Purpose Reduced retinal image contrast produced by accommodative lag is implicated

Purpose Reduced retinal image contrast produced by accommodative lag is implicated with myopia development. as the target vergence that optimizes image quality using a visual contrast metric (VSMTF) computed from wavefront errors. Results Accommodation was most accurate TGX-221 (and image quality best) during binocular acuity whereas accommodation was least accurate (and image quality worst) while watching a movie. When viewing distance was reduced accommodative lag increased and image quality (as quantified by VSMTF) declined for all tasks in both refractive groups. For any given viewing distance computed image quality was consistently worse in myopes than in emmetropes more so for the acuity than for reading/movie watching. Although myopes showed greater lags and worse image quality for the acuity experiments compared to emmetropes acuity was not measurably worse in myopes compared to emmetropes. Conclusions Retinal image quality present when performing a visually demanding task (e.g. during clinical examination) is likely to be greater than for less demanding tasks (e.g. reading/movie watching). Although reductions in image quality lead to reductions in acuity the image quality metric VSMTF is not necessarily an absolute indicator of visual performance because myopes achieved slightly better acuity than emmetropes despite showing greater lags and worse image quality. Reduced visual contrast in myopes compared TGX-221 to emmetropes is usually consistent with theories of myopia progression that point to image contrast as an inhibitory signal for ocular growth. Keywords: myopia image quality accommodation aberrations Myopia has shown dramatic increase in the prevalence rate in many regions of the world 1 suggesting a strong role of environmental factors. Several environmental factors have been attributed to the development and progression of myopia. One of these hypotheses is related to accommodation. It has been suspected that myopic TGX-221 individuals have high levels of aberration2-5 and display larger accommodative lags6-9 than emmetropes. As a result a markedly blurred optical image around the retina may lead to excessive axial growth in the eye as well as myopia due to either a moderate form deprivation or a hyperopically defocused retinal image. This hypothesis is largely based on evidence from animal models that suggest that the eye grows in a Rabbit polyclonal to MET. direction that eliminates blur.10 11 The animal model of lens-induced myopia suggests that the hyperopic blur induced by accommodative lags reduces image contrast which signals the eyes to elongate axially to reduce the degree of hyperopic blur. According to Wallman and Winawer10 and Smith et al. 11 eyes have an intrinsic propensity for growth and will continue to grow unless actively inhibited by retinal activity brought on by image contrast. An implicit assumption in the foregoing account is usually that increased accommodative lag reduces image contrast around the retina thereby releasing the inhibition of axial elongation. This assumption is usually supported by evidence that myopes show reduced accommodation under monocular viewing conditions 12 13 when viewing thorough full correction 14 15 and when accommodation is usually stimulated using minus lenses.7-9 However the implication that accommodative lag necessarily reduces image quality is less certain. Depending on how accommodation is usually measured and how accommodative lag is usually defined large artifacts can lead to misleading results.16-20 This lingering uncertainty suggests a need to measure image quality directly using wavefront aberrometry to determine whether retinal image is indeed reduced in myopic eyes when accommodating to a near target and whether that reduction is larger than for emmetropic eyes. Moreover the visual task used to elicit accommodative responses may influence the magnitude of that response21 TGX-221 and therefore would temper our attempt to generalize laboratory results into the real world of daily living. Collins et al.5 showed worse image quality in progressing myopic adults than emmetropes before a 2-hour “reading task” performed at each individual’s habitual reading distance (mean in myopes = 35 cm and emmetropes = 41 cm). The use of different reading distances as acknowledged by the.