Principles of operation, accuracy and precision of an Eye Surface Profiler.

PURPOSE: To introduce a newly developed instrument for measuring the topography of the anterior eye, provide principles of its operation and to assess its accuracy and precision. METHODS: The Eye Surface Profiler is a new technology based on Fourier transform profilometry for measuring the anterior eye surface encompassing the corneo-scleral area. Details of technical principles of operation are provided for the particular case of sequential double fringe projection. Technical limits of accuracy have been assessed for several key parameters such as the carrier frequency, image quantisation level, sensor size, carrier frequency inaccuracy, and level and type of noise. Further, results from both artificial test surfaces as well as real eyes are used to assess precision and accuracy of the device (here benchmarked against one of popular Placido disk videokeratoscopes). RESULTS: Technically, the Eye Surface Profiler accuracy can reach levels below 1 µm for a range of considered key parameters. For the unit tested and using calibrated artificial surfaces, the accuracy of measurement (in terms of RMS error) was below 10 µm for a central measurement area of 8 mm diameter and below 40 µm for an extended measurement area of 16 mm. In some cases, the error reached levels of up to 200 µm at the very periphery of the measured surface (up to 20 mm). The SimK estimates of the test surfaces from the Eye Surface Profiler were in close agreement with those from a Placido disk videokeratoscope with differences no greater than ±0.1 D. For real eyes, the benchmarked accuracy was within ±0.5D for both the spherical and cylindrical SimK components. CONCLUSIONS: The Eye Surface Profiler can successfully measure the topography of the entire anterior eye including the cornea, limbus and sclera. It has a great potential to become an optometry clinical tool that could substitute the currently used videokeratoscopes and provide a high quality corneo-scleral topography.

Keratoconus: The ABCD Grading System.

PURPOSE: To propose a new keratoconus classification/staging system that utilises current tomographic data and better reflects the anatomical and functional changes seen in keratoconus. METHOD: A previously published normative database was reanalysed to generate both anterior and posterior average radii of curvature (ARC and PRC) taken from a 3.0 mm optical zone centred on the thinnest point of the cornea. Mean and standard deviations were recorded and anterior data were compared to the existing Amsler-Krumeich (AK) Classification. ARC, PRC, thinnest pachymetry and distance visual acuity were then used to construct a keratoconus classification. RESULTS: 672 eyes of 336 patients were analysed. Anterior and posterior values were 7.65 ± 0.236 mm and 6.26 ± 0.214 mm, respectively, and thinnest pachymetry values were 534.2 ± 30.36 µm. The ARC values were 2.63, 5.47 and 6.44 standard deviations from the mean values of stages 1-3 in the AK classification, respectively. PRC staging uses the same standard deviation gates. The pachymetric values differed by 4.42 and 7.72 standard deviations for stages 2 and 3, respectively. CONCLUSION: A new keratoconus staging incorporates anterior and posterior curvature, thinnest pachymetric values, and distance visual acuity and consists of stages 0-4 (5 stages). The proposed system closely matches the existing AK classification stages 1-4 on anterior curvature. As it incorporates posterior curvature and thickness measurements based on the thinnest point, rather than apical measurements, the new staging system better reflects the anatomical changes seen in keratoconus.

OPD-Scan III: a repeatability and inter-device agreement study of a multifunctional device in emmetropia, ametropia, and keratoconus.

The purpose of this study was to test the measurements of a multifunctional device, the NIDEK OPD-Scan III in terms of repeatability and agreement with retinoscopy and Pentacam in cases with emmetropia, ametropia, and KCN (grade 1-3). We enrolled 170 eyes (40 in each group of emmetropia and ametropia, and 90 in the 3 KCN subgroups). Acquisitions were done twice by a single technician to check the intra class correlation, repeatability index, and precision. To assess agreement, we compared OPD-Scan III with retinoscopy and Pentacam results by two blinded technicians. All device functions had acceptable precision in groups with emmetropia, ametropia, and KCN1, except spherical error in ammetropics (0.97 D). In KCN2, repeatability was acceptable with the refractive function, topography, and ocular aberrations but was more than 1.0 D for corneal aberrations. In KCN3, repeatability was low for the refractive function and corneal spherical aberration. Refractive data were not convertible to those obtained by retinoscopy in any group. OPD-Scan III keratometry data were interchangeable with Pentacam counterparts in emmetropes, ammetropes, and KCN1. In KCN2, the OPD-Scan III-Pentacam agreement for Kmax was 0.71 D, and there was 1.25 D difference in Kmin. No OPD-Scan III-Pentacam agreement was observed in KCN3. OPD- Scan III is a multifunctional device with acceptable repeatability in emmetropic, ammetropic, and KCN cases. Its measurements of corneal curvature and ocular aberrations are better than other functions. In cases with high degrees of refractive error and corneal irregularities, device repeatability and agreement with Pentacam is decreased.

A novel Hartman Shack-based topography system: repeatability and agreement for corneal power with Scheimpflug+Placido topographer and rotating prism auto-keratorefractor.

The purpose of this study is to analyze the repeatability and agreement of corneal power using a new Hartman type topographer in comparison to Scheimpflug+Placido and autorefractor devices. In this cross sectional, observational study performed at the cornea services of a specialty hospital, 100 normal eyes (100 consecutive candidates) without any previous ocular surgery or morbidity except refractive error were evaluated. All candidates underwent three measurements each on a Full gradient, Hartman type topographer (FG) (iDesign, AMO), Scheimpflug+Placido topographer (SP) (Sirius, CSO) and rotating prism auto-keratorefractor (AR) (KR1, Nidek). The parameters assessed were flat keratometry (K1), steep keratometry (K2), steep axis (K2 axis), mean K, J 0 and J 45. Intra-device repeatability and inter-device agreement were evaluated. On repeatability analysis, the intra-device means were not significantly different (ANOVA, p > 0.05). Intraclass correlations (ICC) were >0.98 except for J 0 and J 45. In terms of intra-measurement standard deviation (Sw), the SP and FG groups fared better than AR group (p < 0.001, ANOVA). On Sw versus Average plots, no significantly predictive fit was seen (p > 0.05, R (2) < 0.1 for all the values). On inter-device agreement analysis, there was no difference in means (ANOVA, p > 0.05). ICC ranged from 0.92 to 0.99 (p < 0.001). Regression fits on Bland-Altman plots suggested no clinically significant effect of average values over difference in means. The repeatability of Hartman type topographer in normal eyes is comparable to SP combination device and better than AR. The agreement between the three devices is good. However, we recommend against interchanging these devices between follow-ups or pooling their data.

Repeatability of placido-based corneal topography in keratoconus.

PURPOSE: To determine and compare the repeatability of a Placido-based corneal topography (Oculus Keratograph) in a sample of healthy and keratoconus eyes. METHODS: The corneal topography, determined using the Oculus Keratograph, of 25 healthy and 25 keratoconus eyes was assessed three consecutive times. A single randomized eye was included per patient. Coefficient of variation (CV) of the eccentricity, corneal diameter, index of surface variance, index of vertical asymmetry, keratoconus index (KI), smallest sagittal curvature radius (Rmin), aberration coefficient, and maximum corneal power and minimum corneal power (diopters) in the 3.0-mm zone in addition to the maximum corneal power point (MCPP) (diopters) were calculated and compared between healthy and keratoconus eyes. RESULTS: Healthy eyes showed lower topographic values (p < 0.05) than keratoconus eyes, except with regard to the Rmin value. Corneal diameter (p = 0.45) was similar in both groups. All variables showed good CVs in healthy and keratoconus eyes (maximum corneal power [0.21 and 0.47%, respectively], minimum corneal power [0.19 and 0.36%], MCPP [0.22 and 0.77%], corneal diameter [0.27 and 0.33%], index of surface variance [4.82 and 3.10%], index of vertical asymmetry [7.05 and 3.80%], KI [0.29 and 0.72%], Rmin [0.53 and 0.78%], and aberration coefficient [0 and 4.00%]) except for the eccentricity CV (5.79 and 14.53%, respectively). Statistically significant differences (p < 0.05) between healthy and keratoconus groups were found for all variables, except with respect to the MCPP, eccentricity, corneal diameter, KI, and Rmin (p > 0.07). CONCLUSIONS: The Oculus Keratograph provides repeatable measurements of corneal topography in healthy and keratoconus eyes. These results could improve the topographical diagnosis of keratoconus, thus aiding in patient management.

Predictive value of corneal topography for ClearKone hybrid contact lenses.

PURPOSE: The purpose of this study was to evaluate the predictive value of corneal topography data for fitting ClearKone hybrid contact lenses on eyes with corneal ectasia. METHODS: Ophthalmic records from eyes with established corneal ectasia that had been successfully fitted with SynergEyes ClearKone lenses (n = 73) were retrospectively reviewed. Correlations between corneal parameters (simulated steep and flat keratometry values, average corneal sagittal height, inferior-superior index for keratoconus, corneal eccentricity, cone displacement, and cone diameter) and ClearKone lens parameters (vault and skirt curvature) were analyzed. RESULTS: Two topographical correlates to ClearKone lens parameters were identified. Mean weighted corneal sagittal height at a 7.4-mm chord was strongly predictive of the optimal ClearKone lens vault; a linear relationship was observed between these parameters (R = 0.96). More significant vertical decentration of the corneal apex was found to be associated with the need for a steeper lens skirt curvature (p < 0.05). CONCLUSIONS: This study demonstrates that baseline corneal topography-derived data are valuable for predicting lens parameters for an optimally fit SynergEyes ClearKone hybrid contact lens.

Precision analysis of posterior corneal topography measured by Visante Omni: repeatability, reproducibility, and agreement with Orbscan II.

PURPOSE: To evaluate the repeatability and reproducibility of posterior corneal curvature and posterior corneal elevation best-fit sphere (BFS) obtained with the Visante Omni (Carl Zeiss Meditec) and to compare the results with the Orbscan II (Bausch & Lomb). METHODS: Thirty eyes from 30 healthy volunteers were included in this study. All patients were examined 5 times with the Visante Omni and Orbscan II by 2 independent operators. The posterior corneal curvature (3- and 6-mm zone) and posterior corneal elevation BFS (5- and 8-mm zone) were generated for each system. Intraoperator repeatability and interoperator reproducibility and agreement between the systems were evaluated using the intraclass correlation coefficient (ICC) and the Bland-Altman method. RESULTS: The repeatability of posterior corneal curvature and posterior corneal elevation BFS measured by the Visante Omni was high for all analysis zones (ICC, 0.99 to 1.00). The reproducibility also showed similar results (ICC, 0.99 to 1.00). Agreement between the Visante Omni and Orbscan II was high for posterior corneal curvature (ICC, 0.94 to 0.97) and posterior corneal elevation BFS (ICC, 0.96 to 0.98) with 95% limits of agreement at -0.26 to 0.22 diopters for posterior corneal curvature and 0.11 to 0.69 mm for posterior corneal elevation BFS. CONCLUSIONS: The Visante Omni provides good repeatability and reproducibility of posterior corneal topography. Overall agreement with the Orbscan II system was high.

Future directions in non-invasive measurements of tear film surface kinetics.

PURPOSE: To review the methods for dynamic, non-invasive, and objective assessment of tear film surface quality and to outline their current state-of-the-art and their future potential. METHODS: Among the methods available, high-speed videokeratoscopy, lateral shearing interferometry, and dynamic wavefront sensing are being considered. RESULTS: The principles of operations, their advantages and disadvantages, and limitations of each method are being outlined. The possible future directions of each method are also discussed. CONCLUSIONS: To gain a better understanding of tear film, its structure and function, it is essential to combine macroimaging technologies with those focusing on tear film microstructure. In this way, one can envisage a clinical device that could help, in future, early diagnosis of dry eye syndrome and development of better materials for contact lenses and eye lubricants.

Accuracy and repeatability of a new tono-pachymeter for measuring central corneal thickness.

OBJECTIVES: The recently developed noncontact tonopachymeter Tonopachy NT-530 P provides intraocular pressure values corrected for central corneal thickness (CCT). The purpose of this study was to assess the accuracy and repeatability of its CCT measurements. METHODS: The CCT measurements were obtained in 64 right eyes of 64 young healthy subjects using the Orbscan corneal topography system followed by the Tonopachy and then by ultrasound pachymetry (UP). Another sample of 31 subjects was used to test the repeatability of the tonopachy measurements in 2 separate sessions 1 week apart. To compare the tonometers and determine intersession repeatability for the tonopachymeter, differences in the readings provided by pairs of the instruments or obtained in the two sessions were plotted against mean differences. The hypothesis of zero bias was examined by a paired t-test. The coefficient of repeatability was calculated as the 95% limits of agreement (LoAs) of differences between the 2 sessions. RESULTS: Measurements made using the three instruments were significantly correlated (P<0.001). Mean CCTs (±SD) measured using the Tonopachy, Orbscan (acoustic factor set at 0.92) and ultrasound pachymeter were 530.42 ± 34.96, 526.73 ± 39.53, and 550.69 ± 37.26 µm, respectively. The differences between modalities (±95% LoAs) were -3.68 ± 24.36 for Orbscan versus Tonopachy, 20.66 ± 14.69 for UP versus Tonopachy, and 23.95 ± 24.21 for UP versus Orbscan. The coefficient of repeatability for the tonopachymeter was ±15.11 µm. CONCLUSIONS: The Tonopachy offers similar CCT measurements to those provided by conventional pachymeters with good repeatability.

Clinical validation of point-source corneal topography in keratoplasty.

PURPOSE: To validate the clinical performance of point-source corneal topography (PCT) in postpenetrating keratoplasty (PKP) eyes and to compare it with conventional Placido-based topography. METHODS: Corneal elevation maps of the anterior corneal surface were obtained from 20 post-PKP corneas using PCT (VU topographer, prototype; VU University Medical Center, Amsterdam, The Netherlands) and Placido-based topography (Keratron, Optikon 2000, Rome, Italy). Corneal surface parameters are calculated in terms of radius and asphericity. Corneal aberrations were characterized using standard Zernike convention. An artificial surface with quadrafoil feature (SUMIPRO, Almelo, The Netherlands) was measured and used as a reference to assess instrument performance compared with the gold standard. RESULTS: The differences (mean ± std of PCT - Placido) found between the two types of topographers in measurements of post-PKP eyes are 0.02 ± 0.21 mm (p=0.64) for radius of curvature, 0.14 ± 0.49 (p=0.23) for asphericity, -0.19 ± 1.67 µm (p=0.61) for corneal astigmatism, -0.25 ± 1.34 µm (p=0.41) for corneal coma, 0.23 ± 0.82 µm (p=0.23) for corneal trefoil, and 0.15 ± 0.28 µm (p=0.02) for corneal quadrafoil. The PCT measured the artificial surface more accurate (rms error 0.16 µm; 0.12 eq. Dpt.) than the Placido-based topographer (rms error 1.50 µm; 1.15 eq. Dpt.). CONCLUSIONS: PCT is more accurate than Placido-based topography in measuring quadrafoil aberration.

Central corneal thickness measured with three optical devices and ultrasound pachometry.

PURPOSE: To evaluate the reliability of three noninvasive pachometry methods against the ultrasound pachometer considered the gold standard. METHODS: Central corneal thickness (CCT) was measured using a Paxis ultrasound (US) pachometer, Orbscan II, Pentacam, and Topcon SP-3000 specular microscope in 22 right eyes of 22 healthy adults (7 men, 15 women). Three repeated measures were obtained and then compared to obtain the repeatability of each instrument and the agreement between pachometers. RESULTS: Pentacam is the optical system that renders values of CCT closer to those obtained with US pachometry. Conversely, a specular microscope shows a poorer agreement with US measures, and differences depend on the thickness being measured. The Orbscan system shows a consistent trend toward underestimation of CCT compared with US and Pentacam irrespective of the value measured. CONCLUSION: Different optical methods used to measure CCT showed significantly different results compared with US pachometry except for the Pentacam system. Clinicians should take into account the fact that specular microscopy might either underestimate or overestimate values of CCT, whereas Orbscan systematically overestimates CCT compared with US and Pentacam.

[An algorithm of corneal reconstruction based on precise location of corneal center].

Placido disk is widely used in corneal topography. In order to solve the problem that the convex of the corneal can not be precisely located in the Placido corneal topography system, an algorithm of corneal reconstruction based on the Placido disk was introduced. The key of this method is the calculation of radius of corneal convex by using the innermost ring data. Based on image analysis result, we precisely calculated the radius of corneal convex iteratively by connecting the convex and the first ring using a circle, and then calculated the location of all the reflect point and its power. At last we created the pseudo color map of the human corneal. The corneal was simulated by using standard steel sphere, and the calculating errors of the result were all below 0.25D. It showed that the algorithm used in this work could get relatively accurate powers and would have fair stability.

Precision of the Nidek Tonoref II autokeratometer: how many repeated measurements are required?

PURPOSE: To determine the minimal number of repeated measurements required for precise Nidek Tonoref II autokeratometry. METHODS: This prospective, non-intervention study was performed at the Department of Ophthalmology, Randers, Denmark. We used the Nidek Tonoref II autokeratometer to perform 10 successive measurements on 100 right eyes of cooperative individuals. Each keratometry was converted to the spherical equivalent power (SE), while the net astigmatism was converted to polar values along zero (KP(0)) and 45 degrees (KP(45)). All units were in dioptres (D). The precision was calculated as the mean absolute difference between paired measurements, using one or the average of two, three, four or five autokeratometries. Statistical assessment was performed with Dunn's test for repeated measurements with a Bonferroni correction. RESULTS: The precision of SE, KP(0) and KP(45) increased statistically significantly from one to three measurements, with no significant improvement for autokeratometries based on four or five measurements. There was no significant precision difference between one and two measurements. CONCLUSION: A single keratometry is inadequate, but the vector average of three measurements is sufficient for precise autokeratometry with the Tonoref II device. The consistent use of three keratometries with this device may increase the precision of spherical and toric IOL calculation.

Videokeratoscopic indices in relation to epidemiological exposure to keratoconus.

BACKGROUND: To establish the relationship between videokeratoscopic indices and the degree of epidemiological exposure to keratoconus in three groups of clinically normal subjects. METHODS: Cross-sectional study in which 75 subjects lacking clinical signs of keratoconus were divided into three groups according to epidemiological exposure to the condition: 25 fellow eyes of subjects with clinical signs on the contralateral eye only (the "fellow eye" group), to be compared to 25 first-degree relatives of patients with keratoconus (the "relatives" group) and 25 controls without a family history of the disease (the "control" group). Qualitative patterns and quantitative parameters describing curvature (central curvature), irregularity (root mean square of the higher-order corneal wavefront aberration), and asymmetry (inferior-superior dioptric asymmetry, Zernike vertical coma) obtained from videokeratoscopy were used for comparison between groups. RESULTS: Members of the fellow eye group featured a greater number of asymmetric curvature patterns and increased values in indices describing asymmetry and irregularity than subjects included in both control and relatives groups. Control and relatives groups were not significantly different. Despite significant differences in the distribution of values between the groups, no single index was able to effectively discriminate between groups using ROC curve analysis. CONCLUSIONS: A prior threefold classification of clinically normal subjects according to epidemiological exposure to keratoconus was not sustained by significant differences in videokeratoscopic indices when comparing between groups.

Precision of orbscan II assessment of anterior corneal curvature and asphericity.

PURPOSE: To determine the number of measurements required to produce a representative mean result for corneal apical radius and asphericity and to examine the repeatability of this mean result. METHODS: The Bausch & Lomb Orbscan II corneal topographer was used to take 10 measurements of right eyes of 20 normal individuals. These were used to determine the number of measurements required to obtain a representative result. The apical radius and p-value were derived from the instrument software for the entire surface and also calculated from the raw data for a single meridian. RESULTS: Both apical radius and asphericity stabilized as the number of responses contributing to the mean increased. Repeat measurement for the entire surface of a three-measurement mean result was +/-0.090 mm for apical radius and +/- 0.151 for the p-value. The results for a single meridian, on repeat measurement, will lie within +/- 0.069 mm and +/- 0.051, respectively. CONCLUSIONS: Little improvement in stability or repeatability was observed after a three-measurement mean. The error and repeatability of the measurement appear to be better in this investigation when only a single meridian is analyzed. Thus, instrument software might be improved by providing analysis of apical radius and asphericity for a single, selectable meridian.

Importance of fixation, pupil center, and reference axis in ocular wavefront sensing, videokeratography, and retinal image quality.

PURPOSE: To examine the impact of the location of the fixation target, pupil center, and reference axis of ophthalmic aberrometers and videokeratographers on the measurement of corneal aberrations relevant to vision. SETTING: Clinical Research, Visual Optics Institute, College of Optometry, University of Houston, Houston, Texas, USA. METHODS: The design features of a generic aberrometer and videokeratographer and their interaction with the eye were examined. The results provided a theoretical framework for experimental assessment of pupil translation errors on corneal aberrations relevant to vision and their correction in 129 eyes. RESULTS: Two key principles emerged. First, the aberrometer's measurement axis must coincide with the eye's line-of-sight (LoS). Second, the videokeratographer's measurement axis (the vertex normal) must be parallel with the eye's LoS. When these principles are satisfied, the eye will be in the same state of angular rotation and direct comparison of measurements is justified, provided any translation of the pupil from the vertex normal is taken into account. The error incurred by ignoring pupil displacement in videokeratography varies between eyes and depends on the type of aberration and amount of displacement, with the largest residual correction root-mean-square wavefront error being 1.26 mum over a 6.0 mm pupil, which markedly decreases retinal image quality. CONCLUSION: Translation of the pupil center with respect to the vertex normal in videokeratography should not be ignored in the calculation of the corneal first-surface, internal aberrations of the eye relevant to vision, or the design of refractive corrections based on videokeratography.

Corneal topographer based on the Hartmann test.

PURPOSE: The purpose of this article is to show the performance of a topographer based on the Hartmann test for convex surfaces of F/# approximately 1. This topographer, called "Hartmann Test topographer (HT topographer)," is a prototype developed in the Physics Department of the Universidad Nacional de Colombia. METHODS: From the Hartmann pattern generated by the surface under test, and by the Fourier analysis and the optical aberration theory we obtain the sagitta (elevation map) of the surface. Then, taking the first and the second derivatives of the sagitta in the radial direction we obtain the meridional curvature map. The method is illustrated with an example. RESULTS: To check the performance of the HT topographer a toric surface, a revolution aspherical surface, and two human corneas were measured. Our results are compared with those obtained with a Placido ring topographer (Tomey TMS-4 videokeratoscope), and we show that our curvature maps are similar to those obtained with the Placido ring topographer. CONCLUSIONS: The HT topographer is able to reconstruct the corneal topography potentially eradicating the skew ray problem, therefore, corneal defects can be visualized more. The results are presented by elevation and meridional curvature maps.

A comparison of the Goldmann applanation and non-contact (Keeler Pulsair EasyEye) tonometers and the effect of central corneal thickness in indigenous African eyes.

UNLABELLED: The Keeler Pulsair EasyEye non-contact tonometer (NCT) was introduced into practice at Rachel Eye Center Abuja, Nigeria, where the patients are indigenous Africans. This was compared to the 'gold standard' Goldmann applanation tonometer (GAT) to determine if the instrument was accurate in Africans, with particular reference to the influence of central corneal thickness (CCT). PATIENTS AND METHODS: 174 eyes of 88 patients were analysed. Pachymetry was performed using Sonomed PacScan AP300, and GAT with the Haag Streit R-900. Pachymetric corrections of NCT (NCTc) and GAT (GATc) were carried out with the Sonomed algorithm. Pearson's correlation r, linear regression analysis, Student t-test and Bland-Altman analysis were used to compare the instruments. RESULTS: Mean NCT readings were similar (17.36 mmHg) to mean GAT (17.42 mmHg; p = 0.769). GAT/NCT correlation coefficient, r, was 0.883 as compared with 0.868 for GATc/NCTc. The linear regression equation was GAT = 2.79 + 0.84*NCT (r(2) = 0.78). Forty-five per cent of differences were within 1 mmHg, while 79% were within 3 mmHg. This was similar to findings in some studies on Caucasians. Bland-Altman analysis however suggested that the spread of differences was wider than in those studies. Outliers (differences more than 5 mmHg) sometimes reflected difficulties encountered with GAT in routine practice. Mean CCT was 537.9 microm, (S.D. 38.4, 95% confidence interval 532.1-543.7 microm) and CCT appeared lower than in Caucasians. Both GAT and NCT IOP tended to rise with increasing CCT but NCT had a greater tendency to do so. Regression analysis suggested that NCT IOP increased by 0.6 mmHg for every 10 mum increase in CCT, compared to 0.4 mmHg for GAT. Thirty-eight per cent of the patients preferred NCT as opposed to 25% GAT. CONCLUSIONS: The Keeler Pulsair EasyEye gives reliable measurements of IOP in African eyes but is significantly affected by CCT. Particularly in borderline cases where management decisions have to be taken, it may be necessary to have pachymetric corrections based on an NCT algorithm, which appears steeper than the GAT algorithm.

Tear film surface quality with soft contact lenses using dynamic-area high-speed videokeratoscopy.

OBJECTIVES: To evaluate the performance of the dynamic-area high-speed videokeratoscopy technique in the assessment of tear film surface quality with and without the presence of soft contact lenses on eye. METHODS: Retrospective data from a tear film study (Kopf et al., J Optom. 2008;1:14-21) using basic high-speed videokeratoscopy, captured at 25 frames per sec, were used. Eleven subjects underwent tear film analysis conducted in the morning, midday, and evening on the first and seventh day of 1 week of no lens wear. Five of the 11 subjects then completed an extra week of hydrogel lens wear, followed by a week of silicone hydrogel lens wear. Analysis was performed on a 6-sec period of the interblink recording. The dynamic-area high-speed videokeratoscopy technique uses the maximum available area of Placido ring pattern reflected from the tear interface and eliminates regions of disturbance because of shadows from the eyelashes. A value of tear film surface quality was derived using image-processing techniques based on the quality of the reflected ring pattern orientation. RESULTS: The group mean tear film surface quality and the standard deviations for each of the conditions (bare eye, hydrogel lens, and silicone hydrogel lens) showed a much lower coefficient of variation than that of previous methods (average reduction of approximately 92%). Bare eye measurements from the right and left eyes of 11 individuals showed high correlation values (Pearson correlation r = 0.73, P<0.05). Repeated measures ANOVA across the 6-sec period of measurement in the normal interblink period for the bare eye condition showed no statistically significant changes. However, across the 6-sec interblink period with both the contact lenses, statistically significant changes were observed (P<0.001). Overall, wearing hydrogel and silicone hydrogel lenses caused the tear film surface quality to worsen compared with that of the bare eye condition (repeated measures ANOVA, P<0.0001 for both the hydrogel and silicone hydrogel). CONCLUSIONS: The results suggest that the dynamic-area method of high-speed videokeratoscopy was able to distinguish and quantify the subtle, but systematic worsening of tear film surface quality in the interblink interval in contact lens wear. It was also able to clearly show a difference between bare eye and contact lens wearing conditions.

Analysis of Intrasession Repeatability of Ocular Aberrometric Measurements and Validation of Keratometry Provided by a New Integrated System in Mild to Moderate Keratoconus.

PURPOSE: To evaluate the intrasession repeatability and validity of corneal curvature measurements provided by a new multifunctional device and to assess the intrasession repeatability of its ocular aberrometric measures. METHODS: This prospective study comprises 37 mild to moderate keratoconus eyes of 37 patients. In all cases, 3 repeated measures of corneal topography and ocular aberrometry were performed with the iDesign 2 system (iD2; Johnson & Johnson Vision Care Inc, Jacksonville, FL) and one keratometric measurement was performed with the intraocular lens-(IOL) Master 500 (Carl Zeiss Meditec Inc, Dublin, CA) and Sirius (CSO) (SIR) systems. RESULTS: The within-subject SD (Sw) was <0.50 D for all iD2 keratometric measurements, with intraclass correlation coefficient (ICC) >0.980. Sw and ICC for the keratometric axis were 2.60 degrees and 0.992, respectively. Concerning aberrations, all Sw values for high-order Zernike terms were ≤0.11 µm (ICC > 0.900), and all Sw values for refraction data were <0.75 D (ICC > 0.95), except for J45. No statistically significant differences were found between the devices in any keratometric parameter evaluated (P ≥ 0.222), but the limits of agreement between the devices were clinically relevant. The magnitude of K readings and astigmatism correlated significantly with the difference in these parameters between iD2 and SIR (0.432 ≤ r ≤ 0.489, P ≤ 0.041). CONCLUSIONS: The iD2 system provides consistent measures of keratometry and ocular aberrometry in eyes with mild to moderate keratoconus. Keratometric data obtained with this system in these eyes cannot be considered as interchangeable with data provided by intraocular lens-Master 500 and SIR.