Central Corneal Thickness Values Research Articles

Stabilization Time of Anterior Segment Parameters After Trabeculectomy Surgery

To investigate the postoperative changes in the anterior segment parameters by Scheimpflug imaging method in patients undergoing trabeculectomy surgery. This prospective study included 38 phakic eyes of 38 patients with primary open-angle glaucoma who underwent trabeculectomy. Anterior chamber angle (ACA), anterior chamber depth (ACD), anterior chamber volume (ACV), and central corneal thickness (CCT) of the eyes were measured by performing Scheimpflug imaging in preoperative (baseline) and postoperative periods (1st week and 1st, 3rd, and 6th months after the surgery). Significant differences were observed in all the anterior segment parameters during the postoperative period (P<0.001 for ACA, ACD, and CCT; P=0.001 for ACV). Compared with preoperative values, ACA, ACD, and ACV values decreased and CCT value increased in the 1st postoperative week (P<0.001 for all the parameters). Compared with the 1st postoperative-week values, ACA, ACD, and ACV values significantly increased and CCT value significantly decreased in the 1st postoperative month (P=0.002 for ACV; P<0.001 for ACA, ACD, and CCT). However, no significant differences were observed between the baseline and 1st postoperative-month values (P>0.05 for all the parameters). Moreover, the changes in the anterior segment parameters were not statistically significant after the 1st postoperative month. Our results showed that the changes in the anterior segment parameters observed in the early postoperative period after trabeculectomy returned to their baseline values after approximately 1 month after the surgery and remained stable thereafter.

Corneal Biomechanical Properties and Central Corneal Thickness in Pediatric Noninfectious Uveitis: A Controlled Study

To compare the corneal biomechanics, intraocular pressure (IOP), and central corneal thickness (CCT) of 37 patients with pediatric noninfectious uveitis with 36 healthy children. Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated and corneal-compensated IOP (IOPg and IOPcc, respectively), and CCT were measured. The mean CRF was significantly lower in the pediatric uveitic eyes than controls (9.7±1.9 vs. 10.8±1.5 mm Hg, P=0.009), whereas there was no significant difference for mean CH, IOPg, IOPcc, and CCT between the two groups (10.1±1.9 vs. 10.8±1.7, 12.9±3.3 vs. 13.9±3.1, 13.8±2.8 vs. 13.6±3.2 mm Hg, and 550.7±49.5 vs. 555.1±33.5 μm, respectively, all P>0.05). The CCT values correlated with CH and CRF, with a Pearson correlation of 0.511 and 0.670 (P=0.013 and P<0.001, respectively), whereas disease duration did not correlate with any corneal biomechanics or CCT in pediatric uveitic eyes (all P>0.05). Pediatric noninfectious uveitic eyes have lower CRF than controls but the CH, IOPg, IOPcc, and CCT values are similar.

Comparison of ultrasonic pachymetry and Fourier-domain optical coherence tomography for measurement of corneal thickness in dogs with and without corneal disease

Several ultrasonic and Fourier-domain optical coherence tomography (FD-OCT) pachymeters are used to measure corneal thickness in canine patients and research subjects. This study assessed the reliability of and consistency between two ultrasonic pachymetry (USP) devices, Pachette 3 and Accupach VI, as well as automated and manual measurements obtained using FD-OCT in dogs with and without corneal disease. Corneal thickness measurements were compiled from 108 dogs and analyzed using mixed effects linear regression, with Bonferonni adjustments for post-hoc comparisons, to determine the effects of age, weight and disease state. Data are presented as predicted mean±standard error.Canine corneal disease can result in marked increases in thickness that frequently exceed the upper limits of measurement of some pachymetry devices developed for human use. In this study, the corneas of dogs with endothelial disease or injury frequently exceeded the upper limits of quantitation of 999 and 800μm for the Accupach VI and automated FD-OCT pachymeters, respectively. Using values <800μm, the Pachette 3 generated significantly greater values for central corneal thickness (CCT) than the Accupach VI, manual FD-OCT and automated FD-OCT at 625±7.0, 615±7.2, 613±7.2, and 606±7.4μm respectively (P<0.001). Of the two devices where measurements >1000μm were obtained, manual FD-OCT demonstrated less variability than the Pachette 3. Corneal thickness increased linearly with age and weight with an increase of 6.9±1.8μm/year and 1.6±0.8μm/kg body weight (P<0.005 and P=0.038, respectively).

On the reliability (repeatability) of single pachymetry measures taken with specular microscope-based assessments of the human corneal endothelium.

To assess agreement between 3 measures of central corneal thickness (CCT) taken over a few minutes from nominally normal eyes with a non-contact specular microscope. 100 eyes from 100 healthy adults (with an average age of 22 y) were assessed using the Topcon 3000 P instrument to obtain a high quality image of the endothelium and pachymetry. The group mean CCT values from the 1st, 2nd and 3rd measures were 0.519, 0.520 and 0.520 mm, but the sets of values could differ by between - 0.020 mm and + 0.029 mm, i.e. between - 4.0 and + 5.6% of the average values. Paired comparisons (e.g. 2nd vs. 1st set) indicated limits of agreement (LoA) to be between - 0.020 and + 0.020 mm of the averaged value. Across the 3 measures, the averaged SD was 0.005 mm to give an estimate of the intra-subject variability (as the coefficient of variation, COV) of 0.91% (range 0 to 2.3%). The variability in the pachymetry measures was not predictably related to the averaged values of CCT (r = 0.022) or self-reported refractive error of the subjects (r = 0.012). Some repeat pachymetry assessments obviously included the same region of the endothelium. Single pachymetry measures with a non-contact specular microscope are only likely to be able to generate CCT estimates within +/- 4% of the expected average values. This repeatability is comparable to single image estimates of endothelial cell density and therefore acceptable in most cases.

A comparison of NCT, Goldman application tonometry values with and without fluorescein.

PurposeThe aim of the study was to statistically compare intraocular pressure (IOP) values measured using noncontact tonometer (NCT), Goldmann applanation tonometry (GAT) with fluorescein (fGAT), and GAT without fluorescein (nGAT). The study was also performed to test whether the values obtained using each technique change in accordance with the central corneal thickness (CCT) and refractive and keratometric values.Study designThis study was a prospective study of 188 eyes of 94 healthy volunteers. Methods: IOP was measured using fGAT, nGAT and NCT. CCT, refractive values, and keratometric values were measured, and the correlations and differences in the IOP for each tonometer were investigated.ResultsThe mean IOP values obtained with the NCT, nGAT, and fGAT were 17.5±3.7, 12.3±2.7, and 12.5±2 mmHg. The mean CCT was 538.2±34.4 µm, the mean refractive value was 0.9±1.2 D, and the mean keratometric value was 43.5±1.5 D. NCT was positively correlated with fGAT and GAT values and was significantly higher than both the values. There were no differences between fGAT and GAT values. No correlation was observed between the CCT and keratometric and refractive values and the difference between NCT and nGAT or fGAT.ConclusionDifferences in the measurements obtained using nGAT and fGAT were insignificant (P>0.05). Both values were positively correlated with NCT measurements (r =0.354, P<0.05) and were independent of CCT, keratometry, and refraction values. nGAT appears to be suitable for use in routine clinic practice.

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.

Effect of dexamethasone intravitreal implant (Ozurdex\xae) on corneal endothelium in retinal vein occlusion patients

BackgroundTo assess corneal endothelial cell changes after intravitreal dexamethasone (DEX) implant (Ozurdex®) injection in patients with macular edema secondary to retinal vein occlusion (RVO).MethodsTwenty-two eyes of 22 patients were assessed prospectively after intravitreal 0.7 mg DEX implant injection. Twenty-two eyes of 22 healthy volunteers served as control group. Corneal endothelial cell parameters including endothelial cell density (ECD), coefficient of variation of cell size (CV), percentage of hexagonality (Hex) and central corneal thickness (CCT) were analyzed before and 1 and 3 months after injection by specular microscopy. The results of the study were compared statistically.ResultsThere were 17 (77.3%) patients with branch RVO and 5 (22.7%) patients with central RVO. Mean intraocular pressure (IOP) was 14.73 mmHg before injection, 17.05 mmHg at 1 month and 17.15 mmHg at 3 months after injection. Mean IOP at 1 and 3 months were significantly higher than pre-injection value (p = 0.002 and p = 0.003, respectively). There was a statistically significant reduction in mean ECD at 3 months after injection compared to pre-injection and 1 month (p = 0.013, p = 0.009, respectively) in the injected eyes. Mean ECD showed no significant difference in the uninjected fellow eyes during the follow up (p>0.05). Mean CV and Hex did not reveal a statistically significant difference in injected and uninjected fellow eyes (p > 0.05). No significant change was observed in mean CCT values during the follow up (p = 0.8).ConclusionIntravitreal dexamethasone implant may cause a transient reduction in corneal endothelial cell density in short term without changing cell morphology.

Cumulative Effects of Smoking and Diabetes Mellitus on Corneal Endothelial Cell Parameters.

To compare the corneal endothelial morphometric properties and central corneal thickness (CCT) values in patients with diabetes mellitus (DM) and age-matched healthy subjects and to determine whether smoking increases the effects of DM on these corneal parameters. This prospective study included patients with type 2 DM and their age-matched controls. The smoking history of all participants was evaluated. Corneal endothelial cell properties including endothelial cell density (ECD), average cell area (AVG), coefficient of variation of cell area (CV), and percentage of hexagonal cells (HEX) were obtained using a noncontact specular microscope. Consequently, CCT was measured using an ultrasound pachymeter. This research analyzed 153 subjects in the DM group and 146 subjects in the control group. There were no statistically significant differences in the age, sex, and smoking status of the participants in 2 groups (P > 0.05). The corneal endothelial cell measurements including ECD, AVG, CV, and HEX did not show any statistically significant differences between these groups (P > 0.05). However, CCT of patients with DM was statistically significantly thicker than that of the controls (P = 0.005). The ECD values of the smokers with DM (2435 ± 325 cells/mm) were statistically significantly lower than those of nonsmoker healthy subjects (2559 ± 279 cells/mm P = 0.008). However, the AVG, CV, HEX, and CCT values of the smokers with DM were not statistically significantly different compared with nonsmoker healthy subjects (P > 0.05). Although neither only DM nor only smoking has a statistically significant effect on corneal endothelial morphometric properties, coexistence of DM and smoking causes a significant decrease in ECD.

Glaucoma and Alzheimer Disease: One Age-Related Neurodegenerative Disease of the Brain.

Background: Open Angle Glaucoma (POAG) is the leading causes of irreversible blindness worldwide. Elevated intraocular pressure is considered an important risk factor for glaucoma; however, a subset of patients experiences a progression of the disease even in presence of normal intraocular pressure values. This implies that risk factors other than intraocular pressure are involved in the pathogenesis of glaucoma. A possible relationship between glaucoma and neurodegenerative diseases such as Alzheimer Disease has been suggested. In this regard, we recently described a high prevalence of alterations typical of glaucoma, using Heidelberg Retinal Tomograph-3, in a group of patients with Alzheimer Disease. Interestingly, these alterations were not associated with elevated intraocular pressure or abnormal Central Corneal Thickness values. Alzheimer Disease is the most common form of dementia with progressive deterioration of memory and cognition. Complaints related to vision are common among Alzheimer Disease patients.Methods: In this paper researches related to glaucoma and Alzheimer disease are reviewed.Results: Diseases characteristics, i.e. common features, risk factors and pathophysiological mechanisms gathered in the recent literature do suggest that Alzheimer Disease and glaucoma can be considered both age-related neurodegenerative diseases that may co-exist in the elderly.Conclusion: In conclusion, preclinical and clinical evidence gathered so far support the notion that glaucoma is a widespread neurodegenerative condition whose common pathogenetic mechanisms with other diseases, i.e. Alzheimer Disease, should be further investigated as they may shed new light on these diseases improving both diagnosis and treatments.

Ocular and Systemic Risk Factors and Correlation with Glaucomatous Damage in Normal Tension Glaucoma.

BackgroundNormal tension glaucoma (NTG) is a clinical entity that poses a diagnostic and therapeutic challenge. The study elaborates ocular and systemic risk factors of NTG in the South Indian population. It determines the correlation between risk factors and severity of glaucomatous damage.MethodsThis descriptive study was done on 81 eyes of 41 patients. A brief history of hypertension, heart disease, migraine, and family history of glaucoma were noted. The parameters measured include blood pressure, lipid profile, visual acuity, refraction, intraocular pressure (IOP) by applanation tonometry, diurnal variation, slit lamp biomicroscopy, central corneal thickness (CCT), and perimetry (Humphrey 24-2).ResultsThe mean age was 51.75 years. There was female predilection (63.41%). Thirteen patients (32.5%) had hypertension, five (12.5%) had migraine, and seven had hyperlipidemia (17.5%). Perfusion pressure demonstrated a negative correlation value of -0.319 (rho value) with visual field defects (p<0.05) and -0.266 (rho value) with glaucomatous cupping (p=0.093). The IOP varied from 10 mmHg to 19 mmHg with a mean of 15.34. The average CCT was 522.06±36.09 microns. Neuroretinal rim thinning was seen in 12 eyes (14.8%), polar notching in six eyes (7.4%), and peripapillary atrophy in 20 eyes (24.6%). Two eyes (2.4%) had splinter hemorrhage at disc margin. A lower value of CCT was associated with lower IOP, a weak positive correlation (r value 0.121). Optic disc cupping is strongly associated with severity of field defects, r value 0.743, (p<0.00).ConclusionNormal tension glaucoma is common in females. Hypertension and lower diastolic perfusion pressure are important risk factors. Lower CCT is associated with lower IOP (applanation tonometry). Optic disc cupping and diastolic perfusion pressure strongly correlate with severity of visual field defects.

Effects of artificial tear treatment on corneal epithelial thickness and corneal topography findings in dry eye patients

To investigate the effects of artificial tear treatment on central corneal epithelial thickness, and central, mid-peripheral and peripheral corneal thicknesses in patients with dry eye disease (DED). Patients with DED underwent ocular examinations, including Schirmer-2 test, slit lamp examination for tear break-up time (BUT), corneal topography (CT) for measuring mean central, mid-peripheral and peripheral corneal thickness values and anterior segment optic coherence tomography (AS-OCT) for obtaining central corneal epithelial thickness. After artificial tear treatment (carboxymethylcellulose and sodium hyaluronate formulations) for one month, patients were examined again at a second visit and the results were compared. Sixty-one eyes of 33 female dry eye patients (mean age: 38.3±5.7 years) were enrolled. The mean follow-up time was 36.4±3.3 days. The mean tear BUT and Schirmer-1 tests revealed significant improvement after treatment (P=0.000, P=0.000, respectively). Central corneal epithelium and mean mid-peripheral corneal thicknesses measured significantly higher after treatment (P=0.001, P=0.02). Changes in central and peripheral corneal thicknesses were not statistically significant. Artificial tear treatment in dry eye patients seems to increase central corneal epithelial and mid-peripheral corneal thicknesses. Measurement of corneal epithelial thickness can be a useful tool for evaluation of treatment response in dry eye patients. Further long-term prospective studies are needed to investigate this item.

Conventional and transepithelial corneal cross-linking for patients with keratoconus.

Previous studies investigating the effectiveness of conventional corneal collagen cross-linking (CXL) and transepithelial CXL in keratoconus treatment have reported conflicting outcomes. Therefore, we conducted a meta-analysis to compare the effectiveness of these treatments. We searched MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials for prospective randomized controlled trials (RCTs) with no restrictions. We included visual acuity (corrected distance visual acuity, uncorrected distance visual acuity) and corneal keratometry (K) as primary outcome parameters, and spherical equivalent, central corneal thickness (CCT), and endothelial cell density, as secondary parameters. We finally included seven reports (including six RCTs involving 305 participants and 344 eyes). Our analysis revealed significant postoperative differences in average K and CCT values between conventional and transepithelial CXL-treated patients [K: weighted mean difference (WMD) = 0.79, 95% confidence interval (CI) = 0.04–1.53, p = 0.04; CCT: WMD = 4.53, 95% CI = 0.42–8.64, p = 0.03]. In contrast, we did not find any significant differences in visual acuity, flattest K value, steepest K value, cylinder K value, apex K value, spherical equivalent, or endothelial cell density between groups. In conclusion, transepithelial CXL has a more protective influence on corneal thickness than conventional CXL, and results in lesser postoperative corneal flattening. Further investigation of the clinical outcomes of transepithelial CXL is required.

Study of central corneal thickness using non-contact techniques: Specular microscopy (Nidek CEM-530), corneal tomography (Pentacam HR), and optical coherence tomography (Cirrus HD-OCT 5000) in healthy adult patients

Objective: To study and compare the value of central corneal thickness in a healthy adult population, using different non-contact techniques from daily clinical practice. Method: This work examines and compares the pachymetric measurements of 71 eyes of 36 healthy adult patients. Corneal thickness was evaluated using three non-contact instruments: a CEM-530 specular microscope (Nidek), Pentacam HR corneal tomography (Oculus), and Cirrus HD-OCT 5000 optical coherence tomography (Carl Zeiss Meditec). Tests were performed consecutively by a single observer in the same session and under the same environmental conditions. Results: The results obtained using the three devices are interchangeable, given that no statistically significant difference was observed among them. The study did not find statistically significant difference with respect to gender either. Conclusion: These three non-contact methods for the measurement of corneal central pachymetry are a reliable alternative to ultrasonic contact pachymetry.

Relationship between corneal sensitivity, corneal thickness, corneal diameter, and intraocular pressure in normal cats and cats with congenital glaucoma.

To determine the effect of feline congenital glaucoma (FCG) on corneal sensitivity, and relationships between corneal sensitivity, central corneal thickness (CT), and corneal diameter (CD). Corneal sensitivity (estimated by corneal touch threshold [CTT] using Cochet-Bonnet esthesiometry); CT using ultrasonic pachymetry; intraocular pressure (IOP) using rebound tonometry; and maximal horizontal CD were measured in 16 normal and 14 FCG cats, both males and females, aged 7months-3.5years. All procedures complied with an Institutional Animal Care and Use Committee-approved protocol. Data were analyzed by linear regression: paired Student's t tests for between-eye comparisons, and unpaired Student's t tests for comparisons between groups. Relationships between parameters were evaluated by Pearson correlation coefficients and linear mixed effects modeling. For statistical tests, with the exception of values that were Benjamini-Hochberg adjusted for multiple comparisons, P-values < 0.05 were considered significant. Mean CTT and CT values were lower in FCG eyes relative to normal eyes, but differences were not statistically significant. Mean CD was significantly larger in FCG eyes relative to normal eyes, and there was a significant negative correlation between CD and CTT in FCG (r=-0.8564, corrected P=0.005). These associations were confirmed in linear mixed effects models. Eyes with FCG have significantly larger CDs when compared with normal eyes, and larger CDs correlated with decreased corneal sensitivity in this group. Further studies are warranted to explore the effect of buphthalmos and corneal enlargement on corneal sensitivity and innervation in feline subjects with chronic glaucoma.

Comparison of Central Corneal Thickness with Ultrasound Pachymetry, Noncontact Specular Microscopy and Spectral Domain Optical Coherence Tomography

ABSTRACTBackground: To determine the agreement of central corneal thickness (CCT) measurements taken with ultrasonic pachymetry (USP), spectral domain optical coherence tomography (SD-OCT) and noncontact specular microscopy (NSM).Methods: A prospective, observational, cross-sectional study was performed in the outpatient ophthalmology clinic. CCT was measured in a total of 147 eyes of 147 consecutive healthy patients with USP, NSM, and SD-OCT. Same examiner performed all examinations. Bland–Altman plots were used to evaluate the agreement between instruments.Results: The average CCT values obtained by USP, NSM, and SD-OCT were 555 ± 37 µm, 554 ± 34 µm, and 546 ± 34 µm, respectively. There was a strong correlation between instruments: USP with SD-OCT (r = 0.937, p < 0.01), USP with NSM (r = 0.943, p < 0.01) SD-OCT with NSM (r = 0.975, p < 0.01) for CCT. The mean differences (lower/upper limit of agreement) for CCT measurements were −10 ± 12.9 µm (15.28/−35.28) between SD-OCT and USP, −8.1 ± 7.7 µm (7/−23.2) between SD-OCT and NSM, and 1.8 ± 12.3 µm (25.9/−22.3) between USP and NSM.Conclusions: USP and NSM were found to have comparable CCT measurements and these two methods can be used correspondingly. However, CCT measurements by SD-OCT were lower when compared to other methods.

Precision (repeatability and reproducibility) of ocular parameters obtained by the Tomey OA-2000 biometer compared to the IOLMaster in healthy eyes.

PurposeTo assess the precision (repeatability and reproducibility) of ocular parameters measured by the Tomey OA-2000 biometer, and to compare them with those measured by the IOLMaster.MethodsIn this prospective study, the right eyes of 108 healthy subjects were included. Three consecutive scans were obtained by 2 observers using the Tomey OA-2000, and in the same session one observer used the IOLMaster (version 5.4.4.0006) for the measurements. About 1 week later, 3 scans were obtained by one observer using the Tomey OA-2000. The axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), keratometer readings, pupil diameter (PD) and corneal diameter (CD) values measured by the Tomey OA-2000 and IOLMaster were analyzed. The coefficient of variation (CoV), intraclass correlation coefficient (ICC), within subject standard deviation (Sw) and 2.77Sw were calculated to assess the repeatability and reproducibility. The paired t test and Bland-Altman plots were used to analyze the differences and agreements of parameters measured by the two devices, respectively.ResultsIntraobserver repeatability, and interobserver and intersession reproducibility of the AL, CCT, ACD, LT, Kf, Ks, Km, PD and CD values measured by the Tomey OA-2000 biometer showed a CoV of less than 1% except that for PD, and an ICC of more than 0.97 except that for PD and CD. The AL, Kf, Ks, Km and CD values measured by the Tomey OA-2000 were 0.058 ± 0.094 mm, 0.088± 0.150 diopters (D), 0.163 ± 0.170 D, 0.127 ± 0.117 D and 0.171 ± 0.217 mm lower than those measured by the IOLMaster, respectively (all Ps < 0.05). However, the ACD values from the two devices were comparable (P = 0.169). The 95% linite of agreement (LoA) of the AL, ACD, CD and all keratometer readings were no more than 0.24 mm, 0.14 mm 0.60 mm and 0.5 D, respectively.ConclusionExcept for the PD and CD, the ocular parameters measured by the Tomey OA-2000 were highly repeatable and reproducible. Except for the CD value, there was good agreement of ocular parameters measured by the Tomey OA-2000 and the IOLMaster in healthy eyes.

A comparative study of central corneal thickness, mean keratometry and astigmatism in persons with and without refractive errors in Taif

Background: Corneal topography is an important parameter in the evaluation of corneal disease, but there is no average value of normal corneal geometry in Saudi individuals is known. So, this study aimed to establish a standard normal value for central corneal thickness (CCT), mean keratometry (km), and astigmatism in Saudi individuals to be used as a reference value, and to compare these results with the same parameters in patients who have refractive errors. Methods: This study was performed from January 2016 to July 2017 at King Faisal Hospital in Taif, KSA, and included a current group of 105 eyes without refractive errors, and 250 eyes with refractor errors. Results: The mean CCT value was 551.681 µm, km value was 43.426 D, and astigmatism was 0.784 D for all eyes with normal visual acuity. However, these values are the statistically significant difference between different ages, but no significant differences according to sex. Regarding the eyes with refractive error, it was found that the mean CCT was 509.66 µm, km was 46.79 D, and for astigmatism was 3.97 D. When the results of two groups were compared, there was a significant difference between them except for km in the group a; (12-20 years). Conclusions: The standard value of central corneal thickness, mean keratometry, and astigmatism in Saudi individuals is differing according to the age but it is the same in both genders. These values are differing statistically in patients with refractor error.

Precision of a new ocular biometer in children and comparison with IOLMaster

To assess the repeatability and reproducibility of AL-Scan in agreement with those by the IOLMaster in healthy children, two skilled operators measured ocular parameters in 58 children. The parameters included keratometry (K) values, anterior chamber depth (ACD), axial length (AL), central corneal thickness (CCT), pupil diameter (PD), and corneal diameter (CD). The cohort comprised of 32 boys and 26 girls. The AL-Scan measurements showed high repeatability, as the test-retest repeatability (TRT) values of AL, CCT, ACD, Kf, Ks, Km, CD, and PD were 0.09 mm, 5.1 μm, 0.04 mm, 0.28 D, 0.24 D, 0.21 D, 0.39 mm, and 0.22 mm, respectively. The within-subject coefficient of variation (CoV) was low (<0.35%) and the intraclass correlation coefficients (ICC) of all parameters were >0.85. The interobserver reproducibility was excellent with low values of TRT and ICC > 0.95. The CoV of AL, CCT, ACD, and K was <0.22%. The 95% limits of agreement between the AL-Scan and the IOLMaster were narrow for all parameters except for CD. The repeatability and reproducibility of the new biometer, Al-Scan, was excellent for all parameters and can be routinely used in children to measure the biometric values.

South African Eye Study (SAES): ethnic differences in central corneal thickness and intraocular pressure.

PurposeGlaucoma is the leading cause of irreversible blindness worldwide. South Africa has a diverse population but there is a lack of published ethnic specific normative data. The purpose of the study is to determine the distribution of intraocular pressure (IOP) and central corneal thickness (CCT) values in a multi-ethnic South African population and to determine additional systemic and ocular factors that influence IOP and CCT.Patients and methodsThis cross-sectional study included a total of 402 participants with 706 eyes aged 18-94 years. Participants underwent a standardized interviewer-administered questionnaire for risk factor assessment followed by a full ophthalmic examination. The averages of six IOP readings were measured with an Icare PRO tonometer and CCT was measured with a Pentacam.ResultsThe mean CCT readings in the African, Mixed ethnicity, and Caucasian participants were 514.77±31.86, 531.77±35.17, and 549.97±30.51 μm (P<0.001). The mean IOP in the African, Mixed ethnicity, and Caucasian participants were 15.51±2.49, 15.09±2.12, and 15.13±2.53 mm Hg (P=0.07). Africans had significantly higher IOP than Mixed ethnicity (P=0.034) and Caucasians (P=0.011). Hypertensives had a higher IOP (P=0.03). Age and pseudophakia were associated with a lower IOP (P<0.001) and higher CCT (P<0.001). There was a strongly positive correlation between CCT and IOP (β=0.021; P<0.001).ConclusionsIn the South African Eye Study (SAES), Africans had the thinnest corneas and highest IOP followed by Mixed ethnicity and Caucasians. Including systemic and ocular factors that influence IOP specific to each population and ethnic group, will lead to a more accurate clinical risk stratification in glaucoma management.

Goldmann and error correcting tonometry prisms compared to intracameral pressure

BackgroundCompare Goldmann applanation tonometer (GAT) prism and correcting applanation tonometry surface (CATS) prism to intracameral intraocular pressure (IOP), in vivo and in vitro.MethodsPressure transducer intracameral IOP was measured on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically to 10, 20, and 40 mmHg. Simultaneously, IOP was measured using a Perkins tonometer with a standard GAT prism and a CATS prism at each of the intracameral pressures. Statistical comparison was made between true intracameral pressures and the two prism measurements. Differences between the two prism measurements were correlated to central corneal thickness (CCT) and corneal resistance factor (CRF). Human cadaver eyes were used to assess measurement repeatability.ResultsThe CATS tonometer prism measured closer to true intracameral IOP than the GAT prism by 1.7+/−2.7 mmHg across all pressures and corneal properties. The difference in CATS and GAT measurements was greater in thin CCT corneas (2.7+/−1.9 mmHg) and low resistance (CRF) corneas (2.8+/−2.1 mmHg). The difference in prisms was negligible at high CCT and CRF values. No difference was seen in measurement repeatability between the two prisms.ConclusionA CATS prism in Goldmann tonometer armatures significantly improve the accuracy of IOP measurement compared to true intracameral pressure across a physiologic range of IOP values. The CATS prism is significantly more accurate compared to the GAT prism in thin and less rigid corneas. The in vivo intracameral study validates mathematical models and clinical findings in IOP measurement between the GAT and CATS prisms.