purpose: to determine peripapillary retinal nerve fiber layer (rnfl) thickness by three-dimensional optical coherence tomography (3d-oct) in a normal iranian population and to evaluate the concordance of these measurements with those obtained by the second generation of optical coherence tomography (oct ii). methods: in a cross-sectional observational study, 96 normal iranian subjects 20-53 yea...

PURPOSE To evaluate the performance of corneal topographic astigmatism (CorT) based on total corneal power measurements. METHODS Anterior, posterior, and total corneal power measurements of 526 virgin eyes obtained using the CSO Sirius tomographer (Costuzione Strumenti Oftalmici, Scandicci, Florence, Italy) were analyzed. Individual CorTs were created from each set of data. These CorTs were a...

This study examines the extent to which a Zernike-based optical correction can restore acuity in keratoconus as a function of disease severity and contrast level. Increasingly complete Zernike corrections in the presence of Zernike-fit error were simulated. Acuity for keratoconic eyes with <60 D maximum corneal power reached 20/13 with a fifth-order Zernike correction under high-contrast condit...

here, we propose an optical filter and an optical power splitter based on two-dimensionalphotonic crystal all circular ring resonators. these structures are made of a square lattice ofsilicon rods with the refractive index n1=3.464 surrounded by air (with refractive indexn2=1). first, we have designed the filter and by using that, we designed a power splitter. thetransmission efficiency and qua...

Corneal and ocular aberrations were measured in a group of eyes before and after cataract surgery with spherical intraocular lens (IOL) implantation by use of well-tested techniques developed in our laboratory. By subtraction of corneal from total aberration maps, we also estimated the optical quality of the intraocular lens in vivo. We found that aberrations in pseudophakic eyes are not signif...

The cornea is a transparent tissue in front of the eye that refracts light and facilitates vision. A slight change in the geometry of the cornea remarkably affects the optical power. Because of this sensitivity, biomechanical study of the cornea can reveal much about its performance and function. In vivo and in vitro studies have been conducted to investigate the mechanics of the cornea and det...

Purpose. To evaluate surgically induced astigmatism (SIA) and the average corneal power change in symmetric intrastromal corneal ring segment (ICRS) implantation. Methods. The study included 34 eyes of 34 keratoconus patients who underwent symmetric Intacs SK ICRS implantation. The corneal pocket incision meridian was the preoperative steep meridian. Corneal power data were obtained before and ...

AIMS This study examined the occurrence, magnitude, and the consequences of a possible tilt between the corneal surface and optical axis of the EyeSys videokeratoscope. METHODS Initially, a theoretical model was developed to calculate the angle of tilt. The predictions of the model were verified empirically using a convex conicoid surface and were found to predict the tilt to within 0.5 degre...

PURPOSE To quantify optical and biomechanical properties of the feline cornea before and after photorefractive keratectomy (PRK) and assess the relative contribution of different biological factors to refractive outcome. SETTING Department of Ophthalmology, University of Rochester, Rochester, New York, USA. METHODS Adult cats had 6.0 diopter (D) myopic or 4.0 D hyperopic PRK over 6.0 or 8.0...

Purpose To evaluate the accuracy of IOL power calculation using adjusted corneal power according to the posterior/anterior corneal curvature radii ratio. Methods Nine hundred twenty-eight eyes from 928 reference subjects and 158 eyes from 158 cataract patients who underwent phacoemulsification surgery were enrolled. Adjusted corneal power of cataract patients was calculated using the fictitio...