The Role of Corneal Astigmatism When Fitting Orthokeratology Contact Lenses



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Purpose: About one-third of children aged 5-17 years old have astigmatism. Children with increasing astigmatism can also have an accompanying increase in myopia via axial elongation. All of the randomized clinical trials to date have excluded patients with more than 1.50 D of astigmatism and there are limited data on the success of orthokeratology in patients with moderate to high astigmatism. The purpose of this thesis was to assess the fit of sphere and toric lenses and quantify the amount of corneal astigmatism corrected, and to determine the effect of peripheral elevation and central corneal astigmatism on toric orthokeratology fitting.

Methods: Two different studies were performed. The first was a retrospective analysis on 32 eyes of 16 subjects, half fitted with sphere and half with toric orthokeratology lenses. The post-treatment data after 1-3 months of successful nightly wear were compared to pre-treatment data to analyze the change in corneal astigmatism. The second study was a prospective analysis of the Pentacam tomography of 25 moderate refractive myopic astigmats (1.25 to 3.50 DC), ages 19 to 38 years. A subset of 20 subjects were fitted with Paragon Dual Axis Corneal Refractive Therapy (CRT) lenses that were worn for 10  2 days.

Results: Three methods of analysis showed that the decrease in corneal astigmatism for the spherical lens group was 0.10 - 0.22 D, which was approximately 22 - 31% correction, and the toric group was 0.29 - 0.57 D, which was 20 - 36% correction (all p < 0.006). There was a strong correlation between central corneal astigmatism and corneal elevation at the 4, 6, and 8 mm chords (r = 0.979, r = 0.961, r = 0.927, respectively; all p < 0.001). After Dual Axis lens wear, the average decentration of the treatment zone from the pupil center was 0.29 ± 0.23 mm temporal and 0.13 ± 0.26 mm inferior.

Conclusion: Toric orthokeratology lenses correct slightly more corneal astigmatism than spherical lenses. Central corneal astigmatism was highly correlated to peripheral elevation and may be a more expedient measure for clinical use when fitting toric orthokeratology lenses. The amount of treatment zone decentration with toric lenses was minimal which may lead to better visual performance.



Orthokeratology, Contact lenses, Astigmatism