Reactive oxygen species, oxidative stress, glaucoma and hyperbaric oxygen therapy

© 2017 Spanish General Council of Optometry This review examines the role of oxidative stress in damage to cells of the trabecular meshwork and associated impaired aqueous drainage as well as damage to retinal ganglion cells and associated visual field losses. Consideration is given to the interaction between vascular and mechanical explanations for pathological changes in glaucoma. For example, elevated intraocular pressure (IOP) forces may contribute to ischaemia but there is increasing evidence that altered blood flow in a wider sense is also involved. Both vascular and mechanical theories are involved through fluctuations in intraocular pressure and dysregulation of blood flow. Retinal function is very sensitive to changes in haemoglobin oxygen concentration and the associated variations in the production of reactive oxygen species. Reperfusion injury and production of reactive oxygen species occurs when IOP is elevated or blood pressure is low and beyond the capacity for blood flow autoregulation to maintain appropriate oxygen concentration. Activities such as those associated with postural changes, muscular effort, eye wiping and rubbing which cause IOP fluctuation, may have significant vascular, mechanical, reperfusion and oxidative stress consequences. Hyperbaric oxygen therapy exposes the eye to increased oxygen concentration and the risk of oxidative damage in susceptible individuals. However, oxygen concentration in aqueous humour, and the risk of damage to trabecular meshwork cells may be greater if hyperbaric oxygen is delivered by a hood which exposes the anterior ocular surface to higher than normal oxygen levels. Oronasal mask delivery of hyperbaric oxygen therapy appears to be indicated in these cases

Menopause, hormone replacement therapy and tear function

This pilot study investigates the effect of menopause, hormone replacement therapy (HRT) and gender on tear function. Hormones affect the incidence and course of dry eye conditions, and anecdotal evidence suggests the incidence of dry eye increases in women after menopause. Estrogen HRT alleviates some of the side effects of menopause, but whether systemic HRT benefits dry eye sufferers is not known. HRT may restore hormonal support to the lacrimal gland and tear function to normal levels. Pre-menopausal women, post-menopausal women, hysterectomized women taking HRT and age-matched men were enrolled. We examined ocular symptomatology, tear film function and tear film composition in the four groups, In particular, we examined tear lipocalin secretion. Tear lipocalin is a marker of lacrimal function and may be important in maintaining tear film stability. A difference in tear lipocalin secretion among groups was expected to reflect differences in signs and symptoms of dry eye