Ioannis G. Pallikaris

Excimer Laser In Situ Keratomileusis and Photorefractive Keratectomy for Correction of High Myopia

BACKGROUND The purpose of this research was to study the visual outcome of excimer laser photorefractive keratectomy and laser in situ keratomileusis (LASIK) for the correction of moderate and high myopia. METHODS Twenty partially-sighted eyes of 20 patients were divided into two groups, LASIK and photorefractive keratectomy. Ten eyes underwent LASIK and the other 10 photorefractive keratectomy. Follow up was at 1, 3, 6, and 12 months. The LASIK technique included a nasally based, 150 microns thick, 8.0 x 9.0 mm diameter, truncated, disc-shaped corneal flap created with a microkeratome; and the ablation of the stroma with a 193-nanometer ArF excimer laser. The flap was returned to its original position and held in place by apposition. The photorefractive keratectomy technique included mechanical removal of the epithelium and ablation of the stroma with a 193-nanometer ArF excimer laser. RESULTS LASIK series: One eye had a ruptured globe during the second postoperative month and was excluded from the study. The preoperative spherical equivalent refraction ranged from -10.62 to -25.87 diopters (D). The attempted correction ranged from -8.00 to -16.00 D. Postoperative refraction and corneal topography stabilized between 4 and 12 weeks. Spectacle-corrected visual acuity was within 1 Snellen line of preoperative in all eyes. The refraction in six eyes (66.6%) was within +/- 1.00 D of the intended correction, and in eight eyes was within +/- 2.00 D (88.8%) at 12 months. The mean attempted correction (11.40 +/- 2.60 D) was close to the mean achieved correction at 12 months (11.96 +/- 3.10 D). The mean postoperative refractive astigmatism (1.50 +/- 0.97; range, 0.25 to 3.50 D) was close to the preoperative astigmatism (1.70 +/- 1.15; range, 0 to 3.75 D). Endothelial cell density at 12 months showed an average 8.67% of cell loss. All eyes showed a clear interface. Photorefractive keratectomy series: The preoperative spherical equivalent refraction ranged from -10.75 to -23.12 D. The attempted correction ranged from -8.80 to -17.60 D. Postoperative refraction showed regression throughout the follow-up period, and corneal topography did not stabilize. Spectacle-corrected visual acuity was within 1 Snellen line in eight eyes. Two eyes lost 2 and 3 Snellen lines. One eye was within +/- 1.00 D, and three eyes (30%) were within +/- 2.00 D of the intended correction at 12 months. The achieved correction mean (7.17 +/- 5.29 D) was 61% of the attempted mean (11.72 +/- 2.81 D) at 12 months. The postoperative refractive astigmatism (1.80 +/- 0.95; range, 0.50 to 4.00 D) was very close to the preoperative (1.90 +/- 1.33; range, 0 to 5.00 D). Endothelial cell density showed an average of 10.56% cell loss at 12 months. The mean haze at 12 months was 1.2 (0 to 4 scale). CONCLUSION LASIK, although more complicated because of the use of a microkeratome, was more effective than photorefractive keratectomy in higher myopes. LASIK created less corneal haze. The refraction was more stable with LASIK in the correction of high myopia. Its predictability was three times that of PRK.

Corneal ectasia induced by laser in situ keratomileusis

Purpose: To identify factors that can lead to corneal ectasia after laser in situ keratomileusis (LASIK). Setting: University refractive surgery center. Methods: In this retrospective study, the charts of all patients (2873 eyes) who had LASIK between May 1995 and November 1999 were reviewed. Fourteen patients (19 eyes, 0.66%) developed post‐LASIK ectasia. The mean follow‐up was 16.32 months (range 6 to 42 months). Results: No patient with an attempted correction less than 8.00 diopters or a residual corneal bed thickness greater than 325 &mgr;m experienced post‐LASIK ectasia. There was a statistically significant positive correlation between corneal residual bed thickness and increasing patient age. Conclusion: Despite the limitations of the small sample size, the studys results suggest that parameters besides residual corneal bed thickness (eg, age, attempted correction) may have to be considered to avoid post‐LASIK ectasia.

Induced optical aberrations following formation of a laser in situ keratomileusis flap

Purpose: To determine how refractive error, visual acuity, and high‐order aberrations (3rd‐ and 4th‐order) are affected by the formation of a lamellar corneal flap during laser in situ keratomileusis (LASIK). Setting: University refractive surgery center. Methods: The effect of lamellar corneal flap formation was analyzed in 15 myopic eyes (mean preoperative refraction −4.72 diopters [D] [range −1.25 to −7.25 D]). The flap was created using a 2‐step procedure: (1) a nasally hinged lamellar corneal flap was created; (2) the flap was lifted and stromal ablation performed 2 months after the flap was made. A Hartmann‐Shack aberrometer was used to measure the aberrations. Results: There was no significant change in the refractive error (spherical equivalent pre‐flap −4.72 ± 1.99 D and post‐flap −4.62 ± 1.99 D [P = .28]) or visual acuity (pre‐flap uncorrected visual acuity [UCVA] 0.07 and best corrected visual acuity [BCVA] 0.96; post‐flap UCVA 0.08 and BCVA 0.95 [P = .16 and P = .33, respectively]). A statistically significant increase in total higher‐order wavefront aberrations was observed following flap formation (root mean square pre‐flap 0.344 ± 0.125 and post‐flap 0.440 ± 0.221 [P = .04]). Conclusion: Flap formation during LASIK can modify the eyes existing natural higher‐order aberrations (especially spherical and coma‐like aberrations along the axis of the flaps hinge), while visual acuity and refractive error remain unaffected.

Management of keratoconus with Intacs

PURPOSE To prospectively study the effects of the use of Intacs microthin prescription inserts for the management of keratoconus. DESIGN Prospective nonrandomized clinical trial. METHODS Thirty-three eyes of 26 keratoconus patients (17 males and 9 females) ages 21 to 51 years (mean age, 32 +/- 9.7 years) were included in the current study. All patients had clear central corneas and contact lens intolerance. Patients were excluded if any of the following criteria applied after the preoperative examination: previous intraocular or corneal surgery; history of herpes keratitis; diagnosed autoimmune disease; and systemic connective tissue disease. Two Intacs segments of 0.45-mm thickness were inserted in the cornea of each eye, aiming at embracing the keratoconus area to try to achieve maximal flattening. Preoperative examination included uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), manifest refraction, keratometric data, and corneal topography. RESULTS Intacs were successfully implanted in all eyes. In one eye Intacs were removed after 3 months because of their improper (superficial) placement. The follow-up ranged from 1 to 24 months (mean: 11.3 months). The mean UCVA significantly improved from 0.13 +/- 0.14 (range, counting fingers [CF]-0.5) to 0.39 +/- 0.27 (range, CF-1.0) (P <.01). Of 33 eyes, 2 eyes lost 1 line of UCVA, and 3 eyes maintained the preoperative UCVA, whereas the rest (28 eyes) experienced a 1- to 10-line gain. The mean BCVA also improved from 0.47 +/- 0.31 (range, CF-1.0) to 0.64 +/- 0.26 (range, 0.1-1.0) (P <.01). Of 33 eyes, 4 eyes experienced 1- to 2-line loss of BCVA, 4 eyes maintained the preoperative BCVA, whereas the rest (25 eyes), experienced a 1- to 6-line gain. Of 3 patients (3 eyes) with unsatisfactory results, 1 patient improved with one segment removal and in 2 patients the segments were permanently removed. One of these eyes underwent successful PKP. CONCLUSIONS With mean follow-up of 11.3 months, intracorneal ring segments implantation improved UCVA and BCVA in the majority of the keratoconus patients. Even though the results are encouraging, concern still exists regarding the predictability as well as the long-term effect of such an approach for the management of keratoconus.

Simultaneous topography-guided PRK followed by corneal collagen cross-linking for keratoconus.

PURPOSE To present the results after simultaneous photorefractive keratectomy (PRK) followed by corneal collagen cross-linking (CXL) for progressive keratoconus. METHODS Twelve patients (14 eyes) with progressive keratoconus were prospectively treated with customized topography-guided PRK with the Pulzar Z1 (wavelength 213 nm, CustomVis) immediately followed by corneal collagen CXL with the use of riboflavin and ultraviolet A irradiation. RESULTS Mean follow-up was 10.69+/-5.95 months (range: 3 to 16 months). Mean preoperative spherical equivalent refraction (SE) was -3.03+/-3.23 diopters (D) and defocus was 4.67+/-3.29 D; at last follow-up SE and defocus were statistically significantly reduced to -1.29+/-2.05 D and 3.04+/-2.53 D, respectively (P<.01). Preoperative mean (logMAR) uncorrected visual acuity was 0.99+/-0.81 and best spectacle-corrected visual acuity was 0.21+/-0.19, which improved postoperatively to 0.16+/-0.15 and 0.11+/-0.15, respectively. The mean steepest keratometry was reduced from 48.20+/-3.40 D preoperatively to 45.13+/-1.80 D at last follow-up. CONCLUSIONS Simultaneous PRK followed by CXL seems to be a promising treatment capable of offering functional vision in patients with keratoconus.

Primary deep sclerectomy versus primary deep sclerectomy with the use of mitomycin C in primary open-angle glaucoma.

PurposeTo prospectively study and compare the effectiveness and the safety of primary deep sclerectomy with and without the use of mitomycin C in eyes with open-angle glaucoma. Patients and MethodsA total of 90 eyes of 90 patients with primary open-angle glaucoma or pseudoexfoliative glaucoma underwent deep sclerectomy. Patients were enrolled consecutively and assigned randomly to undergo deep sclerectomy without the use of mitomycin C (DS group) and deep sclerectomy with the application of mitomycin C (DSMMC group) in a concentration of 0.2 mg/mL for 2.5 minutes, before the superficial scleral flap formation. ResultsThe intraocular pressure was significantly decreased by 7.13 mm Hg or 27.59% in the DS group and by 11.68 mm Hg or 42.25% in the DSMMC group at the end of the follow-up period. The intraocular pressure reduction in the DSMMC group was statistically significant when compared with that in the DS group (P <0.05). The complete (IOP <22 mm Hg without medication) and qualified (IOP < 22 mm Hg with or without medication) success rates at the end of the follow-up period were 42.5% and 72.5% in the DS group and 50% and 95% in the DSMMC group. The qualified success rate in the DSMMC group was statistically significant when compared with that in the DS group. Differences in complications (choroidal detachment, hyphema, leakage) seen between the two groups were statistically nonsignificant. A hemorrhagic detachment of the Descemet membrane was observed in one eye in the DSMMC group. ConclusionsThe use of intraoperative mitomycin C during deep sclerectomy significantly reduced the postoperative IOP and increased the success rate of the procedure.

Epi-LASIK: Comparative histological evaluation of mechanical and alcohol-assisted epithelial separation

Purpose: To compare the effect of mechanical and alcohol‐assisted excision on the histological ultrastructure of epithelial disks from human corneas. Setting: Vardinoyiannion Eye Institute of Crete, University of Crete, Medical School, Crete, Greece. Methods: Ten eyes of 10 patients were deepithelialized by 1 of 2 two techniques. In 6 eyes, a customized instrument was used to mechanically separate the epithelial layer. In 4 eyes, the epithelial disks were obtained using the conventional laser‐assisted subepithelial keratectomy (LASEK) technique; that is, with alcohol concentrations of 15% and 20%. All specimens were assessed by light and electron microscopy, and the histological findings of the 2 methods were compared. Results: Transmission electron microscopy showed that when the epithelial disks were excised by mechanical separation, the lamina densa and lamina lucida were preserved and the hemidesmosomes had normal morphology along almost the entire length of the basement membrane. The basal epithelial cells of the separated epithelial disks showed minimal trauma and edema. Specimens obtained using 15% and 20% alcohol concentrations showed formation of cytoplasmic fragments of the basal epithelial cells, enlargement of the intercellular spaces, and extensive discontinuities in the basement membrane, which was excised at the level of the lamina lucida. Conclusions: Mechanical separation did not affect the normal cell morphology of the excised epithelial disks. Transmission electron microscopy of the specimens proved the manual technique is less invasive to epithelial integrity than LASEK using either alcohol concentration.

Advances in subepithelial excimer refractive surgery techniques: Epi-LASIK.

The reports of an increasing incidence of iatrogenic ectasia, the evolution of wavefront aberrometry, and the suggestion that the laser in situ keratomileusis flap could lead to unpredictable biomechanical corneal changes have renewed interest in surface ablation and have set the stage for the introduction of alternative photorefractive treatment modalities. The theoretical advantage of surface procedures, such as laser epithelial keratomileusis that preserve the epithelial button, stems from the repositioning of the epithelial flap over the laser-ablated corneal surface. This epithelial sheet is thought to act as a natural contact lens that decreases postoperative pain and haze formation. Epipolis laser in situ keratomileusis is an alternative modality of epithelial separation with the use of a device that features a blunt oscillating blade. This surgical approach does not require the use of alcohol for epithelial loosening.

Laser in situ keratomileusis to treat myopia: Early experience

Purpose: To present our early experience in methodology and results of laser in situ keratomileusis (LASIK) in treating moderate and high myopia. Setting: Vardinoyannion Eye Institute of Crete and the Cornea and Refractive Surgery Service, Department of Ophthalmology, Heraklion University Hospital, Crete, Greece. Methods: Forty‐three moderately to highly myopic eyes had LASIK. Follow‐up was between 12 and 24 months. The Draeger’s rotor microkeratome was used to create a 150 wm thick 8.5 × 9.5 mm corneal flap, and the stromal bed was ablated for the myopic correction using the Munnerlynn photorefractive keratectomy algorithm. The preoperative spherical equivalent ranged from −8.50 to −25.87 diopters (D). Attempted correction ranged from 8.00 to 16.00 D. Four eyes developed complications (i.e., anterior chamber perforation and keratoconus, intrastromal epithelial cells, macular lacquer cracks, and transient endothelial decompensation) and were excluded from the study. The remaining 39 eyes were retrospectively divided into two groups‐A (21 eyes) and B (18 eyes)‐according to the preoperative spherical equivalent (higher or lower than −14.00 D, respectively). Results: Refraction and corneal topography stabilized between 4 and 12 weeks postoperatively. Best spectacle‐corrected visual acuity was within one Snellen line in all eyes. At 24 months, 19 eyes (79.2%) were within 2.00 D of intended correction. Attempted correction (12.20 D ± 2.30 [SD]) was very close to mean achieved correction at 12 and 24 months (11.60 ± 2.65 D). Mean postoperative astigmatism at 24 months (1.41 ± 0.87 D; range 0 to 3.50 D) was close to the mean preoperative value (1.52 ± 1.08 D; range 0 to 4.00 D). An average 2.43% endothelial cell loss was observed at 24 months. Conclusion: With limitations, LASIK could be considered as a treatment for moderate and high myopia.

Comparison of corneal sensation following photorefractive keratectomy and laser in situ keratomileusis.

Purpose: To evaluate the effect of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) on corneal sensation. Setting: Eye Institute, Medical School of the University of Crete, Heraklion, Greece, and Orasis, Hellenic Eye Center of Athens, Greece. Methods: In a masked study, corneal sensation was measured with the CochetBonnet aesthesiometer in 40 consecutive patients 6 to 12 months following PRK and LASIK (60 mm constitutes normal reading and <40 mm, abnormal). Results: After 6 to 12 months, the mean corneal sensation following PRK was 39.2 mm (range 30 to 55 mm) (mean 9.5 months) and after LASIK, 53.6 mm (range 40 to 60 mm) (mean 9.3 months). The mean correction attempted for PRK was 7.05 diopters (D) (range 2.5 to 12.0 D) and for LASIK, 11.71 D (range 6.0 to 20.0 D). Conclusion: In this group of patients, with correction of primarily severe myopia, corneal sensation was significantly greater after LASIK than after PRK.