Structural and functional aspects of myopia in young adults. An investigation of nearwork-induced transient myopia and accommodation in relation to refractive stability.

Abstract

This thesis has investigated nearwork-induced transient myopia and accommodation responses in relation to refractive stability, multichromatic stimuli and orthokeratology. Five individual studies have been carried out. Initially an investigation into the temporal and dioptric aspects of nearwork-induced transient myopia was undertaken, suggesting that increased task duration does not increase the level, or slow the regression of post-task NITM, however an increase in the dioptric demand of the task does. In the second study, a longitudinal myopia progression study, these findings were related to short term myopia progression. The third investigation demonstrates the feasibility of measuring the biometric correlates of nearwork-induced transient myopia using a low coherence reflectometry device (LenStar, Haag Streit Koeniz, Switzerland). Fourthly, a comparison of the differences between static and dynamic accommodative responses, microfluctuations and nearwork-induced transient myopia produced when viewing a black/white target as oppose to a red/blue target has suggested the possibility of four accommodative responses to this multichromatic stimulus. Further investigation will be necessary to investigate if any of these response types are related to myopia progression. 2 The final study investigates the effect of two different designs of orthokeratology contact lenses (C5 and polynomial) on visual function. It appears to be the case that although the polynomial lens design has a larger refractive effect than the C5 lens it reduces both high and low contrast corrected visual acuity to a greater extent. The higher the baseline mean spherical equivalent refractive error the larger the detrimental effect.