BLOG: Ophthalmic contraindications to LASIK, PRK range from ectasia to cataracts
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Not all patients are good candidates for LASIK or PRK, and it is critical for optometrists to be clear about the reasons why.
In this third installment of a three-part series on absolute and relative contraindications, we cover ophthalmic conditions. Parts one and two covered life and systemic considerations.
Ectasia
Because laser vision correction (LVC) is a corneal surgery, corneal conditions present the most common contraindications to surgery. Chief among these is the risk for post-LVC ectasia, the most-feared complication.
The detection of an unacceptably high level of risk for corneal failure is a complex topic and primarily includes these six risk factors: an unusually thin cornea (often standardized as 500 µm), an aberrant topographic pattern, a thin residual stromal bed (< 250 µm or even 300 µm), patients younger than 30 years (and especially younger than 22 years), a preoperative spherical equivalent of greater than 8 D to 10 D of myopia or any family history of keratoconus. Often one or more of these factors are present to a mild degree, and these situations require a careful decision by an experienced clinician.
There has been a surge of interest recently in treating keratoconus with a combined corneal cross-linking and PRK procedure, although this should only be performed by an experienced surgeon (Kymionis GD, et al). The results of this advanced procedure can be highly beneficial to the patient, although the refractive outcomes tend to be much less predictable than with regular corneas.
Refractive limits
In addition to the ectasia risk of treating high myopia, there are technological and biological limits to the ablative treatment of refractive error. All lasers have limits to the amount of myopia, hyperopia and astigmatism they can treat, and you should know those of your favorite refractive surgeon’s laser. Common limits are 10 D of myopia, 4 D of hyperopia and 6 D of astigmatism, although the high ends of these are ambitious ablations and often do not have satisfactory or stable results.
Hyperopia and astigmatism are resistant to aggressive treatments and usually respond better when only attempted up to about 2 D of hyperopia and 3 D of astigmatism. Overly aggressive treatments tend to be less accurate, induce greater inflammation and optical aberrations, and have a greater tendency to regress. Your surgeon will have an individual limit to which he or she is comfortable. In the situation of an unstable refraction, whether due to young age, unstable epithelium or any other reason, LVC should not be performed.
Aggressive PRK treatments are known to provide a less predictable refractive outcome and a higher chance of inducing inflammation and haze compared with LASIK. For this reason, the ablation of myopia over roughly –6 D is relatively contraindicated.
Membrane dystrophy, corneal erosion
Because anterior basement membrane dystrophy can disrupt comfort, a smooth corneal surface and a stable refraction, it is a relative contraindication to LASIK. Its more aggressive cousin, recurrent corneal erosion, is an absolute contraindication to any flap.
PRK can actually offer treatment for these two conditions, as the removal of the epithelium often gives this tissue a chance to regrow in a more ordered manner.
Dry eye disease, lagophthalmos
Dry eye is known to be caused or worsened by LVC, and all patients must be counseled on this risk. Every LVC candidate must be carefully screened for dry eye, and dry eyes secondary to systemic conditions are at particular risk. Patients with moderate or severe pre-existing dry eye cannot undergo LVC until their condition has been successfully treated.
Those with lagophthalmos should never undergo LVC, as the constant exposure of the cornea poses an unacceptably high risk to a healing cornea.
Viral infection
A history of herpes simplex keratitis (HSK) or herpes zoster ophthalmicus (HZO) are in general held to be relative contraindications to LASIK but absolute contraindications to PRK. The risk of reactivation of a virus is thought to be very real but smaller with LASIK, and so surgeons will often offer LASIK if the disease has been inactive for at least 1 year, there is no stromal scarring or topographical abnormalities, the patient is placed on prophylactic oral treatment before and after the surgery, and they are well-counseled regarding the risks.
Because PRK is inherently more inflammatory and its recovery necessitates a longer course of steroids, it should not be performed on any patient with a history of HSK or HZO.
Cataracts, presbyopia
No patient with cataracts should ever receive LVC, even if the cataract is several years away from causing symptoms. If cataracts decrease postoperative vision, either immediately after the surgery or even within a few years, that patient will not be happy. Similarly, any patient with macular disease should not receive LVC for similar liability reasons.
The benefits of LVC are significantly less for patients beginning to experience presbyopia, and this is doubly true for myopes. An early hyperope receiving LVC must be informed that the surgery’s goal is to restore freedom from correction at distance only, and any presbyopic myope must understand they are sacrificing their near vision for distance.
Glaucoma
Glaucoma represents a relative risk for both LASIK and for PRK, but for different reasons. During LASIK, the docking system suctions firmly onto the patient’s eye, and IOP can spike from 70 mm Hg to 100 mm Hg over baseline for up to 1 minute of the surgery (Chaurasia SS, et al). Whether this is an acceptable risk must be evaluated individually.
PRK uses no docking system, and intraoperative IOP remains unaffected, but PRK patients must use long-term steroids during their recovery — often for 3 months — and glaucoma patients are known to have significantly higher rates of steroid response than the normal population.
Informing a hopeful patient that they are not, and may never be, a good candidate for LVC can be a difficult conversation. We must remember that our highest calling is the stewardship of our patients’ vision over their lifetime.
I like to recall the words of Jeff Machat, MD: “I never lose sleep over a patient on whom I don’t perform surgery.”
References:
- Chaurasia SS, et al. Invest Ophthalmol Vis Sci. 2010;doi:10.1167/iovs.10-5228.
- Kymionis GD, et al. J Cataract Refr Surg. 2014;doi:10.1016/j.jcrs.2014.01.040.
Kuhn-Wilken is a staff optometrist at Pacific Cataract and Laser Institute’s Tualatin Clinic in Oregon.
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