Studies show LASIK and LTK are effective tools for refractive surgery re-treatments

LASIK can be used successfully after RK and PRK to treat hyperopia and myopia. LTK is effective for overcorrected LASIK and PRK.

PRK haze after RK. PHOTOGRAPH COURTESY OF ERIC J. LINEBARGER, MD	Suture after RK. PHOTOGRAPH COURTESY OF ERIC J. LINEBARGER, MD
Inflammation after suture. PHOTOGRAPH COURTESY OF ERIC J. LINEBARGER, MD	LASIK after RK at 6 months (diffuse illumination). PHOTOGRAPH COURTESY OF NUSRAT BAS, MD
Same patient as in Figure 4 (slit photo). Radial incisions and LASIK lines can be seen. PHOTOGRAPH COURTESY OF NUSRAT BAS, MD	Good penetration depth 75% of corneal thickness. COURTESY OF FRANK J. GOES, MD
Insufficient penetration. COURTESY OF FRANK J. GOES, MD	Slit lamp sitting.The treatment is done at the slit lamp under topical anesthesia (3 drops of proparacaine). COURTESY OF FRANK J. GOES, MD
Very large optical zone and 3 D effect after Ho:YAG re-treatment for overcorrected PRK. COURTESY OF FRANK J. GOES, MD	Again a very large optical zone and 3.5 D effect after re-treating overcorrected PRK. (Van Koetsem) COURTESY OF FRANK J. GOES, MD
A tremendous 7 D effect obtained at 1 week with a two-ring treatment in a 380 µm cornea. A 3.5 D effect remained at 3 months, so the technique is efficient but sometimes too efficient. COURTESY OF FRANK J. GOES, MD

SEATTLE — Sequential refractive surgery is rarely something physicians or patients seek, but in the event that unintended overcorrections, undercorrections or hyperopic or myopic regression prevent postoperative emmetropia, enhancement procedures may provide or restore the visual acuity patients underwent surgery for in the first place.

Nearly 1 million people in the United States were treated with radial keratotomy (RK) and, according to some estimates, more than 20% are now hyperopic, with between 1,000 and 2,000 additional RK patients experiencing new and significant hyperopic shifts annually. Additionally, large numbers of RK patients also have experienced a myopia shift 3 to 6 years after initial surgery.

While less vulnerable to regression than RK patients, individuals treated with photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) for myopia also are prone to an acuity-damaging hyperopic shift over time.

Fortunately, new studies indicate that LASIK and laser thermokeratoplasty (LTK) are effective tools for correcting or enhancing previous refractive surgery.

LASIK for hyperopia after RK or PRK

The increasing incidence of hyperopia in patients previously treated with RK has been described as “the second great epidemic awaiting anterior segment surgery,” according to Eric J. Linebarger, MD. This epidemic may rival that of pseudophakic bullous keratopathy after the implantation of early anterior chamber lens designs.

Until recently, previous treatment options for overcorrected RK patients revolved around circular compressions or “lasso” sutures. The refractive effect of these sutures was difficult to titrate, and they were frequently fraught with problems such as erosion and infection, leading to their eventual removal (Figure 1).

Limited reports on the use of hyperopic PRK in eyes with previous RK has suggested a higher than normal occurrence of severe post-PRK haze (Figure 2). Anecdotal reports of LTK for correction of hyperopia in this population of patients has suggested somewhat unreliable results and increased incidents of irregular astigmatism.

To evaluate the merits of LASIK for treatment of hyperopia in post-RK patients, Dr. Linebarger participated in the U.S. Food and Drug Administration investigational study. This initial study involved 16 patients who previously underwent RK for correction of low to moderate myopia, and later on developed significant hyperopia.

The mean preoperative spherical equivalent of the patients in this group was +1.64 D, with a range between +1.25 D and +3.12 D. Mean preoperative distance uncorrected visual acuity (UCVA) was approximately 20/40 with a range of 20/25 to 20/200.

All patients in the group underwent RK at least 24 months prior to corrective surgery, and all patients in the study group were treated with hyperopic LASIK using a Bausch & Lomb (Claremont, Calif.) Hansatome with a 9.5 mm ring and a Visx (Santa Clara, Calif.) Star excimer laser. No intraoperative complications were reported.

One month following surgery, approximately 50% of re-treated patients were within ±0.5 D of their intended correction, and more than 90% were within ±1 D. Fifty percent of patients had UCVA of 20/25 or better. The mean percentage of attempted correction achieved at 1 month was 112%.

Six months after surgery, 44% were within ±0.5 D of intended correction, and approximately 80% were within ±1 D. Two-thirds of patients had distance UCVA of 20/25. The mean percentage of attempted correction achieved at 6 months was 104%.

Following surgery, one patient lost one line of best corrected visual acuity (BCVA) and two patients gained one line of BCVA. No significant development of corneal haze was reported. Incidental epithelial ingrowth was identified in one patient at the 1-month visit but remained stable at 3 months follow-up and did not require surgical intervention.

“Hyperopia after RK can pose a distinct challenge … [but] we feel that LASIK can be used successfully to treat this population of patients, providing advantages over previous techniques,” Dr. Linebarger said. “Further studies are certainly warranted.”

LASIK for myopia after RK, PRK

A limited study of LASIK as a corrective procedure for residual myopia following RK or PRK concluded that the technique is an effective correction tool. In the 13-eye study, Athiya Agarwal, MD, preoperatively examined the patients with manifest and cycloplegic refraction, slit lamp biomicroscopy, flare lens visual acuity, radial keratography pachymetry, while also checking for corneal haze.

Of the 13 patients, nine had been treated with RK and four had been treated with PRK. The average age was 24.21 years, with a range of 12.6 years. Seven were right eyes, six were left. Exclusion criteria for LASIK after PRK or RK was previous corneal disease, uveitis, glaucoma, collagen vascular diseases or use of system steroids.

Patients were treated with a conventional LASIK procedure. A 160 µm flap was created, followed by photoablation with a Technolas 217 (Bausch & Lomb) excimer laser.

Preoperatively, patients were on average –5.18 D, with a range of –2.09 D. Following LASIK re-treatments, patients on average improved to 0.8 D, with a range of 0.5 D.

Two patients achieved emmetropia. One patient developed grade 1 corneal haze.

“Patients with residual myopia achieved better visual outcomes and significant improvement of visual acuity, and they were satisfied with their [enhancement] because most were unwilling or unable to tolerate contact lenses,” Dr. Agarwal said.

Further evidence

In a separate study, Nusret Bas, MD, in private practice in Türkiye Hospital, Turkey, also concluded that residual myopia and astigmatism may be effectively reduced by LASIK in eyes that have undergone RK or penetrating keratoplasty (PKP).

Dr. Bas studied six eyes of five patients that underwent LASIK after RK, and four eyes of four patients that were treated with LASIK after PKP.

In the RK group, the mean interval between LASIK and RK was about 3 years. Spherical equivalent in this group was –4.8 D, with a mean astigmatic refraction of about –3 D.

In the PKP group, the mean interval between LASIK and PKP was about 6 years. Here, the mean spherical equivalent was –8 D and mean astigmatic refraction was about –4 D.

Patients were allowed to participate in the study only if they were intolerant of spectacles or contact lenses, had pachymetry of at least 450 µm, the presence of two sighted eyes, absence of active or residual ocular disease, and absence of diabetes or other systemic disease.

There was no alteration to the conventional LASIK procedure for re-treatment cases; however, ablation profiles were adjusted based on individuals’ spherical or astigmatic refractions.

Postop examinations were performed 1 week and 1, 3 , 6 and 12 months after surgery.

“Myopia was reduced markedly in each group,” Dr. Bas reported.

Postoperative myopia was about 1 D in the RK group, down from 4.8 D, and about 2 D in the PKP group, down from 8 D. Most likely, both groups would still depend somewhat on spectacles, but Dr. Bas notes that the reduction of myopia was significant enough to deem the procedures successful.

There were no serious complications.

LTK after LASIK and PRK

---Regression is the drawback of the technique in some eyes. It seems to stabilize at 3 months. Left (12a): Difference map: 2.25 D effect with one ring at 2 months. Right (12b): Less than 0.5 D of regression in this case over a 6 month period.
COURTESY OF FRANK J. GOES, MD

LTK uses heat generated by the absorption of infrared energy from an Ho:YAG laser to thermally modify stromal collagen, shrinking it without causing tissue necrosis. The resultant contraction makes the cornea steeper. In most LTK cases, two concentric rings of 6 mm and 7 mm, and consisting of eight equally spaced spots, are applied on the corneal surface; however, as many as 16 spots can be used in each ring to achieve greater amounts of correction. Spots are about 600 µm in depth, and are typically created with 240 mJ of energy.

As a subset to a larger 350-eye study to evaluate the benefits of LTK for hyperopia using the Sunrise Technologies (Fremont, Calif.) non-contact system, Frank J. Goes, MD, in private practice in Antwerp, Belgium, analyzed a group of 25 eyes that had undergone previous LASIK or PRK for myopia and were overcorrected.

Seventeen eyes in his study had previous PRK and eight had previous LASIK surgery. The average patient was 42 years old. Follow-up for most patients was between 6 and 8 months, and more than 1 year in about one-half of the cases.

Prior to LTK, about 15% of eyes in the study were between –1 D and 1 D from emmetropia. After LTK re-treatment, about 70% were within 1 D of emmetropia. Before re-treatment, about 70% of patients were within 2 D of emmetropia, while 90% were within 2 D following re-treatment.

Mean corneal curvature was 38.97 D before surgery and 40.38 after re-treatment.

In terms of efficacy, UCVA before surgery was 0.37. Following re-treatment it was 0.56. UCVA improved in 18 of 25 eyes. BCVA improved in 17 eyes, remained the same in seven and decreased in one.

Four eyes were overcorrected during re-treatment because the surgeon induced too much hyperopic effect, and there was a myopic shift in these eyes. This explained the decreased UCVA after re-treatment in these eyes.

The corrective procedures induced very little astigmatism, Dr. Goes said.

He found that the effect of LTK seemed to vary depending on the pachymetry of each individual patient.

“Eyes with a very thin cornea — less than 400 µm — could sometimes give a 7 D effect, while eyes with a normal corneal thickness — over 500 µm — around a 3 D to a 4 D effect,” he said. “This is an important finding.”

Dr. Goes said regression was one of the more significant drawbacks to LTK as a re-treatment tool. He observed regression up to 3 months postoperatively in a number of cases. “Following that point, there seems to be some kind of stabilization,” he said.

“In our hands, non-contact Ho:YAG [LTK] is a powerful tool in the treatment of overcorrection resulting from previous PRK and LASIK treatment for myopia; however, in four out of 25 eyes, we had an overshoot,” Dr. Goes said. “The second-generation Sunrise LTK system will allow better fine-tuning of treatment parameters so that the accuracy will improve.”

In a separate, 24-eye study of LTK treatment for undercorrected hyperopic LASIK, Klaus Ditzen, MD, in private practice in Weinheim, Germany, found that non-contact Ho:YAG treatment is an effective re-treatment procedure. “All 24 eyes in this study showed improved refraction and good stability with no severe complications.”

However, the procedure did induce some astigmatism, as well as increased glare and halo. Even after corrective transepithelial LTK, LASIK flap stability was good, he said.

For Your Information:

• Eric J. Linebarger, MD, can be reached at Shiley Eye Center, University of California San Diego, La Jolla, CA 92093; (619) 534-6290. Dr. Linebarger has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
• Nusret Bas, MD, can be reached at Turkiyehastanesi Sisli, Istanbul, Turkey; (90) 212-210-4400; fax: (90) 212-222-9236. Dr. Bas has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
• Athiya Agarwal, MD, can be reached at 13 Cathedral, Chennai, Madras 600086 India; (91) 44-8276233; fax: (91) 44-8265871. Dr. Agarwal has no direct financial interest in any of the products mentioned in this article, nor is she a paid consultant for any companies mentioned.
• Klaus Ditzen, MD, can be reached at Bismarckstrasse 4, 69469 Weinheim, Germany; (49) 6201-12026; fax: (49) 6201-183610. Dr. Ditzen has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
• Frank J. Goes, MD, can be reached at Willem Klooslaan 6, Antwerp 2050, Belgium; (32) 3-219-3925; fax: (32) 3-219-6667. Dr. Goes has no direct financial interest in any of the products mentioned in this article. He is a paid consultant for Sunrise Technologies Inc.