Keratoconus is generally considered a contraindication to LASIK and surface ablation. Weakening of the cornea, as a result of the loss of structural integrity involved in creating the LASIK flap, and removal of tissue significantly increase the risk of exacerbation of ectasia. Although advanced stages of keratoconus can be diagnosed by slit-lamp examination, more sensitive analyses using corneal topography, corneal tomography, and corneal pachymetry can reveal findings early in the disease process. No specific agreed-upon test or measurement is diagnostic of a corneal ectatic disorder, but corneal topography/ tomography, and corneal pachymetry should be part of the evaluation. Subtle corneal thinning, curvature, or elevation changes can be overlooked on slit-lamp evaluation.
In cases of forme fruste keratoconus where the fellow eye is seemingly normal, studies have suggested several risk factors for progression to keratoconus in the fellow eye and post-LASIK ectasia in either eye. These include interocular asymmetry of inferior corneal steepening or asymmetric bow-tie topographic patterns with skewed steep radial axes above and below the horizontal meridian (Fig 10-1). Keratoconus suspect patients have the aforementioned features in either or both eyes. LASIK using current technology should not be considered in such patients. Patients with an inferior “crab-claw” pattern accompanied by central flattening are at risk of developing pellucid marginal degeneration or a “low-sagging cone” variety of keratoconus, even in the absence of clinical signs (Fig 10-2). This pattern may be designated “pellucid suspect,” and LASIK should be avoided in eyes that exhibit it.
Figure 10-1 Corneal topographic map indicating keratoconus with asymmetric irregular steepening.
(Courtesy of Eric D. Donnenfeld, MD.)
Figure 10-2 Topography of pellucid marginal degeneration showing the “crab-claw” appearance. N = nasal; T = temporal.
(Courtesy of M. Bowes Hamill, MD.)
Global pachymetry measurements may help rule out forme fruste keratoconus. Posterior curvature evaluation with newer corneal imaging technology may also prove significant (Fig 10-3). Often, the refractive surgeon is the first physician to detect and inform a patient of the existence of corneal ectasia. The patient may have excellent vision with glasses or contact lenses and may be seeking the convenience of a more permanent correction through LASIK. It is important that the ophthalmologist clearly convey that, although the presence of forme fruste keratoconus does not necessarily indicate the presence of a progressive disease, refractive surgery should not be performed because of the potential for unpredictable results and vision loss. The patient should also be informed of the importance of follow-up for any signs of progression, as corneal crosslinking (CCL) may be an option for stabilization of their corneal condition.
Intrastromal corneal ring segments are FDA approved for keratoconus (see Chapter 4). CCL with riboflavin administration and ultraviolet-A exposure shows promising results and may prove effective in preventing and treating corneal ectasia (see Chapter 7 and BCSC Section 8, External Disease and Cornea). Although some reports have suggested that combining CCL treatments with PRK may offer some benefit to keratoconus patients, the clinical experience remains preliminary.
Alessio G, L’Abbate M, Sborgia C, La Tegola MG. Photorefractive keratectomy followed by cross-linking versus cross-linking alone for management of progressive keratoconus: two-year follow-up. Am J Ophthalmol. 2013;155(1):54–65.
Ambrósio R Jr, Alonso RS, Luz A, Coca Velarde LG. Corneal-thickness spatial profile and corneal-volume distribution: tomographic indices to detect keratoconus. J Cataract RefractSurg. 2006;32(11):1851–1859.
Figure 10-3 A 40-year-old man wishes to correct his myopia and high astigmatism. He does not wear contact lenses. His manifest refraction is –4.00 +3.00 × 4 OD and –3.75 +3.00 × 168 OS; corrected distance visual acuity is 20/20 OU. Both eyes appear normal on slit-lamp examination. A, Although the topographic examination appears normal on first glance, there is subtle inferior steepening that requires close inspection to appreciate. B, A clearly abnormal hot spot (arrow) is apparent on the Galilei dual Scheimpflug analyzer posterior elevation map, which may be concerning for keratoconus suspect. Technologies that evaluate regional corneal thickness and posterior corneal elevation in addition to anterior curvature may improve the identification of patients with early keratoconus. CCT = central corneal thickness; KPI = keratoconus prediction index.
(Courtesy of Douglas D. Koch, MD.)
Belin MW, Asota IM, Ambrósio R, Khachikian SS. What’s in a name: keratoconus, pellucid marginal degeneration, and related thinning disorders. Am J Ophthalmol. 2011;152(2): 157–162.
Binder PS, Lindstrom RL, Stulting RD, et al. Keratoconus and corneal ectasia after LASIK. J Cataract Refract Surg. 2005;31(11):2035–2038.
Kılıç A, Colin J. Advances in the surgical treatment of keratoconus. Focal Points: Clinical Modules for Ophthalmologists. San Francisco: American Academy of Ophthalmology; 2012: module 2.
Randleman JB, Russell B, Ward MA, Thompson KP, Stulting RD. Risk factors and prognosis for corneal ectasia after LASIK. Ophthalmology. 2003;110(2):267–275.
Saad A, Gatinel D. Topographic and tomographic properties of forme fruste keratoconus corneas. Invest Ophthalmol Vis Sci. 2010;51(11):5546–5555.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.