), only half of these were inferior altitudinal defects. The baseline clinical characteristics of patients with NAION were also reviewed by the Ischemic Optic Neu­ropathy Decompression Trial Study Group ( 18). Demo­graphic, historical, and examination data was obtained from 258 patients who were eligible for randomization in the trial and from 162 patients who were eligible for follow- up but not randomization based on visual acuity criteria ( only those with acuity of 20/ 64 or worse were randomized). Of this group of patients, 62% were men and the mean age was 66 years. Forty- two percent re­ported a history of hypertension and 24% reported dia­betes. Higher prevalences of these disorders were ob­served in the randomized vs. non- randomized group, al­though the difference was statistically significant only for hypertension ( 50.8% vs. 40.6%, p < 0.05). Ten per­cent of patients reported pain. The range of visual acu­ities noted was similar to that reported in the Olmsted County incidence study; ( 17) 49% of patients had 20/ 64 or better at baseline, while 34% had 20/ 200 or worse. The authors ( 18) point out that, although clinical trial participants represent a select group of patients, this baseline data was the first to be obtained from a large J Neuro- Ophthalmol, Vol. 17, No. 4, 1997 270 BALCER AND GALETTA prospective study of patients with NAION. As observed previously, hypertension and diabetes mellitus are preva­lent in patients greater than 50 years of age with this disorder. The broad spectrum of clinical severity which may be seen in patients with NAION was emphasized by Gordon et al. ( 19) in a report of two patients with asymptomatic optic disc edema. One patient, a 53- year- old man, was noted to have focal optic disc edema in the left eye three years following an episode of NAION on the right. Vi­sual acuity, color vision, and kinetic perimetry were nor­mal in the left eye and remained unchanged over a 1- year period of follow- up. The second patient was a 77- year-old man in whom asymptomatic left optic disc swelling was discovered at a routine visit five months following cataract surgery. A complete evaluation including MRI and static full field threshold perimetry revealed only mild enlargement of the blind spot on the left. The au­thors ( 19) discuss the possibility of diabetic papillopathy as an alternative diagnosis for the second patient. How­ever, they also emphasize that the pathophysiologic mechanisms for NAION and diabetic papillopathy may be similar, and that a process of graded ischemia may be responsible for the variations observed in the clinical presentation of NAION. Gordon et al. ( 19) reemphasized that nonarteritic an­terior ischemic optic neuropathy may occur sequentially in the fellow eye of up to 25- 50% of patients within a five- year period. Final visual function in the fellow eyes of patients with sequential or bilateral NAION was stud­ied by WuDunn and coworkers ( 20). They reviewed the records of 31 patients with bilateral consecutive NAION for several visual function parameters, including Snellen acuity ( converted to logMAR units for statistical analy­sis), color vision as measured by Richmond pseudo-isochromatic plates, and Humphrey visual field mean deviation ( available for 21 patients). Data for these mea­sures was obtained from the latest follow- up examina­tion, usually several months following the onset of symp­toms in the second eye. Patient demographics were simi­lar to those observed in the investigations outline above; ( 17- 19) the the mean age at first episode was 60 years, and hypertension or diabetes were reported in 48% of cases. In terms of logMAR visual acuity, final visual function in the second eye was significantly better than that in the first for patients over 55 years of age ( p = 0.04). This difference achieved higher degrees statistical significance with increasing 5- 10 year age increments. For the group of patients overall, however, no significant differences in final visual outcome were noted between the first and second eyes affected. There was no corre­lation between the two eyes with respect to pattern of visual field loss. It was concluded ( 20) that, except for the possibility of better visual acuity in the affected sec­ond eye for older patients, visual function and pattern of visual field loss in the initially involved eye cannot be used reliably to predict fellow eye outcome in patients with bilateral sequential NAION. To begin to answer the question of whether or not aspirin therapy is effective in reducing the risk of NAION in the fellow eyes of patients following a first episode, Beck et al. ( 21) performed a retrospective co­hort study of 431 patients. The aspirin group consisted of 153 patients, 75 of whom were already taking aspirin at the time of the first episode of NAION, and 78 for whom aspirin was prescribed immediately following diagnosis. There were 278 patients in the non- aspirin group. Records were reviewed for the subsequent development of NAION in the fellow eye, and follow- up times to this endpoint or to the date of the last completed visit were determined. Using the Kaplan- Meier method, cumulative probabilities of developing NAION in the fellow eye were calculated and compared for the aspirin and non-aspirin groups. At two years of follow- up, the cumulative probability was lower in the aspirin group ( 7%) vs. the non- aspirin group ( 15%); this difference was no longer present at five years, with cumulative probabilities of 17% in the aspirin group and 20% in the non- aspirin group. The corresponding rate ratios for the development of fellow eye NAION in the aspirin vs. non- aspirin groups were 0.43 ( 95% CI = 0.19- 0.92) at two years, and 0.68 ( 95% CI = 0.36- 1.26) for the five- year follow up period. Interestingly, the overall five- year risk was 19% ( 12% if it was assumed that none of the patients with incomplete follow- up developed a second episode), much lower than the previously reported 24^ 18% risk. As stated by the authors ( 21), the results indicate a pos­sible benefit of aspirin in preventing fellow eye NAION early in the course of follow- up, but no observed benefit at five years was found. Beck et al. ( 21) appropriately urged caution in the interpretation of studies regarding therapy for which data are obtained retrospectively. However, they also suggest that the requirements for a very large sample size and the high baseline prevalence of daily aspirin use in this age group will limit the fea­sibility of a randomized trial of aspirin therapy for NAION. Retrobulbar ischemic optic neuropathy in elderly pa­tients may be caused by giant cell arteritis, but the pos­sibility of a compressive lesion must also be included in the differential diagnosis. This is emphasized in a case report by Slavin and Liebergall ( 22), with discussion by Dr. Steven Newman. They presented a 61- year- old man with a three- day history of progressive visual loss in the right eye accompanied by low grade fever and a ' ' pres­sure' ' sensation over the right eye and temporal region. Visual acuity in the affected eye was hand motion, and Goldmann perimetry revealed a central scotoma with an island of remaining vision inferiorly. Funduscopic ex­amination was normal. A sedimentation rate was 10 mm/ hour. MRI of the brain and subsequent endoscopic bi­opsy confirmed the presence of a spenoid sinus mu-copyocele encroaching upon the optic canal. Slavin et al. ( 22) presented a thorough discussion of the differential diagnosis and evaluation of retrobulbar optic neuropathy in the elderly patient, emphasizing consideration of both giant cell arteritis and compressive lesions. A recent study by Hayreh and colleagues ( 23) evalu- J Neuro- Ophthalmol, Vol. 17. No. 4, 1997 PREGENICULATE AFFERENT VISUAL SYSTEM: PARTI 271 ated the potential usefulness of several serologic tests, clinical signs, and symptoms as potential predictors of a positive temporal artery biopsy in patients with giant cell arteritis. They collected data from 363 patients who had undergone temporal artery biopsy for suspected giant cell arteritis from 1973 to 1994. A positive biopsy result was obtained in 106 patients, while 257 patients had a negative biopsy. Bilateral biopsies were performed in 76 patients. Significant odds ratios for positive vs. negative temporal artery biopsy were obtained for jaw claudica­tion ( 9.1, 95% CI = 5.0- 16.7, p < 0.0001), neck pain ( 3.4, 95% CI = 1.4- 8.3, p = 0.0085), ESR > 107 mm/ hour ( 2.7, 95% CI = 1.2- 5.9, p = 0.0106), age 3* 75 years ( 2.0, 95% CI = 1.2- 3.4, p = 0.0106), and C-reactive protein > 2.45 mg/ dl ( 3.2, 95% CI = 1.2- 8.6, p = 0.0208). The authors ( 23) conclude that in this group of patients ( all of whom received temporal artery biopsy for suspicion of giant cell arteritis) clinical features of jaw claudication, neck pain, advanced age, and elevated ESR and C- reactive protein levels were suggestive of biopsy- proven disease. Using data from control subjects with NAION and retinal vein occlusion in the absence of systemic disease, both ESR and C- reactive protein were found to have high sensitivities and specificities for giant cell arteritis. In a related editorial, Weyand and Bartley ( 24) discuss the diagnosis and immunologic pathogen­esis of giant cell arteritis, emphasizing the possibility of falsely- negative temporal artery biopsies in these pa­tients. An unusual case of biopsy- proven giant cell ar­teritis presenting with facial swelling and ipsilateral AION ( 25) reminds us that patients with giant cell ar­teritis may present with unusual as well as typical clini­cal manifestations. More than five years following its completion, results from the Optic Neuritis Treatment Trial ( ONTT) con­tinue to emerge. At the same time, assessment of vision-and health- related quality of life has become an ex­tremely important element in the evaluation of patients in clinical trials. For example, the impact of blurred vision on health- related quality of life was recently examined by Lee and coworkers ( 26) using the SF- 36 Health Sur­vey. From patients in the ONTT, data on visual symp­toms and vision- specific quality of life was presented by Cleary et al. ( 27). A 17- item self- administered question­naire was completed by 382 ( 87%) of 438 patients in the ONTT who completed the six- month study visit ( 438/ 457 randomized patients). Detailed questions regarding self- reported visual function and performance of daily activities such as night and day vision, color vision, changes in vision with heat and exercise, and overall assessment of vision, were included. Patients were also asked to evaluate their experiences related to participa­tion in the ONTT itself, including those involving testing and treatment. The questionnaire, published as an appen­dix to the article, appears to be very complete and pa­tient- friendly; many questions were accompanied by clarifying explanations. With respect to perceived vision in the affected eye, Lee et al. ( 27) found that 56% of the ONTT patients questioned ( 215/ 382) reported their vision to be " some­what worse" or " much worse" than it had been prior to the episode of optic neuritis. Thirty- five percent reported that their vision was " about the same," 9% said it was " somewhat better" or " much better." Of the 215 pa­tients who perceived their vision in the affected eye to be " somewhat worse" or " much worse," 20% had normal test results at the six- month visit, including visual acuity, contrast sensitivity, color vision, and visual field mean deviation. Only 20% of the same group had abnormal results on all four tests which, according to the authors ( 27), indicates that some subtle abnormalities perceived by patients may not always be detectable clinically. For most questions ( 26/ 28) regarding visual tasks in day- to­day living, a majority of patients reported " no differ­ence' ' or improvement of vision compared with that ex­perienced prior to optic neuritis. Overall, 63% reported that their vision in the affected eye had not recovered to normal, but indicated that their visual deficits were mild. Interestingly, only 14% of patients reported a severe or moderate problem with symptoms related to Uhthoffs phenomenon. Magnetic resonance imaging continues to be an ex­tremely useful tool for the evaluation of patients with optic neuritis and multiple sclerosis ( MS). The prognos­tic value of MRI in monosymptomatic optic neuritis was assessed by Dunker and Wiegand ( 28). Twenty- two pa­tients with acute optic neuritis were examined using MRI short- time inversion recovery ( STIR) sequences of the brain and orbits. Tests of visual function were also ob­tained within one to five days following the onset of visual loss or pain; these included Snellen visual acuity, contrast sensitivity, color vision, static and kinetic pe­rimetry, and pattern shift visual- evoked responses. Pa­tients were re- examined using identical MRI and clinical testing techniques between 2.5 and 8 years following the initial episode. The length of the area of increased signal intensity along the optic nerve was measured in millime­ters using the MRI sequences. The location of signal abnormality ( intraorbital vs. intracanalicular vs. both) was also determined. These MRI characteristics at the initial examination were correlated with those at follow-up as well as with the initial and final measurements of visual function. Important findings of this study included a correlation between length of optic nerve signal inten­sity abnormality and visual recovery. Those patients with less than 17.5 mm of optic nerve involvement had an excellent chance of attaining a visual acuity of at least 20/ 25 ( p < 0.005). Length of signal abnormality greater than 17.5 mm and intracanalicular location were both highly correlated with partial visual recovery ( visual acu­ity less than 20/ 25 and or deficits in contrast sensitivity, color vision, or visual field). This investigation ( 28) sug­gests that MRI characteristics documenting the extent of optic nerve involvement in acute monosymptomatic op­tic neuritis may be useful in predicting the degree of visual recovery. Nearly all of the 22 patients in this study recovered vision to at least 20/ 30 or better ( 1 patient was 20/ 50 and another < 20/ 400 at follow up), and all had J Neuro- Ophthalmol, Vol. 17, No. 4, 1997 272 BALCER AND GALETTA received oral steroid therapy ( having been treated prior to publication of the ONTT in 1992). MRI findings of optic nerve signal abnormality and enhancement are common findings in patients with acute optic neuritis. Optic nerve enlargement is unusual but may occur in such patients, as demonstrated in a report by Cornblath and Quint ( 29). Both of the patients de­scribed were children who had experienced progressive visual loss over several days with associated pain on eye movement. Since diffuse enlargement of the optic nerve was noted on coronal MRI of the orbits, a diagnosis of optic nerve glioma was considered. However, both pa­tients had spontaneous visual recovery over weeks to months, with resolution of the nerve enhancement and enlargement. The authors ( 29) reviewed the previous lit­erature concerning optic nerve enlargement in optic neu­ritis, and discussed the differential diagnosis and appro­priate orbital MR imaging techniques. Koudriavtseva et al. ( 30) emphasized that the number and volume of gadolinium enhancing MRI lesions at baseline can be a strong predictor of future clinical course and MRI activity in patients with relapsing-remitting MS. Sixty- eight patients with clinically definite relapsing- remitting MS who were participants in an open crossover study of recombinant human interferon ( 3- la were examined at baseline and monthly for six months using gadolinium enhanced MRI. During the same pe­riod, patients received neurologic examinations at the time of each clinical exacerbation. Consistent with pre­vious studies, enhancing lesion number and volume at baseline was significantly associated with the develop­ment of new enhancing lesions during the six month follow- up period ( p < 0.0001), and with the total number of new lesions which accumulated during follow- up as assessed by T2- weighted imaging ( p < 0.0001). Those patients with three or more enhancing lesions at baseline had a higher probability of developing new lesions on T2- weighted imaging ( 100% vs. 60- 68%) during the 6- month period, and also had a higher mean number of new enhancing lesions per month ( 5.1 vs. 1.0- 1.9). However, the probability of clinical relapse in this group was simi­lar to that observed for patients with one or two enhanc­ing lesions at baseline. This particular relationship, be­tween the presence of three or more enhancing lesions and the probability of clinical relapse, may have been limited by the short ( six- month) duration of follow- up. In addition, it is known that clinical activity, as measurable by physical examination or patient self- report, does not always correlate with the degree of MRI activity. Jacobs et al. ( 31) correlated the clinical, MRI, and cerebrospinal fluid ( CSF) findings in a group of patients with monosymptomatic optic neuritis, and determined that both MRI and CSF characteristics may be predictive of the development of clinically definite MS. Of the 74 patients evaluated and followed for a mean time interval of 5.6 years, 21 ( 28%) developed clinically definite MS, 16 ( 76%) of whom had abnormal MRI examinations at presentation. Twenty- six patients had abnormal MRI scans initially but did not develop clinically definite MS during the follow- up period. Kaplan- Meier analysis of time to development of clinically definite MS demon­strated a significant relationship between initial abnor­mal MRI and MS development ( p = 0.05). These find­ings are consistent with those of the ONTT, confirming that an abnormal MRI remains a powerful predictor of MS risk in patients with monosymptomatic optic neuri­tis. Furthermore, the initial presence of increased CSF IgG total synthesis ( p = 0.03) or increased IgG with oligoclonal bands ( p = 0.02) were also associated with MS risk. Oligoclonal bands in the absence of increased IgG were not significantly predictive; the same was true for an abnormal overall CSF profile. Frederiksen and Whitaker ( 32) also examined CSF in patients with acute monosymptomatic optic neuritis and found that highly elevated levels of a myelin basic protein- like material were observed most often in patients with decreased vi­sual acuities or abnormal MRI imaging. In an investigation of HLA typing in patients with acute optic neuritis, Fredericksen et al. ( 33) showed that the frequencies of several HLA alleles were similar in those with monosymptomatic optic neuritis vs. optic neu­ritis with clinically definite MS. This provided evidence, according to the authors ( 33), that monosymptomatic op­tic neuritis and optic with clinically definite MS do not represent immunogenetically distinct disease processes. A new syndrome involving optic neuritis and MS was described by Vernant and colleagues ( 34). They reported the clinical, laboratory, and MRI findings of eight Anti-llean women with recurrent optic neuromyelitis and en-docrinopathies. All of these patients had documented clinically definite MS, were HTLV- I negative, and had demyelinating lesions involving only the optic nerves and spinal cord. Myelopathic signs and symptoms were similar to those of syringomyelia, with dissociated sen­sory loss and autonomic abnormalities. In addition, all patients had significant disturbances of endocrine func­tion, including amenorrhea, galactorrhea, diabetes insipi­dus, hypothyroidism, and hyperphagia. None had cere­bral white matter lesions on MRI examination; however, cavitation of the cervical spinal cord and optic nerve and pituitary enhancement were noted. Autopsy findings in one patient confirmed the absence of granulomatous dis­ease and revealed demyelination in the optic tracts and spinal cord. The authors ( 34) believe that this syndrome, characterized by rapid progression to blindness and paraplegia, is likely to be distinct from Devic's syndrome and may have a post- infectious etiology. Infectious etiologies affecting the optic nerve may also be demonstrable by MR imaging, as illustrated in a photo essay by Frohman and Wolansky ( 35) of syphilitic optic neuritis. They presented the MRI and fundus findings of a 42- year- old woman with progressive monocular visual loss and brow pain. Marked optic disc edema and vitre­ous cells were noted. Enhancement of the optic nerve and orbital fat were demonstrated on orbital MR images with fat suppression. The RPR ( rapid plasma reagin test for syphilis) was positive ( 1: 32), as was the fluorescent tre­ponemal antibody test. Her vision recovered from count- J Neuro- Ophthalmol, Vol. 17, No. 4, 1997 PREGENICULATE AFFERENT VISUAL SYSTEM: PART I 273 ing fingers to 20/ 20 following treatment with intravenous penicillin and Solu- medrol. The clinical characteristics and treatment of neoplastic disorders affecting the optic nerve, including optic nerve sheath meningioma ( 36), optic pathway glioma ( 37- 38), and tuberous sclerosis ( 39) were the topic of several reports and reviews. The successful use of three-dimensional conformal radiation therapy in the treatment of primary optic nerve sheath meningioma was presented by Lee et al. ( 36). This technique of radiation therapy minimizes dosing to surrounding tissues while optimiz­ing delivery to the tumor itself. The patient, a 43- year-old woman, presented initially with asymptomatic optic disc swelling, but during the next year developed inferior altitudinal visual field loss, mildly reduced visual acuity, and proptosis. She underwent conformal radiation therapy over a six- week period, with return of her visual acuity to 20/ 15 and improvement of the visual field de­fect. The authors ( 36) concur that, although treatment of optic nerve sheath meningiomas is, in general, contro­versial, three- dimensional conformal therapy may be a useful alternative to conventional radiation therapy. Recommendations for the screening, follow- up, and treatment of optic pathway gliomas in children with neu­rofibromatosis type 1 ( NF1) were outlined by Listernick and colleagues ( 37) in a recent consensus statement of the NF1 Optic Pathway Glioma Task Force. In that state­ment, the authors ( 37) reviewed the pathology, molecular genetics, and clinical and MR imaging characteristics of optic pathway gliomas associated with NF1. Guidelines for screening of asymptomatic children with NF1 em­phasize the importance of serial ophthalmologic exami­nations. Management of children with symptomatic optic gliomas is centered around careful follow- up with MR imaging and ophthalmologic examinations according to detailed schedules recommended by the Task Force. Be­yond the close observation that may be sufficient in most cases, decisions regarding specific treatment interven­tions are also dependent upon the clinical symptoms and location of the tumor. Castanheira- Dinis et al. ( 38) reviewed the visual func­tion and ocular abnormalities in 75 patients with neuro­fibromatosis. All but three of the patients fulfilled the criteria of the National Institutes of Health Consensus Development Conference for NF1. Abnormalities of the eye and orbit, including Lisch nodules, optic pathway gliomas, lens opacities, retinal hamartomas ( in 2 cases with NF2), sphenoid dysplasia, and congenital glaucoma, were present in 42 ( 56%) patients. Among this group with abnormal findings, only 11 ( 26.2%) demonstrated abnormalities of visual function. Decreased visual acuity was the most common form of dysfunction, occurring mostly in association with optic pathway gliomas. Nys­tagmus, strabismus, visual field defects, and color vision deficits were also noted. Once again, the authors ( 38) emphasized the importance of early diagnosis and care­ful neuro- ophthalmologic follow- up of patients with neu­rofibromatosis. The precise pathophysiologic mechanisms underlying the increased intracranial pressure which characterizes pseudotumor cerebri, another frequently discussed cause of optic nerve dysfunction, remain unknown. According to the Modified Dandy Criteria, the diagnosis of pseu­dotumor cerebri relies upon an elevated CSF opening pressure of > 250 mm of water. However, a recent report by Green et al. ( 39) indicates that some patients may present with CSF opening pressure below that required by the diagnostic criteria, suggesting that some individu­als may be have lower threshold pressures which are within the range of ' ' normal'' but at which papilledema and headache develop. The patient described was an 18- year- old woman hospitalized for depression who had bi­lateral optic disc edema noted on admission examination. She had symptoms of recurrent headache and eye pain. An MRI with gadolinium was normal; CSF examination revealed opening pressure was 150 mm of water with normal constituents. The patient's headaches and, inter­estingly, her affective disorder, improved dramatically one day following the lumbar puncture. Green et al. ( 39) emphasized that patients with CSF opening pressures below 250 mm of water who have signs and symptoms otherwise consistent with idiopathic pseudotumor cerebri may respond, as did this patient, to acetazolamide therapy and lumbar puncture. They also suggest further studies regarding the possibility that depression may be a minor symptom of, or may be exacerbated by, pseudo­tumor cerebri. Two reports were published regarding abnormalities in the intracranial venous system as possible etiologic factors in the development of pseudotumor cerebri ( 40- 41). These reports emphasized the fact that not all neuro-ophthalmologists use the term " pseudotumor cerebri" to indicate truly idiopathic intracranial hypertension. Cre-mer and coworkers ( 40) presented a 40- year- old woman with asymptomatic optic disc swelling and blind spot enlargement in whom MRI demonstrated a 1 cm falcine meningioma and partial superior saggital sinus obstruc­tion. Cerebral venography and manometry revealed ob­struction of the transverse and sigmoid sinuses and mark­edly elevated venous pressures. The authors ( 40) stress that this patient did not have normal MR imaging, and thus did not satisfy clinical criteria for idiopathic pseu­dotumor cerebri. Appropriately, they indicate that con­ventional cerebral venography is not advocated for all patients with papilledema and elevated intracranial pres­sure. This is particularly true given the continued evolu­tion and improvement in MR venography for the detec­tion of venous sinus thrombosis. Sussman et al. ( 41) propose that in some cases of pseudotumor cerebri, non- occlusive thrombus in the ve­nous sinuses, unrecognized by cerebral venography, may impede CSF absorption. They performed a study to de­termine the prevalence of prothrombotic abnormalities in the blood of 38 patients who fulfilled the Modified Dandy Criteria for pseudotumor cerebri; these results were compared with the same prevalences in a healthy, age- and obesity- matched control group ( 16 patients) and in a group of age- matched patients with other neurologic J Neuro- Ophthalmol, Vol. 17, No. 4, 1997 274 BALCER AND GALETTA diseases ( 18 patients). Complete blood counts, plasma fibrinogen, anticardiolipin antibodies, lupus anticoagu­lant, antithrombin III, proteins C and S, kaolin cephalin clotting time, and prothrombin time were measured in all patients. Eleven of the 38 patients with pseudotumor cerebri had a normal body mass index (< 25); prothrom-botic abnormalities occurred more often in this group than in those with elevated body mass index, the most common of which were antiphospholipid antibody and hyperfibrinogenemia. As the authors ( 41) indicate, the 11 patients with normal body mass index did not fit the typical profile of obesity and female sex ( 4 of the 11 were men) which most often characterizes patients with idiopathic pseudotumor cerebri. Testing for prothrom-botic abnormalities was performed in some patients as long as six months following the onset of symptoms, and patients in whom cerebral venography later demon­strated dural sinus thrombosis were also included in this study. Therefore, further investigation of potential pro-thrombotic abnormalities in patients with pseudotumor is warranted, especially in those who are not obese. Lumboperitoneal shunting is one treatment option available for patients with pseudotumor cerebri, particu­larly in those not responding to medical therapy or in whom optic nerve sheath fenestration is not an option. Unfortunately, this procedure is not without potential complications, as we are reminded in a recent report by Miller ( 42). A 42- year- old woman with well- documented pseudotumor cerebri developed confusion, headache, vi­sual loss, and simultagnosia 24 hours after lumboperito­neal shunt placement for worsening, medically refractory papilledema. MRI revealed bilateral occipital infarcts and cerebellar tonsillar herniation. Cerebral angiography disclosed the presence of a ruptured, previously asymp­tomatic aneurysm at the vertebral and posterior- inferior cerebellar artery junction. There was associated vaso­spasm. The authors indicate that the abrupt decrease in intracranial pressure following shunt placement may it­self have led to the aneurysm rupture; alternatively, the mechanical forces of posterior fossa herniation could have also contributed. Consideration of this rare but po­tential complication of lumboperitoneal shunting is rec­ommended ( 42), especially if severe visual loss is not present. Leber's hereditary optic neuropathy ( LHON) was again a topic of discussion, this time in association with brainstem involvement. Funalot et al. ( 43) present a 30- year- old male patient with LHON and documented pres­ence of the 14484 mutation. Clear evidence of maternal transmission was noted in the family history. The patient had developed persistent bilateral visual loss at the age of 4 years but, interestingly, developed vertical gaze palsy and bilateral ptosis at the age of 26. At age 16, he had noted an episode of vertigo, which resolved. Brain MRI obtained to evaluate the vertical gaze palsy demonstrated a symmetric area of increased signal intensity in the dor­sal midbrain on T2- weighted images. CSF analysis and serologic testing were normal. For a presumed diagnosis of multiple sclerosis ( MS), intravenous methylpredniso-lone was given, without improvement. Six months later, the patient developed complete ophthalmoparesis and bi­lateral tinnitus. This resolved spontaneously over several months, but a spastic ataxia subsequently developed. No other family members had experienced symptoms refer­able to the central nervous system. Since the clinical, MRI, and CSF findings were not typical for MS, the authors ( 43) suggest that a separate type of central ner­vous system involvement may occur, as indicated in a few previous cases, in patients with LHON. THE OPTIC CHIASM AND BEYOND ' ' A descent thing to do for the chiasm'' was described by Kosmorsky and Straga ( 44) in their report of a patient with chiasmal prolapse into an empty sella following ventriculojugular shunt placement. A large suprasellar cystic lesion had been revealed by MRI following the discovery of a visual field defect. Following placement of the ventriculojugular shunt, she had experienced a dramatic worsening of her vision; this as well as the MRI- documented chiasmal prolapse resolved after the shunt catheter was tied off. This indicates that changes in intracranial pressure following shunt placement was most likely responsible for the chiasmal descent in this patient. A case of visual loss resulting from downward hernia­tion of the optic chiasm was also reported by Taxel et al. ( 45). The patient was a 64- year- old woman who was treated with bromocriptine for a 4.5 cm macroprolacti-noma. On initial MRI scans, the chiasm was displaced superiorly by the tumor; a bitemporal hemianopsia was present. The visual field defects resolved with increasing doses of bromocriptine therapy over a 2- month period. However, after 6 subsequent months of treatment at a bromocriptine dose of 7.5 mg per day, new visual field defects were noted despite shrinkage of the tumor to 1.5 cm. MRI demonstrated inferior and leftward herniation of the optic chiasm. During the next 4 months, the visual field defects resolved after a decrease in the bromocrip­tine dose to 5 mg per day. The authors ( 45) suggest that inferior and leftward traction on the optic chiasm and its blood supply resulted from reduction in tumor size; this possibility should be considered in patients with pituitary tumors who develop recurrent visual loss on bromocrip­tine therapy. Yet another " sellar misadventure" was presented by Hayman and colleagues ( 46). A patient with chronic pansinusitis and polyps underwent bilateral endoscopic sinus surgery with sphenoidectomy, ethmoidectomy, polyp removal, and nasoantral windows. She reported visual loss the following day, and an asymmetric bitim-poral hemianopsia was noted on automated perimetry. Neuroimaging, including CT and MRI, showed evidence of tension pneumocephalus, hydrocephalus, and a sub-frontal hematoma. Surgical intervention was performed without improvement of the visual deficit. An MRI ob­tained five days later demonstrated a small central zone of abnormal signal hyperintensity within the optic chi­asm on coronal T2- weighted images. Both chiasmal isch- J Neuro- Ophthalmol, Vol. 17, No. 4, 1997 PREGENICULATE AFFERENT VISUAL SYSTEM: PART I 275 emia and direct traumatic injury represent possible mechanisms of injury in this patient. This case was pre­sented to illustrate a rare but potentially vision-threatening intracranial complication of endoscopic sinus surgery. The authors ( 46) suggest the use of both MRI and CT in the evaluation of such patients. A timely review in the neurosurgical literature by Ciric and coworkers ( 47) indicated that visual loss may also occur as a complication of transsphenoidal surgery for sellar tumors. The data was obtained through a ques­tionnaire mailed to 3,172 neurosurgeons, of whom 958 responded and reported having performed transsphenoi­dal surgery. Loss of vision was reported by 179 surgeons as a complication of 1.8% of surgeries performed. Ap­propriately, caution is recommended in the interpretation of these results ( 47) given the low response rate ( 37%) and potential bias that this may have introduced. Other unusual reported " chiasmal disasters" included a case of chiasmal infarction and sudden blindness caused by mucormycosis in a patient with AIDS and diabetes mellitus ( 48). The 47- year- old patient was de­scribed by Lee et al. ( 48) to have had autopsy- proven Rhizopus meningoencephalitis with occlusion of the left internal carotid and basilar arteries and infarction of the optic chiasm. Complete absence of the optic chiasm by MRI scanning was reported by Leitch et al. ( 49) in a child with a midline craniofacial defect and see- saw nys­tagmus. Measurement of the optic chiasm on MRI coronal im­ages may be useful for the early detection of some dis­orders, including optic glioma, meningioma, and sep-tooptic dysplasia. Wagner and colleagues ( 50) sought to develop a reliable and objective technique for measure­ment of optic chiasmal area using coronal Tl- weighted MR images. To determine a range of normal values for optic chiasmal height, width, and area, such data were obtained from 123 MRI studies of patients aged 18- 82 years. All of the scans had been interpreted as normal. Measurements were made using commercially available region- of- interest software. The mean optic chiasmal area for all patients was 43.7 mm2, with a range of 32.2- 58.8 mm2. After separation of studies into groups ac­cording to patient age and sex, an expected small de­crease in area was noted with increasing age. The authors ( 50) emphasize that such measurements are indeed fea­sible and may be useful as a reference for determining the presence of early chiasmal atrophy or enlargement. MRI techniques are being used more and more often to correlate with pathophysiologic mechanisms of degen­erative and other disease processes. Uggetti et al. ( 51) demonstrated signal abnormalities consistent with trans-synaptic degeneration of neurons in the lateral geniculate bodies of blind children. Visual loss in these patients had occurred as the result of periventricular leukomalacia, Chiari I malformation and bilateral occipital infarcts, and neuroaxonal dystrophy with optic disc pallor. Transsyn-aptic degeneration is an alteration of second neurons in the visual pathway following loss of synaptic input, re­sulting in neuronal cell loss and gliosis within the lateral geniculate bodies. A retrospective review of MRI scans obtained on these patients revealed symmetric areas of abnormal increased signal on axial T2- weighted images at the precise location of the lateral geniculate bodies, as mapped by previous studies. The signal abnormality it­self is thought to represent gliosis, since the lateral ge­niculate bodies typically demonstrate signal isointense with gray matter. The authors ( 51) emphasize that such changes may have resulted from anterograde ( pregenicu-late neurons) as well as retrograde ( postgeniculate) neu­ronal degeneration. Homonymous hemianopia may be associated with le­sions of the anterior visual pathway affecting the optic tracts or lateral geniculate nuclei. Whether or not visual function can be restored in patients with homonymous hemianopia is the subject of a review by Pambakian and Kennard ( 52). The pathogenesis of and spontaneous re­covery from such deficits are discussed, as are various options for treatment and rehabilitation. Hemianopic Fresnel prisms are presented as one alternative, with em­phasis on the fact that their use is limited in patients with significant cognitive deficits. Strengthening patients' at­tention toward the blind hemifield and the development of compensatory scanning eye movements are both em­phasized as strategies for cognitive rehabilitation which may be more effective than optical aids in improving performance of day- to- day activities, including reading. BASEBALL AND THE AFFERENT VISUAL SYSTEM In keeping with a tradition established by the 1996 Pregeniculate Afferent Visual System Review, the appli­cation of neuro- ophthalmologic testing to the evaluation of baseball players will again be a topic of brief discus­sion. Hofeldt et al. ( 53) investigated the effects of neutral density filters, placed over one or both eyes, on the hit­ting performance of baseball players at a commercial batting cage facility. For each of the 12 players studied, a 0.6 neutral density filter was placed over one eye, both eyes, or neither eye. Placement of the filter over the dominant eye was associated with a significantly lower hitting score ( 36%) when compared with placement of filters over both eyes ( hitting score 87%) or neither eye ( hitting score 94%). 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