Downloaded By: [National University of Ireland Galway] At: 11:24 29 February 2008 Effects of higher-order aberrations on contrast acuity as a function of light level Euge´nie Dalimier a *, Chris Dainty a and John L. Barbur b a Applied Optics Group, Department of Experimental Physics, National University of Ireland, Galway, Ireland; b Applied Vision Research Centre, City University, London, UK (Received 15 December 2006) The effects of higher-order ocular aberrations on functional visual performance were assessed for seven young healthy subjects, as a function of light level. Contrast acuity thresholds were measured for a functional vision test with and without correction of higher-order aberrations and at a number of different pupil sizes in three of the subjects investigated. A visual simulator incorporating an adaptive optics (AO) system was used for this purpose. The results show that when light level is decreased, the drop in neural contrast sensitivity limits the impact that increased optical degradations have on vision. The expected AO benefit for functional vision is given for scotopic, mesopic and photopic regimes. 1. Introduction Since the implementation of adaptive optics (AO) in vision science, it has been shown that the correction of higher-order (HO) ocular aberrations can yield a great improvement in retinal image quality and hence in visual performance [1]. In particular, Yoon and Williams [2] measured an increase in monochromatic contrast sensitivity by a factor of up to about 3 after correcting ocular aberrations of two subjects. Applications such as wavefront guided refractive surgery [3] or custom contact lenses are now being developed to correct ocular aberrations beyond defocus and astigmatism, with an aim to provide normal people with a so-called ‘super-vision’. These results, however, were obtained with 6 mm large pupils and a relatively high retinal illuminance (60 Td). Pupil size is an important parameter since it governs the magnitude of ocular wavefront aberrations; in fact, measurements with 3 mm diameter pupils in the above study resulted in lower contrast sensitivity benefits. Light level, on the other hand, affects pupil size, and this in turn affects the amount of both light scatter and wavefront aberration. It is also known that, independently from pupil size, neural contrast sensitivity reduces drastically in *Corresponding author. Email: eugenie.dalimier@nuigalway.ie Journal of Modern Optics Vol. 55, Nos. 4–5, 20 February–10 March 2008, 791–803 ISSN 0950–0340 print/ISSN 1362–3044 online # 2008 Taylor & Francis DOI: 10.1080/09500340701469641 http://www.informaworld.com