The mechanism of oxidative damage to the lens through intraocular photochemical generation of superoxide and its derivatization to other oxidants such as singlet oxygen, hydroxyl radical and hydrogen peroxide has been studied. Rat lenses when organ cultured aerobically in TC 199 containing additional amounts of riboflavin were damaged as demonstrated by an inhibition of the uptake of Rb 86 against a concentration gradient. The pump was not affected by light if the culture was conducted in the basal TC 199. However, light was observed to induce significant peroxidative degradation of the tissue lipids even in the basal medium, the degradation being indicated by the formation of malonaldehyde. Both the inhibition of the pump as well as the peroxidative degradation of the tissue lipids, were attenuated considerably by scavengers of superoxide and hydrogen peroxide. In addition, the lipid degradation was prevented by vitamins C and E. The results suggest that the photodynamic injury to the lens cation pump as well as to membrane lipids is incumbent upon an initial generation of superoxide and its derivatization to other oxidants. Thus, the ocular lens is susceptible to oxidative insult and physiological damage through photocatalytic generation of various oxygen radicals. Large concentrations of ascorbic acid in the aqueous humor seems to be able to provide significant protection against such an insult. Thus, this may be one of the functions of high concentration of ascorbic acid in the aqueous humor. The implication of oxidative stress has also been examined in the genesis of cataracts in vivo. Treatment with vitamin E of the Emory mouse led to a decrease in the rate of cataract progression suggesting that at least in some instances an oxidative stress could participate in the formation of cataracts. Oxygen radicals may inflict damage at multifarious biochemical sites. Human lens lipids were also shown to have an absorption maxima at 239 nm indicating their susceptibility to oxidative degradation. In addition the lipid extract has fluorescence similar to that of lipofuscins. The levels of MDA were higher in the brunescent cataracts as compared to that in the nonbrunescent cataracts. The implications of oxidative stress towards the genesis of cataracts in humans is being explored further.

ABSTRACT.Purpose: To conduct a randomized prospective clinical trial to compare primary vitrectomy without scleral buckling versus conventional scleral buckling surgery in pseudophakic primary retinal detachment (PPRD) in terms of anatomic attachment rate, functional outcome and complications. Methods: Fifty consecutive eyes of 50 patients with PPRD were randomized into two groups, with 25 patients in each of group 1 (scleral buckling group) and group 2 (pars plana vitrectomy without buckling group) in a hospital setting and followed up at 1 week, 2 weeks, 6 weeks and 6 months. Results: A primary reattachment rate of 76% (19 retinas) was obtained in group 1, while a reattachment rate of 84% (21 retinas) was achieved in group 2. The final anatomic reattachment rate was 100% in both groups. The causes of failure in group 1 were proliferative vitreoretinopathy in five eyes and open break/ missed break in one eye. The causes of failure in group 2 were missed break/ open break in three eyes and proliferative vitreoretinopathy in one eye. Best corrected visual acuity (BCVA) at 2 weeks was better in group 1, while the final BCVA at end of 6 months was two lines better in group 2. The mean change in refractive error was -1.38 D in group 1 and -0.85 D in group 2. Conclusions: Pars plana vitrectomy without buckling provides an effective treatment for PPRD and results in better longterm visual and anatomic outcomes than conventional scleral buckling.

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Although primary vitrectomy can achieve anatomical and functional success rates comparable with those achieved by scleral buckling in uncomplicated forms of phakic RRD, the major drawback of the procedure is the high incidence of postoperative cataract formation. Moreover, visual rehabilitation takes place earlier with scleral buckling than with vitrectomy. Scleral buckling should thus be used as the primary surgical modality in the treatment of uncomplicated RRD where the media are sufficiently clear.

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