Pentacam System Research Articles

Study on the change of optical zone after femtosecond laser assisted laser in situ keratomileusis

Objective: To explore the change of optical zone after femtosecond laser assisted laser in sitn keratomileusis(FS-LASIK) so as to provide the reference for measurement and design of clinical optical zone. Methods: This retrospective case series study covers 41 eyes of 24 patients (7 males and 17 females, aged from 18 to 42 years old) with myopia and myopic astigmatism who have received FS-LASIK surgery at Corneal Refractive Department of Qingdao Eye Hospital and completed over 6 months of clinical follow-up. Pentacam system (with the application of 6 corneal topographic map modes including: the pure axial curvature topographic map, the pure tangential curvature topographic map, the axial curvature difference topographic map, the tangential curvature difference topographic map, the postoperative front elevation map and the corneal thickness difference topographic map), combined with transparent concentric software (a system independently developed by Qingdao Eye Hospital) was used to measure the optical zone at 1, 3 and 6 months postoperatively, the optical zone diameters measurement results among different follow-up times in group were analyzed with the repeated measures analysis of variance, and the actual measured values and the theoretical design values of the optical zone were analyzed with independent-samples t-testing. Spearman correlation coefficient (r(s)) have been applied to evaluate the relationship between postoperative optical zone measurement values and the potential influencing factors. Results: The optical zone diameters measured by pure axial curvature topographic map at 1, 3 and 6 months after FS-LASIK showed (6.55±0.50)mm, (6.50±0.53)mm and (6.48±0.53)mm respectively. The differences between values are of no statistical significance (F=1.60, P=0.21), the optical zone diameter measured by pure tangential curvature topographic map at 1, 3 and 6 months after FS-LASIK showed (5.44±0.46)mm, (5.46±0.52)mm and (5.44±0.50)mm respectively, the differences between values are of no statistical significance (F=0.17, P=0.85). The optical zone diameters measured by postoperative front elevation map at 1, 3 and 6 months after FS-LASIK showed (5.06±0.28)mm, (5.12±0.32)mm and (5.17±0.28)mm respectively. The differences between the values of 3 and 6 months postoperatively are of no statistical significance (F=6.14, P=0.15), the optical zone diameters measured by axial curvature difference topographic map at 1, 3 and 6 months after FS-LASIK showed (6.51±0.37)mm, (6.45±0.41)mm and (6.41±0.40)mm respectively, and the differences between the values of 3 and 6 months postoperatively are of no statistical significance (F=7.25, P=0.05). The optical zone diameters measured by tangential curvature difference topographic map at 1, 3 and 6 months after FS-LASIK showed (5.21±0.23)mm, (5.16±0.19)mm and (5.17±0.20) mm respectively, and the differences between the values of 1 and 3 months postoperatively are of statistical significance (F=1.75, P=0.04). The optical zone diameters measured by corneal thickness difference topographic map at 1, 3 and 6 months after FS-LASIK showed (6.53±0.40)mm, (6.39±0.43)mm and (6.41±0.47)mm respectively, and the differences between the values of 1 and 3 months postoperatively are of statistical significance (F=1.67, P=0.032). The actual measured optical zone values from the 6 different modes of Pentacam system are less than the theoretical design values (7.75 mm), and the differences were statistical significance (t=-15.42, -29.39, -59.27, -21.47, -81.69, -18.22, P<0.01). Conclusions: The optical zone measurement values tend to be stable at 3 months after FS-LASIK. The actual measured values from all the 6 different modes of Pentacam system were less than the theoretical design values. The results from pure tangential curvature topographic map, the tangential curvature difference topographic map and the postoperative front elevation map showed greater variation with clear border, which was beneficial for eccentric research. The results from pure axial curvature topographic map, the axial curvature difference topographic map and the corneal thickness difference topographic map were close to the theoretically designed values. Furthermore, the axial curvature difference topographic map showed clearer border and less variation thus maybe more favorable for measuring optical zone in clinical application.(Chin J Ophthalmol, 2018, 54: 39-47).

Analysis on the role of Sirius combined topography and tomography system in screening for suspect keratoconus

Objective: To evaluate the role of Sirius combined topography and tomography system in screening for suspect keratoconus among the corneal refractive surgery candidates. Methods: Retrospective case series study. Eight hundred and sixteen consecutive ametropic patients (1 632 eyes) who underwent routine examinations before corneal refractive surgery at Peking University Third Hospital from January 2016 to September 2016 were reviewed. All the cases were analyzed with Sirius combined topography and tomography system. Fifty-nine eyes of 37 patients, aged (28.9±7.4) years, classified as suspect keratoconus by the system were enrolled in the suspect group, including 25 females (40 eyes) and 12 males (19 eyes). A random eye of the first 59 patients, aged (27.1±6.4)years, whose both eyes were classified as normal by Sirius system were enrolled in the control group, including 38 females and 21 males. The corneal anterior surface, posterior surface and minimum thickness data of the suspect group were analyzed and then compared with the control group. The classified results were further verified by Pentacam system. Independent-samples t test and Mann-Whitney U test were applied to analyze the normal distribution and non-normal distribution data respectively. Results: The medians of anterior surface and posterior surface symmetry index and Baiocchi Calossi Versaci index of anterior surface and posterior surface of the suspect group were 0.84, 0.22, 0.58 and 0.51 D, and that of the control group were 0.05, 0.04, 0.09 and 0.06 D, and the differences were of statistical significance (Z=-18.764, -8.351, -12.248, -10.709, P<0.01). Mean corneal minimum thickness data of the suspect group were (504.4±30.0)μm, and that of the control group were (541.2±32.1)μm, the differences were of statistical significance (t=-6.408, P<0.01). In the suspect group, the eyes related with suspect or abnormal corneal anterior indices accounted for 47.5% (28/59), the eyes related with suspect or abnormal corneal posterior indices accounted for 55.9% (33/59), and the eyes related with suspect or abnormal corneal minimum thickness accounted for 40.7% (24/59). In the suspect group, 45 eyes (76.3%) were classified as suspect or abnormal according to the overall variance index "D" by Belin-Ambrósio Display (BAD) of the Pentacam system, and the other 14 eyes exhibited at least one abnormal index related with keratoconus. Conclusions: Sirius 3D combined topography and tomography and its integral automatic classification system is capable to screen out the suspect keratoconus simply and effectively. These indices maybe arranged in descending order in terms of the sensitivity as corneal posterior surface, followed by corneal anterior surface and then corneal thinnest point thickness. (Chin J Ophthalmol, 2018, 54: 33-38).

Validation of Fourier analysis of videokeratographic data.

The aim was to assess the repeatability of Fourier transfom analysis of videokeratographic data using Pentacam in normal (CG), keratoconic (KC) and post-CXL (CXL) corneas. This was a prospective, clinic-based, observational study. One randomly selected eye from all study participants was included in the analysis: 62 normal eyes (CG group), 33 keratoconus eyes (KC group), while 34 eyes, which had already received CXL treatment, formed the CXL group. Fourier analysis of keratometric data were obtained using Pentacam, by two different operators within each of two sessions. Precision, repeatability and Intraclass Correlation Coefficient (ICC), were calculated for evaluating intrassesion and intersession repeatability for the following parameters: Spherical Component (SphRmin, SphEcc), Maximum Decentration (Max Dec), Regular Astigmatism, and Irregularitiy (Irr). Bland-Altman analysis was used for assessing interobserver repeatability. All parameters were presented to be repeatable, reliable and reproductible in all groups. Best intrasession and intersession repeatability and reliability were detected for parameters SphRmin, SphEcc and Max Dec parameters for both operators using ICC (intrasession: ICC>98%, intersession: ICC>94.7%) and within subject standard deviation. Best precision and lowest range of agreement was found for the SphRmin parameter (CG: 0.05, KC: 0.16, and CXL: 0.2) in all groups, while the lowest repeatability, reliability and reproducibility was detected for the Irr parameter. The Pentacam system provides accurate measurements of Fourier tranform keratometric data. A single Pentacam scan will be sufficient for most clinical applications.

Comparison of visual effects of FS-LASIK for myopia centered on the coaxially sighted corneal light reflex or the line of sight.

To compare visual quality after femtosecond laser in situ keratomileusis (FS-LASIK), between the coaxially sighted corneal light reflex (CSCLR) group and conventional ablation line of sight (LOS) group. In total, 243 eyes (122 patients) were treated with centration on the CSCLR (visual axis) and 238 eyes (119 patients) treated with centration on the pupil center (LOS). Postoperative outcomes [uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA)], safety index, efficacy index, refractive outcome, ablation center distance from the visual axis, corneal high-order aberrations, subjective discomfort glare and shadowing incidence rate, and contrast sensitivity at 1, 3, and 6mo were measured and compared. The mean age was 27.77±7.1y in the CSCLR group and 26.03±7.70y in the LOS group. Preoperatively, the manifest refraction spherical equivalent (MRSE) was -6.68±2.60 D in the CSCLR group and -6.65±2.68 D in the LOS group. The postoperative UCVA, BSCVA, MRSE (-0.03±0.263 D in the CSCLR group, -0.05±0.265 D in the LOS group), efficacy index (1.04, 1.03), and safety index (1.09, 1.08) were not significantly different between the groups (all P>0.05). In total, 3% lost one line and more of BSCVA in the CSCLR group, as 9% in the LOS group postoperatively (P<0.05). The ablation center deviation was 0.20±0.15 mm from the visual axis (Pentacam system default setting; range, 0-0.75 mm) in the CSCLR group, and 0.43±0.22 mm (range, 0-1.32 mm) in the LOS group (P<0.0001). Statistically significant greater augmentation of total corneal higher-order aberrations (0.15±0.10 µm and 0.20±0.12 µm respectively, P=0.03) and vertical and horizontal coma (P<0.0001) were noted in the LOS group. Subjective discomfort glare and shadowing incidence rates were 8.59% and 17.5% in the CSCLR and LOS groups, respectively (P<0.05). The 1-month postoperative contrast sensitivity visual acuity in the CSCLR group was significantly higher than that in the LOS group on contrast (100%, 25%, 10%) with a dark background, but there was no significant difference between the groups at 3 or 6m. Myopic LASIK centered on the CSCLR achieves significantly lower induction of loss of BSCVA, corneal high-order aberrations, and lower risk of subjective discomfort glare and shadowing, and lower decline in early contrast sensitivity by comparison with centration on the LOS, giving advantages in visual quality postoperatively.

The effects of tolterodine on anterior segment and choroidal thickness in patients with overactive bladder syndrome.

To evaluate the effects of tolterodine on anterior segment and choroidal thickness by using the Pentacam system and optical coherence tomography (OCT) (Pentacam). A total of 122 eyes of 61 patients (34 female; 27 male) were included in the study. All patients underwent a regular ocular examination and intraocular pressure measurements before and after 3 months of antimuscarinic drug tolterodine treatment, in addition, pupil diameter, anterior chamber depth, anterior chamber volume, anterior chamber angle, and lens thickness were measured through Pentacam (Oculus Inc., Wetzlar, Germany) system. Measurements of choroidal thickness were performed by OCT (Spectralis®, Heidelberg Engineering, Heidelberg, Germany). The mean age was 58.4 ± 7.3 years and 56.5 ± 11.1 years for female and male patients. The mean intraocular pressure was 15.10 ± 2.75 mmHg before treatment and 15.18 ± 2.65 mmHg after treatment. Pupil diameters were 3.09 ± 0.48 mm before treatment and 3.12 ± 0.43 mm after treatment. Anterior chamber depth, before and after treatment were 2.68 ± 0.65 mm and 2.70 ± 0.61 mm. The mean value for subfoveal choroidal thickness was 267.92 ± 81.35 μm before the administration of tolterodine, whereas the mean choroidal thickness was 271.83 ± 75.42 μm after the administration of tolterodine. The alterations in the subfoveal choroidal thickness were not statistically significant (p = 0.862). After 3 months of therapy with tolterodine, there were no significant changes in anterior segment parameters and choroidal thickness.

Corneal Backscatters as an Objective Index for Assessing Fuchs' Endothelial Corneal Dystrophy: A Pilot Study.

Purpose To provide an objective, quantitative approach for monitoring Fuchs' endothelial corneal dystrophy (FECD), with Scheimpflug imaging. Design This is a retrospective case-control pilot study. Methods The study group consisted of 53 eyes in 27 patients diagnosed with FECD, with normal subjects paired as control. Main outcome measures were corneal thickness, morphological patterns on densitograms, and indices of corneal density including the average area density (mean AD) and the average ratio of Descemet's membrane density versus area density (DM/AD) in Pentacam Scheimpflug images. Results There were no significant differences in age and corneal thickness between FECD and normal groups. Morphologically, hanging-hammock patterns were noted on the densitograms of FECD patients, which were different from the high-back chair patterns in normal subjects. Quantitatively, mean AD and DM/AD were both elevated in FECD patients as compared with normal subjects (P = 0.01 and 0.025, resp.). In addition, FECD patients with corneal edema had significantly higher mean AD (P = 0.018) than those without corneal edema. Conclusions This pilot study shows that Pentacam system provides an objective, quantitative way to approach FECD corneas. It can assist ophthalmologists in detecting the early change and in monitoring disease progression of FECD. Further studies are needed to consolidate the findings.

Corneal densitometry and its correlation with age, pachymetry, corneal curvature, and refraction

To determine normative corneal densitometry values in relation to age, sex, refractive error, corneal thickness, and keratometry, measured using the Oculus Pentacam system. Three hundred and thirty-eight healthy subjects (185 men; 153 women) with no corneal disease underwent an exhaustive ocular examination. Corneal densitometry was expressed in standardized grayscale units (GSU). The mean corneal densitometry over the total area was 16.46±1.85 GSU. The Pearson correlation coefficient for total densitometry was r=0.542 (p<0.001). Statistically significant differences were found between men and women for the total area (p=0.006), with readings of 16.22±1.54 GSU and 16.60±1.83 GSU, respectively. When the cornea was divided into layers of different depths, a significant correlation was found for all layers and age: r=0.447 (p<0.001), r=0.563 (p<0.001), and r=0.520 (p<0.001) for the anterior, central, and posterior layers, respectively. However, when the cornea was divided into concentric annuli starting from the center of the cornea, densitometry was strongly correlated only with age in the 6-10-mm annulus (p<0.001). Neither mean keratometry nor spherical equivalent was correlated with corneal densitometry in any zone of the cornea (p>0.05). This is the first report of normative corneal densitometry values in relation to keratometry, corneal thickness, and spherical equivalent measured with the latest Oculus Pentacam software. Corneal densitometry increases with age, but corneal keratometry and refractive parameters do not affect light scattering in the human cornea.

Comparison of visual effects after LASIK in myopia between centered on the coaxially sighted corneal light reflex and line of sight

To compare visual acuity, refractive outcome, high order aberrations, contrast sensitivity and subjective symptom of myopia with laser in situ keratomileusis (LASIK) centered on the coaxially sighted corneal light reflex (CSCLR group) and the conventional ablation of line of sight (LOS group). With prospective, double-blind, randomized, controlled trial, the right eyes of patients were included and divided into two groups according to random stratified grouping. Two hundred and ten myopic eyes were treated with centration on the coaxially sighted corneal light reflex and 210 myopic eyes treated with centration on pupil center(line of sight). The parameters of visual acuity, refractive outcome, ablation center distance from visual axis, corneal high order aberrations, subjective discomfort glare and shadowing incidence rate, contrast sensitivity between the two groups were measured and compared up to 6months post operation. Consistent with the measurement data, normal distribution using the group t-test, non-normal distribution of measurement data using the group wilcoxon rank-sum test and count data using chi-square test. The data of postoperative UCVA, BCVA, MRSE efficacy index and safety index showed no statistical difference between the CSCLR and the LOS group up to 6months post operation(P> 0.05). 3% lost one line or more of BCVA in the CSCLR group,and 9% in the LOS group postoperatively, χ(2)= 6.38, P=0.01. The ablation center deviation was (0.19±0.15) mm from visual axis(pentacam system default setting) in CSCLR group and (0.43±0.22) mm in the LOS group. Ablation center deviation was statistically significantly shorter in the CSCLR group (t=-2.59, P<0.01). The postoperative increased total cornea higher order aberrations was 0.150 μm in CSCLR group and 0.193 μm in LOS group, the difference was statistically significant, Z=3.21, P=0.03. The increased corneal vertical coma of CSCLR group was 0.321 μm,smaller than in the LOS group(0.464 μm), Z=4.33, P<0.01. The increased horizontal coma was 0.242 μm in CSCLR group and also smaller than the LOS group(0.353 μm), Z=4.54,P<0.01. Subjective discomfort glare and shadowing incidence rates were 8.5% and 17.5% respectively in the CSCLR and LOS group, χ(2)=7.16,P< 0.01. The one month postoperative contrast sensitivity visual acuity in the CSCLR was 1.157 ± 0.253, significantly higher than the LOS group (0.797±0.218) on 18 c/d spatial frequency, t=- 2.55, P=0.01, but with no significant difference between the two groups at 3 and 6 months. Myopic LASIK centered on the CSCLR achieved significant lower induction of lost of BCVA, lower induction of high order aberrations, lower risk of subjective discomfort glare and shadowing and lower decline of early contrast sensitivity by comparison to centration on the LOS, improving the quality of vision after operation. (Chin J Ophthalmol, 2016, 52: 499-506).

The variability of corneal and anterior segment parameters in keratoconus.

To analyse, describe and test diverse corneal and anterior segment parameters in normal and keratoconic eyes to better understand the geometry of the keratoconic cornea. 44 eyes from 44 keratoconic patients and 44 eyes from 44 healthy patients were included in the study. The Pentacam System was used for the analysis of the anterior segment parameters. New ad-hoc parameters were defined by measuring the distances on the Scheimpflug image at the horizontal diameter, with chamber depth now comprising of two distinctive distances: corneal sagittal depth and the distance from the endpoint of this segment to the anterior surface of the lens (DL). Statistically significant differences (p<0.05) between normal and keratoconic eyes were found in all of the analysed corneal parameters. Anterior chamber depth presented statistical differences between normal and keratoconic eyes (3.06±0.43mm versus 3.34±0.45mm, respectively; p=0.004). This difference was found to originate in an increase of the DL distance (0.40±0.33mm in normal eyes against 0.61±0.45mm in keratoconic eyes; p=0.014), rather than in the changes in corneal sagittal depth. These findings indicate that keratoconus results in central and peripheral corneal manifestations, as well as changes in the shape of the scleral limbus. The DL parameter was useful in describing the forward elongation and advance of the scleral tissue in keratoconic eyes. This finding may help in the monitoring of disease progression and contact lens design and fitting.

Corneal biomechanics in normal Saudi individuals

PurposeThe aim of this study was to determine and relate corneal biomechanical metrics with demographic, tomographic and refractive data in healthy Saudi people. DesignProspective, cross-sectional, observational study. ParticipantsThe study included 215 normal Saudi adult individuals. MethodsCorneal hysteresis (CH) and corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg) and corneal-compensated intraocular pressure (IOPcc) were measured by ocular response analyzer. The central keratometry (CK), central corneal thickness (CCT), and anterior chamber depth (ACD) were measured using Pentacam system. The spherical equivalent of refraction (SER) was obtained by an Auto-refractometer. ResultsThe mean CH was 11.16±2.11, CRF was 11.07±2.31 and IOP was 15.12±3.5. Mean CK, ACD, CH and CRF were distinct among gender with the significant P values of 0.05, 0.006, 0.020, and 0.047 respectively. CRF was negatively correlated with ACD (r=−0.146, P=0.032). A positive correlation was found between CRF and SER (r=0.176, P=0.010), CCT (r=0.447, p=0.000) and CH (r=0.878 and p=0.000). CH was negatively correlated with IOPcc (−0.433, p=0.000). A positive correlation was found between CH and ACD (r=−0.14, p=0.044), SER (r=0.617, p=0.014), CCT (r=0.412, p=0.000) and IOPg (r=0.183, p=0.007). ConclusionThis study demonstrated a distinct difference among gender values of corneal hysteresis and corneal resistance factor being higher in female Saudi subjects. CH and CRF values were higher in Saudi subjects than values in other populations. This may suggest the presence of ethnic differences in ocular parameters and support the importance of establishing population norms for corneal biomechanical parameters.

Evaluation of corneal higher order aberrations in normal topographic patterns

PurposeThis study reports the characteristics of corneal higher order aberrations (HOAs) in eyes with normal topographic pattern using the Pentacam scheimpflug system. MethodsIn this prospective, observational, comparative study, 165 eyes of 97 patients separated into five groups based on corneal topographic patterns were enrolled. All eyes received a comprehensive ophthalmologic examination including corneal tomographic analysis with the Pentacam system. Keratometry, corneal cylinder, and corneal aberrometric data were recorded and analyzed. Root mean square values (RMS) were calculated for corneal HOAs up to the 6th order, total coma, total trefoil, total spherical aberration, total tetrafoil, and higher order astigmatism. Evaluation of these data to discriminate between the five groups was assessed using the analysis of variance test by Generalized Estimation Equation Linear Model. ResultsCorneal HOAs were found to be significantly higher for Asymmetric Bow Tie and Irregular groups than other groups (p = <0.001). RMS of total coma aberration (Z3−1, Z31, Z5−1, Z51) were significantly greater in the Asymmetric Bow Tie pattern than others, and RMS of total Spherical aberration (Z40, Z60) was significantly higher in the Irregular pattern than other groups (p = <0.001). The results of our study demonstrate that a tendency toward significant higher values of trefoil, tetrafoil, and higher order astigmatism in Irregular pattern (all p < 0.05). Significantly higher amounts of 3rd order RMS in Asymmetric Bow Tie group and 4th to 6th order RMS in Irregular pattern group were other outcomes of our study (p = <0.001). ConclusionsBased on results in this study, there were a good correlation between corneal topographic pattern and corneal HOAs in normal eyes. These results indicate that the corneal HOAs values are largely determined by the topographic patterns. A larger sample size would perhaps have been beneficial to yield in more accurate outcomes.

Errors Associated to Keratoconus Grading using Systems based on Corneal Power

ABSTRACT Purpose To analyze and define the possible errors that may be introduced in keratoconus classification when the keratometric corneal power is used in such classification. Materials and methods Retrospective study including a total of 44 keratoconus eyes. A comprehensive ophthalmologic examination was performed in all cases, which included a corneal analysis with the Pentacam system (Oculus). Classical keratometric corneal power (Pk), Gaussian corneal power (PcGauss), True Net Power (TNP) (Gaussian power neglecting the corneal thickness effect), and an adjusted keratometric corneal power (Pkadj) (keratometric power considering a variable keratometric index) were calculated. All cases included in the study were classified according to five different classification systems: Alió-Shabayek, Amsler-Krumeich, Rabinowitz- McDonnell, collaborative longitudinal evaluation of keratoconus (CLEK), and McMahon. Results When Pk and Pkadj were compared, differences in the type of grading of keratoconus cases was found in 13.6% of eyes when the Alió-Shabayek or the Amsler-Krumeich systems were used. Likewise, grading differences were observed in 22.7% of eyes with the Rabinowitz-McDonnell and McMahon classification systems and in 31.8% of eyes with the CLEK classification system. All reclassified cases using Pkadj were done in a less severe stage, indicating that the use of Pk may lead to the classification of a cornea as keratoconus, being normal. In general, the results obtained using Pkadj, PcGauss or the TNP were equivalent. Differences between Pkadj and PcGauss were within ± 0.7D. Conclusion The use of classical keratometric corneal power may lead to incorrect grading of the severity of keratoconus, with a trend to a more severe grading. How to cite this article Llorens DPP, Camps V, Caravaca-Arens E. Errors Associated to Keratoconus Grading using Systems based on Corneal Power. Int J Kerat Ect Cor Dis 2015;4(2):41-46.

Responses of the Ocular Anterior Segment and Refraction to 0.5% Tropicamide in Chinese School-Aged Children of Myopia, Emmetropia, and Hyperopia.

Purpose. To investigate the changes of anterior segment after cycloplegia and estimate the association of such changes with the changes of refraction in Chinese school-aged children of myopia, emmetropia, and hyperopia. Methods. 309 children were recruited and eligible subjects were assigned to three groups: hyperopia, emmetropia, or myopia. Cycloplegia was achieved with five cycles of 0.5% tropicamide. The Pentacam system was used to measure the parameters of interest before and after cycloplegia. Results. In the myopic group, the lenses were thinner and the lens position was significantly more posterior than that of the emmetropic and hyperopic groups in the cycloplegic status. The correlations between refraction and lens thickness (age adjusted; r = 0.26, P < 0.01), and lens position (age adjusted; r = −0.31, P < 0.01) were found. After cycloplegia, ACD and ACV significantly increased, while ACA significantly decreased. Changes in refraction, ACD, ACV, and ACA were significantly different among the three groups (P < 0.05, all). Changes of refraction were correlated with changes of ACD (r = 0.41, P < 0.01). Conclusions. Myopia presented thinner lenses and smaller changes of anterior segment and refraction after cycloplegia when compared to emmetropia and hyperopia. Changes of anterior chamber depth were correlated with refraction changes. This may contribute to a better understanding of the relationship between anterior segment and myopia.

Comparison of two different scheimpflug devices in the detection of keratoconus, regular astigmatism, and healthy corneas.

Aim. The aim of this study was to determine the intra- and interobserver variability of two Scheimpflug based camera systems, Pentacam and Sirius. In addition, the comparability of the measurements was tested in healthy subjects, subjects with regular astigmatism, and keratoconus patients. Methods. Intra- and interobserver variability were assessed in 20 healthy corneas. Pachymetry values were also compared with ultrasound pachymetry as a reference measurement. To detect possible differences between the two devices, 82 eyes with clinically established keratoconus, 30 eyes with regular astigmatism (>1.5 D), and 60 eyes without corneal pathologies were included in this prospective study. Results. Pachymetry and keratometry showed good intra- and interobserver variability for both devices. Pachymetry values obtained with the Sirius system (579 ± 58 μm) were significantly higher compared to the Pentacam system (551 ± 40 μm, P < 0.001) and to ultrasound pachymetry (550 ± 43 μm, P < 0.001). Significant interdevice differences were found regarding the majority of the detected keratometry parameters. Conclusions. Both devices show almost perfect reproducibility in healthy subjects. However, pachymetry and keratometry values of the two devices should not be used interchangeably.

Comparison of factors of intraocular pressure before and after excimer laser in situ keratomileusis in rabbit

Objective To compare the application value of dynamic contour tonometer （DCT） and non-contact tonometer （NCT） before and after laser-assisted in situ keratomileusis （LASIK） on eyes of rabbit. Methods Central corneal thickness and corneal curvature of 120 healthy New Zealand rabbits were measured by Pentacam system with DCT and NCT before and one month after surgery. Meanwhile, the intraocular pressure （IOP） value was checked by means of Ehlers, Shah, Dresden, Orssengo/Pye and Kohlhaas method. Results The value of DCT was the highest before and after surgery. The differences in DCT values and Ehlers correction values before and after surgery were not statistically significant （P 〉 0.05）; The differences in IOP correction by other methods before and after surgery were statistically significant （P 〈 0.01 ）. There was a positive correlation between preoperative and postoperative IOP values at each group. Conclusion The result of the IOP value measured by DCT is not influenced by the thickness of cornea, the curvature of cornea and axial length, which can be chosen as the preferred method of IOP measurement after LASIK. The NCT correction is a powerful supplement. Key words: Check, pressure, intraocular; Tonometer, contour, dynamic; Tonometer, non-contact; Contrast ; Keratomileusis, laser, excimer

Analysis of refractive status after cataract surgery in age-related cataract patients with shallow anterior chamber

To evaluate the characteristics of postoperative refractive status in age-related cataract patients with shallow anterior chamber and the correlation between pre-operative anterior chamber depth and postoperative refractive status. Prospective case-control study. Sixty-eight cases (90 eyes) with age-related cataract were recruited from October 2010 to January 2012 in People's Hospital Peking University including 28 cases (34 eyes) in control group and 40 cases (56 eyes) in shallow anterior chamber group according to anterior chamber depth (ACD) measured by Pentacam system. Axial length and keratometer were measured by IOL Master and intraocular lens power was calculated using SRK/T formula. Postoperative refraction, ACD and comprehensive eye examination were performed at 1 month and 3 months after cataract surgery. Using SPSS13.0 software to establish a database, the two groups were compared with independent samples t-test and correlation analysis were performed with binary logical regression. The postoperative refractive deviation at 1 month were (-0.39 ± 0.62) D in control group and (+0.73 ± 0.26) D in shallow anterior chamber group respectively which present statistical significance between the two groups (P = 0.00, t = 3.67); the postoperative refractive deviation in 3 month was (-0.37 ± 0.62) D in control group and (+0.79 ± 0.28) D in shallow anterior chamber group operatively which present statistical significance between the two groups (P = 0.00, t = 3.33). In shallow anterior chamber group, with the shallower of ACD, the greater of refractive deviation (P = 0.00, r1 month = -0.57, r3 months = -0.61). Hyperopic shift existed in age-related cataract patients with shallow anterior chamber and the shallower of ACD was, the greater of hyperopic shift happened.

Repeatability, reliability and reproducibility of posterior curvature and wavefront aberrations in keratoconic and cross‐linked corneas

BackgroundThe aim was to assess the intra‐session, inter‐session and inter‐observer repeatability of curvature and aberrometric measurements of Pentacam‐derived posterior corneal surface in normal control (CG), keratoconic (KCG) and after corneal collagen cross‐linked (CXLG) groups.MethodsThis was a prospective, clinic‐based, observational study that was conducted at the Eye Institute of Thrace (EIT) in Alexandroupolis, Greece. Sixty‐two normal eyes formed the control group, 33 were in the keratoconic group, while 34 eyes, which already had received corneal collagen cross‐linking formed the CXLG. Curvature and aberrometric measurements were obtained using the Pentacam by two operators within each of the two sessions. Precision (Pre), repeatability (COR) and the intra‐class correlation coefficient (ICC) were calculated for evaluating intra‐session and inter‐session repeatability. Bland–Altman analysis was used for assessing inter‐observer repeatability.ResultsSimulated keratometric parameters K1 and K2, asphericity at the central 8-mm zone (Q8) and central steepest radius of best fit toric ellipsoid reference body (Rs), achieved an acceptable level of accuracy. Aberrometric parameters were repeatable, reliable and reproducible only in terms of the root mean square (RMS) errors (coma, coma‐like and the RMS of higher order aberrations or HOA RMS). For both observers, best precision and lowest range of agreement (ROA) was found for HOA RMS parameters in all groups (less than 0.27 and less than 0.29 for the control group, less than 0.95 and less than 0.72 for the keratoconic group and less than 0.67 and 0.53 for the collagen cross‐linked group).ConclusionThe Pentacam system provides precise measurements of corneal posterior keratometry, reference body radius and asphericity for large diameter analysis. Although Zernike coefficients for individuals presented poor repeatability, the coma, coma‐like and HOA RMS seem to be accurate indices in characterisation of back corneal aberrations.

Ocular residual astigmatism and topographic disparity vector indexes in normal healthy eyes

To define a range of normality for the vectorial parameters Ocular Residual Astigmatism (ORA) and topography disparity (TD) and to evaluate their relationship with visual, refractive, anterior and posterior corneal curvature, pachymetric and corneal volume data in normal healthy eyes. This study comprised a total of 101 consecutive normal healthy eyes of 101 patients ranging in age from 15 to 64 years old. In all cases, a complete corneal analysis was performed using a Scheimpflug photography-based topography system (Pentacam system Oculus Optikgeräte GmbH). Anterior corneal topographic data were imported from the Pentacam system to the iASSORT software (ASSORT Pty. Ltd.), which allowed the calculation of the ocular residual astigmatism (ORA) and topography disparity (TD). Linear regression analysis was used for obtaining a linear expression relating ORA and posterior corneal astigmatism (PCA). Mean magnitude of ORA was 0.79 D (SD: 0.43), with a normality range from 0 to 1.63D. 90 eyes (89.1%) showed against-the-rule ORA. A weak although statistically significant correlation was found between the magnitudes of posterior corneal astigmatism and ORA (r=0.34, p<0.01). Regression analysis showed the presence of a linear relationship between these two variables, although with a very limited predictability (R(2): 0.08). Mean magnitude of TD was 0.89D (SD: 0.50), with a normality range from 0 to 1.87D. The magnitude of the vector parameters ORA and TD is lower than 1.9D in the healthy human eye.

Anterior Segment Changes Produced in Response to Long-Term Overnight Orthokeratology

Purpose: To evaluate the effect of overnight orthokeratology (OK) on anterior chamber depth (ACD), posterior radius of corneal curvature (PRCC) and axial length (AL) over one year.Methods: In this prospective longitudinal study, measurements were made in 34 right eyes of 34 subjects at baseline, 15 days, 1 and 12 months after starting OK treatment. ACD and PRCC measurements were obtained using a Pentacam system and AL was measured using an IOL-Master. ACD and PRCC were measured along the horizontal and vertical meridians at 1 mm intervals. These measurements were expressed as the distance from the center in the nasal (N), temporal (T), superior (S) and inferior (I) directions.Results: A significant reduction in ACD was observed in both meridians during treatment. PRCC flattened significantly in the (T) direction after 15 d (1 mm, p < 0.05), at the corneal center after 15 d (p < 0.01), in the (T) direction after 1 month (1 mm, p < 0.05), in the (S) direction after 12 months (1 mm p < 0.05), in the (N) direction after 12 months (1 mm p < 0.05), in the (N) and (T) directions after 12 months (3 mm, p < 0.05) and in the (T) direction after 12 months (4 mm p < 0.05), at the corneal center after 12 months (p < 0.01). AL was significantly reduced during treatment (p < 0.05).Conclusions: A long period of OK reduces ACD and AL and changes PRCC.

Evaluation of Corneal and Anterior Chamber Changes Following Pterygium Surgery Using a Pentacam Scheimplug System: A Prospective Study

Purpose: The aim of this study was to evaluate the effects of pterygium surgery on the corneal topography and anterior chamber parameters using a Pentacam system. Methods: Prospective clinical study. Scheimpflug camera was performed in 21 eyes of 21 patients with primary pterygium, both before and 2 months after pterygium excision using conjunctival autograft technique. The topographic parameters such as total mean refractive power, index of surface variance, abberation coefficent, anterior chamber depth, anterior chamber angle were evaluated. The best corrected visual acuity (BCVA) changes were also noted. Differences between preoperative and postoperative values were compared. Results: The mean refractive power was 42.59 ± 3.44 dioptry (D) preoperatively and 43.72 ± 2.07 D postoperatively (p = 0.154). The mean preoperative index of surface variance was 72.24 ± 48.72. It was decreased to 32 ± 23.13 after surgery (p = 0.003). The mean abberation coefficent was 3.04 ± 1.27 preoperatively. It was decreased to 2.4 ± 1.06 postoperatively (p = 0.017). The preoperative and postoperative values of the mean anterior chamber depth were 2.91 ± 0.49 mm and 2.91 ± 0.52 mm, respectively (p = 0.638). The mean preoperative anterior chamber angle was 33.13 ± 6.89°. It was measured as 32.77 ± 4.86° postoperatively (p = 0.779). The mean overall preoperative BCVA was logMar 0.13 ± 0.29. It was significantly improved to logMar 0.0238 ± 0.07 after pterygium surgery (p = 0.011). Conclusions: Corneal topographic changes induced by pterygium are almost reversible after surgical treatment of the pterygium. Pterygium surgery significantly improves the BCVA, and decreases the aberration coefficient and index of surface variance; however, it does not have any effect on the anterior chamber parameters.