Refractive Mini Focus on Intrastromal Corneal Rings

I ntrastromal corneal rings and ring segments work in accordance with the postulates of Barraquer and Blavatskaya, which state that an addition in the periphery of the cornea will result in its flattening. The thickness and diameter of the implant determine how much the cornea will be flattened. That is, the more tissue that is added (ie, ring thickness) and the smaller its diameter, the greater the myopia correction obtained will be.1,2 Intacs Prescription Inserts for Keratoconus (Addition Technology, Sunnyvale, California) are available to physicians in the United States through a humanitarian device exemption3 (HDE) from the US Food and Drug Administration (FDA). According to the HDE, they are intended for the reduction or elimination of myopia and astigmatism in patients who are no longer able to achieve adequate vision with contact lenses and spectacles, so that their functional vision can be restored and the need for corneal transplant may be deferred. The specific subset of keratoconic patients proposed to be treated with Intacs, according to the HDE, are those who (1) have experienced a progressive deterioration in their vision, such that they can no longer achieve adequate functional vision on a daily basis with their contact lenses or spectacles; (2) are 21 years of age or older; (3) have clear central corneas; (4) have a corneal thickness of 450 μm or greater at the proposed incision site; and (5) have corneal transplantation as the only remaining option to improve their functional vision. The literature shows that management of keratoconus varies with disease severity. In early stages of disease, rigid gas permeable (RGP) contact lenses are one of the primary treatment alternatives. In the Collaborative Longitudinal Evaluation of Keratoconus (CLEK), 65% of patients enrolled wore RGP contact lenses at the baseline visit, and 73% reported that their lenses were comfortable.4 Long-term wear of RGPs, however, may be a risk factor for the development of keratoconus.5,6 An apical touch fitting relationship may promote corneal scarring and ultimately contribute to the progression of the disease.7 Fitting with apical touch results in statistically significant but clinically insignificant improved visual acuity.8 In another study, the CLEK authors concluded that there may be a causal relationship between contact lens wear and the development of corneal scarring in keratoconus.9