Abstract
Purpose: Amblyopia and strabismus affect 2%–5% of the population and cause a broad range of visual deficits. The response to treatment is generally assessed using visual acuity, which is an insensitive measure of visual function and may, therefore, underestimate binocular vision gains in these patients. On the other hand, the contrast sensitivity function (CSF) generally takes longer to assess than visual acuity, but it is better correlated with improvement in a range of visual tasks and, notably, with improvements in binocular vision. The present study aims to assess monocular and binocular CSFs in amblyopia and strabismus patients.Methods: Both monocular CSFs and the binocular CSF were assessed for subjects with amblyopia (n = 11), strabismus without amblyopia (n = 20), and normally sighted controls (n = 24) using a tablet-based implementation of the quick CSF, which can assess a full CSF in <3 min. Binocular summation was evaluated against a baseline model of simple probability summation.Results: The CSF of amblyopic eyes was impaired at mid-to-high spatial frequencies compared to fellow eyes, strabismic eyes without amblyopia, and control eyes. Binocular contrast summation exceeded probability summation in controls, but not in subjects with amblyopia (with or without strabismus) or strabismus without amblyopia who were able to fuse at the test distance. Binocular summation was less than probability summation in strabismic subjects who were unable to fuse.Conclusions: We conclude that monocular and binocular contrast sensitivity deficits define important characteristics of amblyopia and strabismus that are not captured by visual acuity alone and can be measured efficiently using the quick CSF.
Highlights
Strabismus is a common cause of amblyopia (Woodruff et al, 1994b; Simons, 2005), amblyopia can be caused by other developmental disorders such as anisometropia or visual deprivation (Helveston, 2010)
The summation index was significantly greater than 1 in strabismus without amblyopia (SWA) subjects who were able to fuse (p < 0.003, t-test; false positive risk (FPR) = 0.013). These results suggest that in strabismus, the lack of binocular summation is a direct consequence of ocular misalignment, whereas in amblyopia there is an additional fundamental developmental deficit in binocular vision
Consistent with earlier findings, the present study demonstrates that individuals with amblyopia show a significant loss of contrast sensitivity in the non-dominant eye while the contrast sensitivity function (CSF) of the dominant eye appears to be normal
Summary
Amblyopia and strabismus are the most common developmental disorders of binocular vision, with an estimated prevalence of around 2%–5% (Graham, 1974; Ross et al, 1977; Friedmann et al, 1980; Cohen, 1981; Simpson et al, 1984; Stayte et al, 1990; Thompson et al, 1991; Satterfield et al, 1993; Kvarnström et al, 2001; Jakobsson et al, 2002; Barry and König, 2003; Robaei et al, 2005). Amblyopia is associated with deficits in spatial vision (Robaei et al, 2005; Zhao et al, 2017) including reduced visual acuity (Kirschen and Flom, 1978; Levi and Klein, 1982, 1985; Kelly and Buckingham, 1998), contrast sensitivity loss (Hess and Howell, 1977; Levi and Harwerth, 1978; Bradley and Freeman, 1981; Kiorpes et al, 1999; McKee et al, 2003), spatial distortion (Pugh, 1958; Hess et al, 1978; Fronius and Sireteanu, 1989; Hess, 2001), abnormal contour integration (Hess et al, 1997; Hess and Demanins, 1998), and binocular acuity summation (Sireteanu, 1982; Chang et al, 2017) deficits
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