STANDARD CRITERION FOR FLUCTUATIONS OF MODULATION TRANSFER-FUNCTION IN THE HUMAN EYE - APPLICATION TO DISPOSABLE CONTACT-LENSES

It is well known that the modulation transfer function (MTF) character izes the optical quality of the eye. Recently, some objective techniqu es have been introduced in order to measure this function in vivo. The se techniques could be employed to display the temporal fluctuations o f the eye + compensation system and to isolate the effect of the compe nsation element provided that the standard fluctuations for a normal o bserver were known. In this work we carry out a study of the MTF of th e human eye over a long period of time to quantify the standard fluctu ations of the retinal image quality and to establish a standard criter ion of normality. We have defined a single quality parameter from each measured MTF to simplify the analysis of the results. We have evaluat ed this merit function on normal observers three times a day for one m onth. As expected, random deviations from the mean value of the merit function have been obtained, although fluctuations with no statistical differences of the merit function (P value from ANOVA test P > 0.01) and the standard deviation of these fluctuations (5%) can be chosen as a standard criterion. We have used this result to study the behaviour of a time-varying compensation element: a disposable contact lens. Th e study of the eye + contact lens system has been carried out with fou r types of disposable contact lenses for one month. In spite of their generally good behaviour, statistically significant differences from t he standard pattern can be observed. This superimposed continuous fluc tuation can be due to lens-dependent processes. (C) 1997 The College o f Optometrists.