Glaucoma Or Myopia? Differentiating Between Glaucomatous and Myopic Optic Discs

CLINICAL STRATEGIES Glaucoma or Myopia? Differentiating between glaucomatous and myopic optic discs.

BY WIDO M. BUDDE, MD

etecting glaucoma in eyes with moderate or no myopia is simi- lar, because the appearance of their optic nerves is more or less D 1 the same (Figure 1). In highly nearsighted eyes, diagnosing glaucoma is difficult, because the visual field is likely to be abnormal due to myopic irregularities of the fundus irrespective of additional glaucomatous field changes. Furthermore, the IOP in highly myopic eyes with open-angle glaucoma (OAG) is more likely to be in the normal range than in glaucomatous eyes without high myopia. For that reason, clinicians often must rely on an examination of the optic disc in order to diagnose glaucoma in high myopes. The ophthalmoscopic appearance and histology of the optic nerve head differ markedly between eyes with and without high myopia (Figure 2).2-5 These abnormali- Figure 1. In the eye with medium myopia (-4.00 D), the right optic disc is ties have to be differentiated from and may slightly enlarged (2.6 mm2).The neural retinal rim has a normal configura- complicate the identification of glaucoma- tion, and the visibility of the nerve fiber layer is excellent.The parapapillary tous damage. Because the contour of the atrophy zone beta is adjacent to the disc temporally, and retinal pigment retinal vessels on the disc is often the sole epithelium is missing.The visibility of the underlying choroid is enhanced indicator of the surface topography, it may with large choroidal vessels and choroidal pigmentation. Adjacent to the be the only means of identifying the width beta zone is the parapapillary atrophy zone alpha with irregularities (hyper- of the neuroretinal rim at a given disc seg- and hypopigmentation) of the retinal pigment epithelium. ment. As a result, clinicians must assume each highly myopic optic disc to be glaucomatous until In severely nearsighted eyes, including the highly my- proven otherwise. opic form of primary open-angle glaucoma, the globe stretches and becomes larger. Correspondingly, the optic INTRAPAPILLARY CHARACTERISTICS disc is abnormally large in the sense of an acquired The size of the optic disc varies among individuals from macrodisc due to the degree of ametropia.2,3 Addition- approximately 0.80 to almost 6.00 mm2 or about 1:7 in a ally, the optic disc in highly myopic eyes is oval, elongat- normal, white population.1 Within a range of -5.00 to ed, and obliquely oriented to a significantly greater de- +5.00 D of ametropia, the optic disc’s size is almost inde- gree than in any other group.3 The cup is also remarkably pendent of the refractive error of the eye, or it may grow shallow. The abnormal shape of the optic disc is much slightly by 1.2% ±0.15% for each 1.00 D increase toward more pronounced in eyes with a myopic refractive error myopia, according to a recent epidemiological study.1,6,7 of more than -12.00 D than in those with ametropia Beyond +5.00 D of refractive error, the optic disc is signifi- ranging from -8.00 to -12.00 D. This difference suggests cantly smaller than in emmetropic eyes, whereas it is sig- that the myopic stretching leading to the secondary nificantly larger beyond -8.00 D.1,6 macrodisc in highly myopic eyes pulls the optic disc

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more strongly in some directions than others. The myopic elongation of the globe stretches the optic disc and thins the lamina cribrosa.4,5 The same pressure difference between the intraocular and retrobulbar spaces is therefore distributed over a shorter length, resulting in a steeper pressure gradient across the lamina cribrosa.8,9 A continuous drop in the pressure difference between the intraocular and extraocular spaces in the lamina cribrosa would produce the same effect as an increase in IOP if the lamina cribrosa were of normal thickness. One can hypothesize that some similarities exist between the stretching of the optic disc in highly myopic eyes and the abnormal deformation and thinning of the lamina cribrosa in glaucoma.3,10 In severe myopia, the increased susceptibility for glaucomatous optic nerve fiber loss may be present mainly in eyes with large, abnormally Figure 2. In the eye with high myopia (-11.50 D) and glaucomatous optic shaped, optic nerve heads. atrophy, the optic disc is very large (6.5 mm2). It is surrounded by a my- It is possible that the secondary enlarge- opic crescent, where only large choroidal vessels and the bare sclera are ment and irregular stretching of the optic visible.The intrapapillary course of the retinal vessels suggests a total loss disc in highly myopic eyes are predisposing of neuroretinal rim at the 6- and 8-o’clock positions. factors to glaucomatous optic nerve damage, even in the presence of statistically normal IOP meas- optic discs do not differ in neuroretinal rim area from urements. That idea is corroborated by the results of a eyes that are not myopic.1,12 recent study that compared glaucomatous eyes with myopia in excess of -8.00 D with glaucomatous eyes PARAPAPILLARY CHORIORETINAL ATROPHY that had a moderate refractive error.11 The neuroretinal The secondary macrodiscs in highly myopic eyes differ rim in the highly myopic glaucoma group was signifi- from the primary macrodiscs in eyes with low-to-moder- cantly smaller than in the subgroup of glaucomatous ate myopia or hyperopia. The latter exhibit deep and eyes with a moderate refractive error when adjusted for large physiologic cupping and unremarkable parapapil- optic disc size. As a corollary, a subgroup of the highly lary atrophy.1 Eyes with the highly myopic type of chronic myopic glaucomatous eyes with especially large optic OAG and highly myopic eyes without glaucoma do not discs had significantly lower IOP measurements com- vary remarkably in the size of parapapillary atrophy.13 The pared with the subgroup of glaucomatous eyes with a large parapapillary atrophy in highly myopic eyes with moderate refractive error. These two groups did not dif- glaucoma may result mainly from nonglaucomatous fer significantly in neuroretinal rim area. causes such as the myopic stretching of the globe. In addition, the IOP measurements were lower, al- Ophthalmoscopically and histopathologically, para- though not significantly so, in the highly myopic papillary atrophy may be divided into a peripheral alpha group. This finding suggests that, at the same level of zone and a central beta zone.1,13 The former is character- IOP and with both subject groups adjusted for optic ized by an irregular hypopigmentation and hyperpigmen- disc area, the neuroretinal rim area was significantly tation of the retinal pigment epithelium and slight thin- smaller in the high myopes. The idea that severely ning of the chorioretinal tissue layer. The beta zone is myopic eyes are more susceptible to developing glau- characterized by a complete loss of the retinal pigment coma than eyes with smaller refractive errors may fit epithelium, marked atrophy of the retinal photoreceptor with the aforementioned histomorphometry of the layer and the choriocapillaris, clear visibility of the large lamina cribrosa in highly myopic eyes and with the choroidal vessels and sclera, and round boundaries to the pathophysiologic role that the anatomy of the lamina adjacent alpha zone on its peripheral side and to the cribrosa may play.4,5 Correspondingly, moderately peripapillary scleral ring on its central side.1,13,14 myopic eyes with chronic OAG and normally sized Parapapillary atrophy is significantly larger, and a beta

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zone occurs more often in eyes with glaucomatous optic disc and the shape of the rim follows the ISNT rule, the nerve atrophy than in normal eyes.1,13-19 In a recent longi- presence of a large cup may not be an indicator of glau- tudinal study, the enlargement of the beta zone occurred coma. If the neuroretinal rim cannot be distinguished significantly more frequently in progressive versus stable due to shallow cupping or if the course of a retinal vessel glaucoma. This finding holds true in hyperopic eyes or in indicates a gap in the neuroretinal rim, glaucoma may be eyes with myopia of less than 3.00 D. For ametropia of assumed. Evaluating the parapapillary atrophy in myopia between -3.00 and -8.00 D, an enlargement of parapapil- will not assist in the diagnosis of glaucoma. ❏ lary atrophy occurred in eyes with both progressive and stable glaucoma.20 That finding suggests that, in the higher Wido M. Budde, MD, is Privatdozent at the myopic range, glaucomatous progression as well as the Department of Ophthalmology and Eye Hospital, myopia itself may have contributed to the enlargement of Faculty of Clinical Medicine Mannheim, Univer- the parapapillary atrophy. In contrast, in moderately sity of Heidelberg, Mannheim, Germany, and he myopic and hyperopic eyes, the progression of glaucoma is in private practice at the Eye Clinic in Essen, alone may have produced an enlarged beta zone. Germany. Dr. Budde may be reached at +49 201 4379490; [email protected]. “Clinicians must differentiate the 1. Jonas JB, Budde WM, Panda-Jonas S. Ophthalmoscopic evaluation of the optic nerve alpha and beta zones from the head. Surv Ophthalmol. 1999;43:293-320. 2. Jonas JB, Gusek GC, Naumann GOH. Optic disk morphometry in high myopia. Graefes myopic scleral crescent in eyes with Arch Clin Exp Ophthalmol. 1988;226:587-590. 3. Jonas JB, Dichtl A. Optic disc morphology in myopic primary open-angle glaucoma. high myopia and from the inferior Graefes Arch Clin Exp Ophthalmol. 1997;235:627-633. 4. Dichtl A, Jonas JB, Naumann GO. Histomorphometry of the optic disc in highly myopic scleral crescent in eyes with eyes with absolute secondary angle closure glaucoma. Br J Ophthalmol. 1998;82:286-289. 5. Jonas JB, Berenshtein E, Holbach L. Lamina cribrosa thickness and spatial relationships ‘tilted optic discs.’” between intraocular space and cerebrospinal fluid space in highly myopic eyes. Invest Ophthalmol Vis Sci. 2004;45:2660-2665. 6. Ramrattan RS, Wolfs RCW, Hofmann A, et al. Determinants of optic disk characteristics in a general population: The Rotterdam Study. Ophthalmology. 1999;106:1588-1596. Clinicians must differentiate the alpha and beta zones 7. Varma R, Tielsch JM, Quigley HA, et al. Race-, age-, gender-, and refractive error-related from the myopic scleral crescent in eyes with high myo- differences in the normal optic disc. Arch Ophthalmol. 1994;112:1068-1076. 4 8. Morgan WH, Yu DY, Cooper RL, et al. The influence of cerebrospinal fluid pressure on the pia and from the inferior scleral crescent in eyes with lamina cribrosa tissue pressure gradient. Invest Ophthalmol Vis Sci. 1995;36:1163-1172. “tilted optic discs.” In the region of the myopic crescent, 9. Morgan WH, Yu DY, Alder VA, et al. The correlation between cerebrospinal fluid pressure and retrolaminar tissue pressure. Invest Ophthalmol Vis Sci. 1998;39:1419-1428. only the inner limiting membrane and the underlying reti- 10. Quigley HA, Hohman RM, Addicks EM, et al. Morphologic changes in the lamina 4 nal nerve fiber layer or its remnants cover the sclera. In cribrosa correlated with neural loss in open-angle glaucoma. Am J Ophthalmol. 1983;95:673-691. contrast, in the glaucomatous beta zone, Bruch’s mem- 11. Jonas JB, Budde WM. Optic nerve damage in highly myopic eyes with chronic open- brane and the choroid are interposed between the rem- angle glaucoma. Eur J Ophthalmol. 2005;15:41-47. 21-23 12. Jonas JB, Martus P, Budde WM. Anisometropia and degree of optic nerve damage in nants of the retina and the sclera. The alpha and beta chronic open-angle glaucoma. Am J Ophthalmol. 2002;134:547-551. zones may also be present in an eye with high myopia. 13. Jonas JB, Nguyen XN, Gusek GC, Naumann GO. Parapapillary chorioretinal atrophy in normal and glaucoma eyes. I. Morphometric data. Invest Ophthalmol Vis Sci. 1989;30:908- Both zones are significantly larger in highly myopic eyes 918. with glaucoma than in glaucomatous eyes that are not 14. Jonas JB, Fernandez MC, Naumann GO. Glaucomatous parapapillary atrophy. 24 Occurrence and correlations. Arch Ophthalmol. 1992;110:214-222. severely nearsighted. 15. Airaksinen PJ, Juvala PA, Tuulonen A, et al. Change of peripapillary atrophy in glau- The histology of the parapapillary region explains why coma. In: Krieglstein GK, ed. Glaucoma Update III. Berlin: Springer; 1987:97-102. 16. Anderson DR. Correlation of the peripapillary damage with the disc anatomy and field the blind spot is enlarged in highly myopic eyes. The abnor- abnormalities in glaucoma. Doc Ophthalmol Proc Series. 1983;35:1-10. mally large optic disc, the big peripapillary scleral ring, and 17. Park KH, Tomita G, Liou SY, Kitazawa Y. Correlation between peripapillary atrophy and optic nerve damage in normal-tension glaucoma. Ophthalmology. 1996;103:1899-1906. the unusually large zone without retinal photoreceptors 18. Kono Y, Zangwill L, Sample PA, et al. Relationship between parapapillary atrophy and correspond to an abnormally large absolute scotoma. The visual field abnormality in primary open-angle glaucoma. Am J Ophthalmol. 1999;127:674- 680. adjacent zone with structural irregularities of the retinal 19. Tezel G, Dorr D, Kolker AE, et al. Concordance of parapapillary chorioretinal atrophy in pigment epithelium represents a relative scotoma. ocular hypertension with visual field defects that accompany glaucoma development. Ophthalmology. 2000;107:1194-1199. 20. Budde WM, Jonas JB. Enlargement of parapapillary atrophy in follow-up of chronic CONCLUSION open-angle glaucoma. Am J Ophthalmol. 2004;137:646-654. 21. Fantes FE, Anderson DR. Clinical histologic correlation of human peripapillary anatomy. Clinicians do not need special techniques for examin- Ophthalmology. 1989;96:20-25. ing the optic discs of eyes with moderate myopia for 22. Jonas JB, Königsreuther KA, Naumann GO. Optic disc histomorphometry in normal eyes and eyes with secondary angle-closure glaucoma. II. Parapapillary region. Graefes Arch glaucomatous damage. In high myopia, however, they Clin Exp Ophthalmol. 1992;230:134-139. must take into account the secondary enlargement of 23. Kubota T, Jonas JB, Naumann GO. Direct clinico-histological correlation of parapapillary chorioretinal atrophy. Br J Ophthalmol. 1993;77:103-106. the disc. In a macrodisc, one may expect to observe a 24. Jonas JB, Budde WM, Lang PJ. Parapapillary atrophy in the chronic open-angle glauco- large cup. If neuroretinal rim is present around the optic mas. Graefes Arch Clin Exp Ophthalmol. 1999;237:793-799.

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