Variations of central corneal curvature during the first year of contact lens wear.

During hard, hydrophilic and silicone lens wear the variations of central corneal curvature in the 2 eyes of each individual were significantly correlated. Mean changes of principal radii of curvature were small in each lens group (-0.075-+0.068 mm). Hydrophilic lens wearers showed an initial mean flattening of corneal curvature, followed by a significant steepening. Hard lens wearers apparently showed the opposite sequence of mean changes. Silicone lens wearers showed a significant mean corneal flattening. Central corneal asphericity was reduced during hard lens wear. Considerable individual curvature changes occurred (-0.35-+0.30 mm), but none of these necessitated lens refitting. Changes of the central corneal thickness and curvature during hard lens wear were apparently inversely correlated, the ratio between the changes being about -0.08:1. Hard and silicone lenses probably exerted a mechanical moulding effect. The exact aetiology of curvature changes in hydrophilic lens wearers remains obscure. Corneal curvature changes appear less reliable than corneal oedema in the detection of lens-induced impairment.