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Is visual efficiency reduced in myopic eyes?
Author(s) -
VeraDíaz F. A.,
McGraw P. V.,
Strang N. C.,
Whitaker D.
Publication year - 2002
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1046/j.1475-1313.2002.00086_13.x
Subject(s) - emmetropia , stimulus (psychology) , mathematics , contrast (vision) , noise (video) , statistics , optics , artificial intelligence , psychology , eye disease , refractive error , ophthalmology , computer science , medicine , physics , image (mathematics) , psychotherapist
Purpose: Myopic eye growth has the potential to modify both optical and neural performance of the human eye. To examine the influence of these factors we measured contrast detection thresholds in the presence of different levels of stimulus noise. Methods: Contrast detection thresholds were measured for a 4 c deg −1 sinusoidal grating windowed by a Gaussian contrast envelope using a 2‐Alternative Force Choice method of constant stimuli. The stimulus (Gabor) was embedded in different levels of external noise (from 9.86 × 10 −5 secdeg 2 to 0 noise). Threshold measures when plotted against noise level produce a linear relationship: the slope provides a measure of sampling efficiency (neural index), and the intercept with the abscissa provides an estimate of internal noise (optical index). Six emmetropes and 15 myopes (≥6.00 D) participated in the study. The data of the emmetropic subjects were used as a baseline for comparison with the myopic group. In addition, biometric data were collected from all subjects. Results: All emmetropic subjects showed similar results ( p > 0.5) with sampling efficiencies of the order of ∼14% and internal noise measures of ∼2.4 × 10 −5 secdeg 2 . All myopic subjects demonstrated reduced visual efficiency ( p < 0.01) which could take the form of a reduced sampling efficiency or increased intrinsic noise levels, although most myopic subjects showed reduced sampling efficiency. Interestingly, reductions in sampling efficiency were compensated by lower levels of internal noise in this group. Conclusions: Myopes show reduced visual efficiency in comparison to emmetropes. This can take the form of either increased internal noise or reduced sampling efficiency. However, deficits in sampling efficiency are associated with lower levels of internal noise. This may represent a compensation mechanism in the visual system of myopes to impaired neural sampling.