The effect of intraocular irrigating solutions on lens clarity in normal and diabetic rabbits

INCIDENCE OF CATARACT EXTRACTION AFTER DIABETIC VITRECTOMY

PURPOSE

To determine the frequency of visually significant cataracts after vitrectomy for complications of diabetic retinopathy.

METHODS

We studied 40 patients and 56 concurrent control patients in a retrospective, consecutive, comparative case series in an institutional setting. Entry criteria included phakic patients with a clear lens or mild lens opacity undergoing anatomically successful diabetic vitrectomy, without lens removal at the time of vitrectomy, without intraocular gas or silicone oil use, and with at least 1 year of postoperative follow-up examination information. Two comparative phakic control groups with the diagnosis of macular hole or epiretinal membrane were selected, also with follow-up examination information of at least 1 year postoperatively. The occurrence of cataract extraction was the principal outcome measure. Its validity as a measure of cataract formation was evaluated by ascertainment of improved visual acuity after cataract extraction. A secondary endpoint analysis included eyes that needed cataract extraction at the final follow-up examination.

RESULTS

For the primary analyses (clear lens preoperatively), there were 26 patients in the study group, 38 in the macular hole control group, and 18 in the epiretinal membrane control group. The cumulative cataract extraction rates at 2 years were 15%, 66%, and 53% respectively. By using multivariate survival analysis, the patient age was an important factor, with a younger age associated with a lower rate of progression to nuclear sclerosis. After controlling for age, the difference in these three groups was still statistically significant. In the four patients with diabetes undergoing cataract surgery, the visual acuity improved at least two lines in only one of the eyes and did not change in three eyes. After expanding the outcome measures to include study patients with mild lens opacities at baseline or those judged to be in need of cataract surgery at the final follow-up examination, there was still a strongly statistically significant difference between the three groups.

CONCLUSION

The rate of cataract extraction after vitrectomy in patients with diabetes is lower than in patients without diabetes undergoing vitrectomy and suggests a lower rate of cataract formation. This inference should be considered when attributing subnormal vision in a patient who has had a diabetic vitrectomy to a cataract. This is especially significant because the risk ratio in patients with diabetes in general and in patients with a previous vitrectomy is likely less favorable compared with the general population.

Effect of intraocular irrigating solutions on the viability of cultured retinal vascular endothelial cells

PURPOSE

To compare the abilities of balanced salt solution, BSS Plus and Hartmann's lactated Ringer's (HLR) solution to maintain the viability of retinal vascular endothelial cells (RVEC) in vitro.

METHODS

Cultured retinal vascular endothelial cells were suspended in each irrigating solution for four hours. Viability was determined by trypan blue exclusion at 30 minute intervals. Regression analysis was used to determine the rate of viability loss. Additional studies were performed to determine the effectiveness of lactate in maintaining cell viability.

RESULTS

Retinal vascular endothelial cells lost viability at a greater rate (p < 0.001) in BSS (8.7%/hr) compared with BSS Plus (3.3%/hr). Cells in Hartmann's lactated Ringer's lost viability at a significantly lower rate (4.4%/hr) than retinal vascular endothelial cells in lactate-free Hartmann's lactated Ringer's solution (8.4%/hr). Lactate was as effective as glucose in preserving RVEC viability. By comparison, the viability of corneal endothelial cells was not effectively maintained by lactate. For these cells, BSS Plus was clearly superior to Hartmann's lactated Ringer's solution in maintaining viability.

CONCLUSIONS

BSS Plus and Hartmann's lactated Ringer's solution are both superior to balanced salt solution in maintaining retinal vascular endothelial cell viability. For retinal vascular endothelial cells, Hartmann's lactated Ringer's solution preserves cell viability as well as BSS Plus, since the retinal vascular endothelial cells, unlike corneal endothelial cells, can apparently utilize lactate as an energy source.

A test for crystalline lens biocompatibility

The current use of monkeys for testing intraocular fluids and viscoelastic materials is being questioned because of the decreasing availability and increasing cost of these scarce animals. The rabbit is an inexpensive, readily available, and convenient animal which might provide an alternative model for this purpose. In this study we have outlined the lens changes (clefts or vacuoles) that are observed in the New Zealand white rabbit as a result of toxicity to intraocular test materials. We used two viscoelastic agents, 1% sodium hyaluronate-Healon and 2% carboxymethylcellulose, and balanced salt solution to evaluate the efficacy and reproducibility of lens changes in this test study. The lens changes in each case were reproducible and could easily be graded. When used in concert with other tests, this new test can help in the preliminary evaluation of an ophthalmic material before its final clinical use in humans.

Drug uptake and release by a hydrogel intraocular lens and the human crystalline lens

Implantation of a hydrogel (IOGEL) intraocular lens in humans has been reported. The polyhydroxyethyl methacrylate (poly HEMA) matrix of this hydrogel is permeable to water soluble drugs and may adsorb agents used intracamerally during cataract extraction or topically during the postoperative period. This study compared the in vitro uptake and release of chloramphenicol, dexamethasone, epinephrine, pilocarpine, and bovine serum albumin by polymethylmethacrylate and hydrogel intraocular lenses with that of the intact crystalline lens of humans and rabbits. An in vivo study compared the uptake and release of chloramphenicol and dexamethasone by hydrogel lenses implanted in the anterior chamber of rabbit eyes with that of the rabbit's crystalline lens. The in vitro uptake and washout of epinephrine and pilocarpine by the hydrogel lens was comparable to the human lens. Uptake of chloramphenicol and dexamethasone by the hydrogel lens exceeded that of the human lens and, following a two-hour washout period, the dexamethasone content of the hydrogel lens remained significantly greater than the human lens. The uptake and washout of bovine serum albumin by the hydrogel lens was half that of the human lens. In vivo, the hydrogel lens efficiently eluted both chloramphenicol and dexamethasone. These studies show that a hydrogel lens will not act as a significant depot for drugs in the eye.

Role of the intraocular irrigating solutions in the pathogenesis of the postvitrectomy retinal edema

Alterations in the vitreo-retinal barrier can modify the exchange of water taking place between the retina and the vitreous body and cause retinal edema to develop. To verify this fact, albino rabbits were subjected to vitrectomies perfusing various intraocular irrigating solutions for various durations. The following conclusions were drawn from these experiments: Ringer's Lactate and physiological saline solutions are more edematogenous than BSS plus; the induced edema is more severe, the longer the perfusion. We have also confirmed that this edema is inhibited by topically administered indomethacin, which proves that in the rupture of blood-retinal barriers during the vitrectomy, prostaglandins play an important role.

Effect of glucose added to intraocular irrigating solutions on the rabbit electroretinogram in vitro

The most adequate concentration of glucose in intraocular irrigating solution for the retina was studied electrophysiologically in the pigmented rabbit in vitro. Comparison of b-wave amplitudes demonstrated that glucose at a concentration of 20 mM/l yielded the highest values. A 40 mM/l glucose solution also increased the b-waves but to a lesser extent than did a solution of 20 mM/l. This result might be due to the detrimental effects of osmolarity. However, under hypoxic conditions the amplitudes of the b-wave obtained with 40 mM/l glucose solution was greater than those with 20 mM/l. It thus appears that slight hyperglycemic concentrations might have favorable effects on the ischemic retina.

Prognostic indicators of success and failure in vitrectomy for diabetic retinopathy

Results of pars plana vitrectomy for complications of diabetic retinopathy were analyzed by logistic regression analysis in 1007 eyes to determine the preoperative and intraoperative factors associated with visual success or failure. Preoperative factors associated with a poorer visual outcome (final visual acuity less than 5/200) include preoperative iris neovascularization, cataract, visual acuity less than 5/200 and traction or rhegmatogenous retinal detachment. Intraoperative factors associated with a greater chance of a poor visual result include use of intravitreal gas or air and creation of an iatrogenic retinal break or detachment. The presence of any one of these factors resulted in a 1.5 to 3.9 times greater risk of a poor final visual result. The regression coefficients may be combined to predict the likelihood of obtaining final acuity greater than or equal to 5/200 in eyes with various preoperative characteristics.

The crystalline lens after vitrectomy for diabetic retinopathy

We reviewed the records of 596 consecutive cases of vitrectomy performed for complications of diabetic retinopathy at the Wilmer Eye Institute. Accidental lens damage occurred during surgery in three eyes. Fourteen (8%) of 180 phakic eyes underwent later cataract removal. Follow-up of at least six months and detailed description of the lens at final examination were available in 151 eyes. Of these, visually significant opacities occurred in 32 eyes (21%), and the lens opacities accounted for substantial loss of final vision in 6 (19%) of these 32 eyes. Moderate or severe lens opacities that developed postoperatively were as follows: anterior subcapsular or cortical changes in 2 eyes (1%), nuclear sclerosis in 11 eyes (7%), posterior subcapsular changes in 25 eyes (17%). One hundred twenty-five preoperative, operative and postoperative factors were analyzed for each patient to detect correlations with postoperative lens changes. Nuclear sclerotic changes correlated with older patient age. Posterior subcapsular changes correlated with three intraoperative factors: longer duration of the operation, use of intravitreal gas, and use of a gas bubble filling more than 50% of the vitreous cavity. Posterior subcapsular changes were progressive with longer follow-up.

Prevention of lens opacification during diabetic vitrectomy

Lensectomy at the time of vitrectomy on diabetic patients markedly increases the risk of postoperative neovascular glaucoma, and is to be avoided when possible. We conducted a randomized prospective double-blind trial to determine if the addition of supplemental glucose to BSS Plus intraocular irrigating solution would lessen or prevent intraoperative lens opacification. Ten subjects received BSS Plus (glucose = 100 mg/dl); five (50%) developed intraoperative lens changes which interfered with the surgeon's view (three to an extent necessitating lensectomy). Ten subjects received glucose fortified BSS Plus (glucose = 400 mg/dl); none developed intraoperative lens changes (P less than 0.03, Mann-Whitney Rank). There was no statistically significant difference between the two study groups with respect to preoperative lens changes, infusion fluid volume, operative time, patient age, duration of diabetes, fasting blood glucose level, hemoglobin A1 level or lens clarity 5 months after surgery. We conclude that glucose fortification of BSS Plus significantly reduces intraoperative lens opacification during diabetic vitrectomy.

Complications of vitreous surgery for diabetic retinopathy. II. Postoperative complications

One hundred seventy-nine eyes were analyzed to determine the incidence of postoperative complications after vitrectomy for proliferative diabetic retinopathy. One hundred twenty-nine (72%) of the 179 eyes achieved improved vision, and 117 (65%) were considered visual successes with final vision in the functional range of 5/200 or better. Corneal epithelial defects occurred in 51 eyes (28%), but severe corneal complications were rare, and no eye developed corneal clouding as the sole cause of later visual loss. The lens was retained in 128 eyes (75%), and visually significant lens opacities occurred later in 17% of the phakic eyes. Postoperative iris neovascularization was reduced by not removing the lens, and rubeosis iridis occurred in 15 (13%) of 114 phakic eyes and in 21 (32%) of 65 aphakic eyes (P = 0.012). Vitreous hemorrhage was present in 75% of eyes immediately after surgery and cleared in an average of 6.2 weeks in phakic eyes and 5.4 weeks in aphakic eyes. Fifty-two eyes (29%) had recurrent vitreous hemorrhage after the initial postoperative period. New retinal detachment occurred after surgery in 16% of eyes and was treated successfully in 38%. Reoperations were done in 45 eyes (25%), and 32 (71%) of these were for repair of retinal detachment or removal of nonclearing vitreous hemorrhage. Six eyes (3%) developed phthisis bulbi, and one other eye was enucleated.

Healing of corneal epithelial wounds in marine and freshwater fish

The corneal epithelium of a fish is in direct contact with the aquatic environment and is a barrier to movement of ions and water into and through the cornea. This tissue layer is thus important in maintenance of corneal transparency. When the epithelium is wounded, its protective function is lost and corneal transparency remains compromised until the epithelial barrier is re-established. This study was undertaken to investigate the healing response of the fish cornea to epithelial abrasion. Wounds were stained with fluorescein and photographed during healing. Wound areas were measured by planimetry. The cornea of the sculpin, a marine teleost, becomes edematous after wounding and heals at 2.54 to 3.42 mm2/hr. Nonswelling corneas of the elasmobranchs--dogfish shark and skate--heal at 1.29 mm2/hr, respectively. The wounded eye of the rainbow trout, a freshwater teleost, is stressed by the low osmolality of the environment. Severe corneal edema and cataracts develop following epithelial wounding, and the cornea heals at 0.64 mm2/hr. Although the healing rates in teleosts differ from those in mammals, histology shows that the corneal healing mechanism is essentially the same in fish and mammals.