Assessment of the ocular response to topical β‐adrenoceptor antagonists using accommodative microfluctuations

Power spectrum analysis of accommodative microfluctuations has identified two dominant frequency components: a low frequency component (LFC < 0.6 Hz) and a high frequency component (1.3 Hz < HFC < 2.5 Hz). Computer‐driven models of accommodation and experimental manipulation of accommodative feedback loops indicate that LFCs are likely to have a functional role in monitoring retinal image contrast during sustained accommodation. In contrast HFCs have been shown lo he correlated with arterial pulse frequency and consequently their characteristics can be modified by the extra‐ and intra‐ocular vascular (and possibly CNS) effects. For example, topical instillation of the non‐selective β‐antagonist timolol maleate has shown previously the ability lo modify the HFC. In an attempt to clarify proposed differences between β‐adrenoceptor antagonist agents with regard to their effects on systemic and ocular vasculature. we extend the potential offered by HFCs as a non‐invasive method of assessing the ocular response to β‐antagonists to the cardioselecttve β‐antagonist betaxolol HCI. Accommodative microfluctuations were measured using a continuously recording infrared optometer on 10 emmetropic subjects (mean age 23.9 × 2.3 years) who viewed a high contrast target located at a vergence of ‐4 D. A double‐blind protocol was employed between saline and hetaxolol (0.5%, 2 x 30 μl) following corneal anaesthesia. Local and systemic effects were separated 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 betaxolol trials.) This demonstrates the utility of microfluctuations as a technique for differentiating ocular responses to β‐adrenoreceptor antagonists that are likely to emanate from a combination of ocular and systemic vascular effects