Changes in refraction, corneaendothelial cells and ocular dimension using MRI in myopic children undergoing orthokeratology treatment for 12 months

Abstract

Myopia generally develops during childhood and can continue to progress to high myopia. High myopia is associated with visual impairment thus, controlling myopia progression is essential. Axial length (AL) elongation a clinical indicator for myopia progression and myopic defocus at the peripheral retina is hypothesized as a signal for AL inhibition. Orthokeratology (Ortho-K) lenses have shown to be effective in inhibiting AL growth and controlling myopia progression. The objective of this study is to investigate the changes in the eyeball dimensions of myopic children undergoing Ortho-K treatment for 12 months using MRI analysis. The results were compared with the single vision spectacle (SVS) group. A total of 70 myopic Chinese school children (35 Males, 35 Females), mean age of 8.31±0.47 years participated in this study. Fortyfive (45) of them were fitted with OK and another 25 with SVS. The parameters measured include cycloplegic for central and peripheral refraction (PR), visual acuity (VA), contrast sensitivity (CS), corneal topography, intraocular pressure (IOP), the morphology of corneal endothelial cells (CEC) and central corneal thickness (CCT). Changes in peripheral eye length (PEL) and ocular dimensions [axial length (AL), horizontal width (HW), vertical height (VH)] were analyzed using MRI. Standard slit lamp examination was performed at every visit. All measurements (except MRI) were taken at baseline and 6 months intervals until 12 months. MRI was taken at baseline and 12 months of intervention. The results were analyzed using t-test and ANOVA. At 12 months, significant differences in refraction, PR, AL, PEL and CCT between Ortho- K and SVS were noted. Myopia had increased by -1.26±1.01D in SVS (p<0.01) but decreased by 2.86 ±1.11D in Ortho-K (p<0.01). AL increased by 0.48±0.47 mm in SVS (p<0.01) but decreased by 0.18±0.38 mm in Ortho-K (p<0.01). Greater central corneal flattening and thinning were evident in the Ortho-K group (p<0.01). However, no significant change was found in the morphology of corneal endothelial cells or IOP. Significant myopic shifts in relative peripheral refraction (RPR) (p<0.01) were noted in Ortho-K, while hyperopic shifts (p<0.01) were noted in SVS. MRI analysis showed that myopia increased with AL in both groups (p<0.01), but more in SVS than Ortho-K. Significant differences in relative peripheral eye length (RPEL) (p=0.00) were noted in Ortho-K but not in SVS, indicating more oblate retinal shape in Ortho-K than in SVS at 12 months. No significant changes in CEC and no adverse response to contact lens wear was found. The results of this study indicate that the Ortho-K lenses inhibit AL growth by 44% and did not alter the cornea health within 12 months of the study period in myopic children. Ortho-K flattens the central cornea and shortens the AL. Long-term Ortho-K wear alters the peripheral retinal shape that may contribute to inhibition of AL growth and myopia progression. This study concludes that long-term Ortho-K wear (12 months) causes changes in ocular dimensions to control myopia progression. Ortho-K is a safe and effective method and should be considered more often by Optometrists for myopia management in children.