Photogrammetric measurement of nerve fiber layer thickness

To measure retinal nerve fiber layer (NFL) thickness, three sets of simultaneous stereophotographs of the optic disc, taken with the Donaldson fundus camera, were measured at 5 degrees intervals in a stereoplotter (Kern PG2) at the surface of the internal limiting membrane (ILM) and the retinal pigment epithelium (RPE) along the disc margin. The NFL thickness was expressed as a ratio of the vertical disc radius. The reproducibility of the method showed that the percent coefficients of variation (CV%) for 15 normal, 10 ocular hypertensive, and 10 glaucomatous subjects were 5.2%, 6.0%, and 3.9%, respectively. The presence of a halo or scleral crescent had no significant effect on reproducibility. The photogrammetric technique for measuring NFL thickness appears to be highly reproducible and sensitive and may be a valuable quantitative method for: (1) early detection of optic nerve damage from glaucoma and other optic neuropathies and (2) monitoring progression of retinal NFL defects.

[Pallor of the optic papilla--an early sign of glaucoma. A clinical controlled study of optic disk pallor and papillar cupping in glaucoma simplex, ocular hypertension and normal eyes with the optic nerve head analyzer]

Double examinations of 99 eyes (34 healthy, 12 with ocular hypertension, 53 with primary open-angle glaucoma) were performed with the Optic Nerve Head Analyzer to evaluate whether an increase in disk pallor or in the cup-disk ratio (CDR) is the earlier sign of glaucoma. In eyes with primary open-angle glaucoma the CDR and the mean optic disk pallor value are significantly higher than in healthy eyes. There is no significant difference in the CDR of patients with ocular hypertension as compared to normals. However, the mean pallor value is significantly higher in eyes with ocular hypertension than in healthy eyes. Therefore, an increase in pallor may precede a significant increase in the CDR or detectable visual field defects.

[Effects of elevated intraocular pressure on the morphology and function of the corneal endothelium in rabbits]

The intraocular pressure in 40 rabbits (80 eyes) was experimentally raised by injection of balanced salt solution into posterior vitreous. The corneal endothelia were studied by slit-lamp, vital staining, compound staining, electron microscopy and corneal pachymetry. The results indicated that elevation of intraocular pressure induced morphological changes and functional disorders of the corneal endothelium in rabbits. The mechanism involved was discussed.

Peripapillary crescents and halos in normal-tension glaucoma and ocular hypertension

In normal-tension glaucoma ("low-tension" glaucoma), 21 of 33 eyes (64%) had a peripapillary chorioscleral crescent or halo, compared with 13 of 38 eyes (34%) with ocular hypertension. The average area of bared choroid and sclera was greater in normal-tension glaucoma (5.8 arbitrary units of area) than in ocular hypertension (1.4 units). Myopic eyes were prevalent among the normal-tension glaucoma group. When eyes with more than 4 diopters (D) of myopia were excluded from the analysis, the difference in prevalence and size of chorioscleral crescents and halos remained. Thus, the presence of a crescent correlates with disc damage, but further work is needed to determine if the correlation represents peripapillary atrophy that accompanies glaucomatous nerve atrophy or represents a greater susceptibility of discs with preexisting peripapillary abnormality.

Evaluation of the nerve fiber layer and peripapillary atrophy in ocular hypertension

A study has been performed with the Canon retinographic equipment on 549 eyes belonging to 3 different groups: normal population, ocular hypertension and glaucoma. The study included the evaluation of the optic disk with special attention to the presence of choroidal peripapillary atrophy, and the distribution and defects in the RNFL. A highly significant association was observed between the presence of peripapillary atrophy and the presence of defects in the RNFL, as well as between the intensity of choroidal atrophy and defects in the RNFL. This association was statistically significant in the population of ocular hypertensives (P = 0.0360) but not in the population of eyes considered normal.

Nerve fiber layer and optic disc fluorescein defects in glaucoma and ocular hypertension

Photographs of the optic discs and fluorescein angiograms of 31 patients with open-angle glaucoma and 43 patients with ocular hypertension were evaluated for nerve fiber layer (NFL) defects and absolute fluorescein filling defects. All of the glaucomatous eyes showed both defects. Of the 43 ocular hypertensive eyes, in which both NFL and absolute fluorescein filling defects were evaluated, 9% had only NFL defects, 19% had only fluorescein filling defects, 14% had both defects, and 58% had neither defect. The percent area of fluorescein defect in the optic disc increased with severity of NFL defect in glaucoma and ocular hypertension. This study confirms the relationship of fluorescein filling defects and NFL defects to glaucomatous abnormalities and thus the association between vascular damage to the optic nerve and axon loss in glaucoma. The earliest objective evidence of glaucomatous damage can be detected with a combination of NFL evaluation and optic disc fluorescein angiography.

Effect of acute medical reduction of intraocular pressure on the visual field and optic disc in ocular hypertension

The effect of acute reduction of intraocular pressure (IOP) through oral administration of glycerol was assessed in 15 eyes of 15 patients with ocular hypertension by means of automated perimetry, Farnsworth-Munsell 100 hue testing, measurement of spatial contrast sensitivity with a laser interferometer and automated optic disc analysis. There was no significant relation between the absolute or relative change in IOP and the corresponding changes in any of the visual field or optic disc indices studied. The colour vision score increased significantly as the IOP decreased (p = 0.03). There was a significant reduction in the logarithm of spatial contrast sensitivity at grating sizes of 3 (p = 0.007) and 7.5 (p = 0.05) cycles per degree as the IOP decreased.

Intraobserver and interobserver agreement in measurement of optic disc characteristics

Reliable measures of optic nerve status are important parameters for epidemiologic and clinical studies of glaucoma. Stereo fundus photography has been used to reduce interobserver variation, but little data have been reported quantifying the level of agreement in these situations. This article examines chance-corrected intraobserver and interobserver agreement for horizontal and vertical cup:disc ratios and width of the narrowest remaining neuroretinal rim on stereo, color, fundus photographs. Intraobserver agreement was substantial to almost perfect for both readers (kappas between 0.82 and 0.86 for horizontal and vertical cup:disc ratios and 0.71 for the neuroretinal rim). Interobserver agreement was also substantial (kappas of 0.71 for horizontal cup:disc ratio, 0.74 for vertical cup:disc ratio, and 0.58 for the neuroretinal rim). Both intraobserver and interobserver agreement were best for glaucoma patients followed by ocular hypertensives and controls. Dichotimizing cup:disc ratios into suspicious or not suspicious using a range of cutoff points (greater than or equal to 0.5, greater than or equal to 0.6, and greater than or equal to 0.7 disc diameters [DD]) had little effect on agreement levels. Estimation of the status of the optic nerve is complex, requiring judgment about the shape and structure of the cup. Agreement is optimized by using stereo photographs, using the same observer and, when evaluating progression, comparing photographs from different points in time at a single sitting.

Increase of pallor and fluorescein-filling defects of the optic disc in the follow-up of ocular hypertensives measured by computerized image analysis

In 24 ocular hypertensive patients, two optic disc fluorescein angiograms were obtained a mean of 3.9 years apart. Using computerized image analysis, we measured the area of pallor and the fluorescein-filling defect area within the disc and the fluorescein circulation parameters representing the filling rates of optic disc, choroid, and retinal vessels. The results indicated that increase in pallor and fluorescein-filling defect areas, as well as a slowed filling rate of the retinal veins, correlated with glaucomatous progression.

Histological study on transient ocular hypertension after laser iridotomy in rabbits

We performed argon-laser iridotomy on pigmented rabbits and examined histologically the tissue of the anterior chamber angle, the iris, and the ciliary body. After laser iridotomy, 9/10 eyes showed an elevation in transient intraocular pressure. Deposits of blood plasma with fibrin were observed in the tissue of the circumferential anterior chamber angle from eyes enucleated at a period of high intraocular pressure. In the eyes in which ocular pressures returned to the baseline, the quantity of blood plasma was small. In the laser-irradiated iris and iris processes, cells constructing the vessel wall were degenerated, and blood plasma and fibrin exuded. In and around the ciliary body, fibrin was not demonstrated. These observations suggest that argon-laser irradiation to the iris leads to a breakdown of the blood-aqueous barrier mainly in the laser-treated iris, and that deposition of blood plasma with fibrin in the anterior chamber angle tissue may cause transient intraocular pressure elevations after laser iridotomy in rabbits.

Laser-induced glaucoma in rabbits

Argon laser energy was applied to the trabecular meshwork of pigmented rabbits in an attempt to develop an animal model of 'glaucoma'. Laser energy was varied to determine the optimal level needed to produce sustained ocular hypertension. An initial response of ocular hypertension followed by hypotension was observed in all of the animals tested. Approximately half of the laser-treated rabbits developed a secondary buphthalmus and sustained ocular hypertension. In these animals outflow facility was decreased by approximately 60%. Histologic examination at 4- and 8 weeks after laser treatment demonstrated a wound-healing response resulting in closure of the intertrabecular spaces and obstruction of outflow to injected carbon particles. Optic nerve cupping and a loss of ganglion cells were also observed. Topical application of L-timolol (0.5%), pilocarpine (2.0%) and forskolin (1.0%) were found to be effective in decreasing intraocular pressure in the laser-treated, hypertensive eye with no significant effect in control non-laser-treated eyes, suggesting that this model can be a useful tool for screening potential antiglaucoma medications.

Anterior chamber depth in open angle glaucoma

Anterior chamber depth was measured in patients with primary open angle glaucoma, low tension glaucoma, pigmentary dispersion syndrome, and glaucoma suspects. Multiple linear regression analysis demonstrated that anterior chamber depth is a function of sex, age, and refractive error. Values for anterior chamber depth corrected for age and refractive error were greater in patients with pigmentary dispersion syndrome than in patients with other forms of open angle glaucoma or in glaucoma suspects.

Correlations between anatomic features and axonal transport in primate optic nerve head

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Measurements of reversibility of optic disc cupping and pallor in ocular hypertension and glaucoma

Four cases are presented of young and elderly glaucoma patients who had both surgical and medical therapy and showed reversal of cupping and pallor of the optic disc. The cupping was measured by photogrammetry and the pallor by computerized image analysis from photographs of the optic disc. Two patients showed regression of visual field loss. The optic disc and visual field changes corresponded to the changes in ocular pressures, generally showing worsening with an increase in ocular pressure. With a decrease in ocular pressure there was regression of visual field loss and a decrease in cupping; pallor did not decrease consistently. The changes in cupping and pallor in some patients followed similar courses but in others behaved in an independent manner. It is proposed that these new sensitive and reproducible techniques for measuring changes in the optic disc may allow the detection of disc changes early in the disease, prior to visual field loss. If treatment is begun at this time, reversal of optic disc changes may occur.

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.