In this study, participants with similar prescriptions were fitted with ortho-k lenses of identical design but manufactured from both 100 Dk and 180 Dk materials, with each material used in one eye. After three nights of wear, the participants were evaluated, and a significant difference in treatment effect was observed, with the Optimum Infinite (180 Dk) material producing greater overall change. While this study involved a small group, the results provided compelling evidence supporting the superior performance of the Optimum Infinite material in ortho-k lenses.

Taking further this observation that the degree of overnight edema affects the rate at which myopia correction occurs during ortho-k, it would be expected that reducing lens thickness would also speed up the treatment effect. Importantly, however, reducing lens thickness will also have the undesirable effect of increasing lens flexure, which may itself slow or reduce the effectiveness of ortho-k treatment. For each material/lens design combination there will be an optimal lens thickness where adaptation time is minimised (Figure 1).

Finally, we considered whether further improvements could be made by developing materials with even higher Dk values. At Contamac, we are able to produce materials with Dk values of 250 or even 300. However, we still needed to determine whether these increases would provide clinically significant benefits, or whether we would reach a point of diminishing returns, where factors such as wettability, manufacturing challenges, and cost would outweigh any marginal advantages.

A subsequent study, also conducted at the University of Montreal, was initiated to evaluate whether there were any significant benefits in using a material of higher Dk than the currently available Optimum Infinite (180 Dk).

In this study, conventional lenses were designed both with different materials (Optimum Infinite, 180 Dk and an experimental 250 Dk material) and different thicknesses (0.20 and 0.26 mm). This produced 4 lens types with Dk/t values of 69 (180/0.26), 125 (250/0.20), 96 (250/0.26, and 90 (180/0.20). All lens diameters were standardised at 9.8 mm and base curves calculated at 0.1 mm flatter than flattest central corneal curvature as is standard for normal GP lens fitting.

20 participants were recruited from the student population at the university and randomly selected into 2 groups to wear lenses under patched eye conditions for 3 hours. In group one lenses had a thickness of 0.26 mm, whereas in group two lenses had a thickness of 0.20 mm. Lens material was assigned at random.

Patches were removed and eyes were then evaluated for keratometry, pachymetry, and densitometry variations from baseline readings with minimum delay.

After 3 days, the experiment was repeated using the other material (same lens thickness).

It has previously been shown (Harvitt and Bonanno) [4] that the minimum Dk/t threshold to avoid hypoxia increases from 35 for daily wear to 125 under closed eye conditions, so it was anticipated that some degree of hypoxia related eye changes would occur during closed-eye lens wear with three of the four investigated lenses.

In practice, however, no statistically significant differences were observed in measurements taken from participants after they wore a 180 Dk lens compared to when they wore a 250 Dk lens or no lens at all, either with the 0.20 mm lenses or the 0.26 mm lenses. This gives an indication that the clinical advantages of moving from a 180 Dk material to a 250 Dk material would be small, although differences could have been masked by the variability associated with the measurement techniques and with individual responses to hypoxia, combined with the relatively small number of participants in the study.

Achieving target refractive outcomes over a weekend rather than over the course of a week, was enabled by switching from a 100 Dk material to Optimum

Infinite (180 Dk). This offers clear benefits for patient convenience, particularly for adults who need to return to work or other daily activities. More importantly, increasing oxygen availability to the cornea through higher Dk materials represents a healthier option for both children and adults undergoing ortho-k treatment.

This clinical journey, which started with a casual remark in Izhevsk, has led us to important advancements in the understanding and development of ortho-k lens materials.