Gordon R. Douglas

Unequal intraocular pressure and its relation to asymmetric visual field defects in low-tension glaucoma.

Fifty-nine low-tension glaucoma patients were reviewed with respect to asymmetry of intraocular pressure (IOP) and visual field defects. In the presence of unequal IOP the visual field damage is almost always greater on the side with higher mean IOP. However, only 13 of 47 patients with asymmetric visual field defects had a mean IOP difference between the two eyes of greater than or equal to 1 mmHg. Although in the case of IOP asymmetry visual field damage is greater in the eye with higher mean IOP, other factors must also play an important role in the development of visual field defects in low-tension glaucoma.

Diffuse and Localized Nerve Fiber Loss in Glaucoma

To estimate the usefulness of photographs of the retinal nerve fiber layer in demonstrating glaucomatous neural tissue changes, we examined such photographs of 51 patients with glaucoma, 52 patients with ocular hypertension, and 29 normal individuals. The photographs were assessed in a masked fashion. A semiquantitative damage score was given in subsectors of the arcuate, papillomacular, and nasal nerve fiber bundle areas, separately for localized and diffuse loss of nerve fibers. The coefficients of variation of the reproducibility of retinal nerve fiber layer assessment were 0.22 for diffuse damage and 0.11 for localized damage. We detected abnormal retinal nerve fiber layer changes in 48 of the patients with glaucoma, in 27 of those with ocular hypertension, and in five of the normal control subjects. Generalized reduction of nerve fibers with or without localized defects was more common in patients with glaucoma than in those with ocular hypertension whose abnormal findings were primarily localized defects.

The Area of the Neuroretinal Rim of the Optic Nerve in Normal Eyes

We randomly photographed 113 eyes in 113 people without ocular disease. The area of the disk and its neuroretinal rim as well as the width of the disk and cup were measured. The measurements were corrected for magnification of each eye by measuring its refraction and axial length. A linear correlation between disk area and neuroretinal rim area was found (r = .75) as well as a correlation between the disk area and the cup area (r = .83). There was no correlation between age and disk area or rim area.

A Comparison of Treated and Untreated Glaucoma Suspects

One hundred forty-three patients with intraocular pressures (IOPs) above 22 mmHg and without visual field defects or any obvious evidence of optic nerve damage were randomly assigned to either a timolol treatment group or no treatment in a 6-year prospective clinical trial. Endpoints were defined as reproducible visual field defects on automatic perimetry, disc hemorrhages, or stereophotographically documented optic nerve head changes. Endpoints developed in 42 patients: 28 visual field defects, 8 changes in disc appearance, and 6 disc hemorrhages. Of the 42 patients, 20 were treated and 22 were not. Survival analysis showed no statistically significant differences in failure time to any endpoints between the two groups. In the untreated group, the time to failure of disc change was related to the mean IOP during the study and also to the changes in the IOP from baseline. A significant correlation was found between initial cup-to-disc ratio and survival time to visual field defects in the untreated group.

Neuroretinal Rim Areas and Visual Field Indices in Glaucoma

Magnification-corrected measurements of neuroretinal rim area of the optic disk were correlated to visual field indices calculated from 49 thresholds of Octopus program JO. The indices express overall reduction and localized disturbances of retinal sensitivity. The study was composed of 123 subjects, including 23 normal subjects, 49 patients suspected of having glaucoma, and 51 patients with glaucoma. The neuroretinal rim area was highly significantly correlated with both visual field indices; the index for overall loss of retinal sensitivity had a somewhat higher correlation coefficient than the index expressing localized visual field changes. Adequate fit of visual field data on rim area was achieved by quadratic regression.

Reliability of Optic Disk Topographic Measurements Recorded with a Video-Ophthalmograph

The video-ophthalmograph records the topography of the optic disk via simultaneous stereoscopic images which are stored and analyzed with the help of a microcomputer. This information is used to generate the vertical cup-disk ratio, the vertical optic disk diameter, the cup volume, and the neuroretinal rim area. To determine the reliability of the data, we recorded information for one eye of each of five patients ten times to determine the interphotographic error variance. We also analyzed one photograph for each of five patients ten times to determine the intraphotographic variance attributable to repeated analysis of the same photograph. The interphotographic and intraphotographic coefficients of variation were 2% to 18% and 2% to 7% respectively for these measurements.

Intraocular Pressure Reduction in Normal-tension Glaucoma Patients

BACKGROUND In a collaborative study, patients with untreated normal-tension glaucoma were randomly assigned to a marked intraocular pressure reduction group or to a no therapy group. It was anticipated that medical therapy and laser trabeculoplasty would generally not achieve adequate pressure lowering and that fistulizing surgery would be required. This hypothesis was examined using current observations in the study. METHODS Patients randomized to the therapy group had a pressure reduction of at least 30% from their last prerandomization level. This was achieved within 6 months by means of fistulizing surgery or with pilocarpine and/or laser trabeculoplasty. Beta-blockers and adrenergic agonists were excluded from both eyes. RESULTS Of 30 patients with documented stable 30% pressure reduction, 17 (57%) achieved this with topical medication and/or laser trabeculoplasty: 8 with pilocarpine alone, 2 with laser trabeculoplasty alone, and 7 with laser trabeculoplasty after initial topical medication. The remaining 13 (43%) patients required a single fistulizing procedure. There was no statistically significant difference between the mean follow-up time for the nonfistulized group (533.8 +/- 437.6 days) and for the fistulized group (502.7 +/- 344.7 days). Both treatment groups had similar baseline profiles. CONCLUSION Marked pressure reduction can be achieved and maintained on a long-term basis by means other than fistulizing surgery in a large proportion of patients with untreated normal-tension glaucoma.

Survival analysis for success of Molteno tube implants

AIM To apply survival analysis in assessing the long term outcome of Molteno tube implantation and to identify risk factors for failure. METHODS A retrospective, 10 year, consecutive case series study of 119 eyes that underwent implantation of a Molteno tube. The main outcome measures considered were intraocular pressure (IOP), visual acuity, and complications. RESULTS A 30% or greater reduction in IOP was achieved in 68.9% of cases. However, the overall, “complete success” rate (IOP <22 mm Hg with no medications) after a mean (SD) follow up period of 43 (33) months (range 6–120) was only 33.6% despite a fall in mean (SD) IOP from 38.2 (8.2) mm Hg to 20.1 (11.0) mm Hg. The “qualified success” rate (IOP <22 mm Hg with or without medications) was 60.5%. Failure was most common in the first postoperative year but could occur after several years, the survival curve having an exponential shape. The only statistically significant risk factor for failure identified was pseudophakia, although eyes with neovascular glaucoma tended to fare poorly. Postoperative IOP tended to be lower after double plate than after single plate implantation. There was no significant difference in outcome based on age, sex, race, previous penetrating keratoplasty, or previous conjunctival surgery. CONCLUSIONS In eyes at high risk of trabeculectomy failure, implantation of an aqueous shunt device should be considered. Pseudophakia should be considered an additional risk factor for failure. Early failure appeared relatively more common but long term follow up of all cases is recommended to ensure adequate management of late failures.

Diffuse Visual Field Loss in Chronic Open-Angle and Low-Tension Glaucoma

We examined 37 eyes of 37 patients with chronic open-angle glaucoma and 24 eyes of 24 patients with low-tension glaucoma. All patients had a scotoma confined to the upper or lower hemifield. Eyes with open-angle glaucoma showed twice as much loss of sensitivity in the spared hemifield as compared to eyes with low-tension glaucoma. These differences were statistically significant.

Comparison of Visual Field Defects in Normal-Tension Glaucoma and High-Tension Glaucoma

In a prospective comparison of visual defects in 23 patients with normal-tension glaucoma and 23 with high-tension glaucoma, the groups were matched for equal involvement of the optic disk. F profiles on the Octopus 201 Perimeter were used to quantify thresholds at 1-degree intervals from fixation to define eccentricity, depth, and slope of the scotoma. The mean eccentricity of scotomas in the normal-tension group was 4.86 degrees from fixation; in the high-tension group it was 2.96 degrees. These differences were statistically significant (P less than .01). No statistically significant differences were found between the slopes of the scotomas or depths of the scotomas in the two groups.