Summary and Future Directions— Basic Science

Abstract

There are three principal clinical issues that urgently need to be addressed by basic laboratory and clinical science studies of orthokeratology lens wear:1. Increased microbial infection rates (especially in children); 2. Permanent corneal warpage effects, especially associated with irregular surface astigmatism; and 3. Concern for exhausting the finite capacity for mitotic proliferation of corneal limbal stem cells over decades of overnight orthokeratology lens wear.The basic premise for such studies is that basic clinical or laboratory science experiments can assess risks, and that once risk is known, it can be managed ethically and scientifically by patients and practitioners.Infection concerns are real. A hyper-oxygen transmissible, alignment-fitted rigid gas-permeable lens that produces no increase in Pseudomonas aeruginosa (PA) binding in 30-night extended wear in humans or 24 hour wear in rabbits, when cast in CRT-design, increases PA binding in the rabbit model. Rabbit fits are not completely like humans, so what does happen in humans? This needs to be studied immediately.Likewise, findings of corneal warpage and induced, irregular surface astigmatism have recently been reported by Hiraoka et al. 1 , who demonstrated both a significant increase in both regular and irregular astigmatism even in clinically successful orthokeratology cases. Interestingly, however, the amount of myopic correction correlated significantly with the increase in the asymmetry component (Pearson correlation coefficient; R ϭ 0.40, P ϭ 0.0009) but not with the increase in regular astigmatism (R ϭ 0.24, P ϭ 0.55). Importantly, these findings were not accompanied by an adverse effect on visual acuity.The take-home message here is clear. The central compressive area needs to be smooth, centered, and predictable in the closed eye. We need the best possible centration lens design, i.e., improved fitting algorithms, preferably fit from inventory.Finally, concerns about potentially increased orthokeratologyinduced demands on long-term corneal limbal stem cell mitotic renewal of the corneal epithelium can only be answered in the animal model (rabbit, cat). The preliminary experiments reported by Matsubara et al. 2 also need to be confirmed and eliminated by better lens centration and compression algorithms.In summary, using properly fit and monitored orthokeratology lenses, there are no major contraindications to date that have been established by currently reported basic or clinical science studies. There are however, concerns that need to be addressed by appropriate future clinical and/or bench investigations.Once we understand how orthokeratology lens wear alters or does not alter significantly corneal health long-term, risk can be assessed and then appropriately addressed in patients of any age. REFERENCES1. Hiraoka T, Furuya A, Matsumota Y, et al. Quantitative evaluation of regular and irregular corneal astigmatism in patients having overnight orthokeratology.