There are many options to treat corneal astigmatism in patients undergoing cataract surgery. This refractive error is found in 15–29 % of prospective cataract patients.1–3 Astigmatic keratotomy at the time of surgery is one option, but although a powerful tool, such corneal relaxing incision has limited predictability and may result in overcorrection – especially in older patients or in patients with lower levels of astigmatism – or undercorrection in younger patients. Limbal relaxing incisions may have better predictability, but wound healing (and concomitant over- or undercorrection) can still be an issue. Another option is to inform patients who choose a monofocal intraocular lens (IOL) that they can undergo excimer laser refractive surgery after cataract surgery in order to correct the anticipated residual corneal astigmatism.
A third option is to consider a toric IOL in patients with pre-operative and anticipated post-operative corneal astigmatism. First described in the ophthalmic peer-review literature in 1994,4 toric IOLs are gaining popularity. The mechanics of small incision cataract extraction are unchanged and toric (monofocal) IOL implantation remains the same except for marking the proper axis on the cornea or limbus and implanting an IOL at that axis. Moreover, toric lens implants are no longer solely the purview of surgeons performing cataract surgery. This article will examine the option of toric IOLs to correct corneal astigmatism during cataract extraction, clear lens extraction, or as a phakic procedure.
History and Overview
One of the first reports in the literature of a toric IOL implant described results obtained with the Nidek NT-98B, a three-piece posterior chamber lens with an oval optic (6.5 x 5.5 mm) and two positioning holes on its major axis.4 It had a toric correction on the concave posterior surface and the axis of cylinder lay on the minor axis of the lens. The anterior surface had a convex surface for implantation in eyes with against-the-rule corneal astigmatism. Therefore, the lens had to bepositioned so that the line linking the positioning holes of the cylinder IOL (the lens axis) lay horizontally. From a review of the literature, this model is no longer available.
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