A new look at refractive vision.

The quest for the optimal method to correct various refractive errors continues. In studying different contact lens designs and refractive procedures we are constantly evaluating different approaches to patient management. Recognizing that the cornea is a dynamic and vibrant anatomic structure, we must include other parameters in the equation of the "perfect contact lens fit" or "the best surgical procedure." This current issue of IMAJ contains an article on the subject [1]. Fulga et al. [1] shed considerable light on the relationship between lactate dehydrogenase levels and corneal metabolism. They found that the use of a peripheral contact lens design to increase and enhance tear flow and exchange under the contact lens led to improved corneal metabolism. However, when evaluating a particular contact lens or procedure, it is essential to also examine those variables that will have an impact on the anatomical and physiological changes. Concluding that a certain contact lens design is healthier for the eyes than another – in this case the novel design of the periphery of a rigid gas-permeable lens described by Fulga et al. – based on only one parameter in the equation could be misleading. On the assumption that there is a vast difference between long and short-term contact lens wear with regard to damage to the eyes, it is important to assess all aspects. If the cornea is exposed to extended wear of contact lenses that lack extended-wear contact lens material, or if a gradual and progressive wearing schedule to allow the cornea to adapt to the rigid lens is not adhered to, the cornea will be overwhelmed. A direct result is a deleterious effect on the integrity and sensitivity of the cornea's innervation in maintaining the high metabolic rate of the epithelium [2–4]. Some of the sequelae or corneal changes that the authors rightfully mention are associated with prolonged contact lens wear. These include corneal deformation, capillary infiltration of the peripheral cornea, giant papillary conjunctivitis, among others. Not only would it be interesting to study their etiology, but it would be challenging to find a correlation between LDH levels and GPC for example, since the cause of GPC is thought to be immunological while the contact lenses are considered to be allergens. This allergenicity is demonstrated by a sample of scrapings from the papillae, which will show lymphocytes, plasma cells, mast cells, eosinophils and basophils, suggesting an antigen-antibody mechanism. Thus, patients who replace their lenses frequently are at a lower risk of developing GPC than those who replace their lenses after longer intervals [5]. The correlation between pinquecula and the long-term effect of contact lens wear has not been conclusively proven, although its pathophysiology has been attributed to both ultraviolet and environmental exposure. Moreover, any investigation of the long-term effect of contact lens wear should incorporate a new lens design, one that will reflect and not affect corneal thickness. Previous studies have indicated that long-term contact lens wear could cause a decrease in corneal thickness and cause surface irregularity [6]. Chronic rigid gas-permeable contact lens-induced hypoxia is associated with altered glucose lactate metabolism in the cornea [7]. Perhaps a lens periphery designed to enhance corneal metabolism will nullify the effect of the lens. Since studies of anatomical changes have shown a clear correlation between corneal damage and contact lens wear [8–13], the development of a new and different contact lens design might well be the solution. Also associated with contact lens wear are changes in the level of polymorphonuclear leukocytes due to an alteration in the tear film integrity and levels of inflammatory mediators, and damage to the mucin layer of the ocular surface epithelium [14,15]. As the authors pointed out, some of the corneas had been detrimentally affected by the lens. It indeed would be interesting to look at the correlation between LDH levels and different corneal insults as compared to LDH levels during active contact lens wear when the cornea is intact. Moreover, evaluating