PURPOSE-To characterize the in vivo epithelial thickness profile in a population of normal eyes. METHODS-An epithelial thickness profile was measured by Artemis 1 (Ultralink LLC) very highfrequency (VHF) digital ultrasound scanning across the central 10-mm diameter of the cornea of 110 eyes of 56 patients who presented for refractive surgery assessment. The average, standard deviation, minimum, maximum, and range of epithelial thickness were calculated for each point in the 10×10mm Cartesian matrix and plotted. Differences between the epithelial thickness at the corneal vertex and peripheral locations at the 3-mm radius were calculated. The location of the thinnest epithelium was found for each eye and averaged. Correlations of corneal vertex epithelial thickness with age, spherical equivalent refraction, and average keratometry were calculated. RESULTS-The mean epithelial thickness at the corneal vertex was 53.4±4.6 μm, with no statistically significant difference between right and left eyes, and no significant differences in age, spherical equivalent refraction, or keratometry. The average epithelial thickness map showed that the corneal epithelium was thicker inferiorly than superiorly (5.9 μm at the 3-mm radius, P<.001) and thicker nasally than temporally (1.3 μm at the 3-mm radius, P< 001). The location of the thinnest epithelium was displaced on average 0.33 mm temporally and 0.90 mm superiorly with reference to the corneal vertex. CONCLUSIONS-Three-dimensional thickness mapping of the corneal epithelium demonstrated that the epithelial thickness is not evenly distributed across the cornea; the epithelium was significantly thicker inferiorly than superiorly and significantly thicker nasally than temporally with a larger inferosuperior difference than nasotemporal difference. The human corneal epithelium has five to seven cell layers and an accepted central thickness of approximately 50 to 52 μm. 1 Bowman's layer, a dense collagenous layer approximately 8 to 10 μm thickness lies between the epithelium and stroma. The anterior margin of Bowman's

PURPOSE To characterize the epithelial, stromal, and total corneal thickness profile in a population of eyes with keratoconus. METHODS Epithelial, stromal, and total corneal thickness profiles were measured in vivo by Artemis very high-frequency (VHF) digital ultrasound scanning (ArcScan) across the central 6- to 10-mm diameter of the cornea on 54 keratoconic eyes. Maps of the average, standard deviation, minimum, maximum, and range of epithelial, stromal, and total corneal thickness were plotted. The average location of the thinnest epithelium, stroma, and total cornea were found. The cross-sectional semi-meridional stromal and total corneal thickness profiles were calculated using annular averaging. The absolute stromal and total corneal thickness progressions relative to the thinnest point were calculated using annular averaging as well as for 8 semi-meridians individually. RESULTS The mean corneal vertex epithelial, stromal, and total corneal thicknesses were 45.7 ± 5.9 µm, 426.4 ± 38.5 µm and 472.2 ± 41.4 µm respectively. The average epithelial thickness profile showed an epithelial doughnut pattern characterized by localized central thinning surrounded by an annulus of thick epithelium. The thinnest epithelium, stroma, and total cornea were displaced on average by 0.48 ± 0.66 mm temporally and 0.32 ± 0.67 mm inferiorly, 0.31 ± 0.45 mm temporally and 0.54 ± 0.37 mm inferiorly, and 0.31 ± 0.43 mm temporally and 0.50 ± 0.35 mm inferiorly, respectively, with reference to the corneal vertex. The increase in semi-meridional absolute stromal and total corneal thickness progressions was greatest inferiorly and lowest temporally. CONCLUSIONS Three-dimensional thickness mapping of the epithelial, stromal, and total corneal thickness profiles characterized thickness changes associated with keratoconus and may help in early diagnosis of keratoconus.

PURPOSE: To illustrate the hypothesis that epithelial thickness profi le maps could be used as an adjunctive tool to improve the sensitivity and specifi city of keratoconus screening by presenting a case series of examples. METHODS:The Artemis very high-frequency digital ultrasound arc-scanner was used to obtain epithelial thickness profi les in addition to a comprehensive ophthalmic examination to screen for keratoconus. Five case examples are presented; a normal eye, an eye with advanced keratoconus, and three cases where a diagnosis of keratoconus was uncertain based only on the ophthalmic examination.

Endokeratophakia appears to be a viable procedure for correcting hyperopia on the cornea by implantation of an extracted myopic SMILE lenticule from a donor patient. However, posterior surface changes and epithelial remodeling resulted in only 50% of the intended correction. No adverse side effects were observed following implantation of donor tissue for 1 year.

PURPOSE-To characterize the stromal thickness profile in a population of normal eyes. METHODS-Stromal thickness profile was measured in vivo byArtemis very high-frequency digital ultrasound scanning (ArcScan, Morrison, Colo) across the central 10-mm corneal diameter on 110 normal eyes. Maps of the average, standard deviation, minimum, maximum, and range of stromal thickness were plotted. The average location of the thinnest stroma was found. The crosssectional hemi-meridional stromal thickness profile was calculated using annular averaging. The absolute stromal thickness progression relative to the thinnest point was calculated using annular averaging as well as for 8 hemi-heridians individually. RESULTS-The mean stromal thickness at the corneal vertex and at the thinnest point were 465.4 ±36.9 μm and 461.8±37.3 μm, respectively. The thinnest stroma was displaced on average 0.17±0.31 mm inferiorly and 0.33±0.40 mm temporally from the corneal vertex. The average absolute stromal thickness progression from the thinnest point could be described by the quadratic equation: stromal thickness = 6.411 × radius 2 + 2.444 × radius (R 2 = 0.999). Absolute stromal thickness progression was independent of stromal thickness at the thinnest point. The increase in hemi-meridional absolute stromal thickness progression was greatest superiorly and lowest temporally.CONCLUSIONS-Three-dimensional thickness mapping of the corneal stroma and stromal thickness progression in a population of normal eyes represent a normative data set, which may help in early diagnosis of corneal abnormalities such as keratoconus and pellucid marginal degeneration. Absolute stromal thickness progression was found to be independent of stromal thickness.The human corneal stroma represents approximately 90% of the total corneal thickness and has an accepted central thickness of approximately 478 to 500 μm. 1-3 Knowledge of the stromal thickness profile is of interest in the area of corneal refractive surgery, as changes in corneal refractive power are achieved through changes in the stromal thickness profile. Measurements of stromal thickness profile pre-and postoperatively allow stromal ablation rate to be quantified and changes in thickness profile to be determined. 4,5 Stromal thickness mapping could help further understand corneal biomechanics. Stromal thickness profiles could also be useful in identifying corneal disorders such as keratoconus; corneal thickness profile has previously been suggested for the early diagnosis of keratoconus 6 following characterization of corneal thickness progression by Mandell in 1969. 7 Different methods have been used to measure stromal thickness: optical coherence tomography, 8,9 confocal microscopy, 1-3,10 and through focusing confocal microscopy. 11,12 All studies measured the average central stromal thickness. Only two studies provided stromal thickness measurements in the peripheral cornea; however, the number of points measured was limited to one point in the temporal cornea. 1,2 NIH Public AccessVer...

PurposePupil size is critical for optimal performance of presbyopic contact lenses. Although the effect of luminance is well known, little information is available regarding other contributing factors such as aging and refractive status.MethodsThe cohort population comprised 304 patients (127 male, 177 female) aged 18 to 78 years. Pupils were photographed at three controlled luminance levels 250, 50, and 2.5 cd/m2 using an infra-red macro video camera. Measurements of pupil diameter were conducted after transforming pixel values to linear values in millimeters.ResultsLuminance was the most influential factor with pupil diameter increasing with decreased luminance (p < 0.001, all comparisons). Age was also found to be a significant factor with a smaller diameter in the older groups, but overall the difference was only significant between the pre-presbyopes and the established presbyopes (p = 0.017). Pupil diameter decreased significantly with increasing age, the effect being most marked at low luminance (<0.001). The smallest pupil diameters were measured for hyperopes and the largest for myopes and although refractive error was not a significant factor alone, there was a significant interaction between luminance and refractive error with the greatest differences in pupil diameter between myopes and emmetropes at low luminance (p < 0.001). Pupil diameter changes modeled by multilinear regression (p < 0.001) identified age, luminance, best sphere refraction, and refractive error as significant factors accounting for just over 70% of the average variation in pupil diameter.ConclusionsBoth age and refractive status were found to affect pupil size with larger pupils measured for younger patients and myopes. Designs for multifocal contact lens corrections should take both age and refractive status into consideration; a faster progression from distance to near corrections across the optical zone of the lens is expected to be required for established presbyopes and hyperopes than it is for early presbyopes, myopes, and emmetropes.

This review summarizes the current status of the small incision lenticule extraction (SMILE) procedure. Following the early work by Sekundo et al. and Shah et al., SMILE has become increasingly popular. The accuracy of the creation of the lenticule with the VisuMax femtosecond laser (Carl Zeiss Meditec) has been verified using very high-frequency (VHF) digital ultrasound and optical coherence tomography (OCT). Visual and refractive outcomes have been shown to be similar to those achieved with laser in situ keratomileusis (LASIK), notably in a large population reported by Hjortdal, Vestergaard et al. Safety in terms of the change in corrected distance visual acuity (CDVA) has also been shown to be similar to LASIK. It was expected that there would be less postoperative dry eye after SMILE compared to LASIK because the anterior stroma is disturbed only by the small incision, meaning that the anterior corneal nerves should be less affected. A number of studies have demonstrated a lower reduction and faster recovery of corneal sensation after SMILE than LASIK. Some studies have also used confocal microscopy to demonstrate a lower decrease in subbasal nerve fiber density after SMILE than LASIK. The potential biomechanical advantages of SMILE have been modeled by Reinstein et al. based on the non-linearity of tensile strength through the stroma. Studies have reported a similar change in Ocular Response Analyzer (Reichert) parameters after SMILE and LASIK, however, these have previously been shown to be unreliable as a representation of corneal biomechanics. Retreatment options after SMILE are discussed. Tissue addition applications of the SMILE procedure are also discussed including the potential for cryo-preservation of the lenticule for later reimplantation (Mohamed-Noriega, Angunawela, Lim et al.), and a new procedure referred to as endokeratophakia in which a myopic SMILE lenticule is implanted into a hyperopic patient (Pradhan et al.). Finally, studies reporting microdistortions in Bowman’s layer and corneal wound healing responses are also described.

A lenticular change occurred in the epithelial thickness profile, with more thickening centrally than paracentrally; 22% of the total increase in central thickness occurred overnight, 58% between 1 day and 1 month, and 20% between 1 and 3 months, with stability between 3 and 12 months. The lenticular epithelial changes contribute to the observed myopic shift after myopic LASIK during the first 3 months.