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24-04-2012 | General practice | Article

Customized lenses no better than RGP lenses in keratoconus


Free abstract

MedWire News: Customized contact lenses offer only a marginal improvement over rigid gas permeable (RGP) contact lenses in patients with keratoconus, research shows.

The customized lens provided optical improvements compared with the RGP lens but only if their movements were constrained within difficult-to-achieve limits, according to Hema Radhakrishnan (University of Manchester, UK) and colleagues.

Customized contact lenses have been proposed as a way to eliminate or partially correct lower-and higher-order aberrations of the individual eye.

The potential for correcting the aberrations in patients with keratoconus is particularly great given the significant decline in visual function among these patients.

The translation or rotation of a customized lens reduces its effectiveness at eliminating higher-order aberrations, however, some movement is needed so that the eye can be supplied with lubrication and nutrients.

As reported in Ophthalmic and Physiological Optics, Radhakrishnan and colleagues measured visual acuity in three patients with bilateral keratoconus when wearing spherical RGP contact lenses and when their eyes were uncorrected. The dominant decline in visual function in the uncorrected eye of all three patients approximated vertical coma.

Next, they simulated visual aberrations of each eye using a customized soft contact lens that was designed to neutralize higher-order aberrations.

Residual aberrations and point-spread functions of the eye were calculated as a function of the angle of rotation of the lens from its ideal orientation, as well as its horizontal and vertical translation.

In the patients with mild, moderate, and severe keratoconic eyes, the RGP lenses reduced lower- and higher-order aberrations, even in the patient with severe keratoconus.

Compared with the RGP lens corrections, the customized lens provided optical improvements only if their movements were set within limits that are difficult to obtain using current technologies, report the researchers.

Overall, the RGP lens reduced the total higher-order root-mean-square wavefront error to one-fifth of the uncorrected values.

"This sets much tighter constraints on the tolerable values of rotation and displacement for any customized lens," write Radhakrishnan and colleagues, especially if customized lenses must be shown to provide a useful benefit over RGP lenses rather than the uncorrected eye.

That said, the researchers note that customized soft contact lenses might be preferred over RGP lenses based on comfort, even if they offer no advantage in visual performance. For selected patients, the customized lens might justify additional cost and complexity of custom corrections.

By MedWire Reporters

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