R.A. Chanis

Comparison of Anterior Segment Structures in Two Rat Glaucoma Models: An Ultrasound Biomicroscopic Study

PURPOSE Optic nerve disease in chronic IOP elevation rat glaucoma models develops at different rates. This study was undertaken to investigate whether anterior chamber (AC) changes develop in two popular models in vivo and whether the changes are related to IOP. METHODS Ten female Wistar rats and 12 male Brown-Norway rats were subjected to episcleral vein cauterization (EVC) and hypertonic saline episcleral vein sclerosis (HSEVS), respectively. Contralateral untreated eyes served as controls. IOP was recorded for a period of 5 to 6 weeks, and with the rats under anesthesia, the eyes were imaged with an ultrasound biomicroscope. Measurements of the AC depth (ACD), trabecular-iris angle (TIA), iris thickness at the thickest point near the pupillary margin (IT), angle opening distance (AOD; at 200 microm from the scleral spur), and ciliary body area (CBA) were compared between control eyes of the two strains and between experimental and control eyes within each strain. The differences were correlated with IOP history. RESULTS Eyes subjected to EVC demonstrated greater increases in IOP than eyes subjected to HSEVS. Between rat strains, control eyes differed significantly in all the parameters studied, except for ACD. No difference was detected between experimental and control eyes in the EVC group. In contrast, experimental eyes in the HSEVS group had approximately 71% larger ACDs and approximately 32% smaller CBAs than did the contralateral control eyes (P < 0.001). ACD and CBA correlated well (R2 = 0.80 and 0.51, respectively) with IOP in the HSEVS group. Two of the experimental eyes in this group showed the presence of ultrasound-scattering material in the AC. CONCLUSIONS Despite apparently higher IOP exposure, eyes in the EVC rat model of glaucoma do not undergo changes in the AC. In contrast, eyes subjected to HSEVS display deepening of the AC and reduction in size of the ciliary body within 5 to 6 weeks. These changes correlate to IOP exposure and may be the result of specific changes induced by the experimental intervention. These models are likely to rely on different mechanisms of pressure elevation and cannot be used interchangeably.

The effect of laser iridotomy on the anterior segment anatomy of patients with plateau iris configuration.

Purpose:To determine if laser iridotomy altered the anterior segment anatomy of patients with plateau iris configuration. Methods:Twenty eyes of 9 female and 1 male patients were imaged using an ultrasound biomicroscope within 19 weeks before and 52 weeks after laser iridotomy. Measurements obtained included the anterior chamber depth (ACD), trabecular-ciliary process distance (TCPD), iris thickness (IT), angle opening distance at 500 micrometers (AOD), iridozonular distance (IZD), and trabecular-iris angle (TIA). Comparisons of the pre- and post- iridotomy measurements were made using a two-tailed paired t test. Results:Laser iridotomy elicited no statistically significant change in ACD, TCPD, IT, AOD, or TIA. However, IZD was decreased (P < 0.05) in both eyes after laser iridotomy. Configuration of the irides was flat before and after laser iridotomies. Conclusion:This study suggests that laser iridotomy did not alter anterior segment anatomy, probably because of the fixed anterior insertion of the iris and ciliary body in plateau iris configuration. The decrease in IZD distance may be the result of a small posterior movement of the iris due to a reduction in relative pupillary block, secondary to laser iridotomy. The small reduction in relative papillary block in plateau iris configuration does not alter the width of the anterior chamber angle as measured by AOD and TIA.

Is intraocular pressure in the early postoperative period predictive of antimetabolite-augmented filtration surgery success?

Purpose:To determine whether intraocular pressure (IOP) in the early postoperative period after trabeculectomy or combined phacoemulsification-trabeculectomy, augmented with antimetabolite, correlates with IOP at one year in surgeries considered to be successful at that time point. Design:Retrospective case series. Methods:A chart review of antimetabolite-augmented surgical procedures done by DJG and JBS between January 1994 and November 2000 identified 82 primary or secondary trabeculectomies and 53 combined phacoemulsification-trabeculectomies with at least one year of follow-up. The success rate for each surgical subgroup was calculated and IOP on postoperative days (POD ± SD) 1, 7 (±2), 30 (±5), 90 (±10), and 180 (±20) was correlated with IOP at one year (POY 1, between month 12 and 15) using linear regression. IOP at each time point was compared among eyes that achieved success at one year with and without the use of IOP-lowering agents. Results:Of the 82 eyes having undergone antimetabolite-augmented trabeculectomies and the 53 eyes having undergone combined surgeries with at least one year of follow-up, the surgical success rates at POY 1 were 87.8% (72 of 82 eyes) and 92.5% (49 of 53 eyes). Of these, 42 eyes (58.3%) from 39 patients in the trabeculectomy group and 27 eyes (55.1%) from 24 patients in the combined surgery group did not require glaucoma medications at one year postsurgically, and were considered complete surgical successes. Mean preoperative IOP mm Hg ± SD was 26.0 ± 8.5 for the trabeculectomy group and 18.2 ± 4.5 for the phaco-trabeculectomy group. Postoperative IOP at POD 1, POD 7, POD 30, POD 90, POD 180, and POY 1 respectively for the eyes undergoing trabeculectomy were 13.9 ± 10.4, 9.5 ± 6.2, 12.0 ± 5.5, 12.0 ± 5.2, 12.8 ± 5.9, and 12.1 ± 4.3, and for the combined surgery group were 20.8 ± 12.5, 9.7 ± 5.7, 12.2 ± 5.4, 11.1 ± 3.4, 11.6 ± 4.6, and 10.3 ± 4.3. Intraocular pressure on postoperative day one correlated poorly with intraocular pressure at POY 1 for the trabeculectomy group (R2 = 0.0788), and not at all for the combined procedures group (R2 = 0.018). The correlation was slightly better for intraocular pressure at postoperative day 90 for the trabeculectomy group (R2 = 0.546), and at postoperative day 180 for the combined group (R2 = 0.37), but still rather low. Eyes requiring glaucoma medication use at POY 1 in the trabeculectomy group had higher (P < 0.009) intraocular pressure at POD 30 and at all subsequent visits than eyes not requiring these medications. Eyes requiring glaucoma medication use at POY 1 in the phaco-trabeculectomy group had higher (P < 0.0025) intraocular pressure at POD 30, POD 180, and POY 1 than eyes not requiring these medications. Conclusion:Intraocular pressure in the early postoperative period correlates very poorly with intraocular pressure one year after successful antimetabolite-augmented trabeculectomy or combined cataract extraction and trabeculectomy. Starting one month after glaucoma surgery, intraocular pressure is substantially lower in eyes that will ultimately not require the use of ocular hypotensive agents to achieve clinical success one year postoperatively.

Additivity of pilocarpine to bimatoprost in ocular hypertension and early glaucoma.

Purpose:To determine if the intraocular pressure (IOP) effect of pilocarpine at various concentrations is additive to that of bimatoprost and to assess the tolerability of this combination. Methods:This was a randomized, prospective trial of patients with IOP > 21 mm Hg following appropriate medication washout. For all visits IOP was measured at 9:00 AM and 11:00 AM. Following baseline visit (#1), bimatoprost 0.03% was instilled qhs OU through visit 6. Following visits 2, 3, and 4 pilocarpine (2%, 4%, 6%) was instilled qid in one randomly selected eye. Pilocarpine was discontinued after visit 5 and bimatoprost after visit 6. Two-tailed, paired t test was used to compare treated and contralateral eyes for their IOP, IOP change, percentage IOP change from baseline, and to compare IOP in the same eye at 9:00 AM and 11:00 AM (before and after pilocarpine administration). IOPs using bimatoprost alone or in combination with various pilocarpine concentrations were compared using single variant Analysis of Variance (ANOVA). Results:Seventeen patients were enrolled and 13 patients completed the study. Bimatoprost reduced IOP 28.7% to 30.5% (P < 0.0001) from baseline to visit 2. IOPs in eyes treated with bimatoprost alone or with bimatoprost and various pilocarpine concentrations were similar (P > 0.81, ANOVA). The IOP (P > 0.17) and percentage IOP change from baseline (P > 0.10) was similar in treated and contralateral eyes with all three strengths of pilocarpine. IOP values at 9:00 AM and 11:00 AM, before and after pilocarpine administration, were similar (P > 0.22). Conclusion:Bimatoprost alone reduces IOP substantially. Pilocarpine added to bimatoprost at concentrations of 2%, 4%, or 6% was neither additive nor antagonistic to the ocular hypotensive efficacy of bimatoprost.