Performing cataract surgery in patients with keratoconus presents many challenges. In order to select the strategy that will lead to the best outcome, several factors must be considered. These include whether the patient has progressive or nonprogressive keratoconus, how to manage individuals who have previously undergone corneal transplantation, and if and when to perform intrastromal corneal ring segment placement or corneal collagen crosslinking— before or after IOL implantation—in those with stable keratoconus.
THE CASE FOR TORIC IOLs
When a cataract patient presents with stable keratoconus, one of the first questions the surgeon tends to ask him or herself is: Which IOL is most suitable? Common answers include spherical, toric, and multifocal toric lenses. Because keratoconus generates varying degrees of astigmatism, I believe that toric IOLs should be given serious consideration for these patients.
Toric IOLs are not labeled for use in keratoconus, but some studies have shown promising results.1,2 Visser et al1 reported that toric IOL implantation in two patients with mild to moderate nonprogressive keratoconus corrected astigmatism and improved visual function. UCVA increased from 20/400 to 20/50 bilaterally in the first patient and from 20/400 to 20/130 in the right eye and 20/400 to 20/30 in the left eye in the second patient. In the first patient, refractive astigmatism decreased by 70% in both eyes (-6.00 to -1.50 D).
Nanavaty et al2 conducted a retrospective, noncomparative study of 12 eyes of nine patients with stable mild to moderate keratoconus who received a toric IOL. At a mean postoperative follow-up of 9 ±8.8 months, distance UCVA was 20/40 or better in 75% of eyes and BCVA was 20/40 or better in 83.3% of eyes. Postoperative mean refractive sphere and cylinder also significantly improved from preoperative levels.
CAREFULLY SELECT PATIENTS
In a retrospective study of 19 patients implanted with the T-flex aspheric toric IOL (Rayner Intraocular Lenses), 14 carefully selected patients had stable (nonprogressive) keratoconus. In this study of patients aged 49 to 64 years, the mean preoperative spherical equivalent was -6.75 ±5.07 D, and the mean refractive cylinder was -3.85 ±1.67 D.
At 1-month postoperative, 68% had achieved a spherical equivalent between 0.50 and -0.50 D and 95% between 1.00 and -1.00 D; this result was stable through 12 months. The attempted versus achieved spherical equivalent was also good. Although there was a slight undercorrection in patients with high refractive cylinder, all patients gained at least 3 lines of vision.
TWO IMPORTANT FACTORS
Toric IOLs are not suitable for all patients with nonprogressive keratoconus, and Figure 1 shows my algorithm for selecting the proper treatment. In my opinion, the two most important factors in determining candidacy for toric IOLs are history and stage of keratoconus.
Keratoconus history. Not all patients are aware that they have keratoconus. In those who do not know, the disease state is usually mild to moderate, and toric IOLs can be considered. However, toric IOLs are unlikely to be a good option in patients with a known history of keratoconus, especially if they wear rigid contact lenses (RCLs). This is because, in the event that correction of refractive error at surgery is inadequate, it will most likely be impossible for these patients to resume RCL use.
Keratoconus severity. Patients with mild to moderate keratoconus (Amsler stage 1 or 2) and stable corneas whose vision improves with refraction are likely good candidates for toric IOLs. In contrast, toric IOLs are rarely considered for patients who have advanced keratoconus (Amsler stage 3 or 4) and unstable corneas and in whom refraction is impossible. Spherical IOLs are more appropriate for these patients.
The corneal apex is decentered in most keratoconus patients, but keratometry (K) readings are taken in the central cornea. Additionally, standard deviations of the differences between the steepest and flattest K readings can vary from 1.00 to more than 5.00 D in these patients, irregular astigmatism changes the anteriorto- posterior corneal curvature ratio, and the value of objective astigmatism based on keratometry (K2 minus K1) is usually reduced to more subjective values. For all these reasons, calculating IOL power is difficult.
Although complex mathematical algorithms have been developed to predict IOL power, they can be difficult to use in everyday practice. Elevation topography systems such as the Pentacam (Oculus Optikgeräte), which provides true net power maps, or the Galilei (Ziemer Ophthalmic Group), which allows total corneal mapping, can simplify IOL power calculation in these eyes. Another option with the T-flex IOL is to use the Raytrace web-based toric IOL calculator3 (Rayner Intraocular Lenses) to calculate IOL power.
Regardless of the chosen calculation method, patients must be informed of the possibility of miscalculation due to the influence of their keratoconus on postoperative refractive power.
Toric IOLs can provide excellent outcomes in carefully selected patients with nonprogressive keratoconus. Although these IOLs may not provide total vision correction, in my experience most patients with keratoconus are pleased with the dramatic improvement they offer.
Julián Cezón, MD, is the Director of the Clínica CIMO, de Sevilla, Spain. Dr. Cezón states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +34 954230303; fax: +34 954232785; e-mail: email@example.com.
- Visser N, Gast ST, Bauer NJ, Nuijts RM. Cataract surgery with toric intraocular lens implantation in keratoconus: A case report. Cornea. 2011;30(6):720-723.
- Nanavaty MA, Lake DB, Daya SM. Outcomes of pseudophakic toric intraocular lens implantation in keratoconic eyes with cataract. J Refract Surg. 2012;28(12):884-889.
- T-flex Aspheric Toric IOL. Rayner website. http://www.rayner.com/products/t-flex. Accessed March 13, 2014.