Correction method may influence myopia progression rate
MedWire News: Researchers have found evidence to support a theoretical benefit of contact lenses over conventional spectacles in people with moderate to high myopia.
They say that using standard spectacles to correct the on-axis refractive error results in hyperopic defocus in the peripheral retina, which could potentially influence the development and progression of myopia.
They therefore call for prospective studies comparing spectacles with contact lenses to determine whether such a difference occurs in clinical practice.
Simon Backhouse (The University of Auckland, New Zealand) and team assessed peripheral refraction in 10 adults with a mean age of 24 years and moderate to high myopia (-5.00 to -8.00 D).
All participants were assessed using open-field autorefraction to measure on- and off-axis refraction. The tests were performed three times: first with the eyes in primary gaze, and then when corrected with spectacles and contact lenses.
Writing in Ophthalmic & Physiological Optics, the researchers report that the average on-axis mean-sphere refraction was 6.33 D and the average axial eye length was 25.99 mm.
Interestingly, the average relative peripheral refraction (RPR) across all eccentricities was hyperopic when uncorrected (+0.90 D) and also when corrected with spectacles (+1.01 D) but changed to a myopic value when corrected with contact lenses (-1.84 D).
The team also detected a highly significant effect of correction on peripheral refraction. RPR did not differ between the uncorrected state and correction with spectacles; however, when corrected with contact lenses there was a highly significant shift from hyperopic RPR to myopic RPR compared with both uncorrected and spectacle-corrected states.
Additionally, the mode of correction influenced relative peripheral astigmatism, report Backhouse et al. Horizontal and vertical astigmatism showed little variation in uncorrected eyes or eyes corrected with spectacles but became significantly more negative on correction with contact lenses (-0.64 D).
Finally, on- and off- axis eye length measures indicated a relatively prolate eye shape, the authors note.
Taken together, the results indicate that when eyes are corrected with conventional spectacles their absolute peripheral refractions tend to be hyperopic, whereas when the same eyes are corrected with conventional soft contact lenses their absolute peripheral refractions become significantly myopic.
"The results of this study have implications for clinical practice because they suggest that if peripheral refraction does influence myopia progression, then the myopic peripheral refractions associated with contact lens wear would be expected to slow progression, whereas the hyperopic peripheral refractions associated with spectacle wear may exacerbate progression," the authors conclude.
"A prospective, longitudinal study in a younger, progressing cohort is warranted to determine whether spectacles and contact lenses are associated with different myopia progression rates."
By Joanna Lyford