Sandra Franco

Corneal imaging with slit‐scanning and Scheimpflug imaging techniques

Modern anterior segment imaging techniques, such as slit‐scanning and Scheimpflug imaging, greatly improved the field of corneal imaging. Devices such as the Orbscan (Bausch & Lomb Surgical, Inc) and, more recently, the Pentacam (Oculus, Inc) and the Galilei (Ziemer Ophthalmic Systems AG) have brought a whole new range of clinical possibilities and sparked interest in the academic community. These new tomographers create three‐dimensional models of the cornea and enable the direct measurement of both the anterior and posterior surface elevations. In this paper, we present a review of some available literature on those systems, regarding their optical principles and their performance in current clinical applications.

Biomechanical properties of the cornea measured by the Ocular Response Analyzer and their association with intraocular pressure and the central corneal curvature

Background:  The aim of this study was to investigate the biomechanical properties of the cornea and their association with intraocular pressure (IOP), central corneal thickness (CCT) and the central corneal radius of curvature (Rc).

Wavefront analysis and Zernike polynomial decomposition for evaluation of corneal optical quality

&NA; Wavefront‐guided excimer laser refractive surgery and new customized intraocular lens and contact lens designs are major clinical applications of corneal wavefront analysis. Other therapeutic applications include corneal disorders, conventional excimer laser refractive surgery, incisional techniques and cataract surgery, corneal transplantation, intrastromal corneal ring segment implantation, and crosslinking therapy. Basic data regarding corneal wavefront aberrations, such as distribution in the population and changes with aging, are essential for understanding the nature of each aberration and correcting it. Corneal aberrometry also improved our comprehension of the optical effects of the aforementioned topics while helping us assess the success of the procedures. Zernike polynomials are representations of the higher‐ and lower‐order aberrations of the cornea, allowing a mathematical approach to their determination. Polynomials are used to model individual components of the wavefront in familiar terms. This article reviews the current knowledge of the wavefront aberrations of the human cornea and analyzes studies in the fields of anterior segment surgery and/or therapy, diseases, and optical quality in the context of this knowledge. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Comparison of the VCTS-6500 and the CSV-1000 tests for visual contrast sensitivity testing.

The aim of this study was to analyze if differences exist between two available contrast sensitivity tests that use similar stimuli, specifically, the CSV-1000 (VectorVision, Greenville, OH)) and the VCTS-6500 (Vistech, Dayton, OH). Contrast sensitivity was measured on 105 healthy patients with ages ranged from 19 to 26 years with visual acuity of 20/25 or better. The tests were performed in the same room and contrast sensitivity was measured with the VCTS-6500 system and CSV-1000. For both tests, the spatial frequencies of 3, 6, 12 and 18 cycles per degree were recorded. Contrast sensitivity values were generally higher for the Vistech VCTS-6500 test being the difference statistically significant (p<0.001) for all the spatial frequencies. This difference was more significant for 3cpd spatial frequency and the two tests showed a better agreement for the 6cpd spatial frequency. Our results showed that there were significant differences between the VCTS-6500 and the CSV-1000 tests. Developments of some general recommendations or regulations in relation to clinical measurement of contrast sensitivity are necessary.

Comparison of the tear film clinical parameters at two different times of the day

Purpose:  The aim of the present study was to analyse the quality and quantity of the tear film in a young, healthy and non‐contact lens‐wearing population with measurements taken in the morning and in the afternoon to establish if changes exist in these parameters.

Effect of three months of soft contact lens wear on conjunctival cytology

The purpose of this study was to investigate the effect of three months of soft contact lens wear on conjunctival goblet cell density and epithelial cell morphology.

Improving the contact lens fitting evaluation by the application of image-processing techniques

Abstract The use of digital image acquisition and image-processing methods is a major issue in today’s medicine and related areas. In vision care, these procedures find wide application. In this paper we deal with evaluating the quality of rigid contact lens fitting. The employment of contact lenses is widespread, but fitting contact lenses is more difficult than fitting spectacles. Apart from the characterization of patients’ refraction problems, the evaluation of other physical characteristics of the eye, including the shape of the cornea’s external surface, must be performed. The simplest and traditional way to check contact lens fit to the cornea is to evaluate the fluorescein pattern. We hope that the described techniques make the process more convenient for both the patient and the fitter. The fluorescein pattern images were acquired by using a CCD television (TV) camera. The images were digitized and processed to enhance contrast and detect relevant features. The analysis of red-green-blue (RGB) color component histograms of the fluorescein pattern images allows a rapid classification of the fitting relation so that the fitter can directly and efficiently analyze the processed images. The obtained images can then be compressed and stored in patients’ files for future reference.

Surface roughness and refractive index changes in contact lens induced by lens care systems.

Purpose: The aim of this study was to analyze the influence of different lens care systems in surface roughness and refractive index (RI) of contact lenses (CL). This information provides us with a better understanding of how care solutions affect CL materials. Methods: Several CL and three commercially available and appropriate lens care solutions were used (two polyhexamethylene biguanide and one hydrogen peroxide care systems). Lenses were immersed in the lens care systems, and then measurements with CLR 12-70 digital automated refractometer and atomic force microscopy analysis on Tapping mode were recorded. The measurements were performed before and after the lenses were immersed in each care solution. Results: Significant changes were observed on the CL materials when exposed to lens care systems. All the materials changed, to a greater or lesser extent, their roughness and RI, after being immersed in the different solutions. The water content varied between 0% (Nelfilcon A in ReNu Multiplus, Senofilcon A in AOSEPT Plus, and Methafilcon A in Solocare Aqua) and 4.1% (Hilafilcon B in Solocare Aqua) The higher change in roughness was obtained with ReNu Multiplus in the lens Comfilcon A (with an increase of 27.2 nm) and Senofilcon A (with an increase of 16.7 nm). Conclusion: This study suggests that lens care systems play an important role in surface roughness and RI of CL.

Goblet cell density association with tear function and ocular surface physiology

PURPOSE To determine the relationship of goblet cell density (GCD) with tear function and ocular surface physiology. METHODS This was a cross-sectional study conducted in 35 asymptomatic subjects with mean age 23.8±3.6 years. Tear film assessment, conjunctiva and cornea examination were done in each subject. Conjunctival impression cytology was performed by applying Nitrocellulose Millipore MF™-Membrane filter over the superior bulbar conjunctiva. The filter paper was than fixed with 96% ethanol and stained with Periodic Acid Schiff, Hematoxylin and Eosin. GCD was determined by optical microscopy. Relation between GCD and Schirmer score, tear break-up time (TBUT), bulbar redness, limbal redness and corneal staining was determined. RESULTS The mean GCD was 151±122 cells/mm(2). GCD was found higher in eyes with higher Schirmer score but it was not significant (p=0.75). There was a significant relationship of GCD with TBUT (p=0.042). GCD was not correlated with bulbar redness (p=0.126), and limbal redness (p=0.054) as well as corneal staining (p=0.079). No relationship of GCD with age and gender of the subjects (p>0.05) was observed. CONCLUSION GCD was found correlated with TBUT but no significant correlation was found with the aqueous portion of the tear, limbal as well as bulbar redness and corneal staining.

Measurement of Corneal Thickness By Videopachymetry: Preliminary Results

Corneal thickness measurements find applications in areas such as diagnosis and management of corneal disorders and corneal surgery. We present a technique for the measurement of corneal thickness using a CCD camera mounted on a slit-lamp biomicroscope and common image processing software. Thickness measurements were performed on three RGP contact lenses of known thickness with an average error of 5 microm, SD of 8 microm. Measurements of a living cornea yielded a thickness of 505 microm and a SD of 8 microm for 10 consecutive measurements; this is an acceptable value.