Monte Carlo simulation of latanoprost induced iris darkening

Lipofuscin-associated photo-oxidative stress during fundus autofluorescence imaging

Purpose

Current standards and guidelines aimed at preventing retinal phototoxicity during intentional exposures do not specifically evaluate the contribution of endogenous photosensitizers. However, certain retinal diseases are characterized by abnormal accumulations of potential photosensitizers such as lipofuscin bisretinoids in the retinal pigment epithelium (RPE). We sought to determine these contributions by a numerical assessment of in-vivo photo-oxidative stress during irradiation of RPE lipofuscin.

Methods

Based on the literature, we calculated the retinal exposure levels, optical filtering of incident radiation by the ocular lens, media, photoreceptors, and RPE melanin, light absorption by lipofuscin, and photochemical effects in the RPE in two situations: exposure to short-wavelength (λ = 488 nm) fundus autofluorescence (SW-AF) excitation light and exposure to indirect (diffuse) sunlight.

Results

In healthy persons at age 20, 40, and 60, respectively, the rate of oxygen photoconsumption by lipofuscin increases by 1.3, 1.7, and 2.4 fold during SW-AF-imaging as compared to diffuse sunlight. In patients with STGD1 below the age of 30, this rate was 3.3-fold higher compared to age-matched controls during either sunlight or SW-AF imaging.

Conclusions

Our results suggest that the RPE of patients with STGD1 is generally at increased risk of photo-oxidative stress, while exposure during SW-AF-imaging amplifies this risk. These theoretical results have not yet been verified with in-vivo data due to a lack of sufficiently sensitive in-vivo measurement techniques.

Bimatoprost in the treatment of eyelash hypotrichosis

Eyelashes hypotrichosis is a condition indicated by an inadequate amount of eyelashes. Hypertrichosis of eyelashes, characterized by excessive eyelash growth, is a regular phenomenon associated with ophthalmic prostaglandin and prostamide analogs. Recently, the US Food and Drug Administration approved Latisse((R)) (bimatoprost 0.03% solution), identical to the ophthalmic solution for glaucoma treatment, for increasing eyelash length, thickness and darkness in patients with hypotrichosis of the eyelashes. When prostaglandin and prostamide analogs interact with the prostanoid receptors in the hair follicle, this most likely stimulates the resting follicles (telogen phase) to growing follicles (anagen phase). Prostaglandin and prostamide analogs may also prolong the anagen phase of eyelashes, leading to an increase of eyelash length. Although bimatoprost is effective in promoting increased growth of healthy eyelashes and adnexal hairs, its effectiveness in patients with eyelash alopecia areata is debatable and its protective effect is not yet studied in patients with eyelash loss secondary to radiation or chemotherapy. Bimatoprost is generally safe when applied to the base of the eyelashes at the lid margin with minimum side effects. However, other ocular or systemic side effects associated with ophthalmic prostaglandin and prostamide analogs may occur when instilled on the surface of the eye, and patients must be informed and monitored.

Side effects associated with prostaglandin analog therapy

Topical prostaglandin analogs, which have become first-line therapy in the medical management of glaucoma, have an excellent safety profile with regard to systemic side effects, but are associated with several ocular side effects. Some of these are common, with no apparent serious consequences other than cosmetic, whereas others are much less common but represent potentially sight-threatening side effects. The former group includes conjunctival hyperemia, elongation and darkening of eyelashes, induced iris darkening, and periocular skin pigmentation. The latter group of side effects, which are relatively rare and lack definitive causal relationship to prostaglandin analog therapy, includes iris cysts, cystoid macular edema, anterior uveitis, and reactivation of herpes simplex keratitis. Most of the literature regarding side effects associated with prostaglandin analogs involves the use of latanoprost, probably because it was the first to be studied. There is no evidence, however, aside from less conjunctival hyperemia with latanoprost, that the commercially available prostaglandin analogs differ significantly with regard to side effects.