Clinicopathologic correlation of surgically removed macular hole opercula.

PURPOSE: To determine the ultrastructural characteristic of the operculum associated with macular holes. METHODS: We developed instrumentation and a technique to capture the operculum observed with macular holes. Two opercula were studied by transmission electron microscopy. RESULTS: The two specimens were attached to a layer of native collagen identified as cortical vitreous and were composed primarily of Mueller cells and fibrous astrocytes without adjacent inner limiting membrane. No distinct retinal neuronal tissue was present. CONCLUSIONS: Our findings indicate that proliferation of fibrous astrocytes and Mueller cells occurs with the formation of a macular hole, that this reparative tissue may be dislodged, and it is the reparative tissue that previously has been interpreted as an operculum.

Bipolar surface electrical stimulation of the vertebrate retina.

BACKGROUND: Retinitis pigmentosa with attendant photoreceptor loss can cause a profound visual handicap. We have postulated that an intraocular prosthesis that could electrically stimulate the inner retina might provide vision to some of these patients. For such a prosthesis to be feasible, electrical stimulation of the inner retina must elicit a focal retinal response. The stimulating current densities required to elicit such a response must not result in irreversible toxic reactions at the electrode-tissue interface. METHODS: To test the feasibility of this approach, we used bipolar platinum wire electrodes to electrically stimulate the inner retinal surface in bullfrog eyecup preparations and, using similar methods, we electrically stimulated rabbit eyes after injecting intravenous sodium iodate (40 mg/kg), a retinal pigment epithelial toxin with secondary effects on the photoreceptors. RESULTS: Surface electrical stimulation of the inner retina in normal eyes and in eyes with outer retinal degeneration can elicit a localized retinal response. The threshold stimulating currents resulted in charge densities of 2.98 microcoulombs per square centimeter (bullfrog), 8.92 microC/cm2 (normal rabbit), and 11.9 microC/cm2 (rabbit retinas with outer retinal degenerations). These charge densities are within the previously delineated safe limits for long-term electrical stimulation of neural tissue using platinum microelectrodes (100 microC/cm2). CONCLUSION: Multifocal electrical stimulation of the retina might be a viable approach to provide some vision to patients who have profound visual loss due to outer retinal degenerations.

In vitro videographic comparison of argon and Nd:YAG laser iridotomy.

We used an in vitro technique with high-magnification video recording to evaluate from the posterior side of the iris the immediate sequence of events during argon and Nd:YAG laser peripheral iridotomy. The observed effects differed strikingly. The argon laser caused a gradual mounding up of iris pigment epithelium with each successive energy application before final penetration. This effect was reduced but not eliminated with higher power levels. The Nd:YAG laser caused complete disruption and dispersal of the pigment epithelium with a single pulse of energy. Additionally, a multiple focal point configuration of the Nd:YAG laser was observed to produce a significantly larger iridotomy than a single focal point configuration for comparable energy settings. These observations may in part explain the observed clinical advantage of the Nd:YAG laser over the argon laser for creation of a patent iridotomy.

The effect of oxygen on corneal neovascularization.

Since tissue oxygen levels are believed to play a pivotal role in new vessel growth in several situations, we studied the effect of several oxygen concentrations (0, 10, 21, 50, 75, or 100%) on corneal vascularization induced in the rat by chemical cautery. We achieved this by perfusing known concentrations of oxygen through goggles fitted over both eyes of the rat after corneal cauterization. Neovascularization was measured in flat corneal preparations with India ink-filled vessels 4 days postcautery using computerized image analysis. The angiogenic response of rats whose eyes were continuously exposed to 0-75% oxygen were not significantly different from each other. The mean response in corneas exposed to 100% oxygen was 10-21% lower than all of the other groups, and this difference was statistically significant when compared to oxygen concentrations of 0, 21 and 75%. The reason for the inhibitory effect of 100% oxygen remains to be determined, but it may represent a toxic effect of oxygen free radicals on the vascular endothelium.

Refinements in microinstrumentation for vitreous surgery.

We developed a series of 25-gauge (0.5 mm) microinstruments for vitreous surgery, including a 25-gauge vitreous cutter, 25-gauge microscissors for limited reuse, and a vitreous membrane dissector. Clinical experience with these instruments in more than 20 cases of advanced proliferative vitreoretinopathy, retinopathy of prematurity, and diabetic retinopathy indicates that these instruments facilitate delicate vitreoretinal dissections, particularly in the vitreous base and when fibrovascular tissues are closely adherent to the retina. Because of their smaller size, the microinstruments are more precise in their cutting capabilities than other instruments.

A new retractable micromagnet for intraocular foreign body removal.

We have developed a new, self-contained, small-gauge, permanent, rare-earth magnet for use in conjunction with pars plana vitrectomy in the treatment of selected magnetic intraocular foreign bodies. This magnet allows controlled grasping and releasing of the foreign body by the surgeon, thus increasing surgical control in magnetic intraocular foreign body removal.

Temporary iris fixation with a micro-iris retractor.

We developed a new micro-iris retractor to achieve temporary intraoperative pupillary mydriasis in selected eyes undergoing pars plana vitreous surgery. The micro-iris retractor and its use were compared with previous methods for obtaining adequate intraoperative pupillary dilation.

An automated aspirating-backflush system for fluid-gas exchange and retinal manipulation.

We have designed a new instrument for use in fluid-gas exchange and retinal manipulation that combines automated aspiration with reflux capabilities. Reflux capability further reduces trauma to the retina when performing procedures using active linear aspiration.

Accuracy of topographic measurements with the Optic Nerve Head Analyzer.

We used a plastic model of the human eye to study the accuracy with which the Optic Nerve Head Analyzer estimates the surface contour and two-dimensional size of the optic nerve head. Computer-generated contour lines were similar to the actual cross-sectional contour of plastic cups as photographed by scanning electron microscopy. The magnification error of computer-measured cup diameters was inversely related to the axial length of the model. The slope of this relationship was reduced with the use of either refraction or axial length as a correction factor for magnification error. Of the two correction factors, the former provided the closest estimation of the known diameters in the phakic model, while the latter performed better in the aphakic model.

Experimental transvitreal cyanoacrylate retinopexy.

We used an experimental rabbit model of rhegmatogenous retinal detachment to compare the onset, quality, and duration of chorioretinal adhesions obtained by transvitreal application of N-butyl-2-cyanoacrylate mixed with iophendylate with those obtained by transscleral retinal cryopexy. The chorioretinal adhesions produced by the cyanoacrylate tissue adhesive were immediate in onset, stronger, and long lasting.

Intraocular cyclophotocoagulation. Histopathologic evaluation in primates.

Intraocular cyclophotocoagulation with endoscopic visualization, following lensectomy and anterior vitrectomy, was performed on 14 eyes of eight rhesus monkeys. Two eyes received lensectomy and vitrectomy without laser treatment. One eye of each animal was studied one to eight months postoperatively, while the contralateral eyes were enucleated for study immediately after surgery. Histopathologic changes in the treated ciliary processes immediately after therapy included variable degrees of disruption in the epithelial layers and bleeding, while the late changes ranged from partial disruption of the epithelium and intrastromal pigment clumping to replacement of the processes by a fibrotic mass. The degree of these structural changes correlated reasonably well with the level of laser energy used and especially with the immediate, visible tissue alteration. These data may be useful in the development of clinical protocol for intraocular cyclophotocoagulation.

The three-port microcannular system for closed vitrectomy.

Microcannulas used during vitreous surgery protect the entry site, avoid vitreous base damage, and allow easy exchange of 20- and 19-gauge (0.9- and 1-mm) instruments. The use of three cannulas of equal size permits interchangeability of all instruments. A locking mechanism allows attachment and exchange of various infusion lines (balanced salt solution, gas, and oil). Temporary plugging of the cannula is possible. Selection of 1 mm as a standard diameter for all cannulas make multiple-function instruments feasible.

Retinal tacks.

An improved retinal tack and applicator can be used to fix the retina to the wall of the eye mechanically. The system consists of a small (1 X 2.7 mm) stainless steel tack with a blade-like tip and a forked applicator that can grasp the tack securely from any position. Two eyes with complex detachments with fixed rolled retinas could not have been repaired without the help of retinal tacks. The advantages of the retinal tack system over other methods include ease of handling, insertion, and removal.