Journal of Neuro-Ophthalmology, December 1985, Volume 5, Issue 4

Optic nerve hypoplasia: papillary diameter and clinical correlation.

Hypoplasia of the optic nerve is often subtle, and reduction in papillary diameter can be difficult to detect during ophthalmoscopic examination. Using a slit-lamp and a posterior fundus contact lens, we evaluated papillary diameter by bringing margins of the light beam to coincide with the limits of the optic nerve head. The method was standardized with 140 presumably normal eyes. Then we studied 17 consecutive eyes showing optic nerve hypoplasia. Hypoplasic discs were separated into two categories: (1) nine cases defined as having ""moderate"" hypoplasia, in which average disc diameters ranged between -2 and -2.5 standard deviations under the mean normal value; and (2) eight eyes with ""severe"" hypoplasia, showing average disc diameters less than the normal mean value by 2.5 standard deviations or more. Double peripapillary ring sign and low disc/artery ratio are clues often used in the diagnosis of optic nerve hypoplasia. The incidence of these signs was also evaluated in the hypoplasic discs studies. The double ring sign was present in two of the nine eyes with moderate hypoplasia, and in seven of the eight eyes with severe hypoplasia. Of eight eyes with moderate hypoplasia, only one showed a disc/artery ratio inferior to the mean normal value -2 standard deviations, whereas this ratio was significantly reduced in all cases of severe hypoplasia. These ophthalmoscopic clues therefore appear to be much less valuable than direct measurement of the optic disc for detecting a subtle reduction in disc diameter. This is of particular interest when one considers that all the nine eyes with moderate hypoplasia had alteration in visual function upon presentation.(ABSTRACT TRUNCATED AT 250 WORDS)

J. Clin. Neuro-ophthamol. 5:249-253, 1985 © 1985 Raven Press, New York Optic Nerve Hypoplasia: Papillary Diameter and Clinical Correlation* LAURENT BEUCHAT, M.D. AVINOAM B. SAFRAN, M.D. Abstract Hypoplasia of the optic nerve is often subtle, and reduction in papillary diameter can be difficult to deled during ophthalmoscopic examination. Using a slit-lamp and a posterior fundus contact lens, we evaluated papillary diameter by bringing margins of the light beam to coincide with the limits of the optic nerve head. The method was standardized with 140 presumably normal eyes. Then we studied 17 consecutive eyes showing optic nerve hypoplasia. Hypoplasic discs were separated into two categories: (l) nine cases defined as having "moderate" hypoplasia, in which average disc di­ameters ranged between -2 and -2.5 standard de­viations under the mean normal value; and (2) eight eyes with "severe" hypoplasia, showing av­erage disc diameters less than the normal mean value by 2.5 standard deviations or more. Double peripapillary ring sign and low disc/artery ratio are clues often used in the diagnosis of optic nerve hy­poplasu. The incidence of these signs was also evaluated in the hypoplasic discs studies. The double ring sign was present in two of the nine eyes with moderate hypoplasia, and in seven of the eight eyes with severe hypoplasia. Of eight eyes with moderate hypoplasia, only one showed a disclartery ratio inferior to the mean normal value - 2 standard deviations, whereas this ratio was significantly reduced in all cases of severe hypo­plasia. These ophthalmoscopic clues therefore ap­pear to be much less valuable than direct measure­ment of the optic disc for detecting a subtle reduction in disc diameter. This is of particular in­terest when one considers that all the nine eyes with moderate hypoplasia had alteration in visual fundion upon presentation. The method we used provides a simple, sensi­tive, and quantitative evaluation of papillary size. From the Neuro-ophthalmology Unit, Department of Oph­thalmology, Geneva University Hospital, Geneva, Switzer­land. • This study was presented in part at the Neuro-Ophthal­mological Symposium, 13th World Congress of the Israel Medical Association, Jerusalem, Israel, May 22, 1985. Write for rqmnts to: A. B. Safran, MO, Unitl! de Neuro­ophtalmologie, Clinique d'ophtalmologie, HOpital cantonal universitaire, CH-1211 Geneva 4, SWitzerland. December 1985 Hypoplasia of the optic nerve is a congenital condition characterized by an abnormally low number ofaxons in the optic nerve. It is often associated with impairment of visual func­tion. 1.2 One of its usual clinical features is a smaller optic disc surface. 3 Hypoplasia is often subtle, and the reduction in papillary diameter can be difficult to detect during ophthalmo­scopic examination. Since visual impairment can also be associ­ated with subtle hypoplasia, the availability of a simple clinical technique allowing direct eval­uation of papillary diameter would be useful. In this article we describe such a technique, using a slit lamp and a Goldmann posterior fundus contact lens. The method was standardized with 140 normal eyes. In addition to reduction in optic disc diam­eter, various ophthalmoscopic clues to the di­agnosis of optic nerve hypoplasia have been de­scribed, including a low disc/artery ratio, 2 and a double peripapillary ring sign.] We evaluated the incidence of these clues in 17 consecutive eyes presenting optic discs with a diameter in­ferior to the normal mean value we had previ­ously established by more than two standard deviations. Subjects and Method Evaluation of disc diameter was first per­formed in a series of 140 eyes presumed to be normal, from 70 subjects presenting for routine ophthalmological examination and showing 20/ 20 or better best corrected visual acuity. The subjects comprised 40 males and 30 females, ranging in age from 13 to 82 years, with an av­erage of 44 years. Thirty were emmetropes, while 40 had ametropia, varying from - 6 to +6 diopters. Seventeen consecutive eyes (15 patients) pre­senting with optic disc diameters inferior to the normal value by more than two standard devia­tions were studied. Ametropia varied trom - 3 to +2 diopters. Patients underwent an ophthal­mological examination, which included evalua­tion of visual acuity, kinetic Goldmann perim- 249 Optic Nerve Hypoplasia etry, and fundus biomicroscopic examination. Tilted discs were excluded from this series. Measurement of the optic nerve head was performed by adjusting the limits of a slit beam to the borders of the optic disc. A Haag-Streit 900 slit lamp (Haag-Streit AG, Bern, Switzer­land) and a Goldmann posterior fundus contact lens were used. Calibration of the slit width was done in the following way. The beam was fo­cused on a micrometer (Roch, Nyon, Switzer­land) and the slit width was enlarged by steps of 0.1 mm, from 0.4 mm to 1.8 mm. Each of these successive widths was matched on the ar­bitrary scale on the knob regulating the beam width. The pupils of the subjects examined were di­lated with tropicamide 0.5%. Through the Gold­mann posterior fundus contact lens, the slit beam was focused on the optic disc plane. The illumination system of the slit lamp was rotated some 150 to the side of the examined eye, so that the slit beam could be projected perpendic­ularly to the plane of the optic disc. The main axis of the slit was horizontal for vertical di­ameter measurements, and vertical for hori­zontal diameter measurements. The margins of the beam were then brought to coincide with the limits of the optic nerve head (Fig. 1). The slit was calibrated with systematic errors of up to 5%. When 10 successive readings were made by the same operator, variations in scale reading \ \ I I I Figure 1. Evaluation of optic disc diameter. The margins of the slit beam are brought to coincide with the limits of the optic nerve head (arrows). Values obtained from the scale of the slit-lamp knob are then corrected according to the refractive error of the examined eye. taking into account the magnification factor indicated on Figure 2. 250 were less than 2.5% of width values ( :!: 0.125 of the units displayed on the scale). It has been established that fundus magnifi­cation obtained by using a contact lens is deter­mined by various factors, including the optical properties of the instrument used and the re­fractive error of the examined eye4 (Fig. 2). When evaluating dimensions of structures in the ocular fundus by means of a slit lamp and a fundus contact lens, values obtained from ex­amination with a graticule-fitted ocular, as per­formed by Franceschetti and Bock,4 are identical with those obtained using comparison with a calibrated slit of light. t In addition, we used a slit lamp and a contact lens similar to those used by Franceschetti and Bock, according to the re­fractive error of the examined eye. The mean diameter of the optic disc was ob­tained by averaging horizontal and vertical di­ameter values. All fundi were photographed with Koda­chrome 25 film and were analyzed for compar­ison of diameters of the disc with the central retinal artery or the largest arteriole appearing on the disc (disc/artery ratio), as well as for the occurrence of a peripapillary double ring sign. Results Measurements in the 140 optic discs pre­sumed to be normal provided the following values: • Mean horizontal diameter was 1.38 rom :!: 0.27 (1 SO); • Mean vertical diameter was 1.46 :!: 0.24 (1 SO); • Mean average diameter was 1.42 mm :!: 0.24 (l SO); • Mean disc/artery ratio was 17.3 :!: 2.8 (1 SO); • Peripapillary double ring was present in only one of 140 (0.7%) presumably normal eyes. t We experimentally demonstrated this in the following way: (1) A sheet of paper displaying a 5-mm-wide pattern was VIewed through the slit lamp microscope; (2) a 5-mm­wide slit of light was focused onto the plane of the paper; (3) one of the slit lamp oculars was fitted with a graticule allowing evaluation of dimensions of examined structures· using the graticule. it was verified that both the paper pat: te~ and slit width appeared to be 5 mm wide through the mIcroscope; (4) a +20 diopter lens was then placed in hont of.the paper palle~. so that the light beam passes through thIS lens; (5) the slit of light was refocused onto the plane of the sheet of paper; (6) using the graticule it was found that the ~aper p.attem alone appeared magnified, whereas th~ sht ~dth still appeared with the graticule to be 5 mm WIde. ThIS shows that evaluation of a (magnified) structure by means of the graticu1e provides values identical with those obtained using comparison with the width of a cali­brated slit of light. Journal of Clinical Neuro-ophthalmology Beuchat, Safran M Figure 2. Graph demonstrating the relation between magnification of the fundus using a contact glass of Goldmann (M) and ametropia in diopters (D). (From Franceschetti and Bock. ~ Published with permission from the American Joumal of Ophthalmology. C by the Ophthalmic Publishing Company.) Optic discs in which the average values of the two orthogonal axes ranged between - 2 and - 2.5 standard deviations under the normal mean value were defined as having "moderate" hypoplasia, whereas discs showing average values that were less than the normal mean value by 2.5 standard deviations or more were considered as having "severe" hypoplasia. Clinical findings in 17 consecutive eyes pre­senting with optic nerve hypoplasia are sum­marized in Table 1. Nine showed moderate hy­poplasia, and eight showed severe hypoplasia. Two eyes with severe hypoplasia were exo­tropic. In eight of the eyes with moderate hy­poplasia, disdartery ratios were equal or supe­rior to 11 (mean 13.25). In the remaining eye of this group, the ratio could not be evaluated. Seven cases of severe hypoplasia demonstrated disdartery ratios equal or inferior to 8, whereas in the remaining eye it was 9. A double ring sign was present in only two of the nine cases of moderate hypoplasia, one of which was in­complete. This sign was present in all but one case of severe hypoplasia. Discussion Diagnosis of optic nerve hypoplasia is greatly facilitated by the observation of several clinical features, including a peripapillary double ring sign and a reduction in optic nerve diameter. The double ring sign consists of a yellow-gray peripapillary halo, delineated by an outer ring corresponding to the junction between the sclera and the lamina cribrosa, and an inner December 1985 ring, the termination of the retinal pigmentary epithelium. s This sign can, however, be absent in eyes with discrete optic nerve hypoplasia, and can even occur in clinically normal eyes.] Reduction in optic nerve head diameter is a cardinal feature of optic nerve hypoplasia. Eval­uation, however, is often difficult in clinical practice, and various methods have been sug­gested. Morgan,6 and later Lambert,7 used a di­rect ophthalmoscope, which projected a grati­cule on the fundus; this method nevertheless gave inaccurate and only relative readings. 4 Somewhat more accurate results were obtained by Spinelli8 and others, who proposed indirect ophthalmoscopic measurement with a grad­uated scale on the frontal or ocular lens. In a paper devoted to the study of a case of mega­lopapilla, Franceschetti and Bock4 measured the disc diameter by means of focal illumination of the fundus with a slit lamp, using a Goldmann posterior fundus contact lens and an ocular fitted with a micrometer scale. Disc size was cal­culated, taking into account the refractive error of the examined eye; we found, however, that visualization of the scale is not easy during focal illumination of the fundus. Kennedy et al.9 sug­gested measuring ocular fundus structures by projecting interference fringes; this provides very precise values but requires sophisticated instrumentation not available to most ophthal­mologists. Several methods for evaluation of disc diam­eter have been proposed using photogrametric analysis. These include comparison of diame­ters of the disc with a 30° fundus photograph 251 Optic Nerve Hypoplasia TABLE I. Clinical Findings in 17 Eyes with Optic Nerve Hypoplasia Papillary Diameter (mm)' Double DisciArtery A".' Visu.,1 Visual Vertical Average Ring Sign RatiO" Cd"'-' ()'r) Awily Fidds Huri~unlal Moderate Hypoplasia 0.86 (-2.7) 0.96(-2.1) 0.90 (-2.2) Present 12 (-1.9) I 26 20/25 Normal 2 62 20/50 Nasal def~ct 0.86 (-2.7) 0.94(-2.1) 0.92(-2.1) Absent 14 (-1.2) 41 20/25 Normal 0.83 (-2.4) 0.93(-2.2) 0.88 (-2.3) Absent 16 (- 0.5) 3 4 40 20/35 Constricted, paracentral temporal defect 0.98 (-1.7) 0.90 (- 2.3) 0.94(-2.1) Absent 11 (-2.3) 5 57 20/35 Superior defect. 0.92 (-2.1) 0.90 (-2.3) 0.90 (-2.2) Present 13 (-1.5) enlarged blind (sectorial) spot 6 58 20/60 Constricted. arcuate scotoma 0.93 (- 2.0) 0.90 (-2.3) 0.91 (-2.1) Absent Not available 7 SO 20/20- 2 Superior temporal defect 0.91 (- 2.1) 0.91 (-2.2) 0.91 (-2.2) Absent 16 (-0.5) 8 50 20/20- 1 Superior altitudinal defect 0.91 (- 2.1) 0.91 (- 2.2) 0.91 (-2.2) Absent 15 (-0.8) 9 54 20/25 Arcuate scotoma 0.87 (-2.2) 0.92 (-2.2) 0.89 (-2.3) Absent 12 (-1.9) Severe Hypoplasia 10 25 Finger counting Nasal defect, 0.37 (-4.4) 0.74 (-3.0) 0.55 (-3.6) Present 7 (-3.7) enlarged blind spot 11 57 20/25 Arcuate scotoma 0.60 (-3.4) 0.83 (-1.5) 0.72 (-3.0) Present 8 (-3.3) 12 57 20125 Arcuate scotoma 0.74 (-2.7) 0.83 (-2.6) 0.78 (-2.6) Present 8 (-3.3) 13 40 20/35 Marked constriction 0.73 (-2.8) 0.73 (-3.0) 0.73 (-2.8) Present 7.5 (-3.5) 14 31 Hand movement NA 0.60 (3.4) 0.83 (- 2.5) 0.71 (-3.0) Present 8 (-3.3) perception 15 75 Hand movement NA 0.78 (-2.6) 0.90 (-2.3) 0.84 (-2.5) Absent 7.5 (-3.5) perception 16 63 20/40 NA 0.80 (-2.5) 0.73 (-3.0) 0.76 (- 2.7) Present 9 (-3.0) 17 9 Hand movement NA 0.28 (-4,8) 0.46 (-4.0) 0.37 (-4.0) Present 3.5 (-4.9) perception NA '"' not available. • Standard deviations from mean normal value are shown in parentheses. field,IO and comparison of diameter of the disc with either the central retinal artery or the largest arteriole appearing on the disc. 2,10 Normal mean ratio has been found to be 14.6 ± 2.4 (1 SD). II Evaluation of the retinal nerve fiber layer has been suggested by Frisen and Holmegaard,3 as an alternative approach to the problem of detection of optic nerve hypoplasia. The method we used in this study (suggested by B. S. Grimson, personal communication, 1980) allows a quantitated evaluation of the size of the optic nerve head, and requires no special instrumentation. The only prerequisite is the calibration of slit widths with either a graticule­fitted ocular or a micrometer, and the matching of the values on the scale of the knob regulating the slit width; this is done within 15 min. This 252 method is comparable to that of Franceschetti and Bock.4 Interestingly, all nine eyes with moderate hy­poplasia presented with alteration either in vi­sual acuity or in visual fields. This emphasizes the importance of detecting even subtle hypo­plasia of the optic nerve with precise quantita­tive methods. The technique used in this study proved to be a useful tool for such an evalua­tion. Although it did not prOVide absolute values of disc diameters (minor optical factors having not been taken into account), this simple, sensitive and quantitative method al­lowed valuable clinical comparison of normal mean values with those obtained from the ex­amined eye. It proved to be much more valuable for detection of optic nerve hypoplasia than ob- Journal of Clinical NeurCH>phthalmology servation of other classic ophthalmoscopic clues, such as peripapillary double ring sign or low disc/artery ratio smaller than the normal mean value - 2 standard deviations, whereas the ratio was significantly reduced in all cases of severe hypoplasia. It has recently been demonstrated that both retinal blood flow 12 and diameter of retinal arterioles!3 are reduced in eyes with optic atrophy. Since the number ofaxons in hypo­plasic optic nerves is smaller than in normal optic nerves, we hypothesize that with optic nerve hypoplasia, as with optic atrophy, reduc­tion in the number ofaxons is associated with a decrease in both retinal blood flow and di­ameter of retinal arterioles. This would explain the fact that disc/artery ratio was not found to be significantly altered in seven of eight eyes with moderate hypoplasia. We further suggest that ability of retinal vessels to adapt is limited, and that therefore beyond a certain degree of reduction in number ofaxons, a decrease in disc/artery ratio occurs, as demonstrated in the group of eyes with severe hypoplasia. The technique of disc evaluation used in this study has certain limitations. It is probably not very reliable in measurement of markedly tilted discs, because in such cases the slit beam might not be projected perpendicularly onto the plane of the optic disc. This is why tilted discs were excluded from our series. It is also conceivable that sectorial hypoplasia of the optic disc can be overlooked if hypoplasic sectors of the disc are located outside the axes of horizontal and ver­tical diameter measurement. Finally, when measuring optic disc diameter, care should be taken not to confuse actual disc margins with the limits of adjacent structures. Since hypo­plasic discs are often surrounded by a yellowish ring of approximately normal disc diameter, or by a dysplasic crescent, small discs combined with surrounding halo may incorrectly be inter­preted as presenting normal dimensions. Acknowledgment The authors thank Professor Hans Goldmann, Uni- December 1985 Beuchat, Safran versity Eye Clinic, Bern, Switzerland, and Professor Pierre Descouts, University Institute of Physics, Ge­neva, Switzerland, for reviewing the manuscript. References 1. Walton, D. 5., and Robb, R. M.: Optic nerve hy­poplasia. Arch. Ophthalmol. 84: 572-578, 1970 2. Edwards, W. c., and Layden, W. E.: Optic nerve hypoplasia. Am. f. Ophthalmol. 70: 950-959,1970. 3. Frisen, L., and Holmegaard, L.: Spectrum of optic nerve hypoplasia. Br. J. Ophthalmol. 62: 7­15, 1978. 4. Franceschetti. A., and Bock, R. H.: Megalopa­pilla: A new congenital anomaly. Am. J. Ophthalmol. 33: 227-234, 1950. 5. Mosier, M. A., Liberman, M. F., Green, W. R., and Knox, D. L.: Hyoplasia of the optic nerve. Arch Ophthalmol. 96: 1437-1442, 1978. 6. Morgan, O. G.: A retinal graticule. Br. J. Ophtlull mol. 11: 339-341, 1927. 7. Lambert, R.: A simplified retinal measuring grid. Arch. Ophtlull mol. 7: 440-443, 1932. 8. Spinelli, F.: Mikrometrie des Augenhinter­grundes, Bestimmung und sklerale Lokalisation von Netzhautpunkten, ausgefiihrt mit speziellen Zusatzteilen am vereinfachten Gullstrandschen Ophthalmoskop. Klin. Monatsbl. Augenheilk. 92: 93-107, 1934. 9. Kennedy, S. I., Schwartz, B., Takamoto, T., and Eu, I. K.: Interference fringe scale for absolute ocular fundus measurement. Invest. Ophthalmol. Vis. Sci. 24: 169-174, 1983. 10. Romano, P.: Photogrammetric diagnosis of optic nerve hypoplasia. American Academy of Oph­thalmology, Poster Abstract, November 1981. 11. Robin, A. L., Quigley, H. A., Pollack, I. P., Maumenee, A. E., and Maumenee, I. H.: An analysis of visual acuity, visual field and disk cupping in childhood glaucoma. Am. J. Ophthalmol. 88: 847-858, 1979. 12. Sebag, I., Feke, G. T., Delori, F. c., and Weiter, I. I.: Anterior optic nerve blood flow in experi­mental optic atrophy. In: A. Neetens, ed. Neuro­ophthalmology. Proceedings of the Neuro-ophtltal­mology Joint World Meeting, May 14-18, 1984. Antwerp: University of Antwerp, 1984: 367-369. 13. Frisen, L., and Claesson, M.: Narrowing of the retinal arterioles in descending optic atrophy. Ophthalmology 91: 1342-1346, 1984. 253