Faculty Bibliography

PURPOSE: To determine the relative contributions to aqueous outflow resistance of the tissues distal to the inner wall of Schlemm's canal. METHODS: While performing constant pressure perfusion at 10 mm Hg, a 193-nm excimer laser (Questek) was used to precisely remove portions of sclera, unroofing Schlemm's canal while leaving the inner wall intact. The laser beam was masked to produce a beam 2 mm by 1 mm. The laser output was constant at a fluency of 75 mJ/cm2 and 20 Hz. The excimer laser at a frequency of 1 Hz was used as the aiming beam. Photoablation was performed on human cadaver eyes at the limbus at an angle of 0 degrees to 45 degrees from the optical axis. As the excimer photoablations progressed, Schlemm's canal was visualized by the fluorescence of the Barany's solution containing fluorescein dye. After perfusion fixation the eyes were immersion-fixed overnight. The facility of outflow before (Co) and after (Ce) the excimer ablation was measured in 7 eyes. RESULTS: The facility of outflow increased in all eyes after the excimer sinusotomy, from a mean of 0.29+/-0.02 before the sinusotomy to 0.37+/-0.03 microl/min per mm Hg after (P < 0.05). The mean ratio of outflow facility after and before ablation (Ce/Co) was 1.27+/-0.08 (range, 1.20-1.39), a reduction of outflow resistance of 21.3%. Using the formula of Ellingsen and Grant (1972), percentage of resistance to outflow eliminated = 100 [1 - alphaCo/Ce - (1 - alpha)Co], where alpha = fraction of the circumference dissected. Assuming that because of circumferential flow approximately 50% of Schlemm's canal is drained by the single opening made in the outer wall ablation studies, this results in resistance to outflow eliminated of 35%, which is consistent with the calculated eliminated resistance derived from the data of Rosenquist et al., 1989. Light and scanning electron microscopy confirmed the integrity of the inner wall Schlemm's canal underlying the area of ablation. CONCLUSIONS: The results provide direct evidence indicating that approximately one third of resistance to outflow in the human eye lies distal to the inner wall Schlemm's canal in an enucleated perfused human eye.

Objective: To analyze glaucomatous eyes with known focal defects of the nerve fiber layer (NFL), relating optical coherence tomography (OCT) findings to clinical examination, NFL and stereoscopic optic nerve head (ONH) photography, and Humphrey 24-2 visual fields. Design: Cross-sectional prevalence study. Participants: The authors followed 19 patients in the study group and 14 patients in the control group. Intervention: Imaging with OCT was performed circumferentially around the ONH with a circle diameter of 3.4 mm using an internal fixation technique, One hundred OCT scan points taken within 2.5 seconds were analyzed. Main Outcome Measures: Measurements of NFL thickness using OCT were performed. Results: In most eyes with focal NFL defects, OCTs showed significant thinning of the NFL in areas closely corresponding to focal defects visible on clinical examination, to red-free photographs, and to defects on the Humphrey visual fields. Optical coherence tomography enabled the detection of focal defects in the NFL with a sensitivity of 65% and a specificity of 81%,. Conclusions Analysis of NFL thickness in eyes with focal defects showed good structural and functional correlation with clinical parameters, Optical coherence tomography contributes to the identification of focal defects in the NFL that occur in early stages of glaucoma.

OBJECTIVE:The purpose of the study was to evaluate the effect of optic nerve head drusen (ONHD) on nerve fiber layer (NFL) thickness by visual field testing, red-free photography of NFL, and optical coherence tomography (OCT). DESIGN/METHODS:The study design was a prospective clinical study. PARTICIPANTS/METHODS:Twenty-three eyes of 15 consecutive patients with ONHD and 27 eyes of 27 age-matched control subjects participated. INTERVENTION/METHODS:Ophthalmologic examination, color and red-free photography, automated Humphrey visual field testing, and OCT were performed. Each of the drusen study eyes were graded on a scale of 0 to III based on the amount of visible ONHD. Grade 0 represented the absence of clinically visible ONHD, and grade III represented an optic nerve head with abundant drusen. MAIN OUTCOME MEASURES/METHODS:Findings from clinical evaluation and color optic nerve head photographs and NFL evaluation by red-free photography, visual fields, and OCT were measured. RESULTS:The number of study eyes with visual field defects increased with the higher grade drusen discs, corresponding both with progressively thinner NFL measurements by OCT and NFL loss shown by NFL photography. The NFL evaluation showed NFL thinning by red-free photography in 12 (71%) of 17 eyes with visible drusen (grades I-III discs) and visual field defects in 9 (53%) of 17 eyes in this group. By OCT measurements, the superior and inferior NFLs were significantly thinner in the eyes with visible ONHD compared with those of control eyes in the superior quadrant (P < 0.001) and inferior quadrant (P = 0.004). Compared with grade 0 discs, grades I through III discs showed statistically significant thinning of the NFL superiorly (P < 0.001). No statistical significant thinning of the NFL was seen in grade 0 discs compared with those of control subjects. CONCLUSIONS:Optical coherence tomography is able to detect NFL thinning in eyes with ONHD and appears to be a sensitive and early indicator of NFL thinning. Increased numbers of clinically visible ONHD correlated with NFL thinning shown by OCT measurements and both visual field defects and NFL loss seen by red-free photography.