LASIK is first choice for enhancement of refractive surgery

LASIK is considered preferable to other surgical options for varied reasons, according to the members of a panel convened in Milan.

ByMichela Cimberle

A slight undercorrection after LASIK (top) is improved with re-treatment. Residual error was reduced from -0.75 D to +0.25 D.

MILAN – LASIK was the first choice of all panelists in a discussion of refractive surgery enhancement techniques here at the annual Videorefractive meeting, organized by Lucio Buratto, MD. The round-table symposium was chaired by Roberto Bellucci, MD, of Salo, Italy.

LASIK after LASIK

Post-LASIK enhancement was the first issue.

“Re-LASIK is the best choice when treating residual refractive errors after LASIK, whether they are due to undercorrection or regression,” Dr. Bellucci said.

In case of undercorrection, the residual refractive error can be immediately recognized and easily corrected by re-lifting the flap and performing a second ablation on the selected area (figures 1 and 2), he said.

Regressions are a more complex matter and can be divided into two groups, mild and severe.

Mild regressions may be connected with tissue repairing phenomena or with a progression of myopia, but they can also be due to a biomechanical increase in curvature of the posterior corneal surface.

“This type of regression appears a few weeks after surgery and can be laser-corrected by lifting the flap if there is a sufficient quantity of tissue to be ablated,” Dr. Bellucci said.

Severe regressions are, in most cases, due to corneal tissue deformation and bulging of the posterior corneal surface (figure 3).

“Initially, there is a regular increase in curvature, which later takes the shape of a keratoconus ectasia (figures 4 and 5),” he said.

These eyes, in his opinion, should never be retreated with the laser, because further tissue ablation promotes the formation of the ectasia.

Measuring corneal thickness

Corneal thickness is a crucial factor in preventing this type of ectatic complication, according to Michael Knorz, MD.

“In the case of overcorrection, attention should be paid to how much corneal thickness you have to spare, as enhancements remove a large amount of tissue,” he said.

High undercorrection after LASIK may hide posterior corneal bulging.	In a case of severe regression, a re-treatment ...
... resulted in a keratoconic ectasia with +14 D refractive error.	Grade 2 haze after unsuccessful hyperopic PRK, eventually treated by LASIK.
LASIK is a better choice than PRK to treat low hyperopia after RK.	LASIK after PK can be effective, although results are not always good.

The panelists agreed that postoperative corneal pachymetry is not a reliable means of calculating the amount of available corneal tissue for re-treatment, because pachymetry measures the total amount of corneal tissue without subtracting the thickness of the LASIK flap. According to Dr. Bellucci, confocal microscopy is far more reliable, because it can measure the interface depth and its distance from the corneal apex. Because post-LASIK ectasia is so far extremely rare with corneal beds thicker than 250 µm, this is commonly accepted as the minimum residual thickness of the ablated cornea.

Techniques of flap lifting for LASIK re-treatment were shown on video. Thomas Kohnen, MD, explained that he performs a small epithelial abrasion near the hinge and inserts a small, blunt spatula under the flap parallel to the hinge.

“In this way, the flap can be lifted opposite to the direction of the microkeratome cut rather than in the same direction, and this considerably reduces the epithelial damage,” he said.

Other cases

Enhancements after photorefractive keratectomy (PRK) were discussed in some special cases, and LASIK treatment was also the preferred method. In particular, the case of a hyperopic patient was illustrated.

“After PRK, this patient had an increase in astigmatism from 2 D to 8 D due to severe haze (figure 6). After LASIK re-treatment, refraction was good, there was no haze and the astigmatism was considerably reduced,” Dr. Bellucci said.

A small, blunt spatula is inserted under the flap parallel to the hinge to lift the flap for re-treatment. (Photo courtesy of Thomas Kohnen, MD.)

By general agreement, PRK should never be performed after radial keratotomy (RK), as the cornea reacts too strongly to the treatment, producing severe haze.

“LASIK is a far better choice, which allows for both myopic and hyperopic correction (figure 7). However, enhancements after RK can only be considered if topographic maps show that the cornea is not too irregular. Attempts to correct irregular astigmatism, for example, have been generally very disappointing,” Dr. Bellucci said.

Customized ablation is not the answer, either, at least to date.

“Results have not come up to expectation,” Dr. Knorz said.

A final session of the round table concerned enhancing techniques after corneal transplant and cataract surgery.

Dr. Bellucci showed the results of 3-year follow-up in eight cases, which were on the whole satisfactory.

“On a corneal graft, we usually perform LASIK. However, only two of these eyes achieved uncorrected visual acuity equal to or better than 20/25 (figure 8),” he said.

Today, against-the-rule astigmatism secondary to extracapsular cataract extraction has a very good chance of being successfully and easily corrected by LASIK, he said.

For Your Information:

Roberto Bellucci, MD, can be reached at via degli Abeti 17, 25087 Salo (BS), Italy; +(39) 347-657-5001; fax: +(39) 036-543-678; e-mail: robbell@tin.it.

Michael Knorz, MD, can be reached at 14 Leibniz St., 68165 Mannheim, Germany; phone: +(49) 621-383-3410; fax: +(49) 621-383-1984; e-mail: knorz@eyes.de.

Thomas Kohnen, MD, can be reached at Johann Wolfgang Goethe University, Theodor Stern kai 7, Frankfurt am Mein, 60590, Germany; +(49) 696-301-6739; fax: +(49) 696-301-3893; e-mail: kohnen@em.uni-frankfurt.de.