BLOG: What to expect with cataract surgery in patients with keratoconus
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In patients with keratoconus who are undergoing cataract surgery, the risk for continued progression must be evaluated, as well as IOL options, power calculation challenges and the likelihood of good acuity after surgery.
Certainly, if the patient has a known history of keratoconus (KC), that should be communicated to the cataract surgeon with the referral; it may be prudent for the primary care optometrist to refer specifically to a cornea-trained cataract surgeon who would have all the latest corneal diagnostic technology.
Diagnosis, progression of KC
It is fairly common in our practice to see patients presenting for cataract surgery who have KC but have never been diagnosed or treated. In fact, for about half of our KC patients undergoing cataract surgery, the diagnosis is a new one. These patients may have never had a topography or tomography exam that is needed to confirm the diagnosis. But unfortunately, we often see that there were KC clues, such as high or irregular cylinder, unusual keratometry and even frank slit lamp signs that were missed by previous doctors.
In such cases, it is important to first evaluate whether KC is still progressing. Although the cornea typically undergoes natural cross-linking with age, it cannot be assumed that progression has completely stopped. Reviewing previous records can bolster confidence that the cornea is stable. If there is any concern that progressive corneal changes are ongoing, cataract surgery should be delayed until the cornea can be reassessed and, if necessary, treated with iLink (Glaukos) cross-linking to stabilize the cornea.
If the KC is not progressive, it is still important to determine how many visual disturbances are secondary to the cataractous lens vs. the ectatic cornea. Using a diagnostic specialty lens can be invaluable in making the decision to proceed with surgery, guiding IOL selection and setting appropriate patient expectations for vision after surgery. Minimal improvement in visual acuity with the specialty lens, for example, indicates that it is mostly the lens affecting vision and cataract surgery should improve the patient’s vision.
Significant improvement in vision with the specialty lens points to greater corneal involvement. For example, if I see a patient who has been referred for cataract surgery because he is seeing 20/40 in glasses, but he then improves to 20/20 with a rigid or hybrid contact lens, we are not moving forward with cataract surgery in that patient for at least 6 months, until we can confirm he is not progressing.
IOL selection, planning
IOL power selection can be challenging in patients with concurrent KC and visually significant cataracts. Because the biometry measurements taken for cataract surgery rely heavily on keratometry, the variable keratometry in a keratoconic eye can lead to unexpected outcomes and wider than usual gaps between predicted and actual postoperative refractive error.
A 2023 Journal of Refractive Surgery study aimed to guide practitioners on IOL calculations in KC eyes. From this paper, three conclusions stood out to me:
- Hyperopic surprise outcomes were most common and correlated with increasing anterior corneal curvature.
- In patients with preoperative Ks less than 50 D, 58% to 74% of eyes had outcomes within 0.5 D of intended refractive error, compared with 0% to 18% of patients with preoperative Ks greater than 50 D. In other words, results in steeper corneas were much less predictable.
- Of the 11 power calculation formulas tested in the study, not all performed equally. KC-specific formulas or adjustments provided greater refractive accuracy.
Another consideration is the type of IOL that will be suitable for the patient. Eyes with mild KC and only mildly irregular anterior corneal curvature, in which the steep and flat axis are close to 90 degrees apart, may be good candidates for a toric implant that can correct all or most of the astigmatism.
Motivated patients with more asymmetrical axes may be good candidates for the IC-8 Apthera IOL (Bausch + Lomb), which utilizes pinhole optics to increase depth of focus and block unfocused peripheral straylight. This IOL has the potential to mask some of the visual disturbances from the ectatic cornea, thereby improving acuity and potentially even providing some gain in near vision (Shajari M, et al).
In any case, patients with KC must have realistic expectations of any premium IOL. A reasonable goal might be to get out of rigid contact lenses and into spectacles after surgery, rather than full spectacle independence.
If the patient’s vision improved significantly with a diagnostic specialty lens preoperatively or the Ks are greater than 50 D, I’m very hesitant to recommend a premium toric or small-aperture IOL at all, and the patient should be counseled to expect to need specialty contact lenses after cataract surgery.
Finally, we don’t know exactly how the cornea will respond after undergoing cataract surgery, so it is a good idea to repeat topography or tomography down the road to ensure that progression doesn’t resume after cataract surgery. With these considerations, cataract surgery in patients with KC can be successful and help to improve visual quality and acuity.
References:
- Kozhaya K, et al. J Refract Surg. 2023;doi:10.3928/1081597X-20230124-01.
- Shajari M, et al. J Cataract Refract Surg. 2020;doi:10.1097/j.jcrs.0000000000000045.
For more information:
Mitch Ibach, OD, is a cornea, glaucoma, cataract and refractive surgery specialist at Vance Thompson Vision in Sioux Falls, South Dakota. He can be reached at mitch.ibach@vancethompsonvision.com.
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