Cataract surgery is one of the most effective forms of refractive
surgery, because the new lens implant can correct just about any degree of
hyperopia, myopia and even astigmatism at the time of surgery. The highly
myopic patients are often the happiest, because a lifetime of nearsightedness
is finally cured with successful cataract surgery. However, these myopic eyes
pose challenges and additional risks during surgery and in the perioperative
Myopic eyes have a higher risk of retinal complications, such as retinal
detachment, compared with emmetropic eyes. During the preoperative exam, look
carefully for any retina breaks, holes or weaknesses, as well as any macular
pathology. The highly myopic patients may also have myopic macular
degeneration, epiretinal membranes or other significant changes. These may
limit the postoperative vision achieved and may influence the development of
postoperative complications such as cystoid macular edema. If any posterior
segment issues are noted, referral to a vitreoretinal colleague for treatment
is recommended before cataract surgery.
In addition to the typical cataract evaluation, care must be taken to
accurately assess the retinal status and measure the axial length of the eye.
Highly myopic eyes often have a posterior staphyloma, which can give an
erroneously long axial length when measured with the standard A-scan
ultrasound. This would cause an error in lens calculations and residual postop
hyperopia, resulting in an unhappy patient. Using an optical method for
measurement tends to be more accurate, as it measures directly at the fovea.
The IOL calculation formulae are less accurate at the extremes, and this is
particularly true for highly myopic eyes. Of the two-variable formulae, the
SRK/T tends to perform particularly well, as do more complex formulae such as
the Haigis and Holladay 2. A postoperative refractive goal of a mild amount of
residual myopia, such as –0.5 D, can be helpful to avoid a hyperopic
The selection of the IOL depends on each patient’s ocular status
and needs. Patients with large degrees of myopia and corneal astigmatism are
particularly well suited to toric IOLs, while others may do well with
multifocal or accommodating IOL designs. Multiple manufacturers make an
extended range of IOLs, including minus power lenses that can correct patients
with up to –30 D of preoperative refractive myopia. Examples of these
lenses are the Abbott Medical Optics Sensar AR40M acrylic IOL (as low as
–10 D), the Alcon AcrySof acrylic IOL (as low as –5 D), the STAAR
AQ5010V silicone IOL (as low as –4 D), the Bausch & Lomb Crystalens AO
(as low as +4 D) and the Hoya Surgical Optics iSymm (as low as +6 D).
The advantage of cataract surgery in myopic patients is the larger
anterior chamber depth, which allows more working room during
phacoemulsification. However, the infusion pressure from the phaco handpiece
can cause over-inflation of the anterior chamber and a tendency to push the
entire lens-iris diaphragm posteriorly. With an overly deep anterior chamber,
surgery becomes difficult and uncomfortable for both the surgeon and patient.
To address this issue, the infusion pressure can be decreased by lowering the
bottle height; however, this will result in less inflow of fluid and a higher
tendency for surge. A better solution is to break the reverse pupillary block
by making sure that there is fluid flow under the iris to equalize the anterior
and posterior chamber pressures. By neutralizing this pressure gradient, the
cataract will not be pushed so deeply within the eye, and adequate infusion
pressure can be used. I prefer to use the chopper to slightly tent up the iris
at the papillary margin in order to establish a channel for anterior-posterior
fluid flow. Alternatively, a single nasal iris hook can be placed for the
duration of the surgery.
examination of the retina before cataract surgery is important to identify
posterior segment pathology. Myopic degeneration can affect the macula while
peripheral retinal weakness can increase the risk of a postoperative retinal
detachment. Despite the retinal changes noted in this photo, the patient
achieved 20/20 vision after successful cataract surgery.
Images: Devgan U
|Highly myopic eyes are prone to excessive deepening of the
anterior chamber upon pressurization during cataract surgery due to a reverse
pupillary block. (A) In this figure, the nucleus has been removed and is ready
for cortical cleanup; (B) The anterior chamber becomes overly deep upon
insertion of the probe; (C) The chopper is used to briefly tent up the iris to
break the pupillary block and equilibrate the anterior and posterior chamber
pressures; (D) Removal of the remaining cataract material can be completed in a
safe manner with restoration of the normal anterior chamber anatomy.
Myopic patients are at a higher risk for postop retinal detachment if
there is tension or traction on the vitreous base during surgery. The primary
culprit is allowing the anterior chamber to collapse when removing the phaco
probe or irrigation and aspiration probe from the eye. Once the anterior
chamber collapses from lack of infusion, the posterior capsule and vitreous
have a tendency to move anteriorly, often quite abruptly and significantly.
This can be avoided by one simple technique: fully inflating the eye with
viscoelastic via the paracentesis before removing the phaco probe or I&A
probe from the eye. At the end of the case, once the IOL has been placed into
the capsular bag, remove the viscoelastic completely and use balanced salt
solution via the paracentesis to keep the eye pressurized as the I&A probe
is withdrawn. These techniques will prevent collapse of the anterior chamber,
increase patient comfort and lessen the risks.
The postop refraction in myopes can take time to stabilize due to the
variation in effective lens position as the capsular bag shrink-wraps around
the IOL. During this period, inflammation can be controlled using topical
steroids and NSAIDs. During the postoperative period, a repeat dilated fundus
examination is indicated in order to search for possible retinal breaks or
weaknesses that may have been created during surgery.
Finally, keep in mind that there may be a large degree of anisometropia
between the eyes, so performing timely surgery on the fellow eye will minimize
the imbalance. While patients will be functionally emmetropic after bilateral
cataract surgery, they will always have the elongated axial lengths and myopic
retinal changes that need to be followed on a regular basis.
While cataract surgery in myopic patients can pose many challenges,
these patients tend to be among the happiest of all. In a safe, efficient
surgery that has taken just minutes, their cataract has been removed, their
myopia has been treated, and they can now enjoy a lifetime of excellent vision.
- Uday Devgan, MD, FACS, is in private practice at Devgan Eye in Los
Angeles, chief of ophthalmology at Olive View UCLA Medical Center and an
associate clinical professor at the UCLA School of Medicine. Dr. Devgan can be
reached at 11600 Wilshire Blvd., Suite 200, Los Angeles, CA 90025;
800-337-1969; fax: 310-388-3028; e-mail: firstname.lastname@example.org; Web site:
Devgan is a consultant to Abbott Medical Optics, Bausch & Lomb, Hoya
Surgical Optics, and a stockholder in Alcon Laboratories and formerly in STAAR