K. M. Rocha

Thresholds for Interface Haze Formation After Thin-Flap Femtosecond Laser In Situ Keratomileusis for Myopia

PURPOSE To evaluate the risk factors for interface haze formation after thin-flap femtosecond laser--laser in situ keratomileusis (LASIK). DESIGN Prospective case series. METHODS One hundred and ninety-nine consecutive eyes that underwent femtosecond laser LASIK with a LADAR 4000 excimer laser (Alcon Laboratories, Fort Worth, Texas, USA), were analyzed from January 1 to April 30, 2008. Treated eyes were divided into 2 groups according to desired flap thickness: 90 microm (106 eyes), and 100 to 110 microm (93 eyes). Cycloplegic refraction, spherical equivalent (SE), uncorrected visual acuity, best spectacle-corrected visual acuity (BSCVA), depth of ablation, central corneal thickness, flap thickness (optical coherence tomography), Scheimpflug images (Pentacam; Oculus Inc, Lynnwood, Washington, USA), and light scattering were assessed in all eyes that developed haze postoperatively. RESULTS Haze was observed in 32 eyes treated for moderate to high myopia (SE -6.23 +/- 1.67 diopters and depth of ablation 94.6 +/- 22.9 microm) at 3 months postoperatively. Ultra-thin IntraLASIK flaps (<or=90 microm) and younger age were strongly associated with risk of postoperative haze (P = .003 and P = .01, respectively). SE, depth of ablation, and self-reported history of dry eyes were not independently associated with an increased risk of corneal haze. Patients who developed any degree of haze had significantly higher logarithmic value of scatter (log S) values (mean difference =0.24 units, P < .0005) compared with those who did not develop haze. The mean postoperative BSCVA was good in all eyes with haze (logarithm of the minimal angle of resolution 0.05 +/- 0.04). CONCLUSION Interface haze is associated with an ultra-thin femtosecond laser flap setting of 90 microm and younger age among eyes following LASIK for myopia.

Incidence of rainbow glare after laser in situ keratomileusis flap creation with a 60 kHz femtosecond laser

PURPOSE: To report the incidence of and factors associated with rainbow glare after laser in situ keratomileusis (LASIK) flap creation with a 60 kHz femtosecond laser. SETTING: Department of Refractive Surgery, Cleveland Clinic Cole Eye Institute, Cleveland, Ohio, USA. METHODS: Consecutive patients having LASIK by the same surgeon were questioned during postoperative examinations or by telephone about postoperative rainbow glare (radiating colors around a white light at night). Femtosecond laser (IntraLase) settings included pulse frequency 60 kHz, flap thickness 90 to 110 μm, and spot/line separation 8 μm. Raster energy was 0.8 μJ (75% of eyes) and 1.0 to 1.1 μJ (25%). Excimer laser ablation was performed with the LADAR 4000 or 6000 platform using custom or conventional treatments. RESULTS: Of 260 consecutive patients, 256 (98.5%) were successfully contacted. Fifteen patients (28 eyes) reported postoperative rainbow glare (5.8%), described as 4 to 12 bands of color around a white light, with 6 bands most common. The symptom did not correlate with refractive error, age, or sex but was more frequent at 1.0 μJ or 1.1 μJ raster energy (11.6%) than at 0.8 μJ (4.1%). The incidence followed a bimodal distribution, with the first grouping due to inadequate alignment and higher energy just after laser installation and the second just before a later maintenance service call. CONCLUSION: Rainbow glare is a mild optical side effect of femtosecond LASIK. In this study, higher raster energy levels and length of time between service calls were associated with the occurrence of rainbow glare.

Applications of wavefront technology

&NA; This review of wavefront technology looks at 2 major aspects. The first is the basics and principles of the optics of the eye, how to decompose the wavefront in a more adequate way for interpretation, and how these aberrations affect the visual acuity. It also addresses the diversity and complexity of wavefront sensors; how these devices transform the principles into clinically useful data, with the advantages and limitations of each system. The second major aspect is the clinical uses of the technology: wavefront‐guided and newer and enhanced profiles related to wavefront as well as the limitations of the technology. Finally, recent innovations made possible by wavefront technology that are not limited to refractive surgery are reviewed. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Spectral-domain optical coherence tomography epithelial and flap thickness mapping in femtosecond laser-assisted in situ keratomileusis.

PURPOSE To evaluate the change of epithelial and flap thickness after femtosecond laser-assisted in situ keratomileusis (LASIK) using spectral-domain optical coherence tomography (SD OCT) in correlation with the spherical equivalent refraction treated and clinical outcomes. DESIGN Prospective, randomized, contralateral-eye study. METHODS Forty myopic eyes underwent LASIK using an excimer laser with refraction ranging from -1.00 to -7.25 diopters (mean -3.25±1.9). Flap creation was randomized between eyes, using the IntraLASE FS60 laser (IL) in 1 eye and WaveLight FS200 laser (FS) in the contralateral eye. SD OCT was used to evaluate the epithelial and flap thickness profiles and corneal power preoperatively and at 1 week and 1, 3, and 9 months postoperatively. Manifest and wavefront refractions were performed at each postoperative visit. RESULTS Statistically significant epithelial thickening was observed in both IL and FS groups as early as 1 month postoperatively (P=.033 and P=.042), but this stabilized between 3 (P=.042 and P=.035) and 9 months (P=.043 and P=.041). Femtosecond-LASIK flaps were thicker in the IL group in comparison to the FS group at 3 and 9 months postoperatively (P=.003 and P=.005, respectively). There was a statistically significant correlation between the magnitude of preoperative myopic refraction and the central epithelial thickness at 1, 3, and 9 months (Pearson correlation coefficients 0.485, 0.587 and 0.576) (P=.0021, P=.0010, and P=.0011), respectively. SD OCT corneal power maps showed steepening at 3 and 9 months along with mild myopic shift. CONCLUSION Progressive epithelial and flap thickening with increased corneal power were observed after femtosecond laser-assisted in situ keratomileusis for myopia with consequent stabilization between 3 to 9 months postoperatively. The magnitude of epithelial and flap thickness remodeling correlated to the preoperative myopic refractive error.

Novel applications of an adaptive optics visual simulator in the clinical setting

Purpose: To evaluate the clinical benefit of using an adaptive optics visual simulator (AOVS) and its impact in different clinical settings. Methods: An adaptive optics visual simulator performed the experimental procedure and was used to optically introduce aberrations in 9 normal eyes for visual acuity (VA) change, and in 10 cyclopleged eyes for enhancing depth of focus (DoF). AOVS was also used to correct 20 highly aberrated eyes. Results: The correction/induction of high order aberrations (HOA) alters the best-corrected visual acuity (BCVA) by a mean of ~1 to 1.5 lines compared to the best spectacle correction. The depth of focus (DoF) was most enhanced (~2.0 D) with the introduction of negative and positive spherical aberration of 0.6 μm magnitude. The correction of HOAs in highly aberrated eyes improved BCVA by a mean of ~1.5 to 2 lines in two groups of pathological eyes. Conclusions: Aberrations have differing effects according to their clinical use. The AOVS defines the clinical response of HOAs on VA, visual perceptions and DoF.

Restoration of accommodation: new perspectives

Presbyopia is the loss of accommodative ability that occurs with age. Current accommodative theory postulates that the lens is primarily responsible for the refractive change that allows us to read. Our understanding of this process has grown substantially with the advent of new technologies, including ultrasound biomicroscopy (UBM), endoscopy, optical coherence tomography (OCT), ray-tracing and wavefront analysis. Goldberg’s Postulate incorporates all elements of the zonular apparatus into the phenomenon of accommodation. The ciliary body contracts during accommodation. Biometry has shown that the lens thickness increases and the anterior chamber depth decreases. It has also demonstrated the lens capsule steepens, as the posterior-lens surface moves backwards. In addition, there is a decrease in the distance from scleral spur to the ora serrata. UBM identified an attachment zone of the posterior zonules adjacent to the ora, and contraction of these zonules is thought to be the etiology of the decrease in distance found with accommodation. This complex action of the zonules is suspected to be reciprocal. As the same time the anterior zonules relax, reducing their tension on the lens such that the lens changes shape anteriorly, the posterior zonules contract, moving the posterior capsule backward. This vitreal-zonular complex stiffens with age, losing its elasticity. The age-related changes in these structures and their biomechanical interactions with the ciliary-lens complex may contribute to presbyopia It has been newly discovered that there are also changes in extralenticular structures which may have an impact on the loss of accommodation which were previously deemed to be of very little importance, namely the sclera and choroid. All ocular tissues are made of collagen and are impacted like all other connective tissues by age. Ocular rigidity has been correlated with age and the sclera undergoes scleral sclerosis as well as metabolic physiological stress. With the loss of elasticity, the more rigid sclera elicits compression and loading stresses upon underlying structures, specifically those related to accommodative function. Increased ocular rigidity affects other tissues as well, including ocular blood flow through the sclera and optic nerve. It has been correlated to the pathogenesis of macular degeneration and other age-related eye diseases. Ocular rigidity may not only impact the loss of visual accommodation but also have more extensive clinical significance. The impact of age on the lenticular-based model of loss of accommodation is well documented. The amount of accommodation lost with age related to extralenticular apparatus (primarily the zonules, choroid, and sclera) was only recently investigated. It is also now known that the sclera becomes less deformable during accommodation in the nasal area with age. New models suggest up to 2 diopters that might be contributed by ex tralenticular structures. To date, there has been at least up to 1-2 diopters of a loss of accommodation unaccounted for that might be contributed by extralenticular structures. The investigation improving ocular resilience for the restoration of accommodation is of clinical importance. The Laser anterior ciliary excision procedure is designed to do so by altering biomechanical scleral properties. This is achieved by creating micropores in a matrix over four oblique quadrants. The VisioLite erbium-YAG laser creates micro-excisions in critical zones of physiologic importance overlying the ciliary-lens complex. The matrix pattern of nine 600 μm laser spots in the sclera of each quadrant aims to increase plasticity in those regions across the anterior globe. The Laser anterior cilary excision primary mechanism of action is to decrease scleral resistive forces in order to restore accommodative ability in the aging eye by increasing resultant ciliary muscle constriction (Figure 1). Laboratory studies of ocular rigidity demonstrated use of a reference model, and effect of laser anterior ciliary ablation on aging porcine eyes in vitro. Investigators concluded that the scleral crosslinking method might be useful for correlation of age-related rigidity, as well as the efficacy of the laser anterior ciliary ablation procedure to decrease ocular rigidity.