Before recommending laser vision correction for your patient, there are a number of factors you as an eyecare practitioner must consider.
Before recommending laser vision correction for your patient, there are a number of factors you as an eyecare practitioner must consider. In a previous issue (“Is your patient healthy enough for LASIK surgery?” Optometry Times, February 2014), we discussed how your patient’s systemic health can affect the safety and efficacy of refractive surgery.
Today, I would like to consider the ocular conditions that must be considered before making a patient candidacy decision. Most refractive surgeons base their criteria for patient candidacy on the original criteria described in the original FDA approval of LASIK more than a decade ago (see Table 1).
Keratoconus is a progressive thinning disorder of the cornea that results in irregular astigmatism causing impairment of visual function. Corneal refractive surgery is associated with an increased risk of progressive ectasia and loss of vision.1
While moderate to severe keratoconus can often be diagnosed with a biomicroscope, early subclinical forms of keratoconus can often be detected only with corneal topography (see Figure 1) or corneal tomography (see Figure 2).2,3
Additionally, recent evidence suggests that elevated corneal wavefront analysis (vertical coma) and biomechanical analysis may improve the early detection of corneas susceptible to the development of keratoconus.4,5
Related: Keratoconus: Cracking the corneal code
The FDA classification of keratoconus as an absolute contraindication to laser vision correction is currently being questioned by many surgeons. Outside of the U.S., it has become more common to utilize photorefractive keratectomy combined with corneal collagen cross-linking to improve vision and stabilize the cornea of patients with keratoconus.6
Next: Corneal herpes simplex and herpes zoster
Reports of reactivation of herpes simplex and herpes zoster virus after excimer refractive surgery can be found in the literature.7,8 Recent evidence suggests that LASIK is safe in patients with a history of ocular herpes that has been inactive for more than one year.9 Perioperative use of systemic antiviral prophylaxis is recommended to reduce the risk of virus reactivation.
Both LASIK and PRK are known to increase dryness symptoms after surgery. Possible mechanisms include loss of neurotrophic effect, damage of goblet cells, and altered corneal shape. Despite the fact that most dryness symptoms are usually temporary and resolve in the first six to 12 months after surgery, significant preoperative dry eye signs and symptoms should be resolved prior to corneal refractive surgery to reduce the risk of patient’s dissatisfaction.10
Next: Other considerations
In addition to these contraindications, several other precautions are recommended when screening your patients for corneal refractive surgery (see Table 2). Overall, most surgeons agree that any patient with active eye disease should not be a considered candidate for an elective refractive procedure due to increased risk of sight-threatening complications and poor visual outcomes.
The transient significant rise in intraocular pressure (IOP) with femtosecond and mechanical microkeratome used in LASIK surgery may not be safe for patients with glaucomatous visual field loss or optic nerve compromise. Corneal scars and prior corneal surgery can reduce the safety, efficacy, and predictability of corneal refractive surgery.
Related: Measuring LASIK patient satisfaction
Patients with thin corneas may be at increased risk of corneal destabilization due to LASIK flap creation and excimer ablation. Many surgeons use a cutoff of 480-500 µm for LASIK and 460-480 µm for PRK when screening patients for surgery. Evidence shows that LASIK and PRK in patients with thin corneas (less than 500 µm) is safe and predicable providing no other risk factors such as abnormal topography exist.11
Patients with early crystalline lens changes should be cautioned about corneal refractive surgery. Corneal refractive surgery can reduce the accuracy of intraocular lens (IOL) power selection.
The unpredictable progression of crystalline lens changes makes it impossible to accurately predict the timing of significant vision loss. Visually significant cataracts are best addressed with lens extraction and IOL implantation, which can also accurately correct long-standing refractive error.
Related: Comanaging non-corneal refractive surgery
Early forms of corneal refractive surgery were often associated with night vision disturbances. Early evidence suggested that large scotopic and mesopic pupil size may play a role in patient symptoms.
Most experts agree that modern excimer lasers and ablation patterns have eliminated the majority night vision disturbances including glare, halo, and starbursts. In a recent study of 10,944 eyes of 5,563 myopic patients treated with wavefront-guided LASIK, low-light pupil diameter was not predictive of surgery satisfaction, ability to perform activities or visual symptoms at one-month postoperatively.12
Having a thorough understanding of your patient’s ocular health is necessary to determine if your patient is a good candidate for refractive surgery.
1. Binder PS. Risk factors for ectasia after LASIK. J Cataract Refract Surg. 2008 Dec;34(12):2010-1.
2. Ramos-LÃ³pez D, MartÃnez-Finkelshtein A, Castro-Luna GM, et al. Screening subclinical keratoconus with placido-based corneal indices. Optom Vis Sci. 2013 Apr;90(4):335-43.
3. Belin MW, Villavicencio OF, AmbrÃ³sio RR Jr. Tomographic parameters for the detection of keratoconus: suggestions for screening and treatment parameters. Eye Contact Lens. 2014 Nov;40(6):326-30.
4. Saad A, Gatinel D. Evaluation of total and corneal wavefront high order aberrations for the detection of forme fruste keratoconus. Invest Ophthalmol Vis Sci. 2012 May 17;53(6):2978-92.
5. Ahmadi Hosseini SM, Abolbashari F, Niyazmand H, et al. Efficacy of corneal tomography parameters and biomechanical characteristic in keratoconus detection. Cont Lens Anterior Eye. 2014 Feb;37(1):26-30.
6. Pasquali T, Krueger R. Topography-guided laser refractive surgery. Curr Opin Ophthalmol. 2012 Jul;23(4):264-8.
7. Levy J, Lapid-Gortzak R, Klemperer I, et al. Herpes simplex virus keratitis after laser in situ keratomileusis. J Refract Surg. 2005 Jul-Aug;21(4):400-2
8. Jarade EF, Tabbara KF. Presumed reactivation of herpes zoster ophthalmicus following laser in situ keratomileusis. J Refract Surg. 2002 Jan-Feb;18(1):79-80
9. de Rojas Silva V, RodrÃguez-Conde R, Cobo-Soriano R, et al. Laser in situ keratomileusis in patients with a history of ocular herpes. J Cataract Refract Surg. 2007 Nov;33(11):1855-9
10. Nettune GR, Pflugfelder SC. Post-LASIK tear dysfunction and dysesthesia. Ocul Surf. 2010 Jul;8(3):135-45
11. Kymionis GD, Bouzoukis D, Diakonis V, et al. Long-term results of thin corneas after refractive laser surgery. Am J Ophthalmol. 2007 Aug;144(2):181-185.
12. Schallhorn S, Brown M, Venter J, et al. The role of the mesopic pupil on patient-reported outcomes in young patients with myopia 1 month after wavefront-guided LASIK. J Refract Surg. 2014 Mar;30(3):159-65