Over the course of the summer (in the Northern hemisphere), a number of interesting papers involving (R)GP lenses were published in peer reviewed journals. A paper in the August issue of Contact Lens & Anterior Eye (journal of the British Contact Lens Association) by Langis Michaud et al of the University of Montreal (Canada) looks at the oxygen consumption beneath a scleral lens. Compared to corneal lenses, scleral lenses have a higher centre thickness and a tear reservoir that could act as another oxygen barrier. The tear film exchange beneath the scleral lens is probably limited. If the traditional Holden-Mertz Dk/t and Harvitt-Bonanno criteria are applied, scleral lenses are usually at best only scratching the transmissiblility levels desired for normal daily wear without additional corneal edema. Based on these theoretical considerations, it seems advised to reduce the centre thickness of the lens (which has limitations in clinical practice because of lens flexure) and/or to decrease the tear clearance (which is not always possible because of the typical indications for scleral lens wear) and surely to use the highest Dk material available as a first choice. Hopefully we will have better materials available to us in the future. On the other hand - in clinical practice, hypoxia signs with scleral lenses are rare. This may in part be obscured as we are often dealing with challenging corneas. But nonetheless, the question remains: what are we missing, or what is the missing link between the clinical observations and the theoretical calculations? Are our clinical skills (e.g. slit lamp signs) not sufficient enough to see minor hypoxic stress on the cornea? Or is there another mechanism that contributes to the oxygen delivery to the cornea?

Also this summer, a couple of interesting scientific papers regarding orthokeratology came out. Jaume Paune and colleagues from the University of Catalonia (Spain) report on toric orthokeratology lenses for the correction of astigmatism in the July issue of Eye & Contact Lens. Selection criteria for this retrospective study included 1.25D of astigmatism. A double tear reservoir toric lens design was used in the 32 patients reviewed. The results: irrespective of axis orientation, corneal versus refractive astigmatism and central versus limbus-to-limbus astigmatism, a successful result was achieved as the resultant post-orthokeratology residual astigmatic error was limited to -0.38 ± 0.41D. Ka Yin Chan and colleagues from the Hong Kong Polytechnic University published a paper in the August issue of Contact Lens & Anterior Eye on the clinical performance of an orthokeratology lens fitted with the aid of computer software in Chinese children aged 6-11. The success rate of the 51 subjects in the study was 90% with the first lens. The spherical equivalent refraction reduction after one night was 57%, and 81% after one week in subjects with low and moderate myopia. Vision and ocular health of subjects were generally good within the first month of lens wear, according to the authors. 

As part of the large orthokeratology puzzle, an important paper came out regarding tear film composition during orthokeratology lens wear. Investigators from the ocular surface and contact lens research laboratory at the University of Santiago de Compostela (Spain) and University of Minho (Portugal) looked at the changes in tear film inflammatory mediators following continuous wear of silicone-hydrogel soft lenses and corneal refractive therapy with reverse geometry contact lenses. Some inflammatory mediators were increased in both therapies, others just in the corneal reshaping group. The inflammatory response for the corneal refractive therapy patients was found to be associated with the degree of myopia corrected, the presence of corneal staining and with the presence of corneal-pigmented arc in this 12-month study.