The Effects Of Extended Wear Hydrogel Contact Lenses On Corneal Topography And Contrast Sensitivity.

Purpose: To study the effect of hydrogel contact lens extended wear on corneal
topography and contrast sensitivity. Methods: Five daily contact lens wearers (four in Biomedics and one in Acuvue) were changed to an extended wear modality. Slit lamp examination, manifest refraction, Bailey-Lovie visual acuities, Pelli-Robson contrast sensitivities, and corneal topography were performed over a four day period in mesopic and photopic conditions. All data, except baseline and end-study data, was gathered within thirty minutes of waking. Results: There were no biomicroscopic changes during the study. Four eyes increased
in myopia while six eyes decreased or remained the same. There was no statistically
significant decrease in Bailey-Lovie VA, high or low contrast, while in extended wear modality. There was a statistically significant decrease in Pelli-Robson contrast sensitivity in mesopic conditions from the beginning of the study to the end of the study (z=0.074), but day to day comparisons proved statistically insignificant. The average of the Corneal Irregularity Measure (CIM) values from the corneal topography showed that corneal irregularity increased over time and approached statistical significance (p=O. 091). The average Shape Factor values, also from corneal topography, significantly worsened during the study (p<O.Ol). Central corneal curvature showed small changes, while selected peripheral points showed large changes ranging from 3.9 diopters of flattening to 6 diopters of steepening. Most changes occurred in the superior cornea.
Conclusions: Extended wear modality of hydrogel contact lenses results in statistically and clinically significant changes in peripheral corneal topography, suggesting that corneal edema may not be a diffuse, but a localized, reaction to decreased oxygen availability. Therefore, the standard tests of evaluating extended wear effects, i.e. VA, slit lamp examination, and possibly contrast sensitivity, may not be sufficient to detect corneal changes secondary to extended wear. Further studies incorporating more test subjects is needed in this area.