ASSESSMENT OF THE OCULAR RESPONSE TO TOPICAL BETA-ADRENOCEPTOR ANTAGONISTS USING ACCOMMODATIVE MICROFLUCTUATIONS

Power spectrum analysis of accommodative microfluctuations has identif ied two dominant frequency components: a low frequency component (LFC < 0.6 Hz) and a high frequency component (1.3 Hz < HFC < 2.5 Hz). Comp uter-driven models of accommodation and experimental manipulation of a ccommodative feedback loops indicate that LFCs are likely to have a fu nctional role in monitoring retinal image contrast during sustained ac commodation. In contrast HFCs have been shown to be correlated with ar terial pulse frequency and consequently their characteristics can be m odified by the extra- and intra-ocular vascular (and possibly CNS) eff ects. For example, topical instillation of the non-selective beta-anta gonist timolol maleate has shown previously the ability to modify the HFC. In an attempt to clarify proposed differences between beta-adreno ceptor antagonist agents with regard to their effects on systemic and ocular vasculature, we extend the potential offered by HFCs as a non-i nvasive method of assessing the ocular response to beta-antagonists to the cardioselective beta-antagonist betaxolol HCI. Accommodative micr ofluctuations were measured using a continuously recording infrared op tometer on 10 emmetropic subjects (mean age 23.9 +/- 2.3 years) who vi ewed a high contrast target located at a vergence of -4 D. A double-bl ind protocol was employed between saline and betaxolol (0.5 %, 2 x 30 mul) following corneal anaesthesia. Local and systemic effects were se parated by examining the treated and untreated eyes of three subjects. Power spectrum analysis indicated that the root mean square (r.m.s.) value and power of LFCs and HFCs were equivalent for the saline and be taxolol trials. This demonstrates the utility of microfluctuations as a technique for differentiating ocular responses to beta-adrenorecepto r antagonists that are likely to emanate from a combination of ocular and systemic vascular effects.