Reproducibility of photogrammetric optic disc cup measurements

To detect early glaucoma-associated changes in the optic disc cup, the authors analyzed reproducibility of optic disc cup measurements by photogrammetry of three age-matched groups: 10 normal, 10 ocular hypertensive, and 10 glaucomatous subjects. For each eye, three simultaneous stereophotographs were taken on the same day and one measurement was made for each stereophotograph. In order to reduce the effects of refractive error of the eye and photographic magnification, the authors computed cup parameters as relative measurements, ie, a ratio to the optic disc area. The median coefficients of variation for glaucomatous eyes were 4.5% for cup volume/disc area, 6.1% for cup depth/disc area, and 4.7% for cup area/disc area. Coefficients of variation of normal and ocular hypertensive subjects were slightly larger than those of glaucomatous subjects. Coefficients of variation generally were larger for quadrants than for total disc area. These findings suggest that the photogrammetric technique is highly reproducible and sensitive and could be a valuable quantitative technique for the clinical study of glaucoma.

Measurement of fluorescein angiograms of the optic disc and retina using computerized image analysis

Computerized image analysis was used to quantify objectively fluorescein angiograms of the optic disc, peripapillary choroid, and retina. Techniques were developed to measure fluorescein filling rates of the optic disc and the retinal vessels and the area of fluorescein filling defects within the optic disc. Two subjects, one with glaucoma and the other with ocular hypertension, showed increases of areas of fluorescein filling defects of the optic disc on follow-up and are presented here as examples of the application of these techniques. This methodology can be applied to the longitudinal follow-up of individual patients with glaucoma and retinal diseases, as well as to cross-sectional studies of patient populations.

A comparison of Peritest automated perimetry and Goldmann perimetry

Both Peritest perimetry and Goldmann visual field testing were performed on three groups of eyes. Eighty-one eyes had glaucoma with elevated intraocular pressures and abnormal visual fields determined by Goldmann perimetry. There were 47 eyes with suspected glaucoma, based on elevated IOPs and normal Goldmann visual fields. Nineteen eyes were normal. All visual fields were evaluated in masked fashion, and the results were compared. The Peritest had a high sensitivity in both glaucomatous (98.8%) and normal (94.7%) eyes. One half of the eyes with suspected glaucoma had abnormal Peritest results but normal Goldmann visual fields. These eyes were examined prospectively with color stereo discs and monochromatic nerve fiber layer photographs. One half of the eyes with suspected glaucoma and abnormal Peritest results also had photographic evidence suggesting optic nerve damage. Thus, early field defects detected by the Peritest perimeter in eyes with suspected glaucoma are likely to be representative of glaucomatous damage.

Detection of increased pallor over time. Computerized image analysis in untreated ocular hypertension

Computerized image analysis was used to measure changes in percent area of pallor of the optic disc in a retrospective study of a group of 16 normals and 39 untreated ocular hypertensives. The optic discs of the subjects were photographed on at least two visits at least one year apart (mean, 2 years). No significant changes in area of pallor for the normal group were observed between visits, except in the inferior quadrant of the left eye. The ocular hypertensive group showed a significant increase in area of pallor between visits for the total disc and for most quadrants of both eyes. Multiple regression analysis revealed that, in addition to ocular hypertension, the significant factors associated with a change in optic disc pallor were change of ocular pressure, standard deviation of the ocular pressures, presence of vascular hypertension, and standard deviation of vascular pulse pressures. Clinical implications of early detection of disc changes for follow-up and treatment of ocular hypertensives are discussed.

Evaluation of nerve fiber layer assessment

More than 1,400 eyes with either ocular hypertension glaucomatous visual field loss, or normal pressures and fields (controls) were studied prospectively in standardized, masked fashion. The appearance of the nerve fiber layer was evaluated independently from red-free photographs with the discs blocked-out by two observers. The vast majority of photographs could be evaluated, the proportion varying with the observer and with the age and clinical status of the subject. Sensitivity (proportion of glaucomatous eyes with nerve fiber defects) and specificity (proportion of normal control eyes without defects) averaged 80% to 94%, varying with the observer and with the age, race, and severity of field loss. In two thirds of presumed false-positive eyes, but only 5% of true-positive eyes, the abnormalities were limited to focal slitlike defects. The prevalence of nerve fiber defects in eyes with elevated pressure and normal visual fields was similar to that in control eyes, approximately 10%. However, the proportion of eyes in which these defects included diffuse loss was considerably higher among the hypertensive eyes.

Acute Intraocular Pressure Elevation Produced by Argon Laser Trabeculoplasty in the Cynomolgus Monkey

The short-term effect of argon laser trabeculoplasty (ALT) was studied in a nonhuman primate model. The ALT treatment produced a consistent intraocular pressure elevation in the treated eye for eight hours. A statistically significant indomethacin-resistant increase in aqueous humor protein concentration was also observed. Morphologic observations using light microscopy and scanning and transmission electron microscopy revealed evidence of a fibrinous material covering the trabecular openings four hours after ALT. Cells and tissue debris appeared to be trapped in this fibrinlike net and may be the cause of the acute rise in IOP. Twenty-eight hours after ALT, the fibrin net was shown to be discontinuous, with fewer cells and less debris present. These acute morphologic alterations were not seen in control eyes or the laser-treated eyes observed later.

Correlation of color vision deficits and observable changes in the optic disc in a population of ocular hypertensives

Both glaucomatous cupping and the presence of acquired color vision deficits have been reported to be precursors to the onset of visual field defects in patients with suspected glaucoma. To examine the relationship between early glaucomatous cupping and acquired color vision anomalies, we performed anomaloscope (Pickford-Nicholson) and Farnsworth-Munsell 100-Hue color vision tests in 48 ocular hypertensive eyes with either clinical evidence of early glaucomatous cupping (group 1) or no evidence of glaucomatous cupping (group 2). All patients had normal visual fields, as determined by extensive static perimetry of the central visual field and kinetic perimetry of the peripheral visual field. Although the overall incidence of blue and blue-green color vision anomalies in the ocular hypertensives was comparable with that reported in previous studies, we found no clear association between early glaucomatous cupping and color vision anomalies. The relationship between these two precursors to visual field loss remains unclear.

Solitary silent venous papillary loops and ocular hypertension

A series of 24 eyes in 23 patients is described showing solitary silent venous papillary loops. These loops are usually associated with a considerable degree of ocular hypertension, presenting when this hypertension is being investigated. They are silent, usually with no previous ocular history, single with a large diameter, affecting veins at the optic disc and not extending into the vitreous. The optic disc is cupped, but usually not more than 0.6 disc diameter, there is good central vision and either a full visual field or only early field loss. Fluorescein angiography shows the loops to be competent with no evidence of any other retinal vascular abnormality. Rarely loss of central vision may occur due to progression to advanced glaucoma. The condition is distinct from prepapillary vascular arterial papillary loops, neovascularization at the optic disc and optociliary shunt vessels. It is also distinct from the venous collateral vessels which develop at the optic disc after acute central or branch retinal vein occlusion. These collaterals are usually multiple, the accompanying ocular hypertension is of lesser degree, cupping of the disc and field loss are usually much more advanced and, while visual acuity may be normal, it is often grossly reduced. On fluorescein angiography all these cases of venous collaterals after retinal vein occlusion showed evidence of other retinal vascular dysfunction. Solitary silent venous papillary loops appear to develop from venules on the optic disc as a bypass to a low grade venous occlusion which is seldom clinically manifest. They form a distinct entity with a good prognosis if the accompanying ocular hypertension is carefully controlled.

Cross-polarization photography of the nerve fiber layer

Cross-polarized photography was used to enhance the visibility of the arcuate bundles of the retinal nerve fiber layer ( NFL ). A fundus camera (Zeiss) was modified to accept a linear polarizing filter in front of the flash and another polarizing filter in front of the film plane. The azimuths of the two filters were kept at right angles to one another. Cross-polarized photographs were taken of the NFL of seven normal eyes and 18 eyes with ocular hypertension. The polarizers were rotated together to obtain four different orientations, equally spaced through 90 degrees. The manner in which visibility of the arcuate fibers was enhanced varied consistently with the orientation of the polarizing filters. Cross-polarization accentuated apparent defects in the NFL when compared with standard red-free illumination.

Corneal endothelial cell density in acute angle-closure glaucoma

The endothelial cell density of 44 eyes after an acute attack of angle-closure glaucoma is statistically lower than the cellular density of 174 control eyes. The decrease in endothelial cell density increases the risk of edematous corneal dystrophy, more specially after surgery (e.g. cataract extraction). The modifications in corneal endothelial cell density are compared with the alterations of the iris after a crisis of angle-closure glaucoma.

Relationship between baring of circumlinear vessels of the optic disc and glaucomatous visual field loss

Stereo disc photographs of the eyes of 232 patients with normal or elevated intraocular pressure were reviewed to assess the value of baring of circumlinear vessels of the optic nerve head as a sign of glaucomatous damage. Baring and the presence of glaucomatous visual field defects were significantly correlated, as were this sign and consistent elevation of the intraocular pressure in patients without a visual field defect. Baring was absent in 35% of the eyes with circumlinear vessels and known glaucomatous visual field defects. However, it was present in only 6% of the eyes with normal pressure, a normal visual field and circumlinear vessels. Therefore, this sign should lead to further evaluation.

High-resolution photography of the retinal nerve fiber layer

Abnormalities in the appearance of the retinal nerve fiber layer can indicate the presence of optic nerve atrophy, but a major problem has been the difficulty of visualizing the nerve fiber layer in some individuals. By selectively illuminating the white nerve fiber layer in comparison with the red retinal pigment epithelium and choroidal background, red-free light increases the visibility of the nerve fiber layer. Compared with the standard red-free photographic technique, a 560-nm short-pass cut-off filter, used with extended-range, high-resolution, extremely fine-grain film (Kodak No. 2415 Technical Pan film), considerably enhanced the ability to resolve nerve fiber bundles.

An optic disc grid: its evaluation in reproducibility studies on the cup/disc ratio

A grid system is described which may be superimposed upon stereoscopic pairs of optic disc photographs. This grid system allowed reproducible inter- and intraobserver measurements of the cup/disc (C/D) ratio. The surface contour of the optic disc was not clear-cut in approximately 10% of the population studied, which led to a reduction in reproducibility of the measurement made within the group as a whole. As a result it was found that a large increase in the C/D ratio would have to occur for such change to be of statistical significance. Even with an optic grid as a reference system the serial measurements of the C/D ratio are unlikely to be of value in the management of patients with chronic glaucoma.

Baring of a circumlinear vessel in glaucoma

We independently examined 144 optic disc stereophotographs. Despite a preliminary learning trial, we were able to agree about the presence of a circumlinear vessel in only 73% of eyes and about baring of a vessel, if present, in only 71% of eyes. Bared vessels were present in 73% of 22 glaucomatous eyes, 41% of 71 ocular hypertensive eyes, and 14% of 51 normal eyes. During several years of follow-up of 44 ocular hypertensive eyes with bared circumlinear vessels, visual field defects developed in only three. We conclude that baring of a circumlinear vessel is a difficult sign for trained observers to detect with certainty and, although present frequently in glaucoma, is of low specificity as a sign or predictor of glaucomatous damage.

Increased pressure of dilated episcleral veins with open-angle glaucoma without exophthalmos

Six unilateral cases and one bilateral case of dilated episcleral veins with elevated intraocular pressure without exophthalmos are described. Episcleral venous pressure measured on six unilateral cases showed increased pressure in the affected eye compared to the other eye and to normal controls. Two eyes had typical glaucomatous disc and visual field changes. Five had more optic disc cupping and pallor in the eye with the elevated episcleral venous pressure and intraocular pressure. A thorough work-up, including orbital venography in two unilateral cases, carotid arteriography in one and episcleral fluorescein angiography in five cases, failed to show venous obstruction or direct arterio-venous communications. The different diagnoses are discussed. This condition should be considered in unilateral or asymmetrical intraocular pressure elevation and in those patients with chronically red eyes without discharge.

Optic nerve axons and acquired alterations in the appearance of the optic disc

The pathophysiologic events in optic nerve axons have recently been recognized as crucial to an understanding of clinically significant acquired alterations in the ophthalmoscopic appearance of the optic disc. Stasis and related abnormalities of axonal transport appear to explain most aspects of optic nerve head swelling, including optic disc drusen and retinal cottonwool spots. Loss of axoplasm and axonal death can be invoked to interpret optic disc pallor, thinning and narrowing of rim tissue, changes in the size and outline of the optic cup, laminar dots, atrophy of the retinal nerve fiber layer, and acquired demyelination and myelination of the retinal nerve fiber layer. It is speculated that the axons may also play a role in the mechanical support of the lamina cribrosa in resisting the pressure gradient across the pars scleralis of the optic nerve head. Axons and their associated glial cells may be involved in those cases where "reversibility" of cupping of the optic disc has been reported. The structure, physiology, and experimental pathologic findings of the optic nerve head have been reviewed. Many aspects concerning the final anatomic appearance of the optic nerve head have been explained. However, many questions remain concerning the intermediate mechanisms by which increased intracranial pressure retards the various components of axonal transport in papilledema and by which increased IOP causes axonal loss in glaucoma. Investigation of the molecular biology of axonal constituents and their responses to abnormalities in their physical and chemical milieu could extend our understanding of the events that result from mechanical compression and local ischemia. Moreover, we have identified a need to further explore the role of axons in the pathophysiology of optic disc cupping.

Central corneal endothelial cell density and central corneal thickness in ocular hypertension and primary open-angle glaucoma

In order to assess the effect of increased intraocular pressure on the corneal endothelium, we classified 254 patients into four groups: Group 1, those with normal intraocular pressures; Group 2, those with untreated ocular hypertension; Group 3, those with treated ocular hypertension; and Group 4, those with primary open-angle glaucoma. One eye of each patient underwent specular microscopy and pachymetry. The eyes in the four groups did not differ significantly as to central corneal endothelial cell density or central corneal thickness. These measurements were not related to sex, race, or intraocular pressure (P greater than .12 in all cases). Increasing age was associated with a decrease in central corneal endothelial cell density (P = .0001), but was not associated with a change in central corneal thickness (P = .22). There was no significant relationship between the use of topical ocular hypotensive medications and central corneal endothelial cell density (P = .38) or central corneal thickness (P = .07) in patients with ocular hypertension or primary open-angle glaucoma. Neither uncomplicated peripheral iridectomy nor trabeculectomy produced significant changes when preoperative measurements were compared to measurements made 12 weeks postoperatively (P greater than .30 in all cases). Two eyes with flat anterior chambers following trabeculectomy had substantial decreases in central corneal endothelial cell density.

Hypertensive retinopathy. Description, classification, and prognosis

In 1898 Marcus Gunn described the changes in retinal vessels noted with hypertension. Arteriolar narrowing, caliber irregularity, alterations of the light reflex, and hiding of the arterial blood column were noted. Arteriovenous crossing changes and capillary bed abnormalities, such as cotton-wool spots, retinal hemorrhages, and retinal edema were also mentioned, as well as blurred discs. In the 83 intervening years, little has been added to the description of hypertensive retinopathy, but our understanding has increased. Retinal vessels respond to elevations of systemic blood pressure by generalized arteriolar constriction. This can lead to arteriolar necrosis, retinal edema, cotton-wool spots, hemorrhage, and disc edema. If the blood pressure is controlled, or slow rising, or if arteriolar sclerosis is present in the retinal arteries, then a picture of arteriolar irregularity will be noted and, depending upon the ability of the retinal vessels to contract, segmental constriction will be seen. In separating hypertensives from nonhypertensives, the most consistent ophthalmoscopic finding is arteriolar narrowing with focal irregularity. In prognosticating for survival, the best method available is the Keith-Wagener-Barker classification. However, the difficulty in separating Groups 1 and 2 of this classification has lead to numerous modifications that make comparisons from one study to another difficult.

[Induced ocular hypertension: experimental investigations on rabbit eyes]

The distribution of fluorescein introduced into the vitreous or respectively the anterior chamber with and without induced ocular hypertension was investigated. In frozen sections it can be seen clearly that with induced hypertension fluid is forced out of the vitreous into the anterior chamber. An important point is that there was no direct discharge of fluorescein into the choroid.