May 2017




Treating the cornea before cataract surgery
Preop corneal irregularity approaches for cataract patients

by Rich Daly EyeWorld Contributing Writer


72-year-old male with marked irregular astigmatism who received topography-guided PRK and CXL. Cataract surgery with a toric implant was performed 6 months after the corneal procedures. Patient did well and functions with glasses for reading only.
Source: Raymond Stein, MD, FRCSC

Surgeons discuss the use of topographic or wavefront ablations, Intacs, and CXL to treat corneal irregular astigmatism or stable
keratoconus patients before cataract surgery

Patients with corneal irregular astigmatism or stable keratoconus can add a layer of complexity to typical treatment of cataract patients. But surgeons have identified effective approaches for them.
In patients wearing rigid gas permeable (RGP) lenses or who have a longstanding history of reduced best spectacle-corrected visual acuity (BSCVA) secondary to irregular astigmatism, Raymond Stein, MD, FRCSC, medical director, Bochner Eye Institute, and associate professor of ophthalmology, University of Toronto, prefers to perform topography-guided PRK and corneal collagen crosslinking (CXL) prior to cataract surgery.
“The goal is to reduce irregular astigmatism so that patients following cataract surgery will be free of RGP lenses and be able to wear glasses, soft contact lenses, or be free of optical aids,” Dr. Stein said.
Patients need to discontinue wearing RGP lenses for at least 1 month or until topographic stability is reached. On average, stability is reached around 6 weeks but may take up to 4 months.
Simon Holland, MB, FRCSC, Pacific Laser Eye Centre, Vancouver, approaches such patients like post-refractive surgery patients. They require additional consent to have realistic expectations amid the increased unpredictability.
He determines the degree of keratoconus—less than 49 K is mild, 50–55 is moderate, and greater than 55 is severe—and identifies the location of the cone. That is followed by multiple programs and imaging, including equivalent K readings with the Pentacam (Oculus, Arlington, Washington) and posterior curve with the Sirius Corneal Topographer (CSO, Scandicci, Italy). Good results also are provided by topography derived or manual K at the 3-mm axial zone with the SRK-T or SRK-II formulas.
“If using actual Ks, he suggests aiming for –1.50 with low KC, –2.0 up to 55, and use 44.0 as the target for over 55 with a view to doing topography-guided PRK with CXL later,” Dr. Holland said.
Dr. Holland advises all such patients that they may need to resume RGP lenses or undergo topography-guided PRK with CXL.

Surgical approach

On the day of surgery, Dr. Stein obtains eight topographic images and transfers that information to the excimer laser for the treatment. The treatment plan is reviewed with the goal of limiting the excimer stromal ablation to 50 μm.
“My preference is to use the larger optical zone of 6.5 mm or 6.0 mm, which reduces regression of the laser treatment,” Dr. Stein said.
A phototherapeutic keratectomy is applied at 50 μm to remove the corneal epithelium, immediately followed by topography-guided PRK. Ice is applied to the cornea immediately after the laser application for 30 seconds, which enhances postop comfort. Mitomycin C is then applied on a sponge for 1 minute. This is followed by CXL using riboflavin drops for 10 minutes and ultraviolet A light for 12 minutes on pulse mode with an energy of 15 mw/cm2. A bandage soft contact lens is then inserted, and typically removed at 5 days postop.
“My preference is to wait for 6 months for corneal stability before performing cataract surgery either with a monofocal or toric implant,” Dr. Stein said.

Preop Intacs or CXL

Dr. Stein prefers to perform topography-guided PRK instead of using Intacs (Addition Technology, Lombard, Illinois) in corneas that are 450 μm or thicker. Topography-guided PRK is a more customized approach that allows the surgeon to flatten steep areas and steepen flat areas to reduce irregular astigmatism. In corneas that are less than 450 μm centrally, Intacs can be used to reduce the irregular astigmatism.
“My preference is not to use Intacs in patients under 60 years of age because of long-term risks of corneal haze, neovascularization, and extrusion,” said Dr. Stein, who was involved in an Intacs study for myopia in the late 1990s, during which many patients developed complications after 10 years postop.
Dr. Holland sees little preop role for Intacs or CXL because he has found good results from topography-guided PRK with CXL after cataract surgery with a monofocal IOL.
“A short CXL is done, as usually older patients have less change of progression, and a shorter CXL is less likely to induce hyperopia,” Dr. Holland said.
Dr. Stein performs topography-guided PRK prior to cataract surgery in patients who either wear RGP lenses or who have a longstanding history of reduced BSCVA secondary to irregular astigmatism.
“In patients that were seeing well with glasses or soft contact lenses prior to the onset of their cataract, then straightforward cataract surgery is all that is required,” Dr. Stein said.

Monofocal lenses

If a cataract patient is prepared to undergo postop topography-guided PRK, then Dr. Holland would use a monofocal rather than a toric IOL. When refractive laser surgery is required after placing a toric IOL, such patients need a standard PRK instead of topography-guided PRK, which is less likely to reduce aberrations from an irregular cornea.
Following topography-guided PRK, if the cornea has less than 1 D of net astigmatism, Dr. Stein would use a monofocal implant. In patients with a net astigmatism of 1 D or more, he would use a toric implant.
“It is important to determine the net astigmatism and axis, which factors in both the anterior cornea and posterior cornea,” Dr. Stein

Editors’ note: Drs. Stein and Holland had no financial relationships related to their comments.

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