Cataract surgery is one of the most commonly performed surgical procedures in all of medicine. One of the particularities of cataract surgery is that the decision on when to operate is usually based on subjective visual impairment rather than objective, clinically measured visual function metrics. Usually, when a patient feels that their cataract interferes significantly with their everyday vision-related activities, the surgeon will proceed to perform cataract surgery.
Despite visual acuity (VA) being the traditionally used functional metric to objectively evaluate visual function in the clinical setting, various vision-related quality of life scales prove that functional vision in cataract patients cannot be adequately approximated by evaluating VA alone. VA seems to correlate poorly with patients' perception of visual disability due to their cataracts.
Contrast sensitivity (CS) quantifies the amount of lightness or darkness required to see an object compared to its background. The lower the contrast needed to detect an object (contrast threshold), the higher the contrast sensitivity. Cataracts increase the intraocular light scattering and thereby reduce the retinal image contrast. Compared to VA, contrast sensitivity seems to correlate better with subjectively perceived visual impairment and vision-related everyday activities, including mobility, target and face identification, driving, walking, and reading, inserting a key into a lock or a plug into a socket. Further, contrast sensitivity has been shown to be impaired earlier in the course of ocular pathologies when VA is still unaffected, the latter often under-estimating the onset and/or severity of visual impairment.
The quantitative contrast sensitivity function method (qCSF) leverages active-learning algorithms to test contrast sensitivity across multiple spatial frequencies, in a clinically feasible manner (2–5minutes per eye) and with both high test-retest reliability and sensitivity in detecting subtle changes in visual function.
Vingopoulos et al presented an initial prospective observational study employing the qCSF method to characterize contrast sensitivity function in cataractous and pseudophakic eyes compared to non-cataractous healthy controls. This was a prospective observational study at an academic medical center. CSF was measured in eyes with visually significant cataract, at least 2+ nuclear sclerosis (NS) and visual acuity (VA) ≥ 20/50, in pseudophakic eyes and in healthy controls with no more than 1+ NS and no visual complaints, using the Manifold Contrast Vision Meter. Outcomes included Area under the Log CSF (AULCSF) and CS thresholds at 1, 1.5, 3, 6, 12, and 18 cycles per degree (cpd). A subgroup analysis as performed on cataract eyes with VA ≥ 20/25.
A total of 167 eyes were included, 58 eyes in the cataract group, 77 controls, and 32 pseudophakic eyes with respective median AULCSF of 1.053 (0.352) vs 1.228 (0.318) vs 1.256 (0.360). In multivariate regression model, cataract was associated with significantly reduced AULCSF (P= 0.04, β= −0.11) and contrast threshold at 6 cpd (P= 0.01, β= −0.16) compared to controls. Contrast threshold at 6 cpd was significantly reduced even in the subgroup of cataractous eyes with VA ≥ 20/25 (P=0.02, β=−0.16).
In this initial prospective cross-sectional observational study, authors employed the novel qCSF method to characterize contrast sensitivity function in cataract disease and pseudophakic eyes compared to healthy controls and detected a generalized decrease in the broad metric of CSF, AULCSF, and disproportionate deficits in contrast sensitivity thresholds in cataract eyes with subjective symptomatology versus healthy controls. Importantly, these disproportionate deficits in contrast sensitivity persisted even in cataract eyes with VA as good as 20/25 or better. This suggests that contrast sensitivity measured with the qCSF method may be able to detect more subtle changes in visual function in eyes with cataract than the VA does.
"In conclusion, employing the qCSF method, we detected disproportionate deficits in contrast sensitivity thresholds in cataract eyes versus controls, at specific spatial frequencies that are particularly linked with vision-related everyday life activities; these disproportionate deficits in persisted even in cataract eyes with VA ≥20/25, suggesting that contrast sensitivity may be able to detect more subtle changes in visual function of eyes with cataract than the traditional VA testing does. These deficits would have been missed using the traditional Pelli-Robson chart. Contrast sensitivity measured with the qCSF emerges as a promising adjunct visual function endpoint, with the potential to be incorporated in the standard routine cataract evaluation to enhance surgical decision-making for cataract surgery."
Source: Vingopoulos et al; Clinical Ophthalmology 2022:16
https://doi.org/10.2147/OPTH.S367490
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