Central Corneal Power Research Articles

In-vivo high-frequency quantitative ultrasound-derived parameters of the anterior sclera correlated with level of myopia and presence of staphyloma.

A high-frequency point-of-care (POC) ultrasound instrument was used to evaluate the microstructural and biomechanical properties of the anterior sclera in vivo using parameters computed from quantitative ultrasound (QUS) methods. In this cross-sectional study, both eyes of 85 enrolled patients were scanned with the POC instrument and ultrasound data were processed to obtain QUS parameters. Pearson correlation and multi-linear regression were used to identify relationships between QUS parameters and refractive error (RE) or axial length. After categorising eyes based on RE, binary support vector machine (SVM) classifiers were trained using the QUS or ophthalmic parameters (anterior chamber depth, central corneal thickness, corneal power, and intraocular pressure) to classify each eye. Classifier performance was evaluated by computing the area under the receiver-operating characteristic curve (AUC). Individual QUS parameters correlated with RE and axial length (p < 0.05). Multi-linear regression revealed significant correlation between the set of QUS parameters and both RE (R = 0.49, p < 0.001) and axial length (R = 0.46, p = 0.001). Classifiers trained with QUS parameters achieved higher AUC (𝑝 = 0.06) for identifying myopic eyes (AUC = 0.71) compared to classifiers trained with ophthalmic parameters (AUC = 0.63). QUS-based classifiers attained the highest AUC when identifying highly myopic eyes (AUC = 0.77). QUS parameters correlate with progressing myopia and may be indicative of myopia-induced microstructural and biomechanical changes in the anterior sclera. These methods may provide critical clinical information complementary to standard ophthalmic measurements for predicting myopia progression and risk assessment for posterior staphyloma formation.

Precision of a new SS-OCT biometer to measure anterior segment parameters and agreement with 3 instruments with different measurement principles.

To evaluate the repeatability of a new swept source optical coherence tomography (SS-OCT)-based biometer to measure anterior segment parameters and to assess the agreement with 3 other imaging devices based on different measurement principles. Unit of Eye and Vision, Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden. Prospective, comparative case series. 3 consecutive measurements were obtained in unoperated eyes with the Eyestar900 (SS-OCT), Lenstar 900, MS-39, and Sirius. The following anterior segment parameters were evaluated: central corneal thickness (CCT), corneal diameter (CD), aqueous depth (AQD), and corneal power metrics. The repeatability limit (Rlim), coefficient of variation (CoV), and a repeated measures Bland-Altman analysis were performed. 74 eyes of 74 participants were measured. The Rlims for CCT, CD, and AQD were lower than 10 μm, 0.3 mm, and 0.10 mm for all devices, respectively. The corresponding CoVs for these parameters never exceeded 1.2%. The Rlim for the corneal power metrics never exceeded 0.60 diopter (D) for any of the instruments. Lenstar showed the best agreement with the MS-39 to measure CCT, CD, and AQD (limit of agreement interval, LoA: 15.54 μm, 0.55 mm, and 0.16 mm, respectively). The mean difference for keratometry parameters was lower than 0.3 D for all device comparisons, and the LoA interval ranged between 0.52 D and 1.21 D. The repeatability for measuring anterior segment parameters was good, and the agreement among all the instruments was good for CD and AQD measurements. However, for CCT and keratometer parameters, the instruments cannot be used interchangeably due to large LoA interval.

PREVALENCE OF KERATOCONUS IN KASHMIR IN NORTH INDIA: A VIDEOKERATOGRAPHIC STUDY

Purpose: To detect the incidence of keratoconus by videokeratography in patients in Kashmir in North India and to describe the clinical characteristics associated with it. Design: Cross sectional study Methodology: This study was carried out on eyes of 212 patients between 5 to 20 years of age presenting to tertiary care hospital of Kashmir in north India over a period of two years. Best Corrected Visual Acuity (BCVA), slit lamp examination, pachymetry, refraction, fundus examination, and corneal topography was done in all the patients and clinical ndings recorded. To detect keratoconus, corneal topography maps were analysed using Rabinowitz-McDonnel criteria. Maps with central corneal power(Kmax) greater than 47.2 diopters and the inferosuperior asymmetry value greater than 1.4 were considered to have a keratoconus pattern. Results: Out of 212 patients, 145 were males and 67 were females. Majority were in the age group of 5- 10 years. Among the study eyes, Kmax&gt; 47.2 D was seen in 10.1 %, Sim K astigmatism &gt; 1.5D in 29%, I-S difference &gt; 1.4 D in 11.79 % , SRAX &gt; 21° in 20% and K max&gt;47.2 D + I-S Difference &gt;1.4 i.e keratoconus pattern was seen in 93 eyes i.e 21.9% Conclusion: Incidence of keratoconus in allergic patients is more when compared to general population of the same age group from previous studies. The videokeratographic examination of patients leads to early detection of mild keratoconus by interpretation of color-coded maps.

Relationship between Diurnal Variation in Intraocular Pressure and Central Corneal Power.

Relationship between intraocular pressure (IOP) change and central corneal curvature is complicated by measurement techniques and corneal biomechanical parameters. Findings from this study indicate that it is worthwhile to observe the association between diurnal change in IOP and corneal power. This study aimed to investigate the relationship between the diurnal change in IOP and central corneal power among eyes with and without myopia. Sixty healthy eyes of 24 emmetropes and 36 myopes were recruited for this cross-sectional study. Both anterior and posterior central corneal powers of the steep (Ks), flat (Kf), mean meridian (Km), best-fit spheres, and central corneal thickness were recorded followed by the IOP (Goldmann-correlated IOP [IOPg] and corneal-compensated IOP) and corneal biomechanics (corneal hysteresis and corneal resistance factor). Measurements were obtained every 3 hours from 9.30 am to 6.30 pm . Linear-mixed model was used to determine the relationship between the change in IOP and the associated change in corneal measurements (adjusted for age, sex, refractive error, central corneal thickness, and biomechanics) among the myopic and nonmyopic eyes. Group mean, amplitude of change, and the diurnal change in IOPg were (mean ± standard deviation) 15.14 ± 2.50, 3.33 ± 1.44, and 1.81 ± 1.25 mmHg, respectively. Overall, an IOP increase was associated with a decrease in the adjusted anterior corneal powers. Myopic eyes were associated with a decrease of 0.04 D (95% confidence interval [CI], 0.07 to 0.01 D; P = .02) in Ks and 0.03 D (95% CI, 0.06 to 0.001 D; P = .047) in Kf per mmHg increase in IOP, whereas for emmetropes, per mmHg increase in IOP only flattened the Kf by 0.03 D (95% CI, 0.06 to 0.004 D; P = .02). Change in anterior corneal power was inversely related to the change in IOPg, with myopic and nonmyopic eyes reporting a significant but differential impact of IOP. Clinicians must keep in mind the impact of large IOP fluctuation on the anterior corneal power.

A review of multivariate methods of analysing refractive data with dioptric power matrices

Background: There are three components to refractive state, namely sphere, cylinder and axis. Similarly, central corneal power is also composed of three components, namely the power along the flat meridian, the power along the steep meridian and the axis of the flat meridian. Most studies that investigate refractive data and corneal power analyse each of the three components individually rather than as a trivariate entity. In doing so, pertinent information may inadvertently be omitted. Aim: The purpose of this review is to provide a brief overview of the multivariate statistics that are available to analyse multivariate data such as dioptric power. This will enable readers to better understand research that is analysed using these methods. Method: An extensive review of databases such as Google Scholar, Science Direct and ResearchGate was done to gather publications on the topic of multivariate statistical analysis. Keywords such as multivariate statistical analysis, dioptric power, stereo-pairs, polar profiles and hypothesis testing were used to conduct the search. Results: The debate for the need to analyse dioptric power using multivariate statistical methods has been a long-standing one. For this review, more than 40 publications were analysed to provide a simplified overview of the multivariate statistical methods that can be used to analyse dioptric power. Conclusion: The use of multivariate statistical methods is a valuable tool in analysing and understanding dioptric power holistically and may provide more insights for research involving refractive error and corneal power.

Comparison study between Pilocarpine and Tropicamide drops on corneal topography and their effect on IL-6 and TNF-α levels in tear

Corneal stability is essential for contact lenses and refractive surgery. It seems that paralyzing eye drops or expansion of the ciliary muscle affect the radius of curvature and the strength of the cornea, and this effect is to increase the strength of the cornea during muscle spasm and decrease it in the relaxed state of the muscle. On the other hand, different factors (such as contact lens wear, ocular surface disorders, trauma, dry eye, and immunosuppression) could alter the immune defense mechanisms of the outer eye and permit microorganisms to invade the cornea. Therefore, the present study compared Pilocarpine and tropicamide drop on corneal topography and their effect on IL-6 and TNF-α levels in tear. This prospective study was performed on sixty normal and healthy eyes of sixty volunteers with a mean age of 38.19 years and without any ocular pathology. Volunteers were divided into two groups of thirty. In the first group, corneal topography of both eyes was measured before and 30 minutes after instillation of topical tropicamide 1% in only one eye. The other eye was the control eye, and no drop was given. The same routine was performed in the second group, except that subject received one drop of Pilocarpine 2% in one eye. Statistical comparison between groups for the central corneal power, corneal radius, and corneal astigmatism was performed using paired t-test. IL-6 and TNF-α levels in tear were analyzed using two Luminex commercial assays with Bio-Plex 200TM System (Bio-Rad, Hercules, California, USA). In group 1, no significant changes were found in corneal radius, power, and astigmatism. However, in group 2 subjects who received pilocarpine eye drops, the mean corneal radius value decreased significantly by 0.05 mm. The mean corneal power increased by +0.32 D. There was no significant difference change in corneal astigmatism in both groups. Evaluation of IL-6 levels in tears showed a significant difference between the control and treatment groups (P = 0.041). But no significant difference was observed between the Pilocarpine and the Tropicamide groups (P = 0.761). Evaluation of TNF-α level in tears also showed no significant difference between these groups (P = 0.088). Pilocarpine induced ciliary muscle contraction, which may cause pressure on the corneal limbus and scleral spur, resulting in changes in corneal curvature. But tropicamide eye drop did not affect corneal radius and other corneal parameters, and corneal topography can be carried out after the installation of tropicamide eye drop.

Novel corneal morphological alterations in Vogt-Koyanagi-Harada disease.

To determine whether visual function, especially when dependent on the anterior segment of ocular tissue, is altered during high-dose steroid treatment for Vogt-Koyanagi-Harada disease (VKH). Retrospective case series METHODS: This case series included 18 eyes of 18 patients with VKH who received high-dose steroid therapy as initial treatment. All patients underwent anterior swept-source optical coherent tomography (CASIA-2) examinations during their clinical course to measure the central corneal thickness (CCT), average central corneal power (ACCP), maximum curvature (Kmax) and anterior chamber depth (ACD). The treatment duration was classified into the initial phase (earliest initial phase eIP; 0-1 month, initial phase: IP; 1-3months), middle phase (MP; 3-6 months), and late phase (LP; 6-9 months). The CCT decreased significantly after treatment (eIP vs. IP, p<0.01, eIP vs. MP, p<0.01; eIP vs. LP, p<0.01). The CCT at eIP was correlated with the flare value at 0M (R2=0.22). The change in Kmax at MP and LP was correlated with the flare value at 0M. Moreover, CCT at MP was correlated with rate of change in nasal angle open distance (AOD) at IP and rate of change in temporal AOD at IP. This study was the first to reveal morphological changes in the anterior segment of the eye in VKH using CASIA-2, which may affect visual acuity and the astigmatic axis. It is vital to assess corneal morphology to determine the cause of visual function deterioration in patients with VKH.

Repeatability of Anterior Eye Surface Topography Parameters from an Anterior Eye Surface Profilometer.

Anterior eye shape measurements are important for clinical contact lens fitting. The detailed assessment of measurement repeatability using the Eye Surface Profiler (ESP; Eaglet Eye B.V., AP Houten, the Netherlands) allows for more reliable interpretation of eye surface topography measurements. This study aimed to determine the repeatability of the ESP for anterior central corneal power and anterior eye surface height measurements. A Badal optometer was mounted on the ESP to provide an external fixation target with appropriate accommodation control and refractive correction. Forty-five healthy young adults underwent two sessions of anterior eye measurements, separated by 20 minutes, using the ESP. In each session, three consecutive scans were captured. Sagittal height data were obtained from 8-mm central cornea and from 8- to 14-mm diameter (encompassing the corneal periphery and anterior sclera). Anterior corneal powers were determined from the central cornea. Intersessional and intrasessional repeatability values were determined as coefficients of repeatability and root mean square error differences. Sagittal height intersessional coefficients of repeatability for central nasal (5 μm) and central temporal (7 μm) were better than peripheral nasal (24 μm) and peripheral temporal (21 μm) regions. Sagittal height intrasessional coefficients of repeatability were 9, 8, 28, and 31 μm for central nasal, central temporal, peripheral nasal, and peripheral temporal regions, respectively. Intersessional coefficients of repeatability of mean sphere, 90/180° (J0) astigmatism, and oblique (J45) astigmatism were 0.67, 0.22, and 0.13 D, respectively, with corresponding intrasessional coefficients of repeatability of 1.27, 0.21, and 0.27 D. The modified measuring procedure for the ESP used in this study provides highly repeatable sagittal height measurements in the central cornea but is less repeatable in the corneal periphery and scleral region. Results of the current study can be considered when using ESP in the interpretation of anterior eye surface shape measurements and in contact lens fitting and design.

Correlations between central corneal power, axial length, anterior chamber depth and central corneal thickness of near-emmetropic young university students in Palestine

Background: Researchers have found that the refractive states of the eye are influenced by a variety of variables. Aim: This study investigated the correlation between the central corneal power (CCP) and a number of variables, which include axial length (AL), anterior chamber depth (ACD) and the central corneal thickness (CCT) in near-emmetropic eyes of students. Setting: The study was conducted in the Optometry Laboratory of the Islamic University-Gaza (IUG), Palestine. Methods: In a prospective analysis, 200 near-emmetropic students were examined from February 2019 to May 2019 with an ultrasound scanner (A-scan), ultrasonic pachymeter and Visionix L79 automated refractometer Keratometer (ARK). Only the data of one eye were randomly chosen for investigation. Results: The means and standard deviations (s.d.) of the CCP, AL, ACD and CCT for male students ( n = 97) were 43.19 dioptre (D) ± 1.34 D, 23.54 mm ± 0.68 mm, 3.59 mm ± 0.26 mm and 549 µm ± 33 µm, respectively. Furthermore, the means ± s.d. of 103 female students were as follows: CCP 43.85 D ± 1.43 D, AL 22.94 mm ± 0.69 mm, ACD 3.35 mm ± 0.25 mm and CCT 543 µm ± 35 µm. There was a significant association between CCP and gender ( p = 0.00). There was a negative significant correlation between CCP and AL for both the male ( r = −0.64; p = 0.00) and the female ( r = −0.71, p = 0.00) participants. Conclusion: This study provided information on CCP, AL, ACD and CCT in near-emmetropic eyes of adults. In male students, CCP was flatter and AL was longer when compared with female Palestinian students.

Predicting corneal refractive power changes after orthokeratology

This study aimed to characterise corneal refractive power (CRP) changes along the principal corneal meridians during orthokeratology (OK). Nineteen myopes (mean age 28 ± 7 years) were fitted with OK lenses in both eyes. Corneal topography was captured before and after 14 nights of OK lens wear. CRP was calculated for the central 8 mm cornea along the horizontal and vertical meridians. The central-paracentral (CPC) power ratio was calculated as the ratio between maximum central and paracentral CRP change from individual data. There was a significant reduction in CRP at all locations in the central 4 mm of the cornea (all p < 0.001) except at 2 mm on the superior cornea (p = 0.071). A significant increase in CRP was evident in the paracentral zone at 2.5, 3 and 3.5 mm on the nasal and superior cornea and at 3.5 and 4 mm on the temporal cornea (all p < 0.05). No significant change in CRP was measured in the inferior cornea except decreased CRP at 2.5 mm (p < 0.001). CPC power ratio in the nasal and temporal paracentral regions was 2.49 and 2.23, respectively, and 2.09 for both the inferior and superior paracentral corneal regions. Our results demonstrates that OK induced significant changes in CRP along the horizontal and vertical corneal meridians. If peripheral defocus changes are inferred from corneal topography, this study suggests that the amount of myopia experienced on the peripheral retina was greater than twice the amount of central corneal power reduction achieved after OK. However, this relationship may be dependent on lens design and vary with pupil size. CPC power ratios may provide an alternative method to estimate peripheral defocus experienced after OK.

A comparison of anterior and posterior central corneal powers in eyes with and without keratoconus

Background: Keratoconus affects the anterior segment of the eye, which directly affects the refractive state of the eye. There are three components for the measurement of a corneal curvature or central corneal power (CCP) of the eye, namely, the power along the flat meridian, the power along the steep meridian and the axis of the flat meridian. Traditionally, CCP is analysed using univariate methods that processes each component separately; however, because of the trivariate nature of CCP, the use of multivariate methods and statistics may be beneficial.Aim: The aim of this study was to compare the short-term variation of the anterior and posterior CCP in eyes with and without keratoconus using multivariate methods of analysis.Setting: Data were extracted from a doctoral study by the first author. The group with keratoconus (KC) was obtained from patients attending a university-based contact lens clinic in Johannesburg, South Africa.Methods: A total of 28 eyes with KC and 28 eyes of 28 healthy control eyes without KC were included in this prospective quantitative study. Measurements were taken with the Oculus Pentacam (Wetzlar, Germany) and data related to the anterior and posterior CCP were analysed using multivariate methods and analysis.Results: For both KC and control groups, short-term variation of CCP of the anterior corneal surfaces was significantly greater than that for the posterior corneal surfaces. Whilst short-term variation was similar for both corneal surfaces in the KC group, variation of the posterior corneal surfaces was significantly different from that of the anterior corneal surfaces for the control group.Conclusion: Multivariate analysis of short-term variation of CCP of both surfaces of the cornea in eyes with or without KC contributed towards a more complete understanding of the disease.

Influence of corneal spherical aberration on prediction error of the Haigis-L formula

The purpose of this study is to investigate the relationships between corneal asphericity and Haigis-L formula prediction errors in routine cataract surgery after refractive surgery for myopic correction. This retrospective study included 102 patients (102 eyes) with a history of previous PRK or LASIK and cataract surgery. Axial length, anterior chamber depth, and central corneal power were measured using the optical biometer. On the anterior corneal surface, Q-value, spherical aberration, and ecentricity at 6.0 and 8.0 mm were measured using a rotating Scheimpflug camera. The postoperative refractive outcome at 6 months, mean error, and mean absolute error were determined. Correlation tests were performed to determine the associations between pre-cataract surgery data and the prediction error. The Q-values for 6.0 and 8.0 mm corneal diameter were 1.57 ± 0.70 (range: 0.03~3.44), and 0.82 ± 0.5 (range: −0.10~−2.66). The spherical aberration for 6.0 and 8.0 mm diameter was 1.16 ± 0.39 µm (range: 0.24~2.08 µm), and 3.69 ± 0.87 µm (range: 0.91~5.91 µm). eccentricity for 6.0 and 8.0 mm diameter was −1.22 ± 0.31 (range: −1.85 to −0.17), and −0.82 ± 0.39 (range: −1.63 to 0.32). The spherical aberration for 8.0 mm cornea diameter showed the highest correlations with the predicion error (r = 0.750; p < 0.001). When the modified Haigis-L formula considering spherical aberration for 8.0 mm produced smaller values in standard deviation of mean error (0.45D versus 0.68D), mean absolute error (0.35D versus 0.55D), and median absolute error (0.31D versus 0.51D) than the Haigis formula. Corneal asphericity influences the predictive accuracy of the Haigis-L formula. The accuracy was enhanced by taking into consideration the corneal spherical aberration for the 8.0 mm zone at pre-cataract surgery state.

Corneal power measurement with a new aberrometer/corneal topographer in eyes after small incision lenticule extraction for myopia.

To assess corneal power measurements obtained by the OPD SCAN III Topographer in eyes with prior myopic small incision lenticule extraction (SMILE) surgery. Sixty untreated myopic eyes of sixty subjects and forty previous myopic SMILE surgery eyes of forty subjects were consecutively enrolled in the present study. Manifest refraction, OPD SCAN III and Pentacam HR were performed. Keratometric measurements assessed by OPD SCAN III-simulated keratometry, average pupil power and effective central corneal power (ECCP) were compared with mean keratometry (Km) obtained by Pentacam HR in the untreated group and the clinical history method (CHM) in the treated group. In the untreated group, no statistically significant differences were revealed between all corneal power measurements obtained with OPD SCAN III and Km. In the treated group, all the corneal power measurements were statistically different from the CHM except for the Haigis method and the Shammas method, while ECCP had a statistically but not clinically significant overestimation of 0.42 D with 95% limit of agreement (LOA) of - 0.81 D to 1.64 D. The three modified ECCP had better prediction performance with narrower 95% of LOA lying in (- 1.20, 1.20 D) (- 1.22, 1.23 D) and (- 0.90, 1.00 D), respectively. The ECCP provided with OPD SCAN III could be used as an alternative option for the CHM after specific modifications in eyes with previous myopic SMILE surgery when the preoperative data are unavailable considering the narrowest agreement between the modified ECCP and the CHM. Otherwise, caution must be raised considering the wide LOA.

Comparative study of wave-front aberration and corneal Asphericity after SMILE and LASEK for myopia: a short and long term study

BackgroundThe study compares the wave-front aberration and corneal asphericity from multiple perspectives after Small Incision Lenticule Extraction and Laser-assisted Subepithelial Keratomileusis for mild to moderate myopia in a short and long time period.MethodsThis prospective and comparative study included 32 eyes in the SMILE group, with a mean spherical equivalent (SE) of − 4.1 ± 0.9D and 32 eyes in the LASEK group, with a mean SE of − 3.7 ± 1.0D. Visual acuity, refractive error, wave-front aberration, corneal Q value and corneal refractive power were analyzed pre-, 3 months and 3 years post-operatively.ResultsThere was no significant difference in refractive error, wave-front aberration, corneal Q value and corneal refractive power before treatment. Three months postoperative, Q value within 6 mm (SMILE: 0.46 ± 0.27, LASEK: 0.63 ± 0.28, p = 0.02), the relative peripheral corneal power (5-8 mm: p < 0.05), change of higher order aberration (SMILE: 0.10 ± 0.16, LASEK: 0.24 ± 0.20, p = 0.004) and spherical aberration (SA, SMILE: -0.07 ± 0.30, LASEK: -0.41 ± 0.40, p < 0.001) were significantly lower in the SMILE than in LASEK group. The visual acuity, refractive error, coma, peripheral Q value, central corneal power had no significant difference between the two groups. Three years post-operation, the corneal power distribution results and SA were similar to that of 3-month, while the Q value had no significant difference between the two groups.ConclusionIn the early stage after SMILE, the HOAs was lower, the corneal refractive power from central to periphery was more uniform than after LASEK; and in the long-term run, SMILE still preceded LASEK in the corneal asphericity and aberration.

Agreement of post-LASIK corneal power and corneal thickness measurements by pentacam and GALILEI corneal tomography systems

BackgroundPost-LASIK corneal conditions cannot be accurately measured by traditional optometric approaches. Therefore, we aimed to analyze the agreement of two rotating Scheimpflug cameras in corneal assessment. MethodsFifty otherwise healthy volunteers who had undergone LASIK were recruited in this study. The values of mean and central total corneal power (TCP), including TCP1, TCP2, and TCP-IOL, were measured by GALILEI Scheimpflug camera. The values of total corneal refractive power (TCRP) readings at both 2 mm ring and 3 and 4 mm zones were detected by Pentacam Scheimpflug camera. Central corneal thickness (CCT) and thinnest corneal thickness (TCT) were quantified by GALILEI and Pentacam respectively. Paired t-tests and Bland–Altman analyses were used to evaluate statistical differences between measurement results obtained by GALILEI and by Pentacam. ResultsAmong these 50 subjects, the mean and central TCP1 values (37.31 ± 2.61 and 37.27 ± 2.64) derived from GALILEI measurements were consistent with the TCRP values (37.08 ± 2.76, 37.11 ± 2.74, and 37.19 ± 2.68; P > 0.05) determined by Pentacam at the 2 mm ring apex, 3 mm zone apex, and 4 mm zone apex. There were no statistically significant differences in central corneal thickness (CCT) values measured by the two cameras (463.64 ± 55.67 μm for GALILEI and 470.69 ± 44.04 μm for Pentacam, respectively; P > 0.05). However, the limits of agreement were wide when comparing mean TCP1 (−1.4 to 1.8 D, −1.4 to 1.8 D, and −1.3 to 1.6 D), central TCP1 (−1.2 to 1.6 D, −1.2 to 1.6 D, and −1.2 to 1.4 D) and CCT (−77.2–63.0 μm). ConclusionCorneal power and corneal thickness are disparate post-LASIK evaluation parameters when comparing the utility of GALILEI with that of Pentacam.

The efficiency of aspheric intraocular lens according to biometric measurements.

PurposeTo analyze internal spherical aberration in pseudophakic eyes that underwent aspheric intraocular lens (IOL) implantation, and to investigate the relationships between biometric data and the effectiveness of aspheric IOL implantation.MethodsThis retrospective study included 40 eyes of 40 patients who underwent implantation of an IOL having a negative spherical aberration of -0.20 μm (CT ASPHINA 509M; Carl Zeiss Meditec Inc., Germany). The IOLMaster (version 5.0; Carl Zeiss AG, Germany) was used for preoperative biometric measurements (axial length, anterior chamber depth, central corneal power) and the measurement of postoperative anterior chamber depth. The spherical aberrations were measured preoperatively and 3 months postoperatively using the iTrace (Tracey Technologies, Houston, TX, USA) at a pupil diameter of 5.0 mm. We investigated the relationships between preoperative biometric data and postoperative internal spherical aberration, and compared biometric measurements between 2 subgroups stratified according to internal spherical aberration (spherical aberration ≤ -0.06 μm vs. spherical aberration > -0.06 μm).ResultsThe mean postoperative internal spherical aberration was -0.087 ± 0.063 μm. Preoperative axial length and residual total spherical aberration showed statistically significant correlations with internal spherical aberration (p = 0.041, 0.002). Preoperative axial length, postoperative anterior chamber depth, IOL power, and residual spherical aberration showed significant differences between the 2 subgroups stratified according to internal spherical aberration (p = 0.020, 0.029, 0.048, 0.041 respectively).ConclusionThe corrective effect of an aspheric IOL is influenced by preoperative axial length and postoperative anterior chamber depth. Not only the amount of negative spherical aberration on the IOL surface but also the preoperative axial length should be considered to optimize spherical aberration after aspheric IOL implantation.

Accuracy of Different Topographic Instruments in Calculating Corneal Power after Myopic Photorefractive Keratectomy.

Purpose:To compare the corneal power measurements obtained using different topographic instruments after myopic photorefractive keratectomy (PRK).Methods:Patients with myopia who were candidates for corneal refractive surgery were sequentially included. Pre-PRK and six months post-PRK corneal powers were measured using Javal manual keratometer, Orbscan II, Galilei, Tomey TMS4, and EyeSys 2000 topographers. Measured values were compared with those obtained using the clinical history method (CHM).Results:This study included 66 eyes of 33 patients. The lowest keratometric measurements were obtained using the Galilei topographer (42.98 ± 1.69 diopters, D) and the highest measurements were obtained using the Javal manual keratometer (43.96 ± 1.54 D) preoperatively. The same order was observed postoperatively. Effective refractive power (EffRP) measured using EyeSys was most similar to the values obtained using CHM (ICC, intraclass correlation coefficient = 0.951), followed by the total corneal power measured using the Galilei system (ICC = 0.943). The values obtained using the adjusted EffRP formula (EffRP – 0.015*Δ Refraction – 0.05) were more consistent with the values obtained using CHM (ICC = 0.954) compared to those obtained with the adjusted average central corneal power formula measured using the Tomey system (ICC = 0.919).Conclusion:Post-PRK corneal powers measured using the adjusted EffRP formula were the most similar to values obtained using CHM.

Short-Term and Long-Term Changes in Corneal Power Are Not Correlated With Axial Elongation of the Eye Induced by Orthokeratology in Children.

To assess the relationship between short-term and long-term changes in power at different corneal locations relative to the change in central corneal power and the 2-year change in axial elongation relative to baseline in children fitted with orthokeratology contact lenses (OK). Thirty-one white European subjects 6 to 12 years of age and with myopia -0.75 to -4.00 DS and astigmatism ≤1.00 DC were fitted with OK. Differences in refractive power 3 and 24 months post-OK in comparison with baseline and relative to the change in central corneal power were determined from corneal topography data in eight different corneal regions (i.e., N[nasal]1, N2, T[temporal]1, T2, I[inferior]1, I2, S[superior]1, S2), and correlated with OK-induced axial length changes at two years relative to baseline. After 2 years of OK lens wear, axial length increased by 0.48±0.18 mm (P<0.001), which corresponded to an increase of 1.94±0.74% ([2-years change in axial length/baseline axial length]×100). However, the change in axial elongation in comparison with baseline was not significantly correlated with changes in corneal power induced by OK relative to baseline for any of the corneal regions assessed (all P>0.05). The reduction in central corneal power and relative increase in paracentral and pericentral power induced by OK over 2 years were not significantly correlated with concurrent changes in axial length of white European children.

Changes in Corneal Curvature After Upper Eyelid Surgery Measured by Corneal Topography.

To analyze corneal curvature changes (eg, central corneal power and corneal astigmatism) after upper eyelid surgery, and to compare the effects of different upper eyelid procedures on corneal curvature. Fifty eyes of 34 patients with various degrees of dermatochalasis or ptosis underwent corneal topography before surgery, and at 6 weeks after blepharoplasty or levator resection. Patients were divided into groups according to the method of surgery. Preoperative and postoperative changes in corneal curvature of each operated eye were compared within each group. At 6 weeks after levator resection, 50% of the eyes showed an increase in corneal power, 34.6% showed a decrease, and 15.4% showed no change. The corneal astigmatism in 50% of eyes with levator resection decreased, increased in 19.2% of eyes, and showed no change in 30.8% of eyes. At 6 weeks after blepharoplasty, 12.5% of the eyes showed an increase in corneal power, 37.5% showed a decrease, and 66.7% showed no change. Regarding corneal astigmatism in patients who underwent blepharoplasty, 16.7% of the eyes decreased, 16.7% increased, and 66.6% showed no change. Comparing eyes treated with the 2 surgical techniques, there was a statistical difference in the percentage eye which showed corneal diopter and astigmatism change using these 2 techniques (P < 0.05). Repositioning of the upper eyelid after levator resection showed greater changes of corneal curvature (eg, central corneal power and corneal astigmatism) than blepharoplasty. The advanced aponeurosis technique may have a greater effect on the lid/cornea interface, by lifting the eyelids pressing against the eyeball to affect corneal curvature.

Estudio comparativo de la medición del poder corneal central usando el queratómetro manual, el IOLMaster® y el tomógrafo Sirius®

ObjectiveTo assess the repeatability and comparability of the central keratometric power measurements obtained from a novel Scheimpflug camera with a Placido-disc topographer (Sirius®), manual keratometer and IOLMaster®. Material and methodsIn a sample of 30 unoperated eyes of healthy subjects, the central corneal power was analyzed by a single examiner using the Sirius®, the manual keratometer and the IOLMaster®. Repeatability of 3 sets of measurements from each device were evaluated using the coefficient of variation, standard deviation, and intraclass correlation coefficient. T-test with Bonferrioni adjustment and Bland and Altman plots were used to assess agreement between devices. ResultsAll instruments showed high reproducibility with coefficient of variation less than 0.30% for all measurements (0.291% and 0.237%, 0.238% and 0.361%, 0.238% and 0.208% for the flattest (FK) and steepest keratometry of Sirius®, manual keratometer and IOLMaster® respectively) and a higher intraclass correlation coefficient of 0.95 in all measurements. The manual keratometer has the lowest keratometric power (FK 41,988 and SK 43,277 D), followed by Sirius® (FK 42.285 D and SK 43.510 D) and finally the IOLMaster® (FK 42.483 D and SK 43.763 D), with a statistically significant differences. ConclusionIn the assessment of normal corneas, central corneal power measured with this 3 devices showed high repeatability however there was no agreement between the equipments and the differences were statistically significant.