M. Kakar

Ascorbate in the Rat Lens: Dependence on Dietary Intake

Purpose: To establish a method for sample preparation to measure ascorbate in whole lenses and to investigate whether lens ascorbate concentration is dependent on dietary ascorbate intake. Methods: Four groups of 3 young Sprague-Dawley rats each were fed chow containing L-ascorbate, either 0.0, 5.7, 57.0 or 114.0 mmol/kg for a duration of 4 weeks. Thereafter, each rat was sacrificed. The lens was extracted, photographed, and lens wet weight was measured. The lens was homogenized in 1.0 ml of 0.25% metaphosphoric acid, the homogenate was centrifuged and the supernatant ultrafiltered. The filtrate was injected into an ion exchange, reversed-phase Polypore H HPLC column equipped with a 254-nm ultraviolet detector. Samples were calibrated against an L-ascorbate standard. Polynomial regression analysis was performed on the data. Results: All lenses were devoid of cataract. A 95% confidence interval for baseline content of ascorbate without any dietary intake was estimated to be 0.16 ± 0.01 µmol/g wet weight of lens. The lens ascorbate concentration increased linearly with dietary ascorbate intake with an increased rate, estimated as a 95% confidence interval of 0.33 ± 0.18 (µmol ascorbate) (g lens)–1 (mol ascorbate)–1 (kg chow) with r2 = 0.62. Conclusion: Lens ascorbate concentration linearly increases with dietary ascorbate intake without cataract development in the rat. The currently presented method for sample preparation to measure the whole-lens content of ascorbate is applicable.

Drinking water supplementation with ascorbate is not protective against UVR-B-induced cataract in the guinea pig.

Purpose:  To study if ascorbate supplementation decreases ultraviolet radiation (UVR)‐induced cataract development in the guinea pig.

High lenticular tolerance to ultraviolet radiation-B by pigmented guinea-pig; application of a safety limit strategy for UVR-induced cataract.

Purpose:  The purpose of this study was to determine a threshold measure, maximum tolerable dose (MTD), for avoidance of UVR‐B‐induced cataract in the pigmented guinea‐pig.

Macular protection with IOLs

The clinical outcome within one month after phacoemulsification cataract extraction with implantation of the blue-blocking SN60AT IOL was examined prospectively and compared to a retrospectively examined material of implantations of the equivalent SA30AL without blue-blocker. There was no difference in best corrected visual acuity gain between the two lenses. In addition, the subjective color perception was examined for with a questionnaire after the first implantation of blue-blocking IOL and after the second implantation of blue-blocking IOL. Only one patient noted a changed color perception. There are thus strong theoretical reasons to block blue light in IOLs and no short term clinical inconvenience. But, it remains to be proven in long term follow up studies that the blue-blocking IOL protects against macular degeneration.

Maximum tolerable dose (MTD), a new index for ultraviolet radiation toxicity in the lens

The maximum tolerable dose (MTD2.3:16) for avoidance of cataract on exposure to UVR-300 nm in the rat was currently estimated to 3.65 kJ/m2. For this, Sprague-Dawley rats were unilaterally exposed to UVR in the 300 nm wavelength region, generated with a high pressure mercury arc source. The intensity of forward light scattering was measured one week after exposure. MTD allows estimation of toxicity for continuous response events with small sample experiments. Current safety standards for avoidance of cataract after exposure to UVR are based on a binary response event. It has however recently been shown that UVR-induced cataract is a continuous dose-dependent event. MTD provides a statistically well defined criterium of toxicity for continuous response events.