Persistent biases in subjective image focus following cataract surgery

Abstract

We explored the perception of image focus in patients with cataracts, and how this perception changed following cataract removal and implantation of an intraocular lens. Thirty-three patients with immature senile cataract and with normal retinal function were tested before surgery and 2 days after surgery, with 18 of the patients retested again at 2 months following surgery. The subjective focus of natural images was quantified in each session by varying the slope of the image amplitude spectra. At each time, short-term adaptation to the spectral slope was also determined by repeating the measurements after exposure to images with blurred or sharpened spectra. Despite pronounced acuity deficits, before surgery images appeared “best-focused” when they were only slightly blurred, consistent with a strong compensation for the acuity losses. Post-operatively, the image slopes that were judged “in focus” before surgery appeared too sharp. This bias remained strong at 2 months, and was independent of the rapid blur after-effects induced by viewing filtered images. The focus settings tended to renormalize more rapidly in patients with higher post-operative acuity, while acuity differences were unrelated to the magnitude of the short-term blur aftereffects. Our results suggest that subjective judgments of image focus are largely compensated as cataracts develop, but potentially through a very long-term form of adaptation that results in persistent biases after the cataract is removed.

Low Vision and Plasticity: Implications for Rehabilitation

“…When cataract patients are asked to make settings such that visual stimuli appear achromatic, the settings tend to be in the bluish region but shift to the yellow region after the cataract surgery to compensate for the additional shortwavelength light reaching the retina (Delahunt et al 2004). Before cataract surgery, patients judge slightly blurred natural-scene images as best focused, but these images are reported to appear too sharp following cataract surgery (Parkosadze et al 2013). Although acuity may return to normal values within days after cataract surgery, these subjective biases in color and sharpness perception may persist for months.…”

Blur Adaptation to Central Retinal Disease

“…To our knowledge, there have been no previous reports on how reduced resolution affects the perception of blur in patients with CVL or other visual impairments, with the exception of a case study on cataracts removed in adulthood 28 and on patients undergoing routine cataract surgery 29 that suggest long-term contrast adaptation in these patients. However, as we noted, cataracts do reduce contrast in a low-pass fashion, unlike the reduced resolution without the contrast reduction associated with the sparse sampling of peripheral retina.…”

What are patients' beliefs about, and experiences of, adaptation to glasses and how does this affect their wearing habits?

“…In addition to the common symptoms of adaptation to new glasses, participants also reported having to adapt to the clear vision in new glasses; this was possibly due to their adaptation to blur in their previous non‐optimal refractive correction biasing their subjective point of best focus towards a blurred image, leading a fully corrected image to appear “too sharp” 32 . Our findings agree that there is much individual variation in the amount of blur that a patient may find acceptable, 48 and not all prefer sharp vision at all times 49 …”

“…This blur adaptation can be defined as an improvement in visual performance following exposure to blur, which is not accompanied by a measurable change in refractive error 28 and cannot be explained by other effects, such as accommodative or psychological effects 27 . Furthermore, blur adaptation can influence patients' subjective perception of how blurred an image appears 32 . Adaptation effects have been shown after just a few minutes of exposure to blur and, once established, the effects can be persistant 30 .…”

“…27 Furthermore, blur adaptation can influence patients' subjective perception of how blurred an image appears. 32 Adaptation effects have been shown after just a few minutes of exposure to blur and, once established, the effects can be persistant. 30 Astigmatic blur adaptation, with meridional adaptation effects, has also been demonstrated.…”