Performance of a new, low-volume, high-surface area aqueous shunt in normal rabbit eyes.

PURPOSE: This experimental study was conducted to report perfusion characteristics of small diameter, cylindrical aqueous shunts in normal rabbit eyes and to test the hypothesis that decreasing bleb diameter would decrease capsular fibrosis, as evidenced by a thinner capsule forming around the implant. These two properties increase hydraulic conductivity of the fibrous membrane forming around the device, resulting in a more effective filtering shunt. METHODS: Cylindrical latex tubes with the distal portion of the sidewall removed were implanted under the conjunctiva. The proximal, intact end of tubing was inserted into the anterior chamber and ligated to prevent hypotony. The ligature was released after 1 week to inflate the bleb. Animals were again anesthetized at 6 or 12 weeks after ligature release and in vivo perfusion experiments conducted using a miniperfusion system and a water manometer. Perfusion of the implant with latex microspheres was performed before the animals were killed. Capsule diameters were measured in situ using calipers under a dissecting microscope after excision of orbital tissues and before fixation for histologic study. Membrane hydraulic conductivity (outflow per unit membrane area at unitary pressure gradient, microL/min/mm2/mmHg) was calculated using data obtained during perfusion experiments and compared with results of other studies. Capsule thickness was measured histologically. RESULTS: Cylindrical filtration membranes with thin (15-20 microm) capsules formed around latex implants. Bleb diameters consistently measured 1 mm at all points along their length before formaldehyde fixation. Hydraulic conductivity was measured and found to be eight times higher than that reported for capsules around conventional implants. Decreased diameter (16:1 for Baerveldt and 13:1 for Molteno implants) produced a proportional decrease in surface tension on the wall. This resulted in decreased capsule thickness, from 222 microm for Baerveldt implants in rabbit eyes and from 150 microm for Molteno implants in monkey eyes to less than 20 microm for the shunting device studied here. CONCLUSION: As a consequence of Laplace's law, reduction in bleb diameter reduces surface tension on the bleb, reducing capsular fibrosis and consequently capsule thickness, thus increasing hydraulic conductivity. Increased hydraulic conductivity increases the effectiveness of the filtering surface. Cylindrical geometry allows reduced bleb volume yet maintains total surface area that is proportional to the length of the implant, which is unlimited and customizable for each eye by simply cutting the length of implant needed.

A randomized study of mitomycin augmentation in combined phacoemulsification and trabeculectomy.

PURPOSE: The purpose of the study is to determine whether the intraoperative application of subconjunctival mitomycin C (MMC), during combined phacoemulsification and trabeculectomy, is an effective means of improving filtration, defined as overall lower intraocular pressure (IOP) and less antiglaucoma medication use. METHODS: Twenty-nine patients with a visually significant cataract and glaucoma were randomized, in a double-masked fashion, to receive intraoperative MMC (0.5 mg/ml) or placebo. RESULTS: Follow-up ranged from 6 to 30 months (mean, 20 months). Postoperative visual acuity at 1 year was 20/40 or better in 14 of 15 eyes operated on in the placebo group and 13 of 14 eyes operated on in the MMC group. Intraocular pressure at 8 months averaged 15.2 +/- 1.5 mmHg in the placebo-treated eyes versus 12.3 +/- 1.6 mmHg in the MMC-treated eyes. At 12 months, IOPs averaged 16.2 +/- 1.5 mmHg in the placebo-treated eyes versus 12.6 +/- 1.0 mmHg in the MMC-treated eyes. On average, the MMC group had postoperative IOP levels 3.0 mmHg lower than did the placebo group (P = 0.04) throughout the study. In the placebo group, laser suture lysis was required in a greater number of patients (80% versus 43%) and to a greater extent (mean = 2.0 versus 0.7 suture lysed) (P < 0.05). At 12 months, 5 of the 15 patients in the placebo group required an average of 1.8 medications for IOP control, whereas 0 of the 14 patients in the MMC group needed IOP-lowering medications. A late endophthalmitis developed through an intact bleb in one patient in the MMC group; otherwise, complications were minimal in each group. CONCLUSION: These results suggest that intraoperative MMC application, during combined phacoemulsification and trabeculectomy surgery, does improve early filtration as shown by overall lower IOPs and less antiglaucoma medication use.

Reduced vision secondary to pigmented cellular membranes on silicone intraocular lenses.

PURPOSE: Visually significant, pigmented cellular membranes may form on intraocular lenses after implantation. We studied a series of patients to determine the onset, visual significance, treatment, and recurrent nature of these pigmented membranes in patients who underwent surgery with silicone lens implantation. METHODS: In nine eyes (eight patients) with visually significant pigmented cellular membranes on their Allergan Medical Optics (Irvine, California) silicone intraocular lenses (model SI18NGB or SI26NB), eight underwent combined phacoemulsification, intraocular lens implantation, and trabeculectomy; one underwent phacoemulsification and lens implantation only. We reviewed medical records to identify preoperative, operative, and postoperative similarities and differences in care. Clinical examinations and slit-lamp photographs, over an average of 21.3 +/- 7.2 months (range, 11 to 31 months), documented the effects of different treatment modalities. RESULTS: The patients sought treatment ten to 20 weeks (mean, 15 weeks) postoperatively. Except for the cellular membranes, each eye was without evidence of inflammation or cystoid macular edema. Subjective complaints decreased, and best-corrected Snellen visual acuity improved with topical corticosteroid therapy alone. Pretreatment best-corrected visual acuities ranged from 20/40 to 20/400 (mean, 20/70 using Snellen fractions) and improved two to eight (mean, five) Snellen lines, to a range of 20/20 to 20/50 (mean, 20/25). All nine eyes had recurrence of the membranes after treatment terminated and required a maintenance regimen of corticosteroid eyedrops. CONCLUSION: The pigmented cellular membranes observed on these silicone lenses were visually significant to each patient. The membranes resolved and visual acuity improved with topical corticosteroid treatment alone but recurred in all patients on cessation of treatment.