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Small gauge vitrectomy utilizing 23- and 25-gauge instrumentation has definite advantages, but also limitations, due to the physics of smaller instruments and sutureless surgery. Higher infusion and aspiration pressures are needed to remove the vitreous using 23- and 25-gauge probes. The advantages include decreased surgical times, less tissue manipulation, reduced inflammation and pain postoperatively with more rapid visual recovery. A disadvantage is greater instrument flexion than 20-gauge probes, making small gauge vitrectomy more appropriate for indications such as vitreous opacities, epiretinal membranes, macular holes, and simple retinal detachments. There are also some increased complications related to small gauge vitrectomy, including dislocation of cannulas intraoperatively, early postoperative hypotony, choroidal detachment, and possibly an increased risk of infectious endophthalmitis., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Purpose: To evaluate the rate of increase in nuclear sclerosis and posterior subcapsular cataracts in eyes as a function of patient age and use of intravitreal gas at the time of vitrectomy., Methods: Nuclear sclerotic cataracts and posterior subcapsular cataracts were graded on a scale of 0 to 4.0 in 301 consecutive eyes prior and subsequent to vitrectomy for macular holes, epiretinal membranes, or vitreomacular traction syndrome. Linear regression analysis was performed to compare the rate of change in cataract score., Results: Nuclear sclerotic cataracts showed minimal increase in patients younger than 50 years of age following vitrectomy (.13 grades per year). Nuclear sclerotic cataracts increased at a rate of .7 to .9 grades per year (mean, .812) in patients from age 50 to 60, 60 to 70, 70 to 80, and 80+ years, even though the baseline nuclear sclerosis scores were progressively greater for each decade. The increase in nuclear sclerotic cataracts in patients younger than 50 years was significantly less (P<.001) than in patients 50 years or older. The fellow nonsurgical eyes of patients 50 years or older also showed smaller increases in nuclear sclerotic cataracts over time (.091 to .342 grades per year; mean, .139). Eyes with intraocular gas use had a higher rate of nuclear sclerosis progression (.8 grades per year) compared to eyes without intraocular gas bubbles (.5 grades per year) (P<.001). Posterior subcapsular cataract scores showed minimal or no increases in all groups., Conclusions: Patients older than 50 years have a similar rate of increase in nuclear sclerotic cataracts independent of age. The rate is sixfold greater than in patients younger than 50 years and also sixfold greater than the progression of nuclear sclerosis in the fellow nonsurgical eyes. Intravitreal gas bubbles cause nuclear sclerosis to increase by 60%, compared to eyes without use of a gas bubble.

Background: Tangential macular traction by the posterior vitreous cortex has been widely accepted as the major causative factor in the development of idiopathic macular holes. Separation of the posterior cortical vitreous should relieve this vitreoretinal traction., Methods: The authors report five patients with idiopathic full-thickness macular hole formation that occurred in the presence of a well-documented pre-existing complete posterior vitreous detachment., Results: Of five eyes, three underwent pars plana vitrectomy and instillation of transforming growth factor-beta. No residual prefoveal cortical vitreous was present at the retinal surface at the time of surgery. Additionally, clinically identifiable epiretinal membranes were present in three of five eyes, but these epiretinal membranes were extremely thin, transparent, induced minimal traction, and did not warrant surgical peeling., Conclusion: It is likely that, in these five patients, some mechanism other than tangential traction by prefoveal vitreous cortex is responsible for idiopathic full-thickness macular hole formation.

Purpose: Vitreous fluid that remains trapped in the peripheral vitreous cavity after vitrectomy with fluid-air exchange can result in a smaller than desired intravitreal gas bubble size. To evaluate the effectiveness of a single fluid-air exchange in dehydrating the vitreous cavity, we measured the rate and volume of posterior vitreous fluid migration after an initial fluid-air exchange., Methods: Thirty-eight eyes undergoing vitrectomy for macular hole closure had measurements of posterior vitreous fluid accumulation at either 5, 10, 15, or 20 minutes after fluid-air exchange., Results: An average of 0.38 ml of fluid accumulated posteriorly within 10 minutes after the initial fluid-air exchange compared to 0.22 ml that accumulated after 5 minutes (P = 0.0003). A mean of 0.04 ml accumulated during each 5-minute interval between 10 and 20 minutes after the initial fluid-air exchange., Conclusion: Fluid composing 10% of the vitreous volume may migrate and accumulate posteriorly within 10 minutes of an apparently complete fluid-air exchange. Fluid aspiration after a 10-minute wait after the initial fluid-air exchange helps maximize vitreous cavity dehydration and should be employed when a large gas bubble is required after vitrectomy.

The dynamics of pressure, flow, and ocular volume relationships were examined with respect to extrusion needle use in simulated vitrectomy. Glass-stoppered bottles used with infusion lines with drip chambers lowered the intraocular pressure 4 to 7 inches below the fluid level in the bottle, varying with the amount of fluid in the bottle. Compared with flow rates using the regular tip needle with the steel infusion cannula, the disposable infusion cannula lowered the flow rate by about 25% and the tapered tip extrusion needle decreased outflow by 40% to 50%. Tracer dilution rates were decreased by the use of the disposable infusion port or the aphakic model eye; however, 2 minutes of infusion at a 30-inch bottle height dilution was still sufficient to wash out the tracer to less than 5% of the original concentration.

To investigate the effect of extracapsular lensectomy with posterior capsulotomy, 20,000- and 70,000-dalton dextran was injected into the vitreous of rabbits. The concentration of the 20,000-dalton dextran in the aqueous of aphakic eyes was 14-fold greater than in phakic eyes 3.5 hours after injection of dextran into the vitreous. The aqueous concentration of the 70,000-dalton dextran was four times greater in aphakic eyes after 3.5 hours. The aqueous concentration of a 20,000-dalton dextran in phakic and aphakic eyes became equal between 15.5 and 22.0 hours after injection. Thus, extracapsular lensectomy with posterior capsulotomy increased the rate of movement of a single bolus of both 20,000- and 70,000-dalton dextran preparations from the vitreous to the anterior chamber.

The final visual acuities and prognostic factors predictive of these results were analyzed in 353 eyes that had pars plana vitrectomy for nonclearing diabetic vitreous hemorrhage. Eighty-one percent of the eyes had improved visual acuities on final examination. The percentage of eyes that achieved a visual acuity of 20/100 or better and the percentage that achieved 5/200 or better increased during the study period. Preoperative factors associated with a favorable visual prognosis included the following: preoperative visual acuity of 5/200 or better, absence of iris neovascularization, absence of neovascular glaucoma, clear lens or minimal cataract, and panretinal photocoagulation of at least one fourth of the fundus. Intraoperative factors associated with a favorable visual prognosis included retaining the crystalline lens and absence of an intraocular gas bubble.

Indentation of the eye wall by a scleral buckle displaces volume from the vitreous cavity. We developed a mathematical formula to calculate the volume displacement caused by a scleral buckle and verified the accuracy of this mathematical model by performing scleral buckles in 21 cadaver eyes and three eyes undergoing retinal reattachment surgery. A single 5-mm radial sponge of moderate height displaces about 0.2 mL of fluid and a circumferential 2.5-mm-wide band of moderate height displaces about 0.5 mL of fluid. Larger circumferential tires of 7- to 10-mm width displace 1.1 to 1.8 mL of fluid, depending on the height and configuration of the scleral buckle. A 7- to 10-mm-wide circumferential scleral buckle with a buckle height of 4 mm may displace up to 45% of the volume of the vitreous cavity. This volume displacement should be considered when injecting expansile gases or pharmacologic agents into the vitreous cavity.

The rate of movement of 20,000- and 70,000-dalton dextran from vitreous to aqueous was determined after extracapsular lensectomy in rabbits with an intact posterior capsule. Dextran was injected into the vitreous, and 3.5 hours later the aqueous concentration of 20,000-dalton dextran was 10.3-fold greater in the aphakic than the phakic eye. The aqueous concentration of the 70,000-dalton dextran was 3.9-fold greater in the aphakic eye after 3.5 hours. Thus, extracapsular lensectomy with an intact posterior capsule increases the rate of movement of 20,000- and 70,000-dalton dextran from the vitreous to the anterior chamber. In addition, the movement of tracers from vitreous to aqueous is increased further when the posterior capsule is opened.

The results of pars plana vitrectomy for diabetic traction-rhegmatogenous retinal detachment were analyzed in 172 eyes, and the factors associated with a final visual acuity of 5/200 or better were identified. Forty-eight percent of eyes had improved vision on final examination. The proportion of eyes with a final visual acuity of 20/100 or better and 5/200 or better remained virtually the same during the ten-year study interval. Preoperative factors associated with a visual acuity of 5/200 or better were a preoperative visual acuity of 5/200 or better, the absence of iris neovascularization, and the absence of retinal detachment involving the macula. The intraoperative factor associated with a final visual acuity of 5/200 or better was the absence of iatrogenic retinal breaks.

The level of final visual acuity results and the prognostic factors predictive of the level were analyzed in 360 eyes that had pars plana vitrectomy for diabetic traction retinal detachment of the macula. Fifty-nine percent of the eyes had improved visual acuity on final examination. The percentage of eyes that achieved a final visual acuity of 20/100 or better and the percentage that achieved 5/200 or better increased from 21% to 36% and from 57% to 72%, respectively, during the study. Preoperative factors associated with a favorable visual prognosis were a visual acuity of 5/200 or better, the absence of iris neovascularization, a clear crystalline lens or only minimal cataract formation, clear media or only mild vitreous hemorrhage, panretinal photocoagulation of at least one fourth of the retina, and the absence of severe preoperative retinal neovascularization. Intraoperative factors associated with a favorable visual prognosis include the avoidance of performing a lensectomy, the absence of iatrogenic retinal breaks, and the avoidance of using intraocular gas bubbles.

Retinal pigment epithelial (RPE) cells were obtained from human cadaver eyes and grown to confluence in 16 mm wells. A sterile intact rabbit vitreous body was isolated and placed on the RPE monolayer. RPE cells with fibrocyte-like morphology appeared over the RPE monolayer within 4 to 6 days. These rapidly proliferating cells were observed to extend cellular processes and migrate into the vitreous body. Migration of the RPE cells progressed over 20 to 40 days, at which time bipolar RPE cells were found in multiple layers of the vitreous body. The contractile properties of the migrating RPE cells were evident as 24% of vitreous bodies contracted into a dense cellular gel. This study provides a model of migration of RPE cells in the vitreous and allows study of the interaction of RPE with the intact vitreous gel.

Intravitreal gases are useful in treating complicated retinal detachments by providing internal tamponade of retinal breaks. The geometry of the intraocular gas bubble and the kinetics of intraocular gas absorption determine the geometry and duration of internal tamponade of the retinal break. The authors derived a mathematical relationship based on a geometric model of the rabbit eye which allows calculation of the volume of an intraocular gas bubble from its observed meniscus height. When compared with actual measured bubble volumes, this technique was found to provide an accurate, noninvasive method for determining true intraocular gas volumes. Using this model, the absorption of nonexpansile concentrations of sulfur hexafluoride (SF6) and perfluoropropane (C3F8) were found to obey first-order kinetics. Both gases were found to have an intraocular half-life two to three times shorter in aphakic rabbit eyes after total vitrectomy than in phakic rabbit eyes with intact vitreous.