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Physicians should consider basing decisions on findings from comprehensive consultation and examination.
Use of a systematic, comprehensive approach to assess candidacy for refractive surgery can optimize surgical success and patient satisfaction, according to George O. Waring IV, MD, FACS.
“Whether undergoing a cornea- or lens-based procedure, patients should be generally healthy, and surgeons need to have a good understanding of the individual’s vision needs and goals,” said Waring, who is the founder and medical director of the Waring Vision Institute in Mount Pleasant, South Carolina, and also an adjunct assistant professor of bioengineering at Clemson University in South Carolina.
“In addition, a complete ocular examination is needed,” he said. “Advanced diagnostics can aid in decisions about candidacy and procedure selection, and more tools that show great promise for guiding surgical decisions are in development.”
Information that includes patient age, refractive error, lens opacity, dry eye status, and overall ocular health provides the foundation for determining whether a patient is a candidate for refractive surgery and the best surgical option that will direct the preoperative work-up.
“In our practice, laser vision correction is more strongly considered for a younger patient who still has good accommodative ability, whereas a refractive lens exchange may be preferable for an older individual,” Waring explained.
Other considerations include the patient’s desire for good uncorrected vision at different distances and the importance of good stereopsis, both of which can take into account the individual’s occupation, hobbies, and recreational activities.
A history of previous ocular surgery, ocular pathologies, and previous use of contact lens monovision are other issues reviewed in the preoperative screening evaluation.
Components of the eye examination include current spectacle prescription; determination of monocular and binocular uncorrected vision acuity and near, best corrected visual acuity; and a surgical manifest refraction, including a cycloplegic refraction.
Ocular dominance is also checked, including optical ocular dominance if the motor is equivocal, Waring said.
Diagnostic technologies are used to screen for corneal pathology that would determine patient candidacy for different procedures as well as for surgical planning.
“Historically, Placido-based topography has been the gold standard for evaluating patient candidacy for corneal refractive surgery, but elevation-based tomography has come into the mainstream and we have been studying in vivo assessments of corneal biomechanics in our center,” Waring said.
With Placido-based topographers, findings of asymmetric bow ties, inferior steepening, or skewed radial axis may be indicative of a patient who has an abnormal cornea and may not be a candidate for LASIK or potentially any corneal refractive surgery, depending on a multifactorial clinical presentation and severity.
Using tomography, surgeons should check for a normal topographic pattern on the sagittal curvature map, normal thickness on the pachymetry map, anterior float less than 8 μm, and posterior elevation less than 18 μm to aid in screening patients as appropriate for LASIK. Other indices also provide useful information.
For example, a Belin-Ambrósio enhanced ectasia display value of less than 1.4 or a maximum Ambrósio relational thickness result of more than 400 are favorable factors for candidacy.
Wavefront aberrometry is used in the preoperative evaluation of refractive surgery candidates to understand higher–order aberrations and for planning wavefront-guided laser vision–correction procedures, whereas biometry is needed in cases involving refractive lens exchange.
Ray tracing technologies that separate internal (lenticular) and external (cornea) optical aberrations can also be helpful for guiding surgical decisions.
As an example, Waring cited data from an eye exhibiting higher internal optical aberrations that indicated suitability for a refractive lens exchange procedure.
Anterior segment optical coherence tomography can provide information on pachymetry, epithelial thickness maps, anterior and, posterior keratometry, lens density, biometry, and in some cases, macular imaging. Lens imaging is also possible using Scheimpflug-based devices or double-pass wavefront technology.
On the horizon
Waring noted that evaluation of corneal biomechanics will be coming into the clinic as a technique to screen for corneal ectasia and ectasia risk in laser vision–correction patients.
Early experience in Warning’s institute indicates that the tomographic and biomechanical index—a metric developed by Renato Ambrósio, MD, that combines Scheimpflug-based corneal tomography and biomechanical evaluation—is very helpful.
The color-coded result identifies eyes that might be considered appropriate candidates for LASIK versus a surface ablation procedure, implantable contact lens, or refractive lens exchange.
Finite element modeling developed by William J. Dupps Jr, MD, is also an exciting development for identifying eyes at risk for ectasia after laser vision correction, Waring said.
“Our experience with both of these technologies [has] been very positive,” he added.
The modeling incorporates information from sets of preoperative and postoperative cornea strain maps, which are generated from Scheimpflug tomography, to predict risk.
In clinical practice, the preoperative strain map of a surgical candidate is compared with the database to see how the features of the cornea match with those of an eye that went on to develop postoperative ectasia.
George O. Waring IV, MD, FACS
This article is based on Waring’s presentation at the American Academy of Ophthalmology’s 2020 virtual annual meeting. Waring is a consultant to Oculus, Reichert, and Visiometrics; receives lecture fees from Oculus; and owns equity in Visiometrics.