Factors influencing the outcome of hyperopic lamellar keratoplasty

2005 ESCRS Ridley Medal Lecture

The literature on keratoconus and progressive post-laser in situ keratomileusis ectasia (PPLK) was studied after a retrospective review of 137 highly myopic eyes (mean -15.58 diopters) 5 to 9 years after LASIK. Only 2 eyes developed keratectasia, 1 after automated lamellar keratolasty for myopia and 1 after myopic LASIK. In neither case was intraoperative pachymetry carried out. In the PPLK case, a residual stromal bed thickness (RSBT) of 120 microm was discovered when a retreatment was attempted on lifting the flap. The PPLK developed 2 years later. The obvious discrepancy between reported cases of PPLK and the expected rate from the incidences in larger retrospective studies and our own 15-year experience suggests that PPLK is not a significant complication provided the standard rules applying to the preoperative total corneal thickness and RSBT are observed. However, newer techniques for the study of posterior corneal changes and those involving corneal biomechanics should be used in the future to study the long-term effects of LASIK on the cornea.

Surgical Correction of Hyperopia

Surgical attempts to correct hyperopia have yielded varying results over the last 130 years. These techniques include the reshaping of the cornea through incisions, burns, or lamellar cuts with removal of peripheral tissue; the addition of central inlays; laser ablations; and the replacement of the crystalline lens. By examining the success of each surgical technique, the refractive surgeon may be able to make an informed decision on its indications and limitations, based on the specific patient's characteristics. Reporting the outcomes and complications of hyperopic surgery will help refine our approach to the management of an increasingly hyperopic and presbyopic population.

The thin-flap LASIK technique

PURPOSE

To determine if LASIK using a 130-microm microkeratome head (thin-flap LASIK) is as visually effective and safe as when using a 160-microm head.

METHODS

A study was performed comparing postoperative day 1 uncorrected visual acuity (UCVA) and flap complications in eyes undergoing myopic LASIK with a 130-microm head versus a 160-microm head using the BD K-3000 microkeratome (BD Ophthalmic Systems, Waltham, Mass).

RESULTS

The mean preoperative myopia in the 155 eyes of 80 patients in the 130-microm head group was -5.00+/-2.53 diopters (D) compared to -3.78+/-1.73 D in the 279 eyes of 148 patients in the 160-microm head group. The groups were otherwise similar in terms of age, preoperative cylinder, and best spectacle-corrected visual acuity. The geometric mean postoperative day 1 UCVA was 20/25 in the 130-microm head group compared to 20/26 in the 160-microm head group. The only flap complication in the series was a single partial flap in the 160-microm head group.

CONCLUSIONS

LASIK with a 130-microm head (thin-flap LASIK) is as visually effective and safe as when using a 160-microm head with the BD K-3000 microkeratome.

Automated Lamellar Keratoplasty for Recurrent Granular Corneal Dystrophy After Phototherapeutic Keratectomy

PURPOSE

To evaluate the safety and efficacy of automated lamellar keratoplasty for the treatment of recurrent granular corneal dystrophy after phototherapeutic keratectomy (PTK).

METHODS

We performed a prospective interventional noncomparative case study of nine eyes (seven patients) with severe recurrent granular corneal dystrophy after PTK. An automated microkeratome was used to cut partial-thickness sections through the anterior surface of the donor and host corneas. The donor disc was placed on the recipient bed with four or eight interrupted sutures. The sutures were removed between 4 and 6 weeks postoperatively. Visual acuity, corneal clarity, corneal thickness, and corneal topography were assessed before and at different time points after surgery.

RESULTS

During a mean follow-up period of 18.9 +/- 4.1 months, all grafts were transparent without visible opacity at the interface, and no serious complications occurred. In all cases, the visual acuity improved: seven eyes had best spectacle-corrected visual acuity of > or = 20/40; two eyes reached 20/25. At last follow-up > 12 months postoperatively, the mean corneal refractive power had significantly increased by 2.34 +/- 0.93 diopters (D) (P<.001), and the corneal astigmatism significantly decreased by 0.91 +/- 0.98 D (P<.05). The mean corneal thickness was 477.4 +/- 26.9 microm preoperatively and 507.8 +/- 23.4 microm at last follow-up (P<.001).

CONCLUSIONS

Our findings suggest that automated lamellar keratoplasty for the treatment of recurrent granular corneal dystrophy is a safe and effective method of improving visual acuity, but recurrence remains a risk.

Changes of posterior corneal astigmatism and tilt after myopic laser in situ keratomileusis

PURPOSE

The purpose of this study was to assess the changes of posterior corneal astigmatism and tilt after laser in situ keratomileusis (LASIK) and to correlate these changes with the amount of correction and the residual stromal bed thickness.

METHODS

This prospective nonrandomized (self-controlled) comparative trial included 57 eyes from 14 females and 15 males, whose mean age (+/- standard deviation [SD]) at the time of surgery was 33 +/- 9 years (range, 19-53), with a spherical equivalent (SEQ) of -1.00 to -15.50 (mean, -5.07 +/- 2.81) diopters (D). All LASIK procedures were accomplished with the Keratom II Coherent-Schwind excimer laser and the Moria Model One microkeratome (150-microm head). Subjective refractometry, Orbscan slit-scanning corneal topography analysis, and pachymetry were performed before and 3 months after LASIK for myopia (n= 35; -1.00 to -15.50 D [mean, -4.75 +/- 3.07]) or myopic astigmatism (n= 22; sphere, 0.00 to -9.75 D [mean, -4.75 +/- 2.36]; cylinder, -0.75 to -3.50 D [-1.68 +/- 0.86]). Intended ablation depth ranged from 12 to 108 (mean, 48 +/- 22) microm. Topographic raw data were decomposed into a set of Zernike polynomials as published in detail previously, and parameters for detection of asymmetric mechanical deformation of the cornea were derived. Posterior corneal astigmatism and tilt before and after LASIK were compared, and changes in these variables were correlated with the SEQ change (DeltaSEQ) and the residual corneal bed thickness (RBT).

RESULTS

The RBT after LASIK ranged from 186 to 373 (mean, 280 +/- 42) microm. Overall, astigmatism (0.19 +/- 0.07 D/0.22 +/- 0.13 D; p= 0.80) and tilt (3.58 +/- 0.35 degrees /3.65 +/- 0.48 degrees; p= 0.61) did not change significantly by 3 months after LASIK. In eyes with RBT < or =250 microm, the average change in astigmatism (0.05 +/- 0.11 versus 0.01 +/- 0.13 D; p= 0.46) and tilt (0.21 +/- 0.45 degrees versus 0.04 +/- 0.55 degrees; p= 0.30) was not greater than in eyes with RBT > 250 microm. Change in astigmatism (p= 0.19) and tilt (p= 0.56) did not correlate with the RBT during LASIK.

CONCLUSIONS

Zernike decomposition of topographic height data discloses that no significant asymmetric mechanical deformation of the posterior corneal curvature occurs after myopic LASIK. Further studies with long-term follow-up are needed to clarify whether this symmetry of the posterior corneal surface can indeed be preserved over time after LASIK if the RBT is < 250 microm.

Posterior corneal curvature changes after myopic laser in situ keratomileusis

OBJECTIVE

To assess the posterior corneal power and asphericity changes after myopic laser in situ keratomileusis (LASIK) and to correlate these changes with the amount of correction and the residual stromal bed thickness.

DESIGN

Prospective nonrandomized (self-controlled) comparative study.

PARTICIPANTS

Fifty-seven eyes of 14 women and 15 men, mean age at the time of surgery 33 +/- 9 (range, 19-53) years with a spherical equivalent (SEQ) of -1.00 to -15.50 (mean, -5.07 +/- 2.81) diopters (DI).

INTERVENTION

All procedures were performed with the Keratom II Coherent-Schwind excimer laser and and the Moria Model One microkeratome (150-microm head). Subjective refractometry, Orbscan slit scanning corneal topography analysis and pachymetry were performed before and 3 months after LASIK for myopia (n=35, -1.00 to -15.50 D, mean -4.75 +/- -3.07 D) or myopic astigmatism (n=22, sphere 0.00 to -9.75 D, mean -4.75 +/- 2.36 D; cylinder -0.75 to -3.50 D, mean -1.68 +/- 0.86 D). Intended ablation depth ranged from 12 to 108 (mean, 48 +/- 22) microm. Topographic raw data were decomposed into a set of Zernike polynomials as published in detail previously, and parameters potentially indicative for detection of a "mild keratectasia" were derived.

MAIN OUTCOME MEASURES

Posterior central corneal power and asphericity before and after LASIK were compared, and changes of these variables were correlated with the SEQ change (deltaSEQ)and the residual corneal bed thickness RBT).

RESULTS

The mean RBT after LASIK was 280 +/- 42 microm. Overall, change of posterior power (-6.28 +/- 0.22 D/ -6.39 +/- 0.23 D, P=0.02) was statistically significant and change of asphericity (0.98 +/-0.07/1.14 +/- -.20, P<0.0001) was highly significant. In eyes with RBT < or =250 microm, the average change of posterior central power (-0.20 +/- 0.10 D vs. -0.08 +/- 0.18 D) was significantly greater than in eyes with RBT >250 microm (P=0.003). The change of posterior corneal power correlated significantly with deltaSEQ (P=0.004) and the RBT (P=0.002).

CONCLUSIONS

Increased negative keratometric diopters and oblate asphericity of the posterior corneal curvature suggest that mild "keratectesia" of the cornea may be common early after LASIK. Further stuudies with longer follow-up are required to clarify whether this biomechanical deformation is progressive and whether a residual bed thickness of >250 microm can completely prevent it.