Journal of Neuro-Ophthalmology, December 1992, Volume 12, Issue 4

Spontaneous recovery of vision in progressive anterior ischemic optic neuropathy.

Four patients with typical anterior ischemic optic neuropathy experienced progressive deterioration of visual function, to acuity levels of finger-counting in two eyes, 20/400 in one, and 20/50 in the fourth. All subsequently enjoyed significant spontaneous recovery of vision to 20/60, 20/60, 20/40, and 20/25, respectively. No previous reports have documented the details of such improvement in the progressive form of anterior ischemic optic neuropathy. The natural history of this common optic nerve disorder is reconsidered in light of these observations. The potential for spontaneous recovery should be taken into account in the interpretation of visual outcome in medical or surgical therapeutic trials for progressive anterior ischemic optic neuropathy.

Journal of Clinical Neuro- ophthalmology 12( 4): 219- 225, 1992. © 1992 Raven Press, Ltd., New York Spontaneous Recovery of Vision in Progressive Anterior Ischemic Optic Neuropathy Debra A. Barrett, M. D., Joel S. Glaser, M. D., Norman J. Schatz, M. D., and Jacqueline M. S. Winterkorn, M. D. Four patients with typical anterior ischemic optic neu­ropathy experienced progressive deterioration of visual function, to acuity levels of finger- counting in two eyes, 20/ 400 in one, and 20/ 50 in the fourth. All subsequently enjoyed significant spontaneous recovery of vision to 20/ 60, 20/ 60, 20/ 40, and 20/ 25, respectively. No previous reports have documented the details of such improve­ment in the progressive form of anterior ischemic optic neuropathy. The natural history of this common optic nerve disorder is reconsidered in light of these observa­tions. The potential for spontaneous recovery should be taken into account in the interpretation of visual out­come in medical or surgical therapeutic trials for pro­gressive anterior ischemic optic neuropathy. Key Words: Anterior ischemic optic neuropathy ( AION}- Progressive AION- Natural history AION­Recovery of vision. From the Department of Ophthalmology ( D. A. B.), Washing­ton University School of Medicine, St. Louis, Missouri; the Neuro- Ophthalmology Unit ( J. S. G., N. J. S.), University of Mi­ami, Miami, Florida; and the Department of Ophthalmology ( J. M. S. W.), North Shore University Hospital, Cornell Univer­Sity Medical College, Manhasset, New York. Address correspondence and reprint requests to Dr. J. S. Glaser, Bascom Palmer Eye Institute, 900 N. W. 17th Street, Mi­ami, FL 33136, USA. 219 Classic clinical descriptions of the natural history of common ( nonarteritic) anterior ischemic optic neuropathy ( AION) have emphasized an abrupt, largely irreversible loss of visual acuity and/ or field function ( 1- 3). This principally monophasic pro­file, with neither progressive deterioration nor im­provement, has been extensively documented in AION, a frequent cause of permanent visual loss in patients over 50 years of age ( 4). No medical therapy, including corticosteroids, has convinc­ingly been shown to be regularly effective in re­versing the visual loss. Indeed, few reports di­rectly address the question of visual recovery in AION ( 5), although some degree of improvement, with or without the use of corticosteroids, may be less rare than generally appreciated ( 6- 8). Recently, optic nerve sheath decompression has been advocated ( 9- 11) as a surgical therapeutic op­tion for the progressive form of AION, in which acuity and fields may deteriorate over weeks to months. This temporal profile of visual decline, as opposed to the apoplectic, fixed pattern, is less frequent, but well documented ( 2,12,13). Based on 32 cases of progressive AION culled from the lit­erature ( 9,12- 14), the prognosis for spontaneous visual recovery is purportedly nil. In light of these poor expectations, and with re­gard to analyzing the results of decompressive nerve sheath surgery, we here document four in­stances of common monocular AION, with pro­gressive loss of visual acuity to levels of count­fingers in two eyes, 20/ 400 in a third eye, and 20/ 50 in the fourth, each of which clearly regained func­tionallevels of acuity. CASE REPORTS Patient 1 On April 10, 1990, a 72- year- old woman under­went an uncomplicated right cataract procedure 220 D. A. BARRETT ET AL. with insertion of a posterior chamber intraocular lens. Preoperative visual acuity was 20/ 60 -, and was 20/ 40 on four postoperative examinations at I­to 2- week intervals. On May 30, the patient com­plained of 3 to 4 days of decreased right vision, and acuity of 20/ 60 + was obtained, without re­corded comments on funduscopic appearance or visual field. Over the following 2 months, right eye vision progressively decreased to count- fingers ( Fig. 1). Examination at the Bascom Palmer Eye Institute ( BPEI), on July 20, 1990, showed right visual acuity of 6/ 200, near J16, and left acuity of 20/ 40, Jl. There was a major right afferent pupillary defect, and no Ishihara color plates were correctly identified with the right eye. Visual field could be assessed only by confrontation technique, demonstrating a dense superior altitudinal loss with a large central scotoma in the right eye; the left visual field was normal. Applanation tensions were 10 mm, au. The right optic disk was swollen with streak linear hemorrhages, and the left disk was normal with a 0.2 cup- to- disk ratio. Laboratory examination showed Westergren erythrocyte sedimentation rates ( ESR) of 47 and 35 mmlh; serum electrolytes, BUN, and glucose were normal. Medical history was remarkable for osteo­arthritis and coronary disease, but no history of hypertension, diabetes mellitus, headaches, scalp tenderness, jaw pain, weight loss, or symptoms suggestive of polymyalgia rheumatica. A right fa­cial palsy had occurred and had resolved at age 50 years. Medications were furosemide, verapamil, propranolol, isordil, nitroglycerin, aspirin, and di­azepam. On July 20, 1990, oral prednisone, 80 mg per day, was commenced, with Zantac, 300 mg at bed­time. Three days later the patient thought the vi­sion was " clearer," and corrected acuity had im­proved to 20/ 200, although the appearance of the optic disk was unchanged. Echography demon­strated right optic disk elevation, but the retrobul­bar optic nerve was normal. By August 2, right visual acuity was further im­proved to 20/ 100 - 2, the superior visual field loss had resolved, and the patient now correctly iden­tified 7/ 14 color plates with the right eye. Right disk swelling had decreased, although fluorescein angiography showed slight leakage from the optic disk, but with no evidence of cystoid macular edema. Prednisone was tapered and discontinued. On September 6, 1990, right visual acuity was 20/ 60 - 1, without an afferent pupil defect. Right color function was 8114 plates correctly identified, the visual field was full to finger- counting in all quadrants, and there was subjective resolution of the central scotoma by Amsler grid testing. The Humphrey 30- 2 program showed an isolated small area of decreased nasal sensitivity with minimal parafovealloss ( Fig. 1). Disk edema resolved, fol­lowed by mild residual pallor. Patient 2 A 61- year- old woman, with a history of hyper­tension, presented to her ophthalmologist on Au­gust 29, 1990, for decreased vision in the left eye. Clinical Summary: Patient 1 PrAecvuioituys 5130190 7/ 19190 7120190 7123190 8/ 2190 9/ 6190 20140 20160 CF 61200 201200 201100 20160 ~ ~ ~ 8 • · 1.. ' .... 11 11 - 1 .....,......"..". 1"'''.'.'-.. 1.. " . JofO"' ...' ....... 1 .. 1 .... · 1,, · J • , J:~~~ I~:;:, J .-..-.." ~ ; 1;:' Ii '. .1. • il . I! r FIG. 1. Patient 1: VIsual FIeld 00 Clinical summary of Visual acu t d f . . . were possible only by confrontation' with re I yan,. leld loss. Initial Visual fields mated perimetry ( 30- 2 program).' covery. mal field by Humphrey auto- VIsual Acuity 00 I Clin Nroro- ophthalmol. Vol. 12. No, 4. 1992 SPONTANEOUS RECOVERY IN AION 221 Visual acuity was 20/ 25 right and 20/ 50 left. Swell­ing of the superior aspect of the left disk with a peripapillary streak hemorrhage was noted. Auto­mated visual fields showed a dense left inferior altitudinal defect ( Fig. 2). On September 14, examination at BPEI revealed right visual acuity of 20/ 25, near J1, and left acuity of 20/ 80 and J16. A major left afferent pupillary defect was present, and there was a dense left in­ferior altitudinal defect; the right field was normal. Applanation tensions were 15 mmHg, OU. The right disk was normal with a 0.3 cup, and the left disk was diffusely swollen with a small splinter hemorrhage. Blood pressure was 150/ 90, Wester­gren ESR was 8 mm/ h, and routine laboratory tests were all normal. On September 17, the patient returned with fur­ther decrease in left acuity to 20/ 400. Humphrey visual field demonstrated a dense left inferior field defect involving fixation ( Fig. 2). Brain and orbit magnetic resonance imaging ( MRI) was normal. The patient was begun on daily oral prednisone, 60 mg for 2 weeks, which was then discontinued. On October 11, left acuity had improved to 20/ 50, but the dense left inferior altitudinal field defect persisted. In mid- December 1990, left acuity was 20/ 60, with a left afferent pupil defect. Color plates were 0/ 15 correct, left eye, and 11/ 15 correct, right eye. Confrontation continued to show a dense in­ferior altitudinal field defect ( Fig. 2). Disk edema resolved with mild superior temporal disk pallor. Patient 3 On April 23, 1991, an 83- year- old woman under­went uncomplicated left cataract procedure with placement of a posterior chamber lens. On May 7, the left visual acuity was 20/ 20, but by May 13, she presented with sudden loss of left vision over the prior 2 days ( Fig. 3). Left acuity was 20/ 30; a left afferent pupillary defect and a dense nasal field defect to confrontation were noted. The superior aspect of the left disk was swollen. By May 21, left acuity had deteriorated to 20/ 200. On May 22, 1991 at BPEI, best- corrected right acuity was 20/ 40, and left acuity was finger­counting at 2 ft. A major left afferent pupil defect was observed. The right visual field was normal; the left field could be assessed only by confronta­tional techniques, showing dense central and nasal field depressions. The right fundus was normal with a 0.4 cup- to- disk ratio. The superior aspect of the left optic nerve was distinctly swollen, with one small peripapillary nerve fiber layer hemor­rhage; there was no macular edema. The Westergren ESR was 50 mm/ h. Medical his­tory was negative for diabetes or hypertension. There was a history of breast cancer in 1963 with­out recurrence after mastectomy, thyroid cancer in 1949, and tuberculosis in 1931. Medications were Synthroid, Buspar, and multivitamins. On July 10, 1991, the patient reported marked subjective improvement. Left visual acuity was now 20/ 40, and a small left afferent defect was still present. Humphrey 30- 2 automated perimetry showed 10/ 27 fixation losses, but suggested the continued presence of dense superior and inferior nasal arcuate field defects ( Fig. 3). However, by confrontation technique the nasal field had dis­tinctly improved from no- hand- motion perception to hand- motion perception. Clinical Summary: Patient 2 VIsual Acuity OS VIsual FIeld OS Previous 8/ 29/ 90 9/ 14/ 90 9/ 17/ 90 10/ 11190 12/ 20190 Acuity 20/ 50 20/ 80 20/ 400 20/ 50 20/ 60 • ....... o. S ~ TI" I.',"........ • • 4./ · , · 1. loS"' .... .1' .,. 1 I - t I J J .. • It~....... ~ .. .. · 11 · .'" - JII ...... ". .. • IS, lfoJl ......... . a • '=..... ~. a•• , - e. e'I- o.. a " I ...... ~. ';............ .:'..................... ~ .. FIG. 2. Patient 2: Clinical summary of visual acuity and field loss. Visual fields by confrontation and Humphrey automated perimetry. 1Clin Neuro- ophthalmol, Vol. 12, No. 4, 1992 222 D. A. BARRETT ET AL. Clinical Summary: Patient 3 Visual Acuity OS VIsual FIeld OS 5/ 21/ 91 5/ 22191 7/ 10/ 91 Previous 5/ 13/ 91 Acuity 20/ 200 CF 2' 20140 20120- 20130 ct ct • 1 ~ .. CD ' ::~ f- -.-. .11I ....... • I ... . lI ........ .. ft 0 .... I ... . a ....... -. ." ...... -; I ... ".. ."" .. · 1 .. · U- II .. , I.'", " .... - 41 ... ",- 11 --- ... ".. :~:•••.• • ••• 41 • ••••• . 1"""" - . ... . ... I " FIG. 3. Patient 3: Progression of visual acuity and field loss. Visual fields obtained by confrontation and Humphrey automated perimetry ( 30- 2 program). Patient 4 A 65- year- old man with posttraumatic left eye " amblyopia with optic atrophy" and acuity of 201 200 since childhood, experienced several weeks of right eye transient visual obscurations. Medical history included hypertension, aortic stenosis, su­praventricular arrythmia, and gout. His regular medications included clonidine hydrochloride, ve­rapamil, furosemide, lanoxin, allopurinoL aspirin, and dipyridamole. On May 25, 1990, visual acuity was right 20/ 20 + 3, left 20/ 200. With right eye, 3 of 10 color plates were identified, OlIO left eye, and there was a 1.2 log unit left afferent pupil defect. Automated Humphrey 30- 2 perimetry showed a right inferior dense arcuate defect ( Fig. 4), and left temporal and inferior depressions were evident. The left optic disk was diffusely pale, while the right was edematous with nerve fiber layer hem­orrhages. All diagnostic ancillary procedures were unremarkable, including Westergren ESR of 14 mm/ h, complete blood counts and hypercoagula­bility studies, MRI and computed tomography ( CT) images, and echocardiography. By June 12, right acuity was still 20/ 20, but the patient complained of " dimming." A new superior arcuate field depression was evident, and pupil­lary light reflexes now showed a right relative af­ferent defect of 0.6 log units. By June 29 ( Fig. 4) the field defect increased further, and acuity dropped to 20/ 50. A lumbar puncture was unremarkable, and the patient was begun on oral prednisone therapy. Optic nerve sheath decompression was discussed, in light of poor visual function in the left eye. JClill Neuro- ophthalmol. Vol. 12. No_ 4. 1992 Acuity continued in the 20/ 50± range until mid­July, then gradually increased from 20/ 40 to 20/ 30 by October 16; the superior arcuate defect. rece~ ed from the fixational area. However, in mld­November, abrupt loss of vision in the left eye oc­curred, with acuity reduced to finger- counting in the superotemporal periphery only, accompanied by left disk swelling, all consistent with anterior ischemic optic neuropathy, as in the first eye. By January 1991, right acuity had stabilized at 201 25 - 1 with some regression of the field defects ( Fig. 4); left acuity remained at finger- counting. DISCUSSION The temporal profiles of common AlaN clearly may include a progressive type characterized by a gradual or stepwise course of visual deterioration over weeks to months ( 2,12,13), in contrast to the more frequently observed monophasic pattern, in which visual loss occurs suddenly, may worsen over several days, and then remains unchanged ( 2,4). Although there are no rigorous means of _ confirming the diagnosis of common AlaN, crite­ria for identifying the clinical syndrome include age at onset, course of abrupt or subacute visual loss, rather typical field defects, optic disk edema, and lack of confirmatory evidence of alternative etiologies ( 2- 4,12,15). The four elderly patients reported here fulfill the clinical criteria for a diagnosis of " progressive" AlaN, as defined by Borchert and Lessell ( 12), and others ( 9,13,14). Patient 1 demonstrated stepwise visual loss over 2V2 months; Patient 2 showed evo- SPONTANEOUS RECOVERY IN AION 223 1011\ OCt III lill IJ.' 15 ' Ill ! f l. lD 00 -........' .. ••..•••..••.( 7. ~ ~ P { I), .• :: .. l, • ( 0 0 ' l~ - 12 12 (; 1. cO n < 0 d' ( I) •• • L' • cO 0 ' I I~ , f 15 .. ••• ,',,'':;''-;:.':; :;~; (~( 1) " II~ \ I?~ 16 (\ f) t~)(!)( fil ,-. • - I: Q :'-""':'- · ,: · < 0 '~* I~ r~~~~ ~ t )~ :......_. .' T •••• H l ...~ I')' ~ 6 .\,' '.~ l' 18 1: 2 22 , o,~ :. , tIn '" : a:• .. •••••• •• 11. 11II ( 0 ( 0 ( I) 1 Pro ~ • I- l? ~ ."]. 9') ( c.~ 11.39 , Ill P ( OS. 3.10 P ( ,"" 11.4 ~ P D,";'. - ( I I~) I~ I~ II n~ 17 ~ B 20 ~ '. ,~::~:~ U::: · :: · ;~::,. lJ (~~ :~) 4H~ 1 H~ I: I~:(~ 1 :;:::::':::'::~:::.:.::~::::':::~ lj. 1 \ SI (. fj .• a ( ) g(}, i) U 1: · :;-:: · ,: ' C: l~',: ..::-':': .~ 13 t 7 22 19 1l • • • C. :::-:::~~::-="---.:-;-:''-'-~'-:::::~"(- I"" l" t,/"-~=-:_::: '. Il , U ~ O If) I ~ I{- l - z- r -((- l - 74<~ I-•--•:~•--•:::: 1_~-:.------ -=--=-=-'="-..,.----- ,.,?':.: ;:-<'~,,::'.,'::~ .. ~ , t) .1) ~ lll~ [; l:,~ 1 ~ r ~ 2ll 2li , N ..... - - .. ~':; :"\?:;(:~~:;::" < c (~ Ill I!'; rll fll~) ~ ;: G, I.' ••••• ..-.::::'::: 10 ~ '< 7'( l ", d:;-"" " ' 0 < 0 I ~ •••• l( l ' 0 ' 0mn P'iJ • • V. fT - IU3! l1 p ( O.~ 12.~) III f < 0,5":. S~ III P ( O.~~ lO~ C! l FlG. 4. Pafi. enr 4: Series of Humphrey visual rreld~ ( 30- 2 program)_ ( Top) ( May 1990) shows dense inferio, r arcuale d8' fect [ mean deviation - 11.75 db] ( Midd'e) ( June 1990) shows new superior n, asal depression ![ meandeviAlIOn - 1993 db]. Wottoml ( Ja uary 1991) shows regression, especia11yol superonasal defect [ mea deviation - 14.13 db], lution over 3 weeks; Patient 3 showed stepwise visual loss over 13 days; and vision in Patient 4 deteriorated during more than 2 months. All four acutely involved eyes had typical disk edema, and in Patients 1 and 2 the contralateral optic nerve had a small cup- to- disk ratio, a morphologic disk con­dition implicated as a risk factor for AION ( 16); Patient 4 had previous contralateral optic atrophy since childhood, but nevertheless experienced typ­ical ION in that eye 7 months after onset in the first eye. The field defects were entirely consistent with the patterns encountered in AION, which may be central scotoma, altitudinal, arcuate, or a combina­tion ( 2,17). Thorough medical evaluation failed to reveal evidence of diabetes mellitus or of any ex­traordinary vasculitic or inflammatory systemic diseases. Hypertension was present in Patients 1, 2, and 4, again entirely consistent with common AION. The onset of symptomatic AION occurred 6 weeks after cataract surgery in Patient 1, and be­gan 3 weeks after cataract surgery in Patient 3. Such temporal susceptibility of AION during the JGin Nellro- ophthalmol. Vol. 12. No, 4. 1992 224 D. A. BARRETT ET AL. postcataract extraction period is also well docu­mented ( 18). Macular lesions likely to account for reversible visual loss, such as cystoid macular edema, were ruled out by scrupulous fundus ob­servation, fluorescein angiography, and presence of afferent pupil, color- sense defects, and periph­eral field depressions. The differential diagnosis of progressive optic neuropathy could also include compressive, infil­trative, inflammatory, and demyelinating dis­eases, but the great weight of clinical and labora­tory evidence in these four cases indicates monot­onously typical AION. Furthermore, it is unlikely that compressive or infiltrative lesions would un­dergo sustained improvement. Although corticosteroid treatment may indeed ameliorate some inflammatory conditions, Patients 1 and 2 were treated for less than 2 weeks, and visual improvements were maintained without continuing steroid therapy. That oral corticoste­roids may have played a role is moot, this therapy never having been rigorously shown to have a reg­ularly beneficial effect in AION ( 4), but it is not possible to exclude some salutary contribution. Demyelinating disease with disk swelling is highly unlikely, especially in the age group of the patients reported here, and MRI of Patients 2 and 4 showed no evidence of demyelinative or other optic nerve or brain lesions. Moreover, there were no other abnormal neurologic features in any of these patients. In fact, these cases are typical of progressive AION in every respect, except the sub­stantial spontaneous improvement in vision. Patient 1 experienced an improvement of central vision from finger- counting to 20/ 60 and resolution of a superior altitudinal defect, with a small resid­ual decrease in paracentral and nasal retinal sensi­tivity. Consistent with these improvements, the af­ferent pupillary defect resolved and color vision improved. Patients 2 and 3 enjoyed an improve­ment only in central visual acuity: from 20/ 400 to 20/ 60, and from finger- counting to 20/ 40. Their pe­ripheral field defects failed to show improvement. Patient 4 maintained 20/ 20 + 3 acuity for 6 weeks, then fell to 20/ 50 for 4 weeks, and gradually re­turned to 20/ 25 - 1. We do not believe that any patient showed a spuriously improved acuity because of heightened degree of effort or of visual searching skill. Multi­ple determinations of consistently and, in three in­stances, profoundly decreased acuity, despite rig­orous encouragement, were obtained in all cases before improvement was observed. As noted previously, the visual loss incurred in progressive AION is widely regarded as perma- JClin Neuro- ophthalmol. Vol. 12. No. 4. 1992 nent. In 4 cases of Beck et al. ( 14), 10 cases of Borchert and Lessell ( 12), 6 cases of Kline ( 13), and 12 cases of Sergott et al. ( 9), all failed to demon­strate any spontaneous improvement. ( with . or without corticosteroids) in visual function, With long- term follow- up. Review of the existing published case reports of nonprogressive AION prior to 1983, reveals ~ ea­ger documentation of Significant spontaneous un­provement in this disease, although the supposed rarity of even minimal improvement may be exag­gerated. Ellenburger et al. ( 6) reported the larg~ st group of " improved" patients, although precise case- by- case data are lacking. Visual acuity is said to have improved more than two lines in 13 of 39 eyes ( 33%), with follow- up averaging 2.9 years. Six of the eight eyes with central scotoma were among the 13 that improved. Four eyes with small altitu­dinal scotomas also improved when the border of the defect receded slightly from fixation. Hayreh ( 19) reported an instance of bilateral simultaneous disk edema in a 40- year- old diabetic man treated with Diamox and corticosteroids, with improve­ment from finger- counting au, to eventual recov­ery of 6/ 18 00 and 6/ 24 as within 3 months. This atypical case, however, may represent the entity of diabetic papillopathy, which appears to have a dis­tinctly more favorable natural history ( 20). In that same report, Hayreh ( 19) observed " improve­ment" in 6 of 8 patients with AlaN while on thera­peutic steroids, and 1 of 6 patients without treat­ment. However, no details of the degree or nature of visual improvement are provided. Eagling and colleagues ( 21) reported 9 of 36 ( 25%) cases of AlaN improved with steroids and 4 of 20 ( 20%) improved without steroids, but again, " improvement" is not defined. This report in­cluded 27 cases associated with vasculitis or other systemic diseases and concluded that such cases were more likely to have an unfavorable outcome. Of 38 patients with AlaN, Boghen and Glaser ( 2) reported improvement in 2 patients. Initial acuity of finger- counting improved to 20/ 200 in 9 weeks in one eye, and in another, improved from finger­counting to 20/ 20. Repka et al. ( 3) reviewed 196 cases of AION, 160 without arteritis. Long- term follow- up data were available on 83 patients, with a mean follow- up of 5 years, but with no improve­ment in vision as defined by an increase of at least two Snellen lines. Cullen ( 22) also failed to show any improvement in 19 cases of idiopathic AlaN. In a control group of untreated, nonprogressive AION, Sergott et al. ( 9) reported improvement in 2 of 15 eyes: from 20/ 80 to 20/ 25, and from 20/ 100 to 20/ 50. Two studies of the natural history of non- SPONTANEOUS RECOVERY IN AlON 225 progressive AION reported improvement in 10 of 84 patients ( 12%) ( 23), and in 1 of 63 patients ( 2%) ( 8). However, in the largest prospective study ( 5), 24 of 116 eyes ( 21 %), with initial vision of worse than or equal to 20/ 60, improved by 3 or more lines, as did 29 of 126 eyes ( 23%) that had initial vision better than 20/ 60. In summary, no prior study of progressive AION has reported any spontaneous improve­ment ( 9,12- 14), whereas in 10 studies of nonpro­gressive AION, rates of improvement range from 0 to 30%. In support of the concept of reversibility of optic nerve injury in AION are the three published re­ports of visual recovery following optic nerve sheath decompression ( 9- 11). Even more remark­able is the observation of visual improvement in eyes with prior AION, but contralateral to optic nerve sheath decompressions ( 9,10). The phenomenon of improvement in visual function in AION, either after surgical interven­tion, or spontaneously occurring, as in the four cases presented here, or in those instances attrib­uted to corticosteroid therapy, strongly suggests that, although irreversible infarction of some pro­portion of optic nerve axons undoubtedly occurs, ischemia may otherwise be the partial or perhaps not the sole pathophysiologic mechanism of nerve dysfunction. We should note that the four patients described here were being considered for optic nerve sheath fenestration at the time of their visual improve­ment. Whether spontaneous improvement is more common than previously reported in progressive AlON awaits the analysis of larger studies. Our observations and review of the literature surely suggest that the natural history of AION deserves reexamination. REFERENCES 1. Miller GR, Smith JL. Ischemic optic neuropathy. Am JOph­thalmol 1966; 62: 103- 15. 2. Boghen DR, Glaser JS. 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Metab Pediatr Syst Ophthalmol 1989; 12: 46- 57. J Clin Neuro- ophthalmol, Vol. 12, No. 4, 1992