In situ measurement of spectral changes in the anterior eye following application of ultraviolet-absorbing compounds.

The ocular structures are very sensitive to damage from ultraviolet (UV) radiation, exposure is linked to corneal and conjunctival damage, cataract formation and may also be implicated in the aetiology of age-related macular degeneration. These structures are usually protected by wearing suitable eyeglasses and goggles. An alternative to conventional eyeglasses/goggles is the concept of "liquid sunglasses" which involve the topical application of eye drops that are designed to block harmful UV radiation reaching the sensitive ocular surfaces. The evaluation of such compounds directly applied to the eye surface requires in situ measurements to compare the efficacy of different formulations. A novel ocular spectrometer system has been used to evaluate changes in the transmission of ultraviolet (UV) radiation through the anterior eye following topical application of candidate UV-absorbing formulations. The key feature of the system is the ability to propagate a beam of light tangentially through the anterior eye using a compact, hand-held lens assembly incorporating UV-transmitting optical fibres. A range of formulations containing UV-absorbing compounds were topically applied to ex vivo rabbit eyes. Significant increases in the absorption of the UV spectrum were detected in seven of the eight formulations studied, demonstrating the potential of this measurement technique in the evaluation of formulations developed as potential topical ocular sunscreens.

A role for photoreceptors in retinal oedema and angiogenesis: an additional explanation for laser treatment?

PURPOSE: To investigate the possible roles of retinal photoreceptors in macular oedema and retinal angiogenesis with particular reference to the mode of action of laser therapy. METHODS: (i) Studies in rats made hypoxic for 2 h by administering an oxygen/nitrogen mixture of reduced oxygen content, and growth factors determined by RT-PCR, western blotting, and immunohistochemistry. Assessment of blood-retinal barrier integrity using fluorescent and electron-dense tracers. (ii) Studies in pigs with one retina made hypoxic by selective embolisation of the retinal capillary circulation with fluorescent microspheres. (iii) Assessment of laser therapy in selected cases of retinal neovascularisation indicating a role for photoreceptors. RESULTS: In the hypoxic retina, angiogenic and vascular permeability factors such as vascular endothelial growth factor (VEGF), nitric oxide synthases (NOSs), and insulin-like growth factor-1 are upregulated in retinal astrocytes and Müller cells but are also present in large amount in the photoreceptors. Hypoxia-inducible factor-1 (HIF-1) is upregulated in retinal glial cells but not in the photoreceptors, suggesting that growth factors in the photoreceptors may not have been generated there. The tracer dye, rhodium isothiocyanate, leaking from an abnormally permeable inner blood-retinal barrier in the hypoxic retina accumulates in the photoreceptors. CONCLUSIONS: The results indicate that laser treatment of macular oedema or retinal neovascularisation may obtain its effect not only by improving oxygen availability in the inner retina, but also by reducing the load of angiogenic/permeability factors that accumulate in the photoreceptors in hypoxic/ischaemic conditions.