Jost B. Jonas

Ophthalmoscopic Evaluation of the Optic Nerve Head

Optic nerve diseases, such as the glaucomas, lead to changes in the intrapapillary and parapapillary region of the optic nerve head. These changes can be described by the following variables: size and shape of the optic disk; size, shape, and pallor of the neuroretinal rim; size of the optic cup in relation to the area of the disk; configuration and depth of the optic cup; ratios of cup-to-disk diameter and cup-to-disk area; position of the exit of the central retinal vessel trunk on the lamina cribrosa surface; presence and location of splinter-shaped hemorrhages; occurrence, size, configuration, and location of parapapillary chorioretinal atrophy; diffuse and/or focal decrease of the diameter of the retinal arterioles; and visibility of the retinal nerve fiber layer (RNFL). These variables can be assessed semiquantitively by ophthalmoscopy without applying sophisticated techniques. For the early detection of glaucomatous optic nerve damage in ocular hypertensive eyes before the development of visual field loss, the most important variables are neuroretinal rim shape, optic cup size in relation to optic disk size, diffusely or segmentally decreased visibility of the RNFL, occurrence of localized RNFL defects, and presence of disk hemorrhages.

Optic disc morphometry in chronic primary open-angle glaucoma. I. Morphometric intrapapillary characteristics.

Four hundred twenty-seven optic discs of 233 unselected patients suffering from chronic primary open-angle glaucoma were morphometrically evaluated and compared with the optic nerve heads of 253 unselected normal subjects. Only one randomly chosen eye per patient was taken into consideration. We found that glaucoma leads to a change in the characteristic configuration of the neuroretinal rim that in normal eyes is significantly (P < 0.001) largest at the lower disc pole, smaller at the upper and nasal disc side, and smallest in the temporal disc region. Based on this information, significant (P < 0.001) morphometric differences between “early” glaucomatous and normal discs are: (a) the neuroretinal rim area in the lower temporal disc sector is smaller than in the upper temporal disc sector; the smallest rim width is outside the horizontal temporal disc sector (“pathognomonic”); the quotient of horizontal to vertical c/d ratio is lowered; and (d) the lower temporal, upper temporal, and total rim area are decreased. No significant difference in overall optic disc size and form exists between normal and glaucomatous eyes. Smaller optic nerve heads are not more susceptible to glaucoma.

Optic disk morphometry in high myopia

The optic nerve head in highly myopic eyes is distinctly different from normal optic disks. We performed magnification-corrected morphometry of photographs of 51 optic nerve heads in highly myopic eyes (myopic refraction of more than −8.00 diopters). Mean refraction was −15.49 ± 5.76 diopters (range, −8.00 to 28.00 diopters), mean age 63.0 ± 12.1 years (range, 27–87 years). The disks were significantly (P < 0.000001; Wilcoxon-Mann-Whitney test) larger and more ovally configurated than 457 unselected normal optic nerve heads with a myopic refraction of less than −8.00 diopters. Refraction, size of the disk, and area of the parapapillary region with chorioretinal atrophy were significantly (P < 0.00001) correlated with each other. The parapapillary vessel diameter was independent from the disk size. Highly myopic disks can be regarded as secondary acquired macrodisks, the size of which is correlated with refraction and possibly age. They should be differentiated from secondary, acquired macrodisks in congenital glaucoma and from primary macrodisks. As in normal eyes, the parapapillary vessel caliber can be used to estimate the optic disk size in relative and approximately absolute units.

Count and density of human retinal photoreceptors.

This investigation was directed at determining the count and regional distribution of photoreceptors in the eyes of 21 human cornea donors aged between 2 and 90 years. Mean count of rods was 60 123 000 ±12907000, and mean cone count was 3173000 ± 555000. Determined 40 μm away from the foveola, cone density measured 125 500 cones/mm2. Extrapolating the distribution curve, cone concentration in the foveal center can be assumed to be about 150 000 cells/mm2 to 180 000 cones/mm2. Towards the retinal periphery, cone density decreased from 6000 cones/mm2 at a distance of 1.5 mm from the fovea to 2500 cells/mm2 close to the ora serrata. Comparing different fundus regions, cone concentration was significantly highest in the nasal region. Cone diameter increased from the center towards the periphery. At a distance of 40 μm away from the foveola, it measured about 3.3 μm, and in the outer retinal regions about 10 μm Rod density was highest in a ring-like area at a distance of about 3–5 mm from the foveola with a mean of 72 246 ± 17 295 cells/mm2. Rod density peaked at 150 000 rods/mm2. It decreased towards the retinal periphery to 30 000–40 000 rods/mm2. Rod diameter increased from 3 μm at the area with the highest rod density to 5.5 μm in the periphery. The hexagonal rod and cone inner segments were regularly arranged in a honey-comb fashion.

Retinal nerve fiber layer thickness in human eyes

Abstract · Background: A study was carried out to measure the thickness of the retinal nerve fiber layer (RNFL) at the optic disc border. · Methods: RNFL thickness at the optic disc border was histomorphometrically measured on histological sections of 22 human eyes with normal optic nerves and 21 human eyes with absolute secondary angle-closure glaucoma. For three eyes with normal optic nerves, serial sections through the whole optic disc area were available. · Results: In the eyes with normal optic nerves, the RNFL at the optic disc border showed a double hump configuration with the highest mean thickness in the inferior quadrant (mean ± S.D: 266±64 µm), followed by the superior quadrant (240±57 µm), the nasal quadrant (220±70 µm), and finally the temporal quadrant (170±58 µm). In the three globes with serial sections, RNFL was thickest at the inferior disc pole (397±58 µm), followed by the superior disc pole (313±38 µm), the nasal disc pole (165±19 µm), and finally the temporal disc pole (131±15 µm). In the eyes with absolute glaucoma, mean thickness of the remainder of the RNFL was 40±18 µm with no marked differences between the disc regions. · Conclusions: In normal eyes, the RNFL shows a double hump configuration with its thinnest part at the temporal disc pole, followed by the nasal disc pole and the superior disc pole. RNFL is thickest at the inferior disc pole. In glaucomatous optic neuropathy, the inner limiting membrane moves backward about 60–100 µm at the temporal disc border, and more than 200 µm at the inferior and superior disc poles.

Optic disk and retinal nerve fiber layer damage after transient central retinal artery occlusion: an experimental study in rhesus monkeys

PURPOSE To evaluate the retinal tolerance time to acute ischemic insult in middle-aged or elderly rhesus monkeys with pre-existing atherosclerosis and arterial hypertension. METHODS In 39 eyes of 39 middle-aged and elderly rhesus monkeys with a mean age of 19.5 +/- 2. 8 years, occlusion of the central retinal artery was produced by temporary clamping of the central retinal artery at its site of entry into the dural sheath of the optic nerve for 97 to 300 minutes. Stereoscopic color fundus photography and fluorescein fundus angiography were performed before central retinal artery occlusion and serially thereafter. Retinal nerve fiber layer damage and optic disk changes were assessed by comparing morphometric evaluation of the color fundus photographs taken before central retinal artery occlusion and color fundus photographs taken at the end of the study. RESULTS There was a significant correlation between duration of central retinal artery occlusion and decreased visibility of retinal nerve fiber layer (P =.018) and increasing optic disk pallor (P =. 014), and a trend between residual retinal circulation and decreased visibility of retinal nerve fiber layer (P =.085) and optic disk pallor (P =.162). However, there was a marked interindividual variation between the length of central retinal artery occlusion and degree of increased optic disk pallor and decreased visibility of the retinal nerve fiber layer, even among eyes with similar duration of central retinal artery occlusion. Complete or almost total optic nerve atrophy and nerve fiber damage were present in all eyes in which the duration of central retinal artery occlusion was 240 minutes or more. CONCLUSIONS The findings of this study, compared with our previous study in young healthy rhesus monkeys, indicate that in middle-aged or elderly atherosclerotic and arterial hypertensive rhesus monkeys, central retinal artery occlusion for less than 100 minutes produced no apparent morphometric evidence of optic nerve damage; however, central retinal artery occlusion of 105 minutes but less than 240 minutes produced a variable degree of damage; central retinal artery occlusion for 240 minutes or more produced total or almost total optic nerve atrophy and nerve fiber damage.

Optic Disk Hemorrhages in Glaucoma

We evaluated the frequency and location of optic disk hemorrhages by examining morphometrically color stereo optic disk photographs of 1,505 glaucomatous eyes and 595 normal eyes. Disk hemorrhages were found in 61 of the glaucomatous eyes (4.1%) and in none of the normal eyes. The frequency of the hemorrhages increased from an early stage of glaucoma to a medium-advanced stage and decreased again toward a far-advanced stage. The disk hemorrhages were not found in disk regions or eyes without detectable neuroretinal rim. In early glaucoma, they were usually located in the inferotemporal or superior disk regions. (The frequency of hemorrhages was 6.3% in normal-pressure glaucoma, 4.9% in primary open-angle glaucoma, and 3.1% in secondary open-angle glaucoma). They were correlated with localized retinal nerve fiber layer defects, neuroretinal rim notches, and circumscribed perimetric loss. These characteristics imply the pathogenetic and diagnostic importance of disk hemorrhages for the detection of glaucoma.

Clinical implications of peripapillary atrophy in glaucoma.

Purpose of review To elucidate peripapillary atrophy in glaucomatous optic neuropathy; its ranking in the morphologic diagnosis of the glaucoma, and its value for the differentiation of various types of chronic open-angle glaucoma, for the separation of glaucomatous eyes from nonglaucomatous eyes, and for the detection of progression of glaucoma. Recent findings Recent studies showed an association of peripapillary atrophy with glaucoma and the eventual development of glaucomatous disc hemorrhages independent of a small neuroretinal rim area, and an association between increasing peripapillary atrophy and progressive glaucoma. A ranking of optic disc parameters to detect glaucomatous damage revealed that the alpha and beta zones of peripapillary atrophy, compared with neuroretinal rim parameters, are less useful. Pseudoexfoliation syndrome without glaucoma is not a risk factor for peripapillary atrophy. In arteritic anterior ischemic optic neuropathy, peripapillary atrophy does not enlarge. Peripapillary atrophy does not differ markedly between Europeans and South Indians. In contrast to the position of the central retinal vessel trunk, the presence and position of cilioretinal arteries do not markedly influence the progression of peripapillary atrophy in glaucoma. Summary Peripapillary chorioretinal atrophy is one among several morphologic variables to detect glaucomatous abnormalities. Ranking optic disc variables for the detection of glaucomatous optic nerve damage, peripapillary atrophy is a variable of second order. It is useful for the differentiation of various types of chronic open-angle glaucomas. In contrast to glaucomatous eyes, eyes with nonglaucomatous optic nerve atrophy, including eyes after arteritic anterior ischemic optic neuropathy, do not show an enlarged peripapillary atrophy.

Evaluation of the retinal nerve fiber layer

In normal eyes, the retinal nerve fiber layer (RNFL) is usually best visible in the inferior temporal part of the fundus, followed by the superior temporal region, the nasal superior region and the nasal inferior region. This distribution correlates with the configuration of the neuroretinal rim, the diameter of the retinal arterioles, the location of the foveola, and the lamina cribrosa morphology. With increasing age, the RNFL visibility decreases diffusely without preferring special fundus regions and without the development of localized defects. With all optic nerve diseases, the visibility of the RNFL is decreased in addition to the age-related loss, in a diffuse and/or a localized manner. The localized defects are wedge-shaped and not spindle-like defects, running toward or touching the optic disk border. Typically occurring in about 20% of all glaucoma eyes, they can be found also in other ocular diseases, such as optic disk drusen, toxoplasmotic retinochoroidal scars, longstanding papilledema or optic neuritis due to multiple sclerosis. Since they are not present in normal eyes, they almost always signify an abnormality. RNFL evaluation is especially helpful for early glaucoma diagnosis and in glaucoma eyes with small optic disks. In advanced optic nerve atrophy, other examination techniques, such as perimetry, may be more helpful for following optic nerve damage. Considering its great importance in the assessment of optic nerve anomalies and diseases and taking into account the feasibility of its ophthalmoscopic evaluation using green light, the retinal nerve fiber layer should be examined during any routine ophthalmoscopy.

Correlation Between Mean Visual Field Loss and Morphometric Optic Disk Variables in the Open-angle Glaucomas

PURPOSE To correlate morphologic changes of the optic disk with mean visual field defect in glaucoma. METHODS Color optic disk photographs of 302 patients with primary open-angle glaucoma, 53 patients with pseudoexfoliative glaucoma, and 55 patients with normal-pressure glaucoma were morphometrically evaluated. The data were correlated with mean visual field defect. RESULTS The correlation between mean visual field defect and neuroretinal rim area was similar to a logarithmic function. The visual field deteriorated slightly in the early stage and markedly in the advanced stages of glaucoma. A discrepancy between normal visual field and abnormal optic disk occurred more often in young than in old patients. Neuroretinal rim shape, total rim area, and rim area in the temporal inferior and temporal superior disk sectors correlated best with mean visual field loss. Alpha and beta zones of peripapillary atrophy and diameter of retinal arterioles were less clearly correlated. Calculated rim variables that were corrected for optic disk area did not markedly improve the correlation coefficients. In eyes with normal visual fields, rim shape was the most important disk variable for detecting glaucomatous optic nerve damage. There were no patients with glaucomatous visual field loss and an unremarkable optic disk. CONCLUSIONS In early glaucoma, changes are more marked in optic disk appearance than in the visual field, suggesting that at least for some patients, for early glaucoma diagnosis, optic disk appearance is more important than perimetry, whereas for follow-up examination, perimetry may be more useful than optic disk morphometry. The most useful planimetric optic disk parameters are neuroretinal rim shape and rim area.