Perry S. Binder

Flap dimensions created with the IntraLase FS laser

Purpose: To assess the safety and predictability of the IntraLase femtosecond laser to create accurate flap thickness and diameter. Setting: Clinical office‐based practice. Methods: In the first 103 eyes in which flaps were created with the IntraLase laser, the flap thickness was measured by the ultrasonic difference between the preoperative and post‐flap‐creation central corneal thickness and the flap diameter was measured with calipers. Results: As the attempted flap thickness decreased from 140.0 &mgr;m to 110.0 &mgr;m in 10.0 &mgr;m increments, the mean flap thickness decreased from 132.5 &mgr;m to 125.0 &mgr;m, with standard deviations decreasing from ±18.5 to ±12.0 &mgr;m. The mean flap diameter differed from the attempted diameter by less than 0.03 &mgr;m in all but the 130.0 &mgr;m group. Two slipped flaps and 20 cases of interface inflammation occurred early in the series. Conclusions: The IntraLase laser, while adding technical complexity to the laser in situ keratomileusis procedure, is able to predictably create flap diameters, hinge location, and flap thickness while eliminating the risk for cap perforations. The technique of flap elevation affects rapidity of visual recovery.

Ectasia after laser in situ keratomileusis.

&NA; Eighty‐five cases of post laser in situ keratomileusis ectasia were reviewed and analyzed. Cases of keratoconus or forme fruste keratoconus were eliminated; many remaining case reports lacked key information. The current literature is unable to define a specific residual corneal thickness or a range of preoperative corneal thickness that would put an eye at risk for developing ectasia. The most logical cause for eyes without preexisting pathology to develop ectasia is a postablation stromal thickness that is mechanically unstable; this “minimal” thickness is probably specific to each eye. The preoperative and postoperative corneal thickness, measured flap thickness, and microkeratome and laser parameters used in a given case are required to determine the range of residual corneal thickness that puts the eye at risk for developing ectasia. Other as yet undetermined factors may play a role in the development of this complication.

Keratoconus and Corneal Ectasia After LASIK

From Gordon Binder Weiss Vision Institute, San Diego, Calif (Binder); Minnesota Eye Consultants, Minneapolis, Minn (Lindstrom); Emory University, Atlanta, Ga (Stulting); Ophthalmic Consultants of Long Island, Rockville Centre, NY (Donnenfeld); Tufts New England Medical Center, Boston, Mass (Wu); Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, Md (McDonnell); and Cornea Genetic Eye Institute, Cedars Sinai Medical Center, Los Angeles, Calif (Rabinowitz).

One thousand consecutive IntraLase laser in situ keratomileusis flaps.

PURPOSE: To measure laser in situ keratomileusis (LASIK) flap dimensions created with the IntraLase FS (IL) laser (Intralase Corporation). SETTING: Private practice, San Diego, California, USA. METHODS: Consecutive LASIK flaps created with the IL were measured with subtraction ultrasound at primary and enhancement surgeries. Data were stored in Outcomes Analysis Software and analyzed using MS Excel (Microsoft Corporation) and SSPS software. RESULTS: The mean achieved flap thickness exceeded the attempted by 9.4 to 34.3 μm. The standard deviation varied from ±10.2 to ±21.7 μm. Preoperative corneal thickness and power did not affect achieved flap thickness. Seventy‐three percent of mate eye flaps were within ±15 μm of each other for the 90 μm attempted. The same flaps measured at enhancement were thicker than the primarily measured flaps (n = 58). Diffuse lamellar keratitis and slipped flaps were eliminated with experience. There were no decentered or irregular flaps, epithelial defects, or flap perforations. CONCLUSIONS: Compared with published results of mechanical microkeratomes, the IL reduced the standard deviation of flap thickness as well as the achieved range. It eliminated physical complications associated with mechanical flap creation, and the impact of preoperative pachymetry and corneal power, thereby permitting more myopia to be corrected without risking deep ablations.

A Prospective, Contralateral Eye Study Comparing Thin-Flap LASIK (Sub-Bowman Keratomileusis) with Photorefractive Keratectomy

PURPOSE To determine the differences in the visual results, pain response, biomechanical effect, quality of vision, and higher-order aberrations, among other parameters, in eyes undergoing either photorefractive keratectomy (PRK) or thin-flap LASIK/sub-Bowman keratomileusis (SBK; intended flap thickness of +/-100 microm and 8.5-mm diameter) at 1, 3, and 6 months after surgery. DESIGN A contralateral eye pilot study. PARTICIPANTS Fifty patients (100 eyes) were enrolled at 2 sites. METHODS The mean preoperative spherical refraction was -3.66 diopters (D) and the mean cylinder was -0.66 D for all eyes. Eyes in the PRK group underwent 8.5-mm ethanol-assisted PRK, whereas in eyes in the SBK group, an 8.5-mm, (intended) 100-microm flap was created with a 60-kHz IntraLase femtosecond laser (Advanced Medical Optics, Santa Ana, CA). All eyes underwent a customized laser ablation using an Alcon LADARVision 4000 CustomCornea excimer laser (Alcon Laboratories, Fort Worth, TX). MAIN OUTCOME MEASURES Preoperative and postoperative tests included best spectacle-corrected visual acuity, uncorrected visual acuity (UCVA), corneal topography, wavefront aberrometry, retinal image quality, and contrast sensitivity. Patients completed subjective questionnaires at each visit. RESULTS One- and 3-month UCVA results showed a statistically significant difference: SBK, 88% 20/20 or better vs. 48% 20/20 or better for PRK. At 6 months, UCVA was 94% 20/20 or better for PRK and 92% for SBK. At 1 and 3 months, the SBK group had lower higher-order aberrations (coma and spherical aberration; P<or=0.05); at 1, 3, and 6 months, there was no statistically significant difference in spherical aberration and vertical and horizontal coma between the 2 groups. CONCLUSIONS At the 1-month follow-up, the thin-flap/SBK group demonstrated clinically and statistically significant better visual acuity than the PRK group. By 3 months, the vision in the 2 groups had begun to equalize, although the SBK eyes continued to have better vision. At 6 months, there were no statistical differences between the 2 groups. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosure may be found after the references.

Estimating residual stromal thickness before and after laser in situ keratomileusis

Purpose: To determine the factor(s) that influences measurement of residual stromal thickness (RST) after laser in situ keratomileusis (LASIK) surgery. Setting: Clinical office‐based excimer laser refractive surgery center. Methods: In this retrospective comparative interventional case study of 6235 eyes, ultrasonic corneal pachymetry was performed immediately before and after flap creation and immediately after laser ablation in the primary procedure and after 647 enhancements. Differences in the methods for calculating RST were compared statistically. Results: Using the RST measured at enhancement as the actual RST, measurements of RST immediately after laser ablation underestimated residual thickness due to laser‐induced stromal dehydration and microkeratome effects (P<.001). Estimates of RST using a “standard” or estimated flap thickness were less accurate predictors of residual thickness (P<.001) than use of the theoretical laser resection with a measured flap thickness (RST–4) (P = .78) or a modified flap thickness subtracted from the postoperative corneal thickness (RST–8) (P = .98), which provided the best RST estimates. Conclusions: Before LASIK, the best means of estimating RST is to subtract the theoretical laser resection obtained from the laser computer and the expected flap thickness normally obtained with a given microkeratome system from the preoperative central corneal thickness. After LASIK, the most accurate means of calculating RST is to subtract the original flap thickness from the postoperative central corneal thickness.

Role of flap thickness in laser in situ keratomileusis enhancement for refractive undercorrection

PURPOSE: To determine which preoperative and/or perioperative factors determine the need for an enhancement for refractive undercorrection in laser in situ keratomileusis (LASIK) for spherical or spherocylindrical myopia. SETTING: Clinical refractive surgery outpatient facility. METHODS: In this nested case‐control study within a retrospective cohort, 3850 of the 9777 eyes operated on between January 1996 and August 2005 who met the selection criteria were studied. Only patients whose refractive goal was plano were included. Control eyes were those whose latest spherical equivalent (SE) refraction was within ±0.37 diopters (D) of emmetropia. Cases were defined as enhancements for undercorrection with an SE refraction worse than or equal to −0.50 D performed less than 6 months following the primary surgery. RESULTS: Factors associated with enhancement included increasing patient age (odds ratio [OR] = 1.048, P<.001), decreasing follow‐up time (OR = 0.994, P<.001), increasing minus laser sphere (OR = 0.700, P<.001) and cylinder settings (OR = 0.718, P<.001), female sex (OR = 1.112, P = .046), and corneal toricity (OR = 1.237, P = .012). The Summit laser had a significant risk for enhancement (OR = 1.726, P<.001) compared with the Visx laser, whereas the Wavelight Allegretto had a lowered risk (OR = 0.630, P = .049). Enhancement risk with the Autonomous was no different from that with the Visx (OR = 1.120, P = .342). Increasing flap thickness (OR = 1.009, P<.001) was more strongly associated with enhancement risk than residual stromal bed thickness. CONCLUSIONS: After controlling for patient age, time to follow‐up or surgery, corneal cylinder, sphere and cylinder laser settings, laser manufacturer, patient sex, and corneal thickness, increasing flap thickness was found to be a more important predictor of enhancement for refractive undercorrection than residual stromal thickness.

Femtosecond Laser-Assisted Intra-Corneal Drug Delivery

Abstract Purpose: To present a case of fungal keratitis that was successfully treated with direct intrastromal medication delivery through a corneal incision created with the femtosecond laser. Methods: A 71-year-old female patient with recurrent episodes of an unresponsive, deep stromal keratitis for six months’ duration, resistant to various therapeutic approaches, was referred to our institute. The 150 kHz Intralase iFS laser (Abbott Medical Optics Inc., Santa Ana, CA) was used to create a corneal pocket in an attempt to permit drug delivery directly into the corneal abscess. Results: Five days after the intrastromal injections, the clinical condition was improved. Two years after the procedure, the cornea is stable and free of any clinical signs or symptoms of recurrence. Conclusions: In this case report, an alternative application of femtosecond laser technology is presented, performing intrastromal drug delivery through a corneal incision for the treatment of fungal keratitis.