The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Andr Mermoud - One of the best experts on this subject based on the ideXlab platform.
-
retinal nerve fiber layer and physiological central corneal thickness
Journal of Glaucoma, 2001Co-Authors: Michele Iester, Andr MermoudAbstract:PURPOSE: To determine the relationship between central corneal thickness and the measurement of retinal nerve fiber layer thickness around the optic nerve head using a confocal scanning laser polarimeter such as the Nerve Fiber Analyzer (GDx). METHODS: Forty-four eyes were recruited for this study. Each patient had a normal visual field and a healthy optic nerve head, which was assessed by slit-lamp biomicroscopy with a 90-diopter lens and by a scanning laser ophthalmoscope (Heidelberg Retina Tomograph). Using the GDx, retinal nerve fiber layer thickness was calculated from 1.75 disc diameters together with some standard GDx parameters, including the number, symmetry, superior ratio, inferior ratio, maximum modulation, and ellipse modulation. Corneal thickness was measured with the DGH-1000 Ultrasonic Pachymeter. Descriptive analysis was used and Pearson's r coefficient of correlation was calculated. RESULTS: Corneal thickness was not significantly correlated to retinal nerve fiber layer thickness, but it was significantly (P < 0.05) correlated to the other GDx parameters. CONCLUSION: From these data. peripapillary retinal nerve fiber layer thickness is shown not to be significantly correlated to the corneal thickness, even if for the standard GDx parameters a significant correlation was found.
Sunil Shah - One of the best experts on this subject based on the ideXlab platform.
-
the use of the ocular response analyser to determine corneal hysteresis in eyes before and after excimer laser refractive surgery
Contact Lens and Anterior Eye, 2009Co-Authors: Sunil Shah, Mohammad Laiquzzaman, Ian Y L Yeung, Xueliang Pan, Cynthia J RobertsAbstract:Abstract Purpose To compare corneal biomechanical parameters and two measures of intraocular pressure (IOP) in eyes before and after excimer laser refractive surgery, with the Ocular Response Analyser (ORA). Materials and methods Eighty normal eyes of 41 patients undergoing excimer laser refractive surgery in Birmingham, U.K. were recruited into three groups: Laser Assisted-Epithelial Keratomileusis (LASEK) (Myopes), Laser Assisted in Situ Keratomileusis (LASIK) (myopes) and LASIK (hyperopes). The preop and 3 months postop Goldmann correlated IOP (IOPg), corneal compensated IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF) were measured by the ORA. Central corneal thickness (CCT) was measured using Ultrasonic Pachymeter. The differences of the changes in IOPg, IOPcc, CH, CRF and CCT between the three groups were estimated. A General Linear Model was selected to investigate the influence of gender, age, initial conditions (CH, CRF, CCT, IOPcc and IOPg) and changes in CCT on the measured IOP. Results The differences between the mean IOPg, CH and CRF after refractive surgery were statistically significant for all three groups. The hyperopic LASIK group had a significantly smaller change compared to the other groups (which had no statistical significance). The preop IOPg, preop CH and gender were significant predictors of the changes in measured pressure and biomechanical parameters after surgery in the myopic groups only. Conclusion CH and CRF were found to decrease after both myopic and hyperopic refractive surgery. CH and CRF measurement may prove important tools to clarify the role of corneal biomechanics for refractive surgery.
-
assessment of the biomechanical properties of the cornea with the ocular response analyzer in normal and keratoconic eyes
Investigative Ophthalmology & Visual Science, 2007Co-Authors: Sunil Shah, Mohammed Laiquzzaman, Rajan Bhojwani, Sanjay Mantry, Ian A CunliffeAbstract:PURPOSE. To compare hysteresis, a novel measure of ocular rigidity (viscoelasticity) in normal and keratoconic eyes. METHODS. The study consisted of 207 normal and 93 keratoconic eyes. Eyes were diagnosed as keratoconic based on clinical examination and corneal topography. The hysteresis was measured by the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY). The data were recorded by Generation 3 software for the ORA. Central corneal thickness (CCT) was measured with a handheld Ultrasonic Pachymeter in the midpupillary axis. RESULTS. The mean hysteresis was 10.7 ± 2.0 (SD) mm Hg (range, 6.1-17.6) in normal eyes compared with 9.6 ± 2.2 mm Hg (range, 4.7-16.7) in keratoconic eyes. The difference was statistically significant (P < 0.0001, unpaired t-test). Mean CCT in the normal and keratoconic eyes was 545.0 ± 36.4 μm (range, 471-650) and 491.8 ± 54.7 μm (range, 341-611), respectively; the difference was significant (P < 0.0001, unpaired t-test). CONCLUSIONS. Hysteresis was significantly higher in normal than in keratoconic eyes. It may be a useful measurement in addition to CCT, when assessing ocular rigidity, and may be of particular importance when trying to correct intraocular measurements for increased or decreased ocular rigidity. Long-term studies of change in hysteresis may provide information on the progression of keratoconus.
-
Assessment of the biomechanical properties of the cornea with the ocular response analyzer in normal and keratoconic eyes. Invest Ophthalmol Vis Sci
2007Co-Authors: Sunil Shah, Mohammed Laiquzzaman, Rajan Bhojwani, Sanjay Mantry, Ian CunliffeAbstract:PURPOSE. To compare hysteresis, a novel measure of ocular rigidity (viscoelasticity) in normal and keratoconic eyes. METHODS. The study consisted of 207 normal and 93 kerato-conic eyes. Eyes were diagnosed as keratoconic based on clinical examination and corneal topography. The hysteresis was measured by the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY). The data were recorded by Generation 3 software for the ORA. Central cor-neal thickness (CCT) was measured with a handheld Ultrasonic Pachymeter in the midpupillary axis. RESULTS. The mean hysteresis was 10.7 2.0 (SD) mm Hg (range, 6.1–17.6) in normal eyes compared with 9.6 2.2 mm Hg (range, 4.7–16.7) in keratoconic eyes. The difference was statistically significant (P 0.0001, unpaired t-test). Mean CCT in the normal and keratoconic eyes was 545.0 36.4
-
the use of the reichert ocular response analyser to establish the relationship between ocular hysteresis corneal resistance factor and central corneal thickness in normal eyes
Contact Lens and Anterior Eye, 2006Co-Authors: Sunil Shah, Mohammed Laiquzzaman, Ian A Cunliffe, Sanjay MantryAbstract:Abstract Purpose The aim of this study was to measure ocular hysteresis and corneal resistance factor (CRF), novel methods of analysing ocular rigidity/elasticity and to determine the relationship between central corneal thickness (CCT), hysteresis and CRF in normal subjects. Design Prospective, cross-sectional, clinical trial. Participants The study included 207 normal eyes. Methods Hysteresis and CRF were measured by the ocular response analyser. The CCT was measured using a hand held Ultrasonic Pachymeter. Main outcome measures Ocular hysteresis and CRF in normal patients and their relationship with CCT. Results The mean hysteresis was 10.7 ± 2.0 mmHg standard deviation (S.D.) (range 6.1–17.6 mmHg); the mean CRF was 10.3 ± 2.0 (range 5.7–17.1 mmHg). The mean CCT was 545.0 ± 36.4 μm (471–650 μm). The relationship between hysteresis and CCT; CRF and CCT; CRF and hysteresis were significant (p Conclusion This study demonstrated that corneal hysteresis increased with increasing CCT, however, the correlation was moderate. It would appear that CCT, hysteresis and CRF may measure different biomechanical aspects of ocular rigidity and are likely to be useful additional measurement to CCT in the assessment of ocular rigidity when measuring intraocular pressure (IOP). This may be of particular importance when trying to correct IOP measurements for increased or decreased ocular rigidity.
-
diurnal variation of ocular hysteresis in normal subjects relevance in clinical context
Clinical and Experimental Ophthalmology, 2006Co-Authors: Mohammad Laiquzzaman, Rajan Bhojwani, Ian A Cunliffe, Sunil ShahAbstract:BACKGROUND This study was conducted to assess the diurnal variation in ocular hysteresis, as measured by the Ocular Response Analyser to establish a relationship between diurnal hysteresis variation and diurnal intraocular pressure (IOP) variation. METHODS Forty-two normal eyes of 21 colleagues and staff in a teaching hospital in Birmingham, UK, were recruited. The IOP and hysteresis were measured by the Ocular Response Analyser. The central corneal thickness (CCT) was measured using a hand-held Ultrasonic Pachymeter in the mid-pupillary axis. RESULTS The mean ocular hysteresis at 8 am was 12.7 +/- 2.3 mmHg, at 11 am was 12.2 +/- 2.0 mmHg, at 2 PM was 12.7 +/- 2.1 mmHg and at 5 PM was 12.7 +/- 1.7 mmHg; the difference between the values at any time of measurement was not statistically significant (P > 0.9, repeated measures). IOP as measured by non-contact tonometry was 18.4 +/- 2.8 mmHg, 17.9 +/- 3.3 mmHg, 16.9 +/- 3.1 mmHg and 16.8 +/- 3.2 mmHg, respectively, for the same time period; the difference between the values in the morning and afternoon was statistically significant (P < 0.0001, repeated measures). The CCT was 548.8 +/- 29.5 microm, 547.0 +/- 31.4 microm, 548.2 +/- 29.6 microm and 548.6 +/- 29.4 microm, respectively; the difference between the values was not statistically significant at any time points. Multiple regression analysis showed the relationship between IOP and hysteresis was not statistically significant (P = 0.9). CONCLUSION The ocular hysteresis reading was almost constant throughout the day, whereas the IOP readings showed highest values in the morning with a reducing trend being lowest in the afternoon. The CCT values were almost stable throughout the day. IOP appears to vary independently of a variation in hysteresis or CCT.
Nilgun Yildirim - One of the best experts on this subject based on the ideXlab platform.
-
the influence of central corneal thickness and corneal curvature on intraocular pressure measured by tono pen and rebound tonometer in children
Journal of Glaucoma, 2008Co-Authors: Afsun Sahin, Hikmet Basmak, Nilgun YildirimAbstract:PURPOSE To find out the effect of central corneal thickness (CCT) and radius of the corneal curvature on intraocular pressure (IOP) measurements using rebound tonometer (RBT) and Tono-Pen in healthy schoolchildren. METHODS IOP was measured with Tono-Pen and RBT, respectively, in 165 healthy schoolchildren with a mean age 9.8+/-3.1 (range: 7 to 12 y) years. Corneal radius of curvature (in mm) was determined using a keratometer before CCT and IOP measurements. CCT was measured using an Ultrasonic Pachymeter after all IOP determinations had been made. The effect of CCT, radius of the corneal curvature, and sex on measured IOP was evaluated by linear regression analysis. RESULTS The mean IOP readings were 17.47+/-2.7 mm Hg using Tono-Pen, and 16.81+/-3.1 mm Hg using RBT. Tono-Pen measured IOP values slightly greater than that of RBT (P=0.006). Mean CCT was found to be 561.37+/-33 microm. A significant association between measured IOP and CCT was found with each device (r=0.220 for the Tono-Pen, r=0.373 for the RBT; P=0.006 for the Tono-Pen and P<0.0001 for the RBT). The IOP increased 2.2 and 3.7 mm Hg for every 100-microm increase in CCT for the Tono-Pen and the RBT, respectively. The relation between IOP and CCT was not different for boys and girls. Mean radius of the corneal curvature readings was 7.68+/-0.41 mm (42.75+/-1.37 D) for both sexes. There was no significant relationship between either the mean corneal curvature readings, or CCT and IOP (r=0.02; P=0.4 for CCT and r=0.01; P=0.5 for IOP). CONCLUSIONS Both the Tono-Pen and RBT have a systematic error in IOP readings caused by its dependence on CCT. The CCT measurements should be considered to ensure proper interpretation of IOP measurements in children, like in adults. The corneal radius of curvature had no significant effect on measured IOP with each device.
-
comparison of the rebound tonometer with the goldmann applanation tonometer in glaucoma patients
Clinical and Experimental Ophthalmology, 2007Co-Authors: Afsun Sahin, Leyla Niyaz, Nilgun YildirimAbstract:Purpose: To determine the agreement between the measurement of intraocular pressure (IOP) by the rebound tonometer (RBT) and by the Goldmann applanation tonometer (GAT) and to find out the effect of central corneal thickness (CCT) values on IOP measurements in glaucoma patients. Methods: IOP was measured with the RBT and GAT, respectively, in 61 eyes of 61 glaucoma patients. CCT was measured using an Ultrasonic Pachymeter after all IOP determinations had been made. The mean IOP measurement by the RBT was compared with the measurement by the GAT, by Student's t-test. Bland–Altman analysis was performed to assess the clinical agreement between the two methods. The effect of CCT on measured IOP was explored by linear regression analysis. Results: The mean patient age was 56.7 ± 21.1 years (range: 30–80 years). There were 32 (52.46%) women and 29 (47.54%) men in the study group. The mean IOP readings were 18.70 ± 4.76 mmHg using the RBT, and 18.27 ± 3.49 mmHg using the GAT. The difference was not statistically significant (mean difference 0.43 ± 2.55, P = 0.2). A frequency distribution of the differences demonstrated that in more than 80% of cases the IOP readings differed by <2.3 mmHg between the RBT and GAT. There was a strong correlation between the RBT and GAT readings (r = 0.852, P < 0.0001). The IOP measurements with the two methods were correlated with CCT (r = 0.40, P = 0.02 for the RBT and r = 0.48, P < 0.0001 for the GAT). The IOP increased 1.1 mmHg and 8 mmHg for every 100-μm increase in CCT for the GAT and RBT, respectively. Conclusion: The RBT slightly overestimated the IOP value by 0.43 mmHg on average when compared with the GAT. Nevertheless, the RBT readings appeared to be more affected by the various thicknesses of different corneas when compared with those obtained using the GAT.
Michele Iester - One of the best experts on this subject based on the ideXlab platform.
-
retinal nerve fiber layer and physiological central corneal thickness
Journal of Glaucoma, 2001Co-Authors: Michele Iester, Andr MermoudAbstract:PURPOSE: To determine the relationship between central corneal thickness and the measurement of retinal nerve fiber layer thickness around the optic nerve head using a confocal scanning laser polarimeter such as the Nerve Fiber Analyzer (GDx). METHODS: Forty-four eyes were recruited for this study. Each patient had a normal visual field and a healthy optic nerve head, which was assessed by slit-lamp biomicroscopy with a 90-diopter lens and by a scanning laser ophthalmoscope (Heidelberg Retina Tomograph). Using the GDx, retinal nerve fiber layer thickness was calculated from 1.75 disc diameters together with some standard GDx parameters, including the number, symmetry, superior ratio, inferior ratio, maximum modulation, and ellipse modulation. Corneal thickness was measured with the DGH-1000 Ultrasonic Pachymeter. Descriptive analysis was used and Pearson's r coefficient of correlation was calculated. RESULTS: Corneal thickness was not significantly correlated to retinal nerve fiber layer thickness, but it was significantly (P < 0.05) correlated to the other GDx parameters. CONCLUSION: From these data. peripapillary retinal nerve fiber layer thickness is shown not to be significantly correlated to the corneal thickness, even if for the standard GDx parameters a significant correlation was found.
Joel S Schuman - One of the best experts on this subject based on the ideXlab platform.
-
assessing the relationship between central corneal thickness and retinal nerve fiber layer thickness in healthy subjects
American Journal of Ophthalmology, 2008Co-Authors: Tarkan Mumcuoglu, K A Townsend, Gadi Wollstein, Hiroshi Ishikawa, Richard A Bilonick, Kyung Rim Sung, Larry Kagemann, Joel S SchumanAbstract:Purpose To determine the relationship between central corneal thickness (CCT) and retinal nerve fiber layer (RNFL) thickness obtained by scanning laser polarimetry (GDx-VCC; Carl Zeiss Meditec, Dublin, California, USA), confocal scanning laser ophthalmoscopy (HRT II; Heidelberg Engineering, Heidelberg, Germany), and optical coherence tomography (Stratus OCT; Carl Zeiss Meditec). Design Multicenter clinical trial, retrospective cross-sectional study. Methods One hundred and nine healthy subjects from the Advanced Imaging in Glaucoma Study were enrolled in this study. All subjects had a standard clinical examination, including visual field (VF) and good-quality scans from all three imaging devices. CCT was measured using an Ultrasonic Pachymeter. A linear mixed-effects model was used to assess the relationship between RNFL thickness and CCT, accounting for clustering of eyes within subjects, testing site, ethnicity, family history of glaucoma, axial length intraocular pressure, and VF global indices. Results For OCT and GDx, there was a slight nonstatistically significant positive relationship between CCT and RNFL thickness. For HRT, there was a slight nonstatistically significant negative relationship between CCT and RNFL thickness. Relationships for each device were found to differ between sites. Conclusions CCT was not statistically significantly related to RNFL thickness in healthy eyes.
