July 6, 2021
Samir Jabbour, MD, CM1; Kraig S. Bower, MD1
Author
Affiliations Article Information JAMA. 2021;326(1):77-78. doi:10.1001/jama.2020.20245
Refractive
surgery, which corrects high degrees of refractive error (the reason most
people wear glasses), is one of the most rapidly evolving fields in
ophthalmology. In the past decade, the field has evolved beyond excimer laser
surgery. Newer platforms, such as the femtosecond laser, have improved outcomes
of traditional procedures and allowed the emergence of novel ones, such as
small incision lenticule extraction. Presbyopia, the loss of accommodation in
virtually all adults older than 40 years, can be addressed with various
strategies. The various types of surgical procedures are described in the Figure.
Figure. Common Refractive Surgical Procedures in the US
Corneal-Based
Refractive Surgery
Laser In Situ Keratomileusis
Laser
in situ keratomileusis (LASIK) is considered the reference standard of laser
refractive surgery. It remains the most popular refractive procedure in the US,
with approximately 800 000 procedures performed annually.1 A 2016 review showed that 99.5%
of patients who undergo LASIK achieve spectacle independence and 98.6% are
within ±1.0 diopter of the attempted correction.2 The transition from mechanical to
femtosecond laser flaps has reduced the risk of complications. Careful patient
screening remains the most important factor in patient satisfaction. Patients
with thin corneas are at higher risk of post-LASIK ectasia, a weakening of
corneal biomechanics that leads to progressive corneal curvature changes and
severe refractive errors (eg, myopia, irregular astigmatism) that may not be
amenable to spectacle correction. Fortunately, new imaging modalities, such as
Scheimpflug imaging, and artificial intelligence algorithms have improved
screening of patients at risk of ectasia and reduced its incidence to roughly 1
in 5000 cases.3
Photorefractive Keratectomy
Photorefractive
keratectomy (PRK) is a safe alternative for many patients who may not qualify
for LASIK, including those with thin corneas or those at risk for trauma, such
as military or law enforcement personnel. A systematic review found no
difference in long-term refractive outcomes between LASIK and PRK.4 Low-dose topical mitomycin C
(0.02%-0.04%), an antimetabolite that modulates stromal keratocyte activation,
has reduced the incidence of post-PRK corneal haze, a potential complication of
the procedure.
Wavefront Refractive Laser Surgery
Conventional
excimer laser ablation (LASIK and PRK) can induce higher-order aberrations
(HOAs), such as spherical aberration, coma, and trefoil, which can result in
unwanted visual effects, such as halos, glare, and starbursts. Wavefront
technology and 3-dimensional corneal imaging have allowed for better ablation
profiles, improving contrast sensitivity and visual quality. Wavefront-guided
ablations are based on preoperative measurements of HOAs to reduce existing
HOAs. Wavefront-optimized ablations are designed to minimize induction of new
HOAs while preserving naturally occurring aberrations of the eye.
Topography-guided ablations use the corneal curvature map to guide treatment
and are particularly beneficial for patients with irregular corneas (eg,
decentered treatments, LASIK flap complications).
Small Incision Lenticule Extraction
Advancements
in femtosecond laser technology have allowed the development of a new
refractive procedure, small incision lenticule extraction, that is rapidly
gaining popularity in the refractive marketplace. More than 80 000 procedures
have been performed worldwide.5
Lens-Based
Refractive Surgery
Phakic Intraocular Implants
Phakic
implants are intraocular lenses implanted without removing the patient’s
natural lens. Two phakic implants are available in the US. The Visian
Implantable Collamer Lens (ICL; STAAR Surgical) is a foldable lens injected
through a 3.0-mm corneal incision in the posterior chamber (between the iris
and the crystalline lens). More than 1 000 000 ICLs have been implanted.6 In a 2018 comparative multicenter
study, 97% of 351 patients with moderate to high myopia achieved an uncorrected
distance visual acuity of 20/20 or better after ICL implantation.6
The
Artisan lens (Ophtec) has claws that attach it to the iris. Although many
patients can preserve excellent vision over many years, a 2018 10-year
follow-up study showed significant corneal endothelial cell loss of 20% after
Artisan implantation,7 risking corneal decompensation
and loss of clarity.
Refractive Lens Exchange
The
removal of the crystalline lens without the presence of a cataract is known
as refractive lens exchange. It can correct many types of
refractive errors and is a particularly useful option for patients with hyperopia
with presbyopia.
Treatments
for Presbyopia
Presbyopia,
age-related loss of near vision, is due to loss of elasticity of the aging lens
with time. Reading glasses and contact lenses remain the safest and cheapest
remedy. Although surgical options exist, a treatment that can prevent its
development or replace the full accommodative range of the natural lens is not
yet available.
Monovision
Monovision,
in which one eye is targeted for distance and the other for near vision,
remains a reliable approach to managing presbyopia and can be achieved with
LASIK, PRK, small incision lenticule extraction, or refractive lens exchange.
One drawback is that not all patients tolerate the disparity between eyes;
therefore, careful screening or testing with a trial of contact lenses prior to
surgery is recommended.
Multifocal Intraocular Lenses
Multifocal
intraocular lenses (IOLs) divide incoming light into several focal points,
allowing improved range of focus with functional vision at near, intermediate,
and far distance. To date, only 1 true trifocal implant is available in the US,
the AcrySof PanOptix (Alcon), which was approved by the US Food and Drug Administration
(FDA) in 2019. The main drawback of all multifocal lenses is reduced contrast
sensitivity and night vision and increased HOAs, which can make them unsuitable
for many patients, warranting an IOL exchange in up to 5% of cases.
Corneal Inlays
Corneal
inlays are miniature devices implanted in the cornea to alter its refractive
power. Two inlays were approved by the FDA to manage presbyopia. The Raindrop
inlay (ReVision Optics) was recalled in 2019 due to high rate of corneal haze.
The Kamra inlay (Acufocus) is a miniature (3.8 mm) implant placed over the
pupil in the cornea of the nondominant eye, acting as a pinhole to improve
range of vision. In the FDA trial, 95% of 373 treated eyes achieved near vision
of 20/40.8 However, associated complications
include glare, halos, and reduced peripheral vision, requiring removal of 3% to
9% of implanted devices.
Conclusions
Patients
often ask physicians whether there are safe and effective surgical alternatives
to glasses or contact lenses. The field of refractive surgery is constantly
evolving and will continue to improve the quality of life of patients. With a
focus on improving safety, new minimally invasive treatments may become
available. Drops to alter the refractive indices of the cornea and lens to
manage presbyopia are under investigation. Multifocal and accommodative IOL
technology continue to evolve to offer a wider range of vision without visual
aberrations. Additionally, treatment to alter biomechanics of the cornea, such
as corneal collagen crosslinking, may find a new role in the correction of
refractive errors.
Corresponding Author: Kraig S. Bower, MD, Wilmer Eye
Institute, 600 N Wolfe St, Baltimore, MD 21287 (kbower5@jhmi.edu).
Conflict of Interest Disclosures: None reported.
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