Regional test-retest variability of confocal scanning laser tomography

PURPOSE

To determine the regional differences in the test-retest variability of topographic measurements of the optic nerve head obtained with a confocal scanning laser retina tomograph.

METHODS

Three 10-degree topographic images centered on the optic disk of 20 individuals (20 eyes), five normal subjects, seven glaucoma suspects, and eight glaucoma patients, were acquired and averaged. For each eye, the standard deviation of the mean height at each pixel was calculated from the three images and displayed as a gray scale map, which represents regional test-retest variability. The standard deviation of the mean height of the eight surrounding pixels of each pixel was calculated and plotted as a gray scale map, which represents regional steepness.

RESULTS

The variability maps and steepness maps showed close correspondence in all eyes. Regions of high steepness had high variability (r = .31; P < .001). The average variability in relatively flat areas (sixth to 15th percentiles for steepness) was 19 microns, whereas steeper areas (81st to 95th percentiles for steepness) had an average variability of 37 microns. The overall mean variability was 28 +/- 7 microns.

CONCLUSIONS

The regional variability of topographic measurements made with the confocal scanning laser tomograph correlates with the steepness of the corresponding region and is highest at the edge of the optic disk cup and along vessels. Because of their high test-retest variability, these steep areas may not be the best locations to follow up patients for progressive glaucomatous damage.

[A case of encapsulated filtering bleb after trabeculectomy]

A case of encapsulated filtering bleb after trabeculectomy is reported. A 57-year-old man with primary open angle glaucoma underwent a trabeculectomy one year ago. Six months after the operation the filtering bleb began to shrink and intraocular pressure (IOP) began to rise. It was suspected that the trabeculectomy site was obstructed by scarring, and so sclerostomy ab interno was performed in the site with a Nd: YAG laser. The IOP was higher elevated, however, and the bleb remained unchanged with severe conjunctival injection and aqueous inflammation. The next day trabeculectomy was performed in a new site and two weeks later a dome-shaped, prominent bleb was observed with an increase in the IOP. This was diagnosed as an encapsulated filtering bleb (Tenon's capsule cyst). Cystectomy of the bleb failed and it recurred, therefore, another trabeculectomy was added and the IOP was kept at a reasonable value. We believe that it is important to pay attention to an encapsulated filtering bleb as a complication of filtering surgery after laser therapy to the anterior chamber angle.

Optic disc measurement: a comparison of indirect ophthalmoscopic methods

AIMS

Two methods of indirect ophthalmoscopic estimation of optic disc size, the 78 dioptre lens and optic disc biometer were evaluated.

METHODS

Twenty nine eyes of 29 patients were measured by both methods and compared with optic disc size calculated using the three planimetric corrections described by Bengtsson and Krakau.

RESULTS

The closest agreement with the clinical measurements was found using correction 3. There was a significant difference between both the 78 D lens (p < 0.0001) and the biometer (p = 0.0027) and the planimetric results. There was also a significant difference between the two clinical methods (p < 0.0001). Both methods showed acceptable intraobserver variation (CoV 2.45% and 3.13% respectively).

CONCLUSION

Overall, both methods give larger measurements than planimetry; the 78 D lens by 0.41 mm and the biometer by 0.15 mm. Neither method gives a satisfactory estimation of optic disc size when compared with planimetry.

[Sensitivity and specificity of the Heidelberg retinal tomograph for imaging nerve fiber bundle defects in glaucoma patients with localized visual field defects. Clinical study]

In order to verify whether nerve fiber bundle defects can be detected by the confocal technique of the Heidelberg Retina Tomograph (HRT), we compared the localization of localized visual field defects with the localization of the expected corresponding nerve fiber bundle defect. We examined 105 patients: 49 with primary open-angle glaucoma (POAG), 26 with low-tension glaucoma (LTG) and 10 with ocular hypertension (OH), and as a control-group 20 healthy eyes. The glaucoma stage had been defined by examination of the central visual field with the Octopus Perimeter 201 program 31 or 32 and/or the Humphrey Perimeter GG program. In healthy eyes, eyes with OH and POAG stage I (n = 19), no nerve fiber bundle defect could be found. In stage II (n = 15) and stage III (n = 14) we found nerve fiber bundle defects in all patients with POAG and LTG (except for one patient with POAG stage III). In stage IV (n = 27) no localized nerve fiber bundle defects were detected in eyes with POAG, but in 4 of 7 patients with LTG, defects could be seen. In glaucoma stages II and III, nerve fiber bundle defects can be detected with the HRT. The control group shows, that the appearance of a nerve fiber bundle defect is no artifact caused by the HRT. However, examination of eyes with OH and POAG stage I also shows that this method is not sensitive enough to be useful for early diagnosis of glaucoma. Nevertheless, it may be possible to develop the confocal HRT method further as a nerve-fiber diagnostic method for glaucoma.

Anatomic features of the optic disc and risk of progression in ocular hypertension

We evaluated characteristics of the optic disc in ocular hypertensive patients which might portend future glaucomatous damage. We included in this study 12 patients with an intraocular pressure > 21 mmHg who on follow-up showed signs of optic nerve head damage. Each of these patients were matched to an ocular hypertensive patient who remained stable for > 5 years. This study found that neither optic disc, neural rim or peripapillary halo areas, vein or artery diameter over non-atrophied or atrophied retinal areas, differed significantly between groups (p > 0.05, Wilcoxon signed rank test). However, peripapillary atrophy was greater in patients who showed signs of glaucomatous disc damage (1.757 +/- 0.36 mm2, p = 0.02, Wilcoxon signed rank test) compared to stable patients (1.064 +/- 0.79 mm2), although this finding was not significant after the Bonferroni correction. Patients with < 0.6 mm2 area of peripapillary atrophy (n = 6), however, did not suffer damage. This study suggests that a relationship between the extent of peripapillary atrophy and the chance of developing optic disc damage in patients with ocular hypertension deserves further study.

Vertical optic disk diameter: discrepancy between planimetric and SLO measurements

PURPOSE

To compare measurements of the vertical diameter of the optic disk using the Heidelberg Retinal Tomograph (HRT) and planimetric methods.

METHODS

On the HRT, three measurements of the vertical disk diameter were made on 32 eyes from a composite image using the circle draw facility and were compared with three measurements of the central image of the 32 tomographic cuts. These were repeated by a second observer. Measurements were compared with those obtained from photographs using the three corrections described by Bengtsson and Krakau.

RESULTS

For the HRT, there was minimal intraobserver variation, coefficient of variation (1.515% to 1.882% for the two observers). Interobserver variation was also small (CoV 1.969%). The authors found the closest agreement with the HRT measurements using regression analysis was obtained using correction 3 (r = 0.8258). HRT measurements were significantly smaller (P < 0.0001) by a constant amount of 0.13 mm across the range of optic disk size. There was a significant difference between the HRT measurement of the composite image and the central cut (P = 0.0003 for observer 1).

CONCLUSIONS

HRT measurements are significantly smaller than those from photographs and, therefore, are not interchangeable.

Dexamethasone-induced ocular hypertension in perfusion-cultured human eyes

PURPOSE

Glucocorticoid administration can lead to the development of ocular hypertension and corticosteroid glaucoma in a subset of the population through a decrease in the aqueous humor outflow facility. The purpose of this study was to determine whether glucocorticoid treatment can directly affect the outflow facility of isolated, perfusion-cultured human eyes.

METHODS

The anterior segments of human donor eyes from regional eye banks were placed in a constant flow, variable pressure perfusion culture system. Paired eyes were perfused in serum-free media with or without 10(-7) M dexamethasone for 12 days. Intraocular pressure was monitored daily. After incubation, the eyes were morphologically characterized by light microscopy, transmission and scanning electron microscopy, and scanning laser confocal microscopy.

RESULTS

A significant increase in intraocular pressure developed in 13 of the 44 pairs of eyes perfused with dexamethasone with an average pressure rise of 17.5 +/- 3.8 mm Hg after 12 days of dexamethasone exposure. The contralateral control eyes, which did not receive dexamethasone, maintained a stable intraocular pressure during the same period. The outflow pathway of the untreated eyes appeared morphologically normal. In contrast, the dexamethasone-treated hypertensive eyes had thickened trabecular beams, decreased intertrabecular spaces, thickened juxtacanalicular tissue, activated trabecular meshwork cells, and increased amounts of amorphogranular extracellular material, especially in the juxtacanalicular tissue and beneath the endothelial lining of the canal of Schlemm. The dexamethasone-treated nonresponder eyes appeared to be morphologically similar to the untreated eyes, although several subtle dexamethasone-induced morphologic changes were evident.

CONCLUSION

Dexamethasone treatment of isolated, perfusion-cultured human eyes led to the generation of ocular hypertension in approximately 30% of the dexamethasone-treated eyes. Steroid treatment resulted in morphologic changes in the trabecular meshwork similar to those reported for corticosteroid glaucoma and open angle glaucoma. This system may provide an acute model in which to study the pathogenic mechanisms involved in steroid glaucoma and primary open angle glaucoma.

Optic nerve axon count and axon diameter in patients with ocular hypertension and normal visual fields

BACKGROUND

At postmortem examination, the authors obtained eight eyes of five individuals with elevated intraocular pressure and normal visual fields to study the axon count and mean axon diameter.

METHODS

Automated image analysis was used to calculate the total axon count and mean axon diameter per nerve and per nerve segment for each eye. The authors applied the method of identification analysis to compare each study eye with a corresponding normal eye of patients of the same age.

RESULTS

There was no statistically significant difference compared with control subjects for total axon count or segmental axon count for any of the eyes. Two eyes showed a statistically significant difference for mean axon diameter for the whole nerve but not for individual segments of the nerve.

CONCLUSIONS

Some eyes subjected to varying duration and magnitude of intraocular pressure elevation with normal visual fields may maintain normal axon counts and mean axon diameters.

Evidence of constriction of optic nerve axons at the lamina cribrosa in the normotensive eye in humans and other mammals

The ultrastructure of optic nerve axons was examined in several mammals (human, cat, rat, sheep, ox, pig, guinea pig, rabbit). Human material was obtained from normotensive, glaucoma-free eyes and from eyes with a history of glaucoma and raised intra-ocular pressure (IOP). We describe accumulations of organelles (principally mitochondria) in optic nerve axons where they traverse the lamina cribrosa. Accumulations were most prominent in unmyelinated lengths of axons close to lamellae of the lamina cribrosa. Comparable accumulations were not apparent in axons in the retina or optic nerve, suggesting that axoplasmic flow is constricted at the lamina cribrosa. Accumulations were observed both centrally and peripherally to the lamellae, suggesting that flow is constricted in both ortho- and anterograde directions. Accumulations of organelles were more marked in unmyelinated axons than in adjacent, myelinated axons. In the rabbit, in which most axons are myelinated as they traverse the optic nerve head, organelle accumulations were observed only in a sparse population of unmyelinated axons. In human eyes with a history of raised IOP and glaucoma, the accumulations were abnormally large and frequent and in many axons showed dense-body and fibrillar changes not seen in normotensive eyes. It is suggested that chronic, partial constriction of axoplasmic flow is present at the lamina cribrosa of normotensive eyes in a wide range of mammals, including humans, that the constriction results from the pressure gradient across the lamina cribrosa and that the constriction may be a factor in the many cases of primary glaucoma in which IOP is not raised.

[Iris neovascularization, increased intraocular pressure and vitreous hemorrhage as risk factors for invasion of the optic nerve and choroid in children with retinoblastoma]

A review of 289 eyes enculeated for retinoblastoma to evaluate prognostic factors for involvement of the choroid or optic nerve revealed choroidal invasion in 67 eyes (22%) and optic nerve invasion in 84 eyes (27%) due to retinoblastoma. Intraocular pressure (IOP) > or = 22 mmHg was found in 85 eyes prior to enucleation. A total of 118 eyes (38% showed histopathologic evidence of the development of glaucoma: 90 of them with iris neovascularisation and 28 with angle closure configuration. Patients with elevated IOP, iris neovascularisation and angle closure configuration had a significantly higher risk of optic nerve (P < 0.005) and choroidal (P < 0.002) involvement. On the other hand, optic nerve invasion due to retinoblastoma was significantly more frequent in eyes with elevated IOP (P < 0.02) and iris neovascularisation or angle closure configuration (P < 0.01). Risk factors for choroidal invasion of retinoblastoma were raised IOP (P < 0.04) and iris neovascularisations or angle closure configuration (P < 0.01) (univariant analysis). Raised IOP, iris neovascularisations and vitreous haemorrhage remained significant in the multivariant analysis. This study emphases the importance of IOP, iris neovascularisation and angle closure configuration as risk factors for outspreading invasion due to retinoblastoma.

Elevated intraocular pressure secondary to rhegmatogenous retinal detachment

Elevated intraocular pressure secondary to rhegmatogenous retinal detachment was described by Ariah Schwartz in 1972, an entity commonly known as Schwartz's syndrome. Photoreceptor outer segments identified in the aqueous of patients with this syndrome are thought to play a role in the elevation of the intraocular pressure. We present two patients with open angles and elevated intraocular pressure associated with retinal detachment. Retinal reattachment surgery resulted in normalization of the intraocular pressure. Electron microscopic examination of aqueous specimens from our patients demonstrated a predominance of photoreceptor outer segments in varying stages of degeneration. In these specimens, inflammatory cells, fibrin, and pigment granules were rarely observed or were absent. We review the literature regarding the epidemiology, clinical characteristics, and pathogenesis of Schwartz's syndrome.

Obstruction of aqueous humor outflow by cross-linked polyacrylamide microgels in bovine, monkey, and human eyes

PURPOSE

Orcolon, a synthetic viscoelastic, may have contributed to refractory intraocular pressure (IOP) elevation after intracameral injection in some patients. Cross-linked polyacrylamide (microgels), an altered form of the polymer, was investigated as an etiologic candidate.

METHODS

Four adult rhesus monkeys underwent anterior chamber exchange with mock aqueous humor containing microgels in one eye and a vehicle in the other. Outflow facility (perfusion) and IOP (applanation) were determined before and at various times thereafter. Facility also was determined before and after microgel or vehicle infusion into organ-cultured individual human (n = 9) and paired calf (n = 6) anterior segments. Representative monkey and human eyes were examined by light and electron microscopy.

RESULTS

In the microgel-infused monkey eyes, IOP was consistently higher, by approximately 5 mmHg for approximately 1 month. In all three species, microgel infusion acutely decreased facility by approximately 50% to 80%. In the living monkeys where longer-term observation and retesting were possible, a facility reduction of approximately 40% to 50% persisted for at least 1 to 2 months, and rechallenge again produced an acute 80% facility decrease and subsequent 10-mmHg IOP rise. Results of electron microscopic examination in human and monkey eyes showed accumulation of microgels in the cribriform meshwork and beneath the inner wall of Schlemm's canal, with no cellular alterations or inflammatory infiltrate.

CONCLUSIONS

Cross-linked polyacrylamide microgels can produce an acute and longstanding obstruction of trabecular drainage experimentally, and might therefore do so clinically.

A study of histology and enzymatic histochemistry on rabbit's retina in acute ocular hypertension

The changes of activities of enzymes relating to energy metabolism in rabbit's retina in acute ocular hypertension were observed. The activities of succinate dehydrogenase and adenosine triphosphatase were found to be reduced, while the activities of the lactatic dehydrogenase and glucose-6-phosphatase increased. The results revealed the metabolic disturbance of energy in retina after acute ocular hypertension might be the underlying factors relating to the defects of the functions and structures of the retina.

[The effect of acute and persistent ocular hypertension on ultrastructure in rabbit tissues of anterior chamber angle]

Sclero-circular compression operation was performed on 20 unilateral rabbit eyes to make a model of intraocular hypertension which persisted for 3 days, 1, 3 and 4 weeks respectively in 4 groups of rabbits and another 4 rabbits were used as normal controls. The trabecular meshwork and aqueous plexus of the experimental rabbits' eyes were examined under transmission electron microscope on various post-operative days: 3 days, 1, 3 and 4 weeks. It was discovered that the corneo-scleral and uveal trabecular meshworks were obviously distended and their core collagenous and elastoid fibers were hyperplastic, the phenomenon being more marked with the prolongation of the duration of the intraocular hypertension. Many endothelial cells were detached from the trabecular cords and freely located in the intertrabecular spaces. Persistent hyperplasia of collagenous fibers and accumulation of extracellular plague materials occurred in the endothelial meshwork, leading to its compactness. The giant vacuoles in the endothelial cells lining the inner wall of the canal of aqueous plexus were gradually decreased in number and the cytoplasm of the cells became attenuated and some fenestrations appeared. The results show that the main site of the resistance of the aqueous outflow occurring during intraocular hypertension is at endothelial meshwork and the above experimental morphological changes are quite similar to those of glaucoma patients.

Deformation of the lamina cribrosa by elevated intraocular pressure

The purpose of this study was to determine the mechanical response of the lamina cribrosa (LC) to elevated intraocular pressure (IOP) so as to identify possible mechanisms of optic nerve damage in early glaucoma. Ten pairs of normal human eyes were fixed after 24 hours' exposure to 50 mm Hg pressure (experimental eyes) or 5 mm Hg pressure (contralateral control eyes). Photomicrographs of the central region of the optic nerve head (ONH) were taken to examine the LC morphologically and to measure the dimensions of the LC. It was found that elevated IOP caused the LC to deflect posteriorly without affecting its thickness. The majority of the posterior displacement in the LC occurred near the periphery of the ONH. This shape change is consistent with a model of force distribution within the LC in which shear stresses are dominant; such stresses are maximal at the periphery and minimal at the centre of the ONH. These findings support a model in which mechanical forces, specifically shearing stresses within the peripheral lamina, play a direct role in the pathology of glaucomatous optic neuropathy.

Reproducibility of retinal nerve fiber layer evaluation by dynamics scanning laser ophthalmoscopy

Scanning laser ophthalmoscopy is a laser-based image acquisition technique, which greatly improves the quality of the examination of the fundus and the retinal nerve fiber layer. To assess retinal nerve fiber layer imaging by scanning laser ophthalmoscopy and evaluate intra- and interobserver reproducibility in the classification of retinal nerve fiber layer defects, three independent observers evaluated on two separate occasions the videotaped images of 150 eyes of 80 consecutive patients with ocular hypertension or glaucoma. Ophthalmoscopy was performed using argon blue light (488 nm), confocal apertures of 3 to 1 mm, and 40-degree and 20-degree field angles. Of 150 eyes, 20 (13.3%) were excluded from the study because of the poor quality of the images (clinically significant cataract or myopic peripapillary atrophy). The retinal nerve fiber layer was evaluated qualitatively according to a standard classification: normal pattern, slit, wedge, and diffuse defects. Intraobserver reproducibility, evaluated by kappa statistic, was excellent (> or = 0.75): observer A = 0.78 (95% confidence limits, 0.67-0.88); observer B = 0.84 (95% confidence limits, 0.72-0.96); and observer C = 0.79 (95% confidence limits, 0.67-0.91). Interobserver reproducibility was also excellent in all cases: observers A-B = 0.84 (95% confidence limits, 0.71-0.98); observers A-C = 0.76 (95% confidence limits, 0.65-0.87); and observers B-C = 0.80 (95% confidence limits, 0.69-0.92). Kappa values ranged between 0.59 and 0.69 for intraobserver reproducibility and between 0.55 and 0.69 for interobserver reproducibility when using only those eyes in which abnormalities were noted by at least one observer.(ABSTRACT TRUNCATED AT 250 WORDS)

Optic disk appearance in ocular hypertensive eyes

We examined the optic disk appearance in ocular hypertensive eyes that had a normal result of conventional computed perimetry. Color stereo-optic disk photographs of 104 ocular hypertensive subjects and of 216 normal individuals were morphometrically evaluated. In the ocular hypertensive eyes as compared to the normal eyes, significant differences (P < .0001) were detected for a smaller area and an abnormal shape of the neuroretinal rim, larger zones alpha and beta of the parapapillary chorioretinal atrophy, a decreased visibility of the retinal nerve fiber layer, and a higher frequency of localized nerve fiber layer defects. The variables most useful to indicate optic nerve damage were an abnormal shape of the neuroretinal rim and a decreased visibility of the nerve fiber layer. The most specific variable was the presence of localized retinal nerve fiber layer defects. Evaluation of these variables may be helpful for the early diagnosis of glaucoma.

[3-dimensional topography of the optic papilla with laser scanning tomography: clinical correlation of cluster analysis]

BACKGROUND The evaluation of optic disc topography is essential for the clinical diagnosis of primary open angle glaucoma. The purpose of this study was (1) to establish a computerized cluster formation of optic nerve head topography based on quantitative three-dimensional parameter values and (2) to describe the resulting clusters according to morphological appearance and visual fields. PATIENTS AND METHODS 337 optic nerve heads (glaucomatous optic neuropathy (n = 99), glaucoma suspects (n = 159), normals (n = 79) were analyzed using laser scanning tomography. A hierarchical cluster analysis was performed based on standardized variables (optic disc area, rim area, area-ratio, cup depth, cup steepness, height variations along the contour-line). Visual fields were tested by computerized static threshold perimetry. RESULTS A seven cluster solution met the optimizing criteria. The characteristic morphology of the clusters can be described as "normal" (N), "normal, large" (NL), "supernormal" (SN), "pseudonormal" (PN), "glaucoma-like-flat" (GF), "glaucoma-like-steep" (GS) and "macropapillary" (M). Visual fields were normal in 180 eyes. 99 eyes had glaucomatous field defects, 58 eyes revealed isolated relative scotomas < 10 db. Presence and degree of visual field defects varied within the automatically classified optic disc groups considerably. Visual field defects were found in 7.7% (SN), 8.3% (N), 18.8% (NL), 33.3% (M), 37% (PN), 64.7% (GF) and 83.3% (GS) respectively. Pseudonormal discs were characterized by a flattening of the height variations along the disc border. CONCLUSIONS (1) Optic nerve heads may be automatically classified based upon a combination of three-dimensional topographic variables. (2) Analysis of optic disc topography and computerized perimetry are supplementary tools in the evaluation of the glaucoma patient. Visual field defects may be present within any cluster. However, the likelyness of the presence of visual field defects differs considerably among the topometrically defined groups of optic nerve heads. Functional damage is to be expected in association with reduced height variations along the disc border, a small rim area and a steep cupping of the optic nerve head.

Reproducibility of the optic nerve head topography with a new laser tomographic scanning device

BACKGROUND

Laser scanning tomography has been shown to be an accurate and reliable method for the assessment of the three-dimensional optic disc topography. The authors investigate the reliability of morphometric measurements with the Heidelberg retina tomograph, a new instrument which was designed based on this technology, which simplifies handling and is much smaller than the laser tomographic scanner.

METHODS

Three independent measurements of the optic disc were performed in 39 eyes of 39 patients which were equally divided into the following three groups: glaucoma, glaucoma suspects, and controls.

RESULTS

The mean coefficient of variation for measurement in the glaucoma, glaucoma suspect, and control groups was 2.9%, 5.0%, and 3.4%, respectively, for cup area; 4.9%, 4.6%, and 4.6%, respectively, for cup volume; 5.2%, 3.8% and 3.3%, respectively, for mean cup depth; and 5.2%, 4.1%, and 4.0%, respectively, for maximal cup depth. The mean standard deviation for one pixel of the total image was 30 +/- 6 microns, 28 +/- 7 microns, and 22 +/- 6 microns for the three groups, respectively.

CONCLUSION

The Heidelberg retina tomograph enables fast and reliable measurement of the optic disc topography and therefore may allow exact follow-up of patients.

Correlation of peripheral displacement thresholds and optic disc parameters in ocular hypertension

Both peripheral displacement thresholds and measurement of optic disc parameters have been advocated in the early diagnosis of glaucoma at the stage before scotomata are detected on conventional visual field assessment. The peripheral movement displacement thresholds were measured in 50 eyes of 50 patients with ocular hypertension and a significant correlation was found with neuroretinal rim areas measured using a computerised image system. There was also a significant correlation with optic disc diameter but no correlation with cup-disc ratio. The results support the proposition that measurement of peripheral movement displacement thresholds may be a useful tool in the detection of early glaucomatous optic nerve damage.

Peripapillary vasoconstriction in the glaucomas and the anterior ischemic optic neuropathies

Proximal constriction (retinal arteries narrower near the disk than further down the stream in the retina) was present in 96 of 226 eyes (42%) with classic glaucoma or normal-tension glaucoma, but it was present in only 11 of 206 eyes (5%) that were normal, had ocular hypertension, or had retinal disease not affecting the optic nerve. In cases of glaucoma with proximal constriction over only part of the disk circumference, its location corresponded to the sector with the greatest cupping in 60 of 66 cases (91%) and likewise corresponded to the sector in which the peripapillary zone of absent retinal pigment epithelium was widest in 48 of 55 cases (87%). Proximal constriction was also present in 16 of 45 eyes (36%) with nonischemic types of non-glaucomatous optic atrophy. The nonarteritic form of anterior ischemic optic neuropathy had proximal constriction in 19 of 28 eyes (68%), which was more frequent than in those with glaucoma (P = .017). Only one of nine eyes with the arteritic form of anterior ischemic optic neuropathy had proximal constriction, which was lower prevalence than in those with glaucoma (P = .066). General arterial narrowing (throughout the retinal course) was present in 111 of 204 (54%) of those with moderate optic nerve damage and 100 of 128 (78%) of those with severe optic nerve damage in all categories, compared with 29 of 208 (14%) of the controls with no optic nerve damage. Unlike proximal constriction, the generalized narrowing was related to severity of optic nerve damage and not to the disease category.

Fluctuations of visual field interpretation related to cluster and scotoma analysis by one interpreter

A total of 189 numerical printouts of the visual fields of 189 eyes of individuals either suspected of or verified as having glaucoma and displaying varying degrees of glaucomatous visual field damage were analyzed by one expert interpreter. The amount of clusters (or scotomas) was counted and delineated in each visual field under both a more stringent and a more liberal criterion. The interpretations of the visual fields differed significantly in both groups, as did the subjective certainty the interpreter allotted to his assessment. In the group of certain decisions, only 144 defects were assessed as opposed to 364 when a more stringent rather than a more liberal criterion was adopted. In uncertain cases, a reverse trend was observed, since only 11 as opposed to 324 defects were assessed when a more liberal rather than a more stringent criterion was adopted. Both trends may be explained by an increase in sensitivity at the expense of specificity (i.e., a change in the receiver-operating characteristic of the expert when the latter is pressed to change the criterion in a subjective cluster or scotoma assessment task). The ambiguity of the task and the difference in the criterion adopted by the interpreter significantly influences the assessment of normality and pathology, in particular its extent and spatial distribution.