Ortho-K + HOA

Ortho-k and HOA
A recent study shows that ortho-k induces high order aberrations (HOA)...which most of us already knew. This isn't earth-shattering news, but it does attempt to quantify what most eye care practitioners assumed was happening with ortho-k, which is that you can't decrease myopia without INCREASING HOA. What the article doesn't mention, of course, is that pretty much the same thing occurs in LASIK, although not as badly since there's corneal destruction in lasik (and not corneal redistribution). Assumedly every corneal refractive procedure (lasik, rk, prk, ortho-k, etc) induces HOA.

The article below is from the Journal of the AAO (ophthalmologists), but the University of Houston School of Optometry was probably the 1st to recognize the HOA effect in ortho-k in a Contact Lens Spectrum article about myopia control. I'll have to find the article, but it was over a year ago. Anyway turns out HOA and corneal asphericity may actually be beneficial to myopia control.

Anyway, I digress. here's the most recent ortho-k/HOA article:

Contrast Sensitivity and Higher-Order Aberrations after Ortho-K

Forty-four eyes of 22 subjects (mean age +/- standard deviation [SD], 24.0 +/- 3.2 years) undergoing overnight orthokeratology, ocular aberrations and mesopic contrast sensitivity were determined before and three months after commencement of the procedure to investigate the effect on night driving. Mean spherical equivalent refraction +/- SD was -2.34 +/- 0.99 diopters at baseline. Mesopic contrast sensitivity with and without glare was assessed using the Mesotest II.

Orthokeratology significantly reduced the log mesopic contrast sensitivity from 0.25 +/- 0.08 to 0.08 +/- 0.10 without glare and from 0.21 +/- 0.11 to 0.07 +/- 0.10 with glare. The proportion of eyes that fulfilled the German standard recommendation level for night driving was 36 percent. The induced changes in log mesopic contrast sensitivity showed significant negative correlation with the changes in third- and fourth-order root mean square. Furthermore, significant correlation was found between the amount of myopic correction and the induced changes in log mesopic contrast sensitivity. The induced changes in higher-order aberrations significantly correlated with the amount of myopic correction.

Mesopic contrast sensitivity after overnight orthokeratology is deteriorated significantly as ocular higher-order aberrations increase. These changes depend on the amount of myopic correction.


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