BLOG: What to know about post-refractive ectasia
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Post-refractive ectasia occurs very rarely, in only about one out of every 10,000 cases of refractive surgery, or 0.09% of LASIK procedures, 0.02% of PRK procedures and 0.01% of SMILE procedures, according to Moshirfar and colleagues.
In some cases, the patient may have had undetected preclinical keratoconus, and the corneal laser surgery procedure was the final straw for an already unstable cornea.
Like keratoconus patients, the post-refractive ectasia patient often presents with progressive myopia, progressive astigmatism and corneal steepening resembling a cone. They are more likely to have unilateral ectasia and may be older than the typical keratoconus patient.
Risk factors
An abnormal topography (ie, one with features such as an asymmetric bowtie, inferior steepening or a skewed radial axis) prior to refractive surgery is the No. 1 risk factor for post-refractive ectasia. That is why topography is such an important screening tool in refractive surgery centers. Other preoperative risk factors for ectasia include high myopia (> 8.00 D), thinner corneas (< 510 µm), habitual eye-rubbing, unstable refractions, corrected acuity worse than 20/20 and younger age.
Younger refractive surgery patients may not yet have developed signs that would have presented as keratoconus later in life. Additionally, young corneas have a lower cohesive tensile strength. Young age is both somewhat controversial and the most overlooked risk factor for ectasia.
Historically, we always thought that residual stromal bed thickness — or the amount of tissue remaining after the laser ablation — was a determining factor. The latest thinking is that it has more to do with the percentage of tissue altered (PTA) rather than an absolute stromal bed value. The PTA can be calculated as the sum of the flap thickness plus the ablation depth divided by central corneal thickness. A PTA above 35% significantly increases the risk for ectasia (Santhiago MR, et al). However, even a low PTA is not dependable if there is a suspicious topography.
Treatment options
Treatment of post-refractive ectasia is the same as for keratoconus. First, we have to arrest the disease. The clinical trial that led to the FDA approval of iLink cross-linking (Glaukos) for post-refractive ectasia demonstrated a 1.3-D difference in Kmax over 12 months between patients who were cross-linked and those in the control group. The treated group also experienced improvements in uncorrected and best corrected acuity (Hersh PS, et al).
Unlike with keratoconus, there is no requirement to demonstrate progression; the fact that ectasia has occurred following refractive surgery is sufficient to justify the need for treatment.
Second, we also need to determine how we can help these patients see better. In my experience, post-refractive ectasia tends to be less advanced upon presentation than keratoconus in terms of the amount of vision loss. In many cases, that means we may be able to correct the vision after cross-linking with glasses or soft contact lenses, although specialty contact lenses may also be helpful.
Even when “regular” vision correction methods suffice, patients may be quite unhappy about the need for vision correction at all. These patients paid for a procedure to correct their vision — specifically so they wouldn’t need to wear glasses or contact lenses — and they can be quite disappointed or depressed to learn they have ectasia. They may feel that the refractive surgeon — or even their own choice to have surgery — is to blame.
I always try to emphasize to the patient that they didn’t do anything wrong and that our modern screening methods almost always screen out those at risk, but that there is still a one in 10,000 chance of ectasia. Rather than looking backwards, I encourage them to focus on the path forward, which fortunately has a very good chance of restoring their vision and halting further ectasia.
References:
- Hersh PS, et al. Ophthalmology. 2017;doi:10.1016/j.ophtha.2017.05.036.
- Moshirfar M, et al. Ophthalmol Ther. 2021;doi:10.1007/s40123-021-00383-w.
- Santhiago MR, et al. Clin Opthalmol. 2016;doi:10.2147/OPTH.S51313.
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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