Correcting corneal astigmatism in many different forms can be incorporated into and should be an integral part of any practice. With the new applications of femtosecond lasers, corneal relaxing incisions (limbal based or more central astigmatic keratotomies) can be performed with more accuracy and less discomfort. Toric IOLs are a necessary part of performing refractive cataract surgery and can yield nice results in patients after penetrating keratoplasty. The successful application of any astigmatism-reducing procedure is dependent on accurate measurements. New research has also shown that surgeons need to account for the posterior cornea when measuring astigmatism.
LIMBAL RELAXING INCISIONS
Limbal relaxing incisions have regularly been used to reduce corneal astigmatism in conjunction with cataract surgery. In general, the effects of relaxing incisions are directly proportional to their depth, length, and how centrally located they are. Hence, astigmatic keratotomies within a 7-mm diameter can produce a greater effect than similar incision created just inside of the limbus. These have been performed successfully with both a blade and the laser.1
Femtosecond laser technology has enabled surgeons to create more accurate long and deep incisions. The discomfort caused by and the concern regarding these incisions’ healing has led to the introduction of intrastromal astigmatic keratotomy that avoids any disturbance of the epithelium.2,3 Because these “modified” relaxing incisions are entirely within the stroma, they are inherently less powerful in their effect and can correct less amounts of astigmatism than their almost-full-thickness counterparts. Further development of nomograms will likely lead to a more efficacious procedure.
Toric IOLs are an essential component to the surgical correction of corneal astigmatism. An obvious advantage of toric IOL technology is the greater precision and accuracy of toricity correction they provide. Also, limbal relaxing incisions can reduce upwards of 2.00 D of astigmatism,4but the effect often regresses over time and the outcomes are often unpredictable. Conversely, current toric IOL technology can correct upwards of 5.00 D of corneal astigmatism. It is important to obtain accurate measurements of astigmatism and have agreement between at least two. This may include manual keratometry, autorefractor measurements, or topography; however, all of these methods take into consideration only the anterior astigmatism. A recent study by Koch et al5 discusses the role of posterior corneal astigmatism. About 84% patients demonstrate with-the-rule posterior corneal astigmatism, which functions like ocular against-the-rule astigmatism. Clinically, this translates to overcorrection of patients with corneal with-the-rule astigmatism and undercorrection of corneal against-the-rule toricity.
Although toric IOLs are only FDA approved for correction of regular astigmatism, they can be utilized off label to correct for mostly regular astigmatism in penetrating keratoplasty or corneal ectasia patients, such as keratoconus or pellucid marginal degeneration.6 If patients demonstrate decent spectacle or soft contact lens correction of their vision prior to the cataract’s formation, a toric IOL can result in greater spectacle or contact lens independence after cataract surgery.
With proper planning, astigmatic correction can help a patient achieve a higher level of satisfaction after cataract surgery. Within the past 5 years, the correction of corneal astigmatism has become less of an art and more of a science with the use of femtosecond lasers and toric IOLs. Experience with such technology and the understanding of posterior corneal astigmatism will lead to tighter nomograms and more predictable outcomes that will provide our patients with more effective refractive cataract surgery.