Comparison of central corneal thickness and anterior chamber depth measurements using three imaging technologies in normal eyes and after phakic intraocular lens implantation

Contains fulltext : 81835.pdf (Publisher’s version ) (Open Access)BACKGROUND: The repeatability and interchangeability of imaging devices measuring central corneal thickness (CCT) and anterior chamber depth (ACD) are important in the assessment of patients considering refractive surgery. The purpose of this study was to investigate the agreement of CCT and ACD measurements using three imaging technologies in healthy eyes and in eyes after phakic intraocular lens implantation (pIOL). METHODS: In this comparative study, CCT and ACD were measured using anterior segment optical coherence tomography (AS-OCT), Orbscan II, and Pentacam in 33 healthy volunteers (66 eyes) and 22 patients (42 eyes) after pIOL implantation. Intraobserver repeatability was evaluated for all three devices in the healthy volunteer group. RESULTS: Pairwise comparison of CCT measurements showed significant differences between all devices (P < 0.001), except for the AS-OCT and Orbscan II in the healthy volunteer group (P = 0.422) and the Orbscan II and Pentacam in the pIOL group (P = 0.214). ACD measurements demonstrated significant differences between all pairwise comparisons in both groups (P < or = 0.001). Intraobserver reliability was high for CCT and ACD measurements in the healthy volunteer group, with coefficients of variation ranging from 0.6% to 1.2% and 0.4% to 0.5% respectively. CONCLUSIONS: CCT and ACD measurements using AS-OCT, Orbscan II, and Pentacam demonstrated high intraobserver reliability. However, these devices should not be used interchangeably for measurements of CCT and ACD in healthy subject and patients after pIOL implantation

Evaluation of the Comparability and Repeatability of Four Wavefront Aberrometers Visual Psychophysics and Physiological Optics

PURPOSE. To compare total ocular aberrations and corneal aberrations identified with four different aberrometers and to determine the repeatability and interobserver variability. METHODS. In this prospective comparative study, 23 healthy subjects underwent bilateral examination with four aberrometers: the Irx3 (Hartmann-Shack; Imagine Eyes, Orsay, France), Keratron (Hartmann-Shack; Optikon, Rome Italy), iTrace (raytracing; Tracey Technologies, Houston, TX), and OPD-Scan (Automated Retinoscopy; Nidek, Gamagori, Japan). Six images per eye were obtained. Second-, third-and fourth-order spherical aberrations were exported for 5.0-mm pupils. RESULTS. Significant differences in measurements were found for several total ocular aberrations (defocus 1-4 Wavefront analysis may be performed to design an ideal refractive correction, which corrects not only lower-order aberrations (sphere and cylinder), but also higher-order aberrations. In addition, it may be used to evaluate eyes with abnormal optics due to ageing or corneal disorders, such as keratoconus and pellucid marginal degeneration. Three different wavefront measuring principles are available to measure aberrations: (1) Hartmann-Shack, (2) Tscherning or ray tracing, and (3) automated retinoscopy. A HartmannShack aberrometer is an outgoing wavefront aberrometer. It measures the shape of the wavefront that is reflected out of the eye from a point source on the fovea. An array of microlenslets is used to subdivide the outgoing wavefront into multiple beams which produce spot images on a video sensor. The displacement of each spot from the corresponding nonaberrated reference position is used to determine the shape of the wavefront. 5,6 A Tscherning, or ray-tracing, aberrometer is an ingoing instrument. It projects a thin laser beam into the eye, parallel to the visual axis and determines the location of the beam on the retina by using a photodetector. Once the position of the first light spot on the retina is determined, the laser beam is moved to a new position, and the location of the second light spot on the retina is determined. Aberrations in the optical system cause a shift in the location of the light spot on the retina. METHODS In this prospective comparative study, 23 healthy volunteers were recruited from the Department of Ophthalmology, University Hospital Maastricht. Informed consent was obtained from all subjects after the nature of the experiment had been explained. The study adhered to the tenets of the Declaration of Helsinki. None of the subjects had a history of ocular surgery or ocular disease. All subjects were measured bilaterally with four different aberrometers. Per eye, six consecutive good-quality images were obtained: three by an expert and three by a nonexpert. An expert was defined as a person who had performed a minimum of 25 measurements with each aberrometer. Nonexperts were medical students with only basic knowledge of ophthalmology and no previous experience with any of the aberrometers. They received an oral instruction an

Habitual higher order aberrations affect Landolt but not Vernier acuity

Reiniger JL, Lobecke A, Sabesan R, et al. Habitual higher order aberrations affect Landolt but not Vernier acuity. Journal of Vision. 2019;19(5): 11.To assess whether the eye's optical imperfections are relevant for hyperacute vision, we measured ocular wave aberrations, visual hyperacuity, and acuity thresholds in 31 eyes of young adults. Although there was a significant positive correlation between the subjects' performance in Vernier- and Landolt-optotype acuity tasks, we found clear differences in how far both acuity measures correlate with the eyes' optics. Landolt acuity thresholds were significantly better in eyes with low higher order aberrations and high visual Strehl ratios (r(2) = 0.22, p = 0.009), and significantly positively correlated with axial length (r(2) = 0.15, p = 0.03). A retinal image quality metric, calculated as two-dimensional correlation between perfect and actual retinal image, was also correlated with Landolt acuity thresholds (r(2 )= 0.27, p = 0.003). No such correlations were found with Vernier acuity performance (r(2) 0.3). Based on these results, hyperacuity thresholds are, contrary to resolution acuity, not affected by higher order aberrations of the eye