Role of central corneal thickness on baseline parameters and progression of visual fields in open angle glaucoma.

PURPOSE: To evaluate the relationship of central corneal thickness (CCT) to baseline visual field parameters and visual field progression in patients with primary open-angle glaucoma (POAG). METHODS: Charts of consecutive patients with POAG were reviewed to obtain visual field data. Visual field was measured by standard threshold static perimetry. Variables analyzed included mean deviation (MD) and pattern standard deviation (PSD). RESULTS: A total of 121 eyes examined over 4 years were evaluated. A significant negative relationship between CCT and PSD (correlation coefficient: -0.02, p<0.05) was found. Analyses comparing CCT to change in PSD and MD (visual field progression) were statistically not significant. CONCLUSIONS: Patients with thinner corneas initially present with a greater visual field defect, indicating that thin corneas may contribute to advanced glaucomatous damage at the time of diagnosis. However, CCT does not seem to be a significant risk factor for progression of the disease.

Vascular effects on ciliary tissue from endoscopic versus trans-scleral cyclophotocoagulation.

AIM: To determine the acute and chronic vascular effects of endoscopic cyclophotocoagulation (ECP) versus trans-scleral cyclophotocoagulation (TCP) in a rabbit model. METHODS: 20 rabbits underwent ECP in one eye and another 20 rabbits had unilateral TCP. Five treated eyes from each group underwent endoscopic fluorescein angiography (EFA) of the treated ciliary processes at each of the following time points: immediate, 1 day, 1 week, and 1 month. Five untreated rabbits were used as controls. The NIH Image software program was used to trace ciliary processes in order to determine their mean intensity, as a measure of their perfusion. Histopathology was also performed on eyes from each time point. RESULTS: Immediately and 1 day after laser, both TCP and ECP eyes demonstrated severely reduced or non-existent blood flow in the areas of treatment. TCP treated processes essentially remained non-perfused at the 1 week and 1 month time points. ECP treated processes showed some reperfusion at 1 week and greater reperfusion by 1 month. Histopathology confirmed the overall greater vascular occlusion seen with TCP. CONCLUSIONS: Chronic poor perfusion of the ciliary body after TCP may account, in part, for its efficacy, as well as the significant complications including hypotony and phthisis. Late reperfusion of this region after ECP may provide some insight into the differences in efficacy and complication rates compared to TCP.

Kinematic constraint analysis of halo orthoses.

A kinematic constraint analysis of the four pin halo orthosis is presented. Halo orthoses are used to immobilize the cervical spine after traumatic injury. Common halo orthoses consist of four pins, a halo ring, a vest, and support rods. The head is secured relative to the halo ring by four pins. These pins are screw-like fasteners that thread into the halo ring and then engage the skull with pointed ends. The halo ring is secured relative to the torso with several rods that attach to a vest. To fully immobilize the head, the pins must constrain six degrees of freedom--three translational degrees of freedom and three rotational degrees of freedom. The constraint system for the skull relative to the halo ring is analyzed by first modeling the system as a mechanism. Then the Grubler/Kutzbach criteria are applied to characterize the nature of the constraint system. From this analysis we find that the four pin halo configuration over constrains the head relative to the halo ring. We hope to use the findings to gain insights into the problem of pin loosening, a significant problem during treatment with a halo orthosis. Once the constraint system is understood, it may be possible to explain the pin loosening problem and to use the concepts of exact kinematic constraint to address the problem.

Presumed activation of herpetic keratouveitis after Argon laser peripheral iridotomy.

PURPOSE: To describe presumed activation of herpetic keratouveitis after argon laser peripheral iridotomy. METHOD: Case report. RESULTS: A 68-year-old man developed chronic, unilateral, anterior uveitis associated with decreased corneal sensation, focal keratitis, and increased intraocular pressure after argon laser peripheral iridotomy. Treatment with oral acyclovir and discontinuation of topical latanoprost resulted in prompt and continued control of both the intraocular inflammation and pressure. CONCLUSION: Herpetic keratouveitis may occur after argon laser iridotomy, and it should be considered when postoperative inflammation persists despite appropriate use of topical corticosteroids, particularly in patients with a history of herpetic eye disease.

Glaucoma screening using the scanning laser polarimeter.

PURPOSE: To determine the ability of scanning laser polarimetry (GDx Nerve Fiber Analyzer; Laser Diagnostic Technologies, Inc., San Diego, CA) to separate normal eyes and those considered likely to have glaucoma in a public glaucoma screening. METHODS: A 2-day public glaucoma screening program was held at two different institutions. Each subject underwent ophthalmologic examination, Humphrey perimetry (24-2 Fastpac program), and imaging using scanning laser polarimetry (GDx) in each eye for allocation into a diagnostic category: normal, ocular hypertensive, glaucoma suspect, or glaucoma. Results from the normal and glaucoma groups were analyzed, using modulation parameters calculated from a measurement band located 1.8 disc diameters from the disc, and selected parameters provided automatically by GDx software. Receiver operating characteristic curves were used to depict the sensitivity/specificity relationship at different GDx parameter cutoff levels. RESULTS: Of 200 subjects, 197 were classified; 122 were classified as normal, 23 were classified with ocular hypertension, 30 were classified as glaucoma suspects, and 22 were classified with definite glaucoma. Three subjects had ocular diseases other than glaucoma. The maximum area under the receiver operating characteristic curve for modulation parameters was 0.935, and for the GDx software parameters was 0.901. CONCLUSIONS: Scanning laser polarimetry may be useful in glaucoma screening.

Screening for glaucoma with frequency-doubling technology and Damato campimetry.

OBJECTIVE: To assess frequency-doubling technology (FDT) perimetry (Humphrey Systems, San Leandro, Calif) and Damato campimetry (Precision Vision, Villa Park, Ill) for detecting glaucoma in a public glaucoma screening. METHODS: A 2-day public glaucoma screening was held at 2 different institutions. Each subject underwent 2 visual field screening tests (Damato campimetry and FDT perimetry in screening mode), an ophthalmologic examination, and Humphrey perimetry (24-2 FASTPAC) for each eye. Eyes were divided into 4 categories: normal, ocular hypertensive, glaucoma suspect, and definite glaucoma. The sensitivity and specificity of FDT perimetry and Damato campimetry for detecting glaucoma were estimated with receiver operating characteristic curves. RESULTS: Among 240 subjects who underwent FDT, the number identified as normal, ocular hypertensive, glaucoma suspect, and definite glaucoma was 151, 28, 35, and 26, respectively; among 175 subjects who underwent Damato campimetry, the numbers for the same groups were 118, 19, 19, and 19, respectively. The areas under the receiver operating characteristic curve for FDT perimetry and Damato campimetry were 0.925 and 0.883, respectively. The optimal sensitivity and specificity for FDT perimetry were 92% and 93%, while those for Damato campimetry were 53% and 90%, respectively. The average test time was 1 minute and 3 minutes per eye for FDT perimetry and Damato campimetry, respectively. CONCLUSION: Frequency-doubling technology perimetry was superior to Damato campimetry in this screening for glaucoma.

Late onset of sequential multifocal bleb leaks after glaucoma filtration surgery with 5-fluorouracil and mitomycin C.

PURPOSE: To describe the late onset of sequential multifocal bleb leaks as a postoperative complication after filtering surgery with antimetabolites. MATERIALS: Retrospectively, 385 consecutive eyes (304 patients) undergoing trabeculectomy with 5-flurouracil (5-FU) or mitomycin C (MMC) from 1989 to 1994 were reviewed. Eyes with filtration bleb leak occurring 6 months or more after trabeculectomy were analyzed, and clinical characteristics of the filtration bleb, response to treatment, and bleb histopathology from eyes undergoing bleb excision were analyzed. RESULTS: In seven (1.8%) of 385 consecutive eyes from 304 patients undergoing glaucoma filtration surgery with 5-FU or MMC, repetitive bleb leaks in different locations of the bleb were observed from 9 to 44 months (mean, 20.4 months) after the procedure. One hundred ninety-three eyes (50%) were treated with 5-FU and the remaining eyes, with MMC. All eyes had transparent, avascular, lobular, cystic blebs. Bleb leaks occurred in five eyes treated postoperatively with subconjunctival 5-FU and in two eyes in which MMC was used intraoperatively. Three eyes (all treated with 5-FU) required surgical excision, and four eyes healed with soft contact lens, cyanoacrylate glue, or intrableb injection of autologous blood. Histopathology of the bleb leak sites demonstrated focal epithelial thinning and interruption with subjacent hypocellularity and stromal collagen degeneration. CONCLUSION: Late sequential multifocal bleb leaks may occur after glaucoma filtration surgery with administration of antimetabolites (5-FU or MMC) and are associated with epithelial break-down, hypocellularity, and stromal collagen necrosis in the filtration bleb.

Midterm follow-up results of combined phacoemulsification, lens implantation, and mitomycin-C trabeculectomy procedure.

PURPOSE: This study evaluates the visual, refractive, perimetric, and intraocular pressure (IOP) results following combined phacoemulsification, lens implantation, and trabeculectomy with mitomycin-C. METHODS: Twenty-nine consecutive eyes of 26 patients with cataract and glaucoma that had undergone combined phacoemulsification, posterior chamber lens implantation, and limbus-based trabeculectomy with mitomycin-C applied after the cataract removal and trabeculectomy had a minimal follow-up time of 12 months (mean follow-up 20 +/- 6.3 months). Each eye was evaluated for visual acuity, corneal astigmatism, IOP, bleb persistence, optic nerve stability, visual field status, and complications. Goldmann visual fields were assessed by a semi-quantitative method and threshold static perimetry by statistical indices of diffuse damage (mean deviation) and focal loss (corrected pattern standard deviation). The preoperative and postoperative results were compared by Student's t-test. RESULTS: All eyes that were free of pre-existing macular disease demonstrated significant improvement in visual acuity by at least 4.5 lines of Snellen acuity. Postoperative astigmatism was negligible (0.29 diopters). The average IOP reduction was 6.5 mm Hg, with the one year or more average of 13.4 mm Hg on virtually no antiglaucoma medicines (0.2 +/- 0.5). Functioning filtering blebs persisted in 86% of eyes. Of 11 patients tested with pre- and postoperative Goldmann perimetry, only two showed visual field defect progression despite IOPs < 15 mm Hg. Of the 12 eyes with pre- and postoperative static threshold perimetry, the mean deviation deteriorated in nine eyes (p = 0.003). The corrected pattern standard deviation changes were not statistically significant (p = 0.69). Complications (including two cases of late-onset endophthalmitis) were comparable with other studies reporting filtration surgery with adjunctive antimetabolites. We detected no untoward effects of applying the mitomycin at the end of the procedure rather than at the beginning. CONCLUSIONS: The combined procedure technique that we describe appears to be effective at restoring visual acuity and significantly reducing IOP. Nevertheless, many visual fields showed continued, diffuse glaucomatous progression in the year or two following surgery and the development of late endophthalmitis in two eyes is a concern.

Interobserver and intraobserver variability in the detection of glaucomatous progression of the optic disc.

PURPOSE: To evaluate the potential value of obtaining follow-up stereoscopic photographs on glaucoma suspects in identifying progressive optic nerve damage. METHODS: Nineteen sets of stereoscopic optic disc photographs, reflecting one eye from each of 19 patients at two time points, were selected from the records of subjects enrolled in the Glaucoma Screening Study. By consensus, three experts judged 13 of these eyes to have progressive glaucomatous optic nerve damage. Four other ophthalmologists who were masked to the expert panel evaluation then assessed glaucomatous progression in the same eyes. They were asked to evaluate glaucomatous progression in three ways: first, by drawing the optic nerve head appearance from initial stereoscopic photographs and later comparing their own drawings to follow-up stereoscopic photographs; second, by comparing serial stereoscopic photographs directly; and third, by comparing drawings of the optic nerve head made by another examiner to the follow-up photographs. RESULTS: Neither sensitivity nor specificity was consistently better for serial stereoscopic photographs than for drawings. Individual ophthalmologist agreement rates with the expert panel's determinations of progression were 23-62% when examiners compared their own drawings to follow-up photographs, 54-71% when examiners compared serial stereoscopic photographs, and 38-85% when comparing another ophthalmologist's drawings to follow-up photographs. CONCLUSION: Baseline stereoscopic photographs of the optic nerve head did not substantially improve recognition of progressive glaucomatous optic nerve damage when compared with the use of baseline drawings of the optic nerve head made from photographs in subjects who developed visual loss in the interim.

Evaluation of optic disc measurements with the glaucoma-scope.

PURPOSE: We evaluated the Glaucoma-Scope's ability to acquire images of the optic disc, the reproducibility of its analysis, and the comparison between it and expert evaluation. METHODS: One hundred and sixty-eight patients with satisfactory standard fundus photography were referred for Glaucoma-Scope analysis. Characteristics of eyes in which Glaucoma-Scope analysis could not be obtained were evaluated. Eight glaucoma patients (15 eyes) were quantitatively evaluated: inter- and intraobserver reproducibility of the Glaucoma-Scope analyses were calculated utilizing weighted Kappa index of agreement and coefficient of variation. The Glaucoma-Scope cup-to-disc ratio was calculated from the gray scale analysis and compared to the ratio as evaluated by a glaucoma expert. RESULTS: Glaucoma-Scope analysis was not achieved in 14% of a total of 336 eyes of 168 patients. The conditions associated with the inability to obtain a satisfactory image were hyperpigmented fundi, pseudophakia, aphakia, corneal opacities, cataract, and contact lenses. The quantitative analysis of the 15 patients showed small inter- and intraobserver means of the coefficient of variation (0.136 +/- 0.023 and 0.129 +/- 0.016) and SD (0.063 +/- 0.0056 and 0.064 +/- 0.0077) and moderate-substantial intra- and interobserver agreement (weighted K = 0.427 +/- 0.1 and 0.61 +/- 0.14, respectively). Significant disagreement (weighted K = -0.11, p = 0.0023) was found between Glaucoma-Scope (mean 0.52 +/- 0.064) and expert's evaluations (0.673) of the cup-to-disc ratio. CONCLUSIONS: The inter- and intraobserver reliability and low variation of the Glaucoma-Scope readings indicates moderate to substantial reproducibility for detecting changes in optic disc's topography under selected conditions. However, eyes with moderate cataract, aphakia, pseudophakia, mild corneal opacity, darkly pigmented fundi or myopia were inconsistently analyzable. In a small group of randomly selected eyes there was very low agreement between the glaucoma expert's evaluation of the optic disc and that of the Glaucoma-Scope. These findings raise questions about the usefulness of the instrument as a diagnostic tool for glaucoma but show promise for detecting change when good images are possible.

Prevent Blindness America visual field screening study. The Prevent Blindness America Glaucoma Advisory Committee.

PURPOSE: To assess the screening efficacy and practical use of two portable devices to detect moderate to severe visual field loss rapidly in population screening. METHODS: Henson visual field analysis and Damato campimetry for glaucoma were performed in a healthy adult population, to determine false-positive rates; in established glaucoma patients and suspects, to determine false-negative rates; and in a general adult population, to assess practical use in actual screenings. RESULTS: There were no false-positive test failures among the 82 normal subjects who completed the Henson two-step screening. Eighty of 83 normal subjects passed Damato campimetry, resulting in a false-positive rate of 3.6%. Among 83 glaucoma suspects and patients, the Henson test identified 49 (84%) of 58 subjects whose full-threshold fields from Humphrey perimetry were abnormal, 38 (97%) of 39 of whom had moderate to severe visual field loss. The Damato campimeter detected 55 (81%) of 68 subjects with any pathologic loss on full-threshold visual fields, 44 (92%) of 48 of whom had moderate to severe visual field loss. Among 1,278 subjects tested in general population screenings, 55 subjects (4.3%) failed either or both tests. CONCLUSIONS: The Henson visual field analyzer can discriminate moderately to severely diseased from normal visual fields with high sensitivity and specificity. The Damato campimeter can reliably detect moderate to severe visual field loss with a tolerably low false-positive rate. To overcome the weakness of glaucoma screening by tonometry alone, some forms of visual field testing may be acceptably brief (cost effective) and accurate (sensitive and specific).

The relative accuracy of a variety of medical diagnostic programs.

Acute abdominal pain is one of the most widely studied applications of computer-aided diagnosis. The usual approach is to apply Bayes' theorem with the assumption of conditional independence ("independence Bayes"). We compared various approaches to designing diagnostic programs for abdominal pain of suspected gynaecological origin. The methods range from statistical to knowledge-based. All programs were evaluated using a database of 1,270 cases collected retrospectively. Our results suggest that in this application no significant improvement in accuracy can be made by taking interactions into account, either by statistical or by knowledge-based means; independence Bayes is near-optimal. As far as accuracy is concerned, there appears to be little point in pursuing knowledge-based approaches. However, the "nearest neighbours" method using a new metric appears to be at least as accurate as independence Bayes. We argue that the nearest neighbours method is more suitable than independence Bayes for clinical use because of greater accountability.

Case-based explanation for medical diagnostic programs, with an example from gynaecology.

One of the most accountable methods of providing machine assistance in medical diagnosis is to retrieve and display similar previously diagnosed cases from a database. In practice, however, classifying cases according to the diagnoses of their nearest neighbours is often significantly less accurate than other statistical classifiers. In this paper the transparency of the nearest neighbours method is combined with the accuracy of another statistical method. This is achieved by using the other statistical method to define a measure of similarity between the presentations of two cases. The diagnosis of abdominal pain of suspected gynaecological origin is used as a case study to evaluate this method. Bayes' theorem, with the usual assumption of conditional independence, is used to define a metric on cases. This new metric was found to correspond as well as Hamming distance to the clinical notion of "similarity" between cases, while significantly increasing accuracy to that of the Bayes' method itself.

The design and construction of a medical simulation model.

This paper describes the design, construction and validation of a probabilistic simulation model of patients who present with abdominal pain. The model incorporates text-book medical knowledge, clinical judgment, and statistics collected from real cases. The knowledge representation combines techniques of Bayesian network modelling with ideas of logistic discrimination. The model is shown to generate convincing, realistic cases; large numbers of artificial cases with no missing observations can be generated quickly. This should make the model a useful tool for investigating factors which limit achievable computer accuracy in the diagnosis of abdominal pain.

The temporal visuogram in ocular hypertension and its progression to glaucoma.

In a study of progression to glaucoma in ocular hypertensive eyes followed for at least 4 years, temporal flicker sensitivity measured at the beginning of the period was evaluated as a predictor of the likelihood of progression. Significantly abnormal temporal visuograms at a 1 criterion predicted progression in 9 of 10 eyes that developed glaucomatous losses. Temporal visuograms for locations in the nasal arcuate area (15 nasal to fixation) showed much greater sensitivity to visual loss than those in the central part of the retina. Comparison with threshold perimetry losses showed that patients within the normal range on the central four points were also within normal range on the temporal visuogram. Peripheral flicker testing was more sensitive than threshold perimetry to losses in the nasal arcuate area in glaucoma patients.

Brimonidine in the prevention of intraocular pressure elevation following argon laser trabeculoplasty.

OBJECTIVE: To evaluate the efficacy of 0.5% brimonidine tartrate, an alpha 2-adrenergic agonist, in preventing intraocular pressure (IOP) elevation following argon laser trabeculoplasty. DESIGN: In a multicenter, double-masked, randomized study, 248 patients (248 eyes) who underwent argon laser trabeculoplasty were allocated to four treatment groups: (1) brimonidine administered before and after the procedure; (2) brimonidine administered before the procedure; (3) brimonidine administered after the procedure; and (4) a vehicle administered before and after the procedure. RESULTS: In the first 3 hours after argon laser trabeculoplasty, only one (0.54%) of the 183 brimonidine-treated patients had a postlaser IOP increase of 10 mm Hg or more, while increases of this magnitude occurred in 13 (23%) of the 56 patients who received only the vehicle (P < .001). The three brimonidine-treatment groups demonstrated significant mean reductions in IOP from the pretrabeculoplasty level (-4 to -8 mm Hg), whereas the vehicle-treated group showed an increase in mean IOP (4 mm Hg). Side effects associated with brimonidine treatment included conjunctival blanching (40.9%), lid retraction (7.6%), and a slight lowering of the systolic blood pressure. CONCLUSIONS: One drop of 0.5% brimonidine administered either before or after surgery was found to be efficacious and safe in preventing posttrabeculoplasty elevations in IOP.