Preventing and Managing Corneal Refractive Complications

Careful planning and execution help avoid refractive errors, haze, infections. Howard Larkin reports from ASCRS 2021 in Las Vegas, USA

Many corneal complications—including over- and undercorrection, infections, and haze—often can be avoided using careful technique and dodging known pitfalls, Jonathan B Rubenstein MD, told a session of the ASCRS Refractive Surgery Day.

This principle applies whether the technique is astigmatic keratotomy (AK), photorefractive keratectomy (PRK), or LASIK, Dr Rubenstein said.

AK For AK, overcorrection can be due to nomogram errors, toolong incisions, or too-central incisions, Dr Rubenstein said. He warned against trying to correct overcorrections by adding incisions at 90 degrees away from the original incisions. Correct by suturing gaping wounds instead, he advised.

AK undercorrection often results from incisions that are too short, too shallow, or made without holding the blade perpendicular to the cornea, Dr Rubenstein said. Remember, the cornea is a dome, and there must be a conscious effort to ensure the blade remains perpendicular to the cornea at all points to achieve a uniform incision at the correct depth. Inexperienced surgeons often plunge the blade in deep at first and make the cut progressively shallower, which he noted leads to under-correction.

In case of a perforation in AK, stop and suture the incision, Dr Rubenstein advised.

“You can take out the suture later and titrate the refractive result based on postoperative keratometry and refraction.”

AK infections are unusual but do occur, especially in with-therule procedures when the incisions are closer to the lid margin. Good lid hygiene and postop antibiotic drops for at least a week or until the epithelium seals are essential to help prevent infections.

AK glare can be reduced by keeping incisions peripheral and outside the 7.0 mm optic zone. Surgeons can avoid irregular astigmatism by keeping incisions paired and symmetrical, Dr Rubenstein said.

PRK Overcorrection and undercorrection can both occur with PRK, especially in patients with higher refractive errors and older age, Dr Rubenstein said. Undercorrection may be primary or due to regression. He recommended waiting six months for refractive stability after surgery before attempting an enhancement.

For PRK cases with haze, he suggested waiting for maximal haze resolution and refractive stability before retreatment with PRK and mitomycin C. The length of postoperative steroids also can influence over- and undercorrection, with a longer course of steroids used for undercorrection and shorter course for overcorrection, he added.

Delayed epithelial healing, sometimes leading to infectious keratitis, is more common in patients with dry eye and concomitant ocular surface disease. Dr Rubenstein recommended treating ocular surface aggressively pre-operatively and not performing PRK until there is a normal surface. Smoking, diabetes, and connective tissue disease can also lead to delayed healing.

Stromal haze and scarring are more common in high refractive-error patients and those with high ultraviolet light exposure, Dr Rubenstein noted. “Warn your patients about wearing protective sunglasses after PRK.”

Haze usually peaks at one to three months and usually regresses by 12 months. If it persists, remove or scrape the haze away and treat with mitomycin C.

“Try to treat the haze with scraping only and avoid additional laser treatment because you are treating an unpredictable refractive error,” Dr Rubenstein said.

Decentred ablations are much less common with modern small-spot lasers but do occasionally happen. They often can be corrected with retreatment, especially with topographicguided ablations. Ectasia is also a risk with PRK and LASIK, Dr Rubenstein noted.

LASIK Overcorrection and undercorrection risks in LASIK are similar to PRK, though refractions usually stabilise earlier with LASIK by three months after surgery. LASIK flap complications can occur whether using a blade or a laser to cut the flap, he observed.

Irregular or incomplete flaps are possible with both technologies. Buttonholes are a larger risk with blade-created flaps. Vertical gas breakthroughs are possible with laser-created flaps. Inadequate side cuts also can cause incomplete laser flaps. Flap striae and traumatic dislocations are also possible with both.

Unrecognised occult epithelial basement membrane dystrophy is always a risk as a complication in LASIK, Dr Rubenstein said. This condition can lead to epithelial defects,

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delayed surface healing, and increased risk of diffuse laminar keratitis (DLK). DLK can be treated with intensive topical steroids, but if grade III or IV, lift the flap and debride and replace the flap.

Central toxic keratopathy leads to corneal thinning and stromal loss, resulting in a central hyperopic shift. It is a noninflammatory process that can occur late after DLK or with no precursor, Dr Rubenstein said.

Epithelial ingrowth can occur as pearls or a sheet from the flap edge. To treat, lift the flap and clean both the stomal interface and under the flap surface. A tight bandage contact lens, sutures, or glue helps keep the flap in place to prevent recurrence. LASIK infections are rare, but when they occur, lift the flap, culture, and treat with appropriate antibiotics.

Pressure-induced stromal keratitis (PISK) can occur due to increased intraocular pressure and should be distinguished from corneal swelling due to inflammation—they require opposite treatments. Reduce steroids in the event of PISK, Dr Rubenstein advised. Dry eye should be treated aggressively and usually will resolve after six to 12 months when corneal nerves reinnervate the LASIK flap, he added.

Jonathan B Rubenstein MD is the Deutsch Family Professor and Chairman, Department of Ophthalmology, Rush University Medical Center, Chicago, USA. jonathan_rubenstein@rush.edu

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