Assessment of Anterior Chamber Angle and Angle to Angle Among Healthy Saudi Individuals by using Pentacam

The measurement of Anterior Chamber Angle (ACA) is very essential in diagnosing a glaucoma patient; specially it allows us to differentiate between primary angle-closure glaucoma (PACG) and primary open-angle glaucoma (POAG), in addition it helps in further management [1] Also, ACA is important in the placement of intraocular lens in phakic patients [2]. The normal range for ACA is between 30.2° and 41.6° [3]. Moreover, Angle to Angle (ATA) helps to provide an accurate estimation of the optimum intra ocular lens (IOL) placement and length since the internal distance is preferable more than the external distance (white to white). Having the ability to measure perfect IOL size is crucial to avoid unwanted events such as lens decentration, rotation or inadequate vaulting. If the IOL size selected is small; it may result in raised IOP or corneal endothelial cell damage. The normal range varies between 11.4- and 12-mm [4,5]. ACA and ATA measurement have been noted to be affected by multiple factors including age, gender, race/ethnicity, corneal curvature, and refractive error [6]. There are multiple devices can assess ACA and ATA, but only few studies have assessed the accuracy and the repeatability of ACA and ATA. Pentacam HR (Oculus, Wetzlar, Germany) is a non-contact rotating Scheimpflug technology that has been shown to be repeatable and reproducible for ACA and ATA measurements [2,7]. There is no study yet done to investigate the repeatability and reproducibility of Pentacam among Saudi population, therefore the purpose of this study is to evaluate the normative values of Saudi individuals, repeatability and reproducibility of ACA and ATA by using Pentacam, as well as, to compare the difference of these values between genders. The results of this study may help in explaining why higher prevalence of angle closure rates are in females.

In this prospective cross-sectional study sixty healthy Saudi individuals aged between 18 to 30 were included in this study, 30 males and 30 females. Screening tests were performed for each subject using slit lamp to exclude any ocular abnormalities and autorefraction was taken from each subject. Healthy subjects without ocular or systemic diseases were included. Participants who use contact lenses had stopped it three days prior taking the examination. Any ocular abnormalities or history of ocular surgery, spherical equivalent of more than ±4.00D, ocular pathology as glaucoma, keratoconus, pregnancy, and smoking. Participants who are taking any systemic or ocular medications were excluded. This study was performed at King Saud University, College of Applied Medicine clinics. It was conducted in accordance with the tenets of the Declaration of Helsinki regarding research involving human subjects. Each subject signed an informed consent form to participate in the study and after receiving information on the objectives of the research. One examiner assessed the repeatability of Pentacam HR by taking the mean of two readings of the ACA as well as ATA from one eye (right eye). Then two examiners assessed the reproducibility by taking, the mean of two readings of each parameter. Before taking each measurement, the patient is asked to place his/her chin on the chin rest and the forehead against the forehead strap. The patient was asked to keep both eyes open and stare at the fixation target. Only the image of good quality was taken and selected. The data were calculated using Excel 2017, it presented as Mean ± SD. Paired t-test was used to calculate the difference between genders in terms of ACA and ATA. The bland- Altman of agreements was used to calculate the repeatability of one examiner and the reproducibility between two examiners.

Demographic Data and Normal Values of ACA and ATA

Data collected from sixty individuals showed that the overall age (Mean ± SD) for all participants was 21.7± 3.1 years. In addition to that, the (Mean ± SD) of the spherical equivalent was -0.67 ± 1.19 D, where males had lower spherical equivalent equal to -0.57 D. Furthermore, the (Mean ± SD) of ACA was 38.11 ± 5.16 °, where females had smaller ACA of 37.18°. Moreover, the (Mean ± SD) of ATA was 12.20 ± 1.12 mm, with females having shorter ATA with a mean of 12.18mm (Table 1). The parameters of ACA and ATA were tested by the normality test, and they were normally distributed.

Table 1: Shows Demographic Data and Normative Values of ACA and ATA.

Comparison of ACA and ATA between genders

The result showed that there was significant difference between males and females in ACA with P-value of 0.049, on the other hand there was no significant difference between males and females in ATA with P-value of 0.867. Despite that the results showed that there were no significant differences in ATA, the mean values of females had a slightly lower ATA compared to males (Table 2).

Table 2: Shows comparison of ACA and ATA between genders.

Repeatability of Pentacam HR in measuring ACA and ATA by one Examiner.

Intra-class correlation coefficient (ICC) and the corresponding 95% confidence interval (CI) calculated for evaluating the repeatability of Pentacam HR in measuring ACA and ATA by one examiner. The ICC value for ACA measurement is 0.861 such result indicates a good level of repeatability, while the ICC value for ATA measurement is 0.649 which indicates a moderate level of repeatability (Table 3). There were no significant differences between the two measurements of ACA and ATA by one examiner with P-value= 0.891, P-value= 0.614 respectively. The Bland-Altman plot showing the agreement of ACA measurements by one examiner where the line shows the mean difference, and the lower and upper 95% confidence levels (-5.74234, 5.638944) respectively (Figure 1). On the other hand, ATA measurements shows the lower and upper 95% confidence levels (-1.95563, 2.090632) respectively (Figure 2).

Table 3: Intra-class Correlation Coefficient (ICC) for ACA and ATA Measurements – Examiner1.

Reproducibility of Pentacam HR in measuring ACA and ATA by two Examiners.

The ICC value for ACA measurement is 0.883 that indicates a good level of reproducibility. In addition, the ICC value for ATA measurement is 0.488 which indicates a poor level of reproducibility. But the average measures result for ATA indicate a moderate level of reproducibility (Table 4). There were no significant differences between the two measurements in case of ACA and ATA by two examiners with P-value= 0.137, P-value = 0.979 respectively. The Bland-Altman plot showing the agreement of ACA measurements by two examiners which shows the lower and upper 95% confidence levels (-5.35837, 4.659972) respectively (Figure 3). While ATA measurements show (-2.59724, 2.59084) respectively (Figure 4).

Table 4: Intre-class Correlation Coefficient (ICC) for ACA and ATA Measurements – Examiner1&2.

Table 5: Anterior segment parameters measured among different populations.

ACA plays an important role in the diagnosis and treatment of glaucoma on the other hand ATA is an important measurement in IOL implantation after cataract surgery or in phakic patient. In this prospective cross-sectional study, by using Pentacam HR, the normative values of ACA and ATA for young Saudi population with a mean refractive error of -0.67 D was 38.11° and 12.20 mm respectively (Table 5). shows the differences in anterior segment parameters measured in different studies conducted on different populations. The differences in the mean of ACA and ATA between the present study and previous studies could be due to ethnicity, genetic, environmental, methodology and design of the study, sample size or other factors. We demonstrated that females had smaller ACA and shorter ATA compared to male, with mean value of 37.18° and 12.18 mm respectively, so the difference between females and males in ACA was statically significant (P=0.049), and the difference of ATA between females and males was not statically significant (P= 0.876). Similarly, ACA was found to be significant between males and females among Iranian [2] with females having smaller ACA which agrees with our results. Moreover, [8] found that ATA was statically significant between gender, which was longer in males, therefore it was the opposite of our result. The explanation of the differences between our study and [8] is maybe due to the manual method when ATA measurement was captured in Pentacam HR since it was the only option in our study (Table 6). shows the differences of ACA and ATA among genders. The present study is compatible with [9] where it showed that Pentacam had excellent reproducibility in measuring ACA. Also, [10] showed similar results as ours since ATA had good repeatability. While [5] stated that ATA wasn’t highly repeatable and reproducible by using Pentacam HR. Our study was limited by some conditions mainly due to COVID-19. One of the unavoidable limitations was the manual method in taking ATA since the automatized option wasn’t available in this version, it would have shown a better repeatability and reproducibility. On the good side, it is the first study of ACA and ATA that have been done in Saudi Arabia and its beneficial since those measurement differs among ethnicities.

Table 6: Shows the differences of ACA and ATA between genders among different studies.

In this study we established the normative values of ACA and ATA among young healthy Saudi individuals, as well as we found that there was significant difference between genders in ACA measurement. But ATA measurements were not significant between genders. Moreover, Pentacam HR showed excellent repeatability and reproducibility in measuring ACA while it showed good repeatability and moderate reproducibility in measuring ATA. The anterior parameters that we have studied are valuable measurements in glaucoma management as well as intraocular lens implantation. We recommend further research with wider age group and larger sample size.

None.

No conflict of interest.

1. Smith SD, Singh K, Lin SC, Chen PP, Chen TC, et al. (2013) Evaluation of the anterior chamber angle in glaucoma: A report by the American Academy of Ophthalmology. Ophthalmology. Published online 120(10): 1985-1997.
2. Hashemi H, Khabazkhoob M, Mohazzab-Torabi S, Emamian MH, Shariati M, et al. (2016) Anterior Chamber Angle and Anterior Chamber Volume in a 40-to 64-Year-Old Population. Eye Contact Lens 42(4): 244-249.
3. Leung CKS, Li H, Weinreb RN (2008) Anterior chamber angle measure with anterior segment optical coherence tomography: A comparison between slit lamp OCT and visante OCT. Investig Ophthalmol Vis Sci 49(8): 3469-3474.
4. Montés-Micó R, Tañá-Rivero P, Aguilar-Córcoles S, Ruiz-Santos M, Rodríguez-Carrillo MD, et al. (2020) Angle-to-angle and spur-to-spur distance analysis with high-resolution optical coherence tomography. Eye Vis 7(1): 1-13.
5. Saito A, Kamiya K, Fujimura F, Takahashi M, Shoji N (2019) Comparison of angle-to-angle distance using three devices in normal eyes. Eye 34(6): 1116-1120.
6. Olusegun A, Makun HA, Ogara IM (2012) We are IntechOpen, the world’s leading publisher of Open Access books Built by scientists, for scientists TOP 1 %. Intech i(tourism): 38.
7. Hashemi H, Yekta AA, Khodamoradi F, Aghamirsalim M, Asharlous A, et al. (2019) Anterior chamber indices in a population-based study using the Pentacam. Int Ophthalmol 39(9): 2033-2040.
8. Pinilla Lozano I, López de la Fuente C, Segura F, Orduna Hospital E, Sánchez-Cano A (2018) Evaluation of anterior chamber parameters with spectral-domain optical coherence tomography. Jpn J Ophthalmol 62(2): 209-215.
9. Li M, Song Y, Zhao Y, Yan X, Zhang H (2018) Influence of exercise on the structure of the anterior chamber of the eye. Acta Ophthalmol 96(2): e247-e253.
10. Domínguez-Vicent A, Brautaset R (2018) Agreement and repeatability of two biometers to measure anterior segment components: Refractive error effect. Med Sci Monit 24: 8056-8063.