astigmatism who desire best distance vision only, or individuals who have tolerated monovision well in the past and want it re-created after cataract surgery, are generally the best candidates for monofocal IOL implantation.

Toric Intraocular Lenses

Recent studies have concluded what many surgeons have long believed, namely, that 0.75 D or more of residual astigmatism impacts visual function and patient satisfaction. Large population analyses indicate that more than 50% of patients have 0.75 D or more corneal astigmatism at presentation for cataract surgery, and 15%–29% have 1.50 D or more corneal astigmatism. Thus, toric IOLs can address a major need for vision correction after crystalline lens removal. Current toric IOLs in the United States generally come in powers that can correct from 1.00 to 4.00 D of astigmatism at the spectacle plane, and wider power ranges are available outside the United States; however, this range is continually evolving.

Patient Selection

A toric IOL is appropriate for patients with regular corneal astigmatism, currently up to 4.00 D in the United States. Patients with astigmatism in amounts exceeding the upper correction limits of these lenses require additional measures to obtain full correction. In addition to understanding the risks associated with intraocular surgery, patients must be capable of understanding the limitations of a toric IOL. Not all patients with toric IOL implantation achieve spectacle independence for distance vision. Further, patients should be informed that toric IOL implantation will not eliminate the need for reading glasses (unless monovision is planned). The patient also needs to be informed that the IOL may rotate in the capsular bag shortly after surgery and that a secondary intraocular surgery may be required to reposition it. A silicone toric IOL may be less appropriate for patients who may carry a significant potential of requiring silicone oil for retinal detachment repair in the future; thus, acrylic IOLs are more appropriate choices for these patients.

Planning and Surgical Technique

The amount, axis, and regularity of the astigmatism should be measured accurately with a keratometer and confirmed if possible with corneal topography. The axis of astigmatism from the refraction should not be used because it may be influenced by lenticular astigmatism, which will be eliminated with cataract surgery.

The manufacturers of toric IOLs have online applications available to aid in surgical planning. After the surgeon enters data such as keratometry measurements, axes, IOL spherical power generated by A-scan, average surgeon-induced astigmatism, and axis of astigmatism, these programs will generate the correct power and model lens as well as orientation of the lens alignment markers.

There are many ways that surgeons mark the cornea prior to surgery. The surgeon should establish and mark the vertical and/or horizontal meridians with the patient in an upright position to avoid potential misalignment resulting from torsional globe rotation, which sometimes occurs in the supine position. Cataract surgery with a wound that induces a predictable amount of astigmatism is necessary to achieve the intended benefit of a toric lens. All online toric IOL software requires input of the expected surgically induced astigmatism for lens power calculations.

After the IOL is injected into the capsular bag, the viscoelastic material behind the IOL is aspirated and the IOL is rotated into position on the steep meridian. Some surgeons prefer to leave the toric IOL