Anterior segment parameters in Indian young adults using the Pentacam

Distribution of anterior chamber angle measurements in South African young adults: an optical coherence tomography study

PURPOSE

Assessment of anterior chamber angle (ACA) variables is important to screen, diagnose and monitor ocular anomalies. Even though data on ACA variables, such as angle-opening distance taken at 500 µm (AOD500) and trabecular-iris angle (TIA), are available in the literature, limited information is available about these variables in African sub-populations. The purpose of this study is to describe the distribution of ACA measurements (AOD500 and TIA) in a South African young adult population.

METHODS

In this cross-sectional study, 700 young adults were recruited from a university student population using two-stage random sampling. The Optovue iVue 100 optical coherence tomographer was used to measure the ACA variables. The distribution of the AOD500 and TIA measurements was analysed using descriptive and inferential statistics. Data from only the right eyes were analysed because the ACA measurements in the two eyes showed high levels of interocular symmetry.

RESULTS

The measurements for the nasal and temporal ACAs were asymmetrically distributed (p < 0.001). The median AOD500 measurements in the nasal and temporal angles were 539 µm and 542 µm, respectively. The median TIA measurements were similar (~ 36°) in the two horizontal angles. The temporal ACA measurements were slightly higher than the nasal ACA measurements. Females had higher median ACA measurements than males (p ≥ 0.029).

CONCLUSION

The ACA measurements in South African young adults resemble non-Gaussian curves. The ACA measurements are different from that reported in other sub-populations worldwide and most participants had ACA measurements associated with non-occludable ACAs.

Normative Values of Various Pentacam HR Parameters for Pediatric Corneas

PURPOSE

To provide a normative database of several Pentacam parameters for a healthy pediatric population.

METHODS

This was a retrospective study conducted at Al Watany Eye Hospitals, Cairo, Egypt. We explored the Pentacam HR database and collected the data of 432 normal right eyes of children and teenagers aged 3 to 18 years. The subjects were classified into the following 3 groups: group 1 (3-6 years, 17 eyes), group 2 (6-12 years, 126 eyes), and group 3 (12-18 years, 289 eyes). The parameters of the study cohort were compared with those of a healthy adult cohort.

RESULTS

The mean age of the study cohort was 13.5 (13.2-13.8) years. There were significant differences in the following indices among the 3 age groups: anterior chamber (depth and volume), curvature (index of height decentration, index of vertical asymmetry, and center keratoconus index), elevation (front and back elevations from the best fit toric ellipsoid), and pachymetric (minimum and average pachymetric progression indices and average Ambrosio relational thickness) parameters (P values 0.001, 0.001, 0.002, 0.04, <0.001, <0.001, 0.03, 0.02, 0.01, and 0.03, respectively).

CONCLUSIONS

There were significant differences in the normative values of several Pentacam indices between the pediatric and adult cohorts. Based on this finding, it is more credible to incorporate separate software cutoff values for pediatric patients. However, because there were no clinically significant differences in the parameters of the pediatric subgroups, there is no need to consider a separate cutoff value for each pediatric age range.

Pseudodominant Nanophthalmos in a Roma Family Caused by a Novel PRSS56 Variant

Background

The aim of the study was to identify the molecular genetic cause of two different Mendelian traits with ocular involvement present in the members of a single consanguineous Czech Roma family.

Methods

We have performed ocular examination and review of medical records in two individuals diagnosed with nanophthalmos (proband and her father) and one individual followed for bilateral congenital cataract and microcornea (uncle of the proband). DNA of subjects with nanophthalmos was analysed by exome sequencing. Sanger sequencing was applied for targeted screening of potentially pathogenic variants and to follow segregation of identified variants within the family.

Results

A homozygous variant c.1509G>C; p.(Met503Ile), in PRSS56 was found in the two individuals affected with nanophthalmos. The change was absent from the gnomAD dataset, but two out of 118 control Roma individuals were also shown to be heterozygous carriers. Analysis of single nucleotide polymorphisms in linkage disequilibrium with the c.1509G>C in PRSS56 suggested a shared chromosomal segment. The nanophthalmos phenotype, characterized in detail in the younger individual, encompassed bilateral corneal steepening, retinal folds, buried optic head drusen, and restricted visual fields, but no signs of retinal dystrophy. A known pathogenic founder CTDP1 variant c.863+389C>T in a homozygous state was identified in the other family member confirming the suspected diagnosis of congenital cataracts, facial dysmorphism, and demyelinating neuropathy syndrome.

Conclusions

Herein, we report the first occurrence of nanophthalmos in the Roma population. We have identified pseudodominant inheritance for this phenotype caused by a novel variant in PRSS56, representing a possible founder effect. Despite advances in genetic technologies such as exome sequencing, careful phenotype evaluation in patients from an isolated population, along with an awareness of population-specific founder effects, is necessary to ensure that accurate molecular diagnoses are made.

Pentacam HR Indices Variation in Normal Corneas with Different Corneal Thickness

Purpose

To evaluate the effect of variable corneal thickness on Pentacam HR diagnostic indices in normal corneas.

Methods

Retrospective study was conducted at Al Watany Eye Hospital, Cairo, Egypt. Consecutive 160 eyes of young myopic subjects without KC were evaluated using Pentacam HR (WaveLight Allegro Oculyzer II, Erlangen, Germany). The elevation- and thickness-based indices were recorded. Enrolled corneas were categorized into three groups according to TCT quartiles; group 1 (39 eyes) included corneas with TCT <523 µm, group 2 (81 eyes) with TCT between 523 and 564 µm, while group 3 (40 eyes) enrolled TCT >564 µm. The possible effect of pachymetry on Pentacam HR indices was assessed using partial correlation tests.

Results

In normal corneas, back elevation from best fit sphere (BE from BFS) and that from best fit toric ellipsoid (BFTE) were the elevation indices that showed statistically significant differences among groups (P=0.013 and 0.019, respectively). Regarding pachymetric indices, maximum pachymetry progression index (PPI max) showed statistical significance (P=0.001). Partial correlations, after excluding age and refractive error effects, showed that TCT was correlated with BE from BFS, BE from BFTE, and PPI max (P=0.001, 0.001,0.002, respectively).

Conclusions

Some Pentacam HR indices varied with different corneal thickness in normal corneas. This necessitates inclusion of pachymetric subgroups in the normative database. The use of the more robust indices (average pachymetry progression index and front elevations) is recommended in relatively thin or thick corneas.

Measurement of anterior segment parameters in Saudi adults with myopia

Purpose

To measure anterior segment parameters of the eye in myopic Saudi population using Pentacam.

Method

This is retrospective cross-sectional study. Subjects were divided into three groups: low, moderate and high myopia groups. Anterior segment parameters including: central corneal thickness (CCT), thinnest corneal thickness (TCT), apex corneal thickness (Apex CT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and corneal astigmatism (CA) were measured by Pentacam.

Results

A total of 504 eyes of 252 Saudi subjects with myopia were included in this study. The mean age ± standard deviation (SD) of subjects was 28.73 ± 6.18 years. The mean CCT, TCT, Apex CT, CV, ACD, ACV and CA for all myopic subjects were 557.21 ± 29.36, 554.09 ± 29.28, 556.10 ± 37.06, 61.30 ± 3.23 μm, 3.31 ± 0.27 mm, 211.15 ± 34.22 mm³ and 0.89 ± 0.52 D, respectively. No significant differences (P > 0.05) were found between right and left eyes in all anterior segment parameters of all myopic eyes. However, a significant difference (P < 0.05) was found in ACD between low (3.27 ± 0.26 mm) and moderate (3.35 ± 0.30 mm) myopic groups. Within low myopia group, significant differences (P < 0.05) were found in ACD, ACV and CA between different genders. Anterior chamber depth and ACV values were lower in females while CA was lower in males. In addition, significant positive correlation was found between ACV and ACD in all myopic groups.

Conclusion

This study provided valuable measurements of the anterior segments parameters of the eye in myopic Saudi population. These parameters could be useful for ophthalmic practitioners in the clinic.

Agreement between Pentacam and optical coherence tomography in the assessment of iridocorneal angle width in a large healthy population

PURPOSE

To analyze the agreement between Pentacam and optical coherence tomography (OCT) in the assessment of trabecular-iris angle (TIA) width in a large population of normal subjects.

METHODS

A cross-sectional study was performed in 989 right eyes of 989 healthy subjects. The trabecular-iris angle (TIA) was measured in the temporal and nasal quadrants using the Pentacam (Oculus, Wetzlar, Germany), a device based on Scheimpflug technology and RTVue 100 OCT (Optovue, Fremont, CA, USA). Intraclass correlation coefficients (ICC) and Bland-Altman plots were used to evaluate agreement between these devices.

RESULTS

Mean age was 49.1±15.2 years (18-84); 61% were women and spherical error range was -14 to 8.25. TIA could be measured by OCT in 94.9% and 94.1% in the temporal and nasal quadrants, with a mean value of 35.8±13.2 degrees (2.5-78.7) and 35.7±12.9 degrees (2.2-76.8) respectively. TIA was able to be measured by Pentacam in 95.2% and 95% in the temporal and nasal quadrants and means were 35.7±7.3 degrees (11-74.2) and 36.4±8.2 degrees (14.5-64) respectively. An ICC of 0.378 (95% confidence interval [CI], 0.322-0.431) and 0.589 (95% CI 0.546-0.629) for the temporal and nasal quadrants was obtained, showing moderate agreement between the devices. Bland-Altman plots revealed that, compared with OCT, Pentacam tends to overestimate measurements in narrow angles and underestimate these in open angles.

CONCLUSIONS

Agreement between OCT and Pentacam was mediocre, indicating the two devices are not interchangeable when used to measure angle width.

Dependence of dynamic contour and Goldmann applanation tonometries on peripheral corneal thickness

AIM

To determine the effects of peripheral corneal thickness (PCT) on dynamic contour tonometry(DCT) and Goldmann applanation tonometry (GAT).

METHODS

A cross-sectional study. We created a software which calculates the corneal contour (CC) as a function of the radius from the corneal apex to each pixel of the contour. The software generates a central circumference with a radius of 1 mm and the remainder of the cornea is segmented in 5 rings concentric with corneal apex being its diameter not constant around the corneal circumference as a consequence of the irregular CC but keeping constant the diameter of each ring in each direction of the contour. PCT was determined as the mean thickness of the most eccentric ring. Locally weighted scatterplot smoothing (LOWESS) regression was used to determine the pattern of the relationship between PCT and both DCT and GAT respectively. Thereafter, two multivariable linear regression models were constructed. In each of them, the dependant variable was intraocular pressure (IOP) as determined using GAT and DCT respectively. In both of the models the predictive variable was PCT though LOWESS regression pattern was used to model the relationship between the dependant variables and the predictor one. Age and sex were also introduced control variables along with their first-degree interactions with PCT. Main outcome measures include amount of IOP variation explained through regression models (R²) and regression coefficients (B).

RESULTS

Subjects included 109 eyes of 109 healthy individuals. LOWESS regression suggested that a 2^nd-degree polynomial would be suitable to model the relationship between both DCT and GAT with PCT. Hence PCT was introduced in both models as a linear and quadratic term. Neither age nor sex nor interactions were statistically significant in both models. For GAT model, R² was 17.14% (F=9.02; P=0.0002), PCT linear term B was -1.163 (95% CI: -1.163, -0.617). PCT quadratic term B was 0.00081 (95% CI: 0.00043, 0.00118). For DCT model R² was 14.28% (F=9.29; P=0.0002), PCT linear term B was -0.712 (95% CI: -1.052, -0.372), PCT quadratic term was B=0.0005 (95% CI: 0.0003, 0.0007).

CONCLUSION

DCT and GAT measurements are conditioned by PCT though this effect, rather than linear, follows a 2^nd-degree polynomial pattern.

Identifying the critical factors that influence intraocular pressure using an automated regression tree

Background: Assessment of intraocular pressure (IOP) is an important test in glaucoma. In addition, anterior segment variables may be useful in screening for glaucoma risk. Studies have investigated the associations between IOP and anterior segment variables using traditional statistical methods. The classification and regression tree (CART) method provides another dimension to detect important variables in a relationship automatically.Aim: To identify the critical factors that influence IOP using a regression tree.Methods: A quantitative cross-sectional research design was used. Anterior segment variables were measured in 700 participants using the iVue100 optical coherence tomographer, Oculus Keratograph and Nidek US-500 ultrasonographer. A Goldmann applanation tonometer was used to measure IOP. Data from only the right eyes were analysed because of high levels of interocular symmetry. A regression tree model was generated with the CART method and Pearson’s correlation coefficients were used to assess the relationships between the ocular variables.Results: The mean IOP for the entire sample was 14.63 mmHg ± 2.40 mmHg. The CART method selected three anterior segment variables in the regression tree model. Central corneal thickness was the most important variable with a cut-off value of 527 µm. The other important variables included average paracentral corneal thickness and axial anterior chamber depth. Corneal thickness measurements increased towards the periphery and were significantly correlated with IOP (r ≥ 0.50, p ≤ 0.001).Conclusion: The CART method identified the anterior segment variables that influenced IOP. Understanding the relationship between IOP and anterior segment variables may help to clinically identify patients with ocular risk factors associated with elevated IOPs.

Interocular anatomical and visual functional differences in pediatric patients with unilateral cataracts

Background

Congenital cataracts are often complicated by anterior segment dysgenesis. This study aims to compare bilateral anterior segment parameters, macular thickness, and best-corrected visual acuity (BCVA) in pediatric cataract patients at 3 months after unilateral cataract extraction with intraocular lens implantation.

Methods

Fifty-three pediatric patients with uncomplicated unilateral total cataracts were included. At 3 months post-surgery, bilateral corneal thickness at the thinnest location (CTTL), anterior chamber depth (ACD), and anterior chamber volume (ACV) were measured using Pentacam. Central macular thickness (CMT) was evaluated using spectral-domain optical coherence tomography. BCVA was measured by experienced optometrists concurrently. Descriptive statistics and bivariate corrections were performed to analyze the interocular differences in bilateral anatomic parameters and their relationships with BCVA.

Results

For all 53 included patients (mean age 5.2 ± 2.3 years), the median BCVA was 10/40 in the operated eyes and 40/40 in the contralateral eyes, which indicates a significant interocular difference. BCVA values in the contralateral eyes were significantly correlated with patient age at surgery, but this result differed for BCVA in the operated eyes. The Pentacam analysis revealed no significant interocular differences in bilateral CTTL and ACV, but significant differences were found for ACD.

Conclusions

At 3 months after surgery, unilateral pediatric cataract patients exhibited no significant interocular differences in identified anatomical parameters (except for ACD), and these parameters were not significantly correlated with BCVA in bilateral eyes. Therefore, amblyopia, but not anatomical factors, might be the main cause of interocular visual functional differences in our study population.

Trial registration

ClinicalTrial.gov, NCT02765230, 05/05/2016, retrospectively registered.

Electronic supplementary material

The online version of this article (doi:10.1186/s12886-016-0371-5) contains supplementary material, which is available to authorized users.

Comparative Evaluation of the Corneal and Anterior Chamber Parameters Derived From Scheimpflug Imaging in Arab and South Asian Normal Eyes

PURPOSE

To evaluate the differences in the normal corneal and anterior segment Scheimpflug parameters in Arab and South Asian eyes.

METHODS

This hospital-based study was performed at a cornea and refractive surgery service in Abu Dhabi. A total of 600 consecutive normal candidates of South Asian (group 1, n = 300) and Arab (group 2, n = 300) origins underwent Scheimpflug imaging (Sirius; Costruzione Strumenti Oftalmici, Italy). One eye was randomly selected for evaluation.

RESULTS

The age and sex distributions in both groups were comparable. The pachymetric variables were statistically higher in group 2 (group 2 vs. group 1, 544.3 ± 32.2 μm vs. 535.1 ± 31.4 μm for central corneal thickness, 541.0 ± 32.6 μm vs. 531.9 ± 31.5 μm for minimum corneal thickness, 571.7 ± 43.2 μm vs. 558.1 ± 42.3 μm for apical thickness, and 58.1 ± 4.2 vs. 57.3 ± 4.3 mm³ for the corneal volume; P < 0.05). The anterior chamber volume (group 2 vs. group 1: 166.4 ± 16.4 vs. 161.6 ± 20.5 mm³) and angle (group 2 vs. group 1: 44.6 ± 6.2 vs. 43.5 ± 5.8 degrees) were also higher for group 2 (P < 0.05). Central corneal curvature and apical corneal curvature (apex K) were higher in group 1 (P < 0.05) with comparable astigmatism. The flat keratometry (K), steep K, and apex K were 43.6 ± 2.2 diopters (D), 44.9 ± 1.8 D, and 45.7 ± 1.8 D for group 1, and 43.1 ± 2.2 D, 44.5 ± 2 D, and 45.2 ± 1.9 D for group 2. The effect size (Cohen d) for significant parameters ranged from 0.2 to 0.3.

CONCLUSIONS

Normal eyes of Arab ethnicity tend to have statistically thicker and flatter corneas and less-crowded anterior segments than those of the South Asian counterparts. These epidemiological differences have a mild to moderate biological effect size (Cohen d), but they should be considered when evaluating these eyes for anterior segment or corneal procedures.