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Observational and non-interventional study to evaluate angle parameters of patients with or without the diagnosis of glaucoma
*Corresponding author: Menaka Devi Kharibam, Department of Ophthalmology, Choudhury Eye Hospital and Research Centre, Silchar, Assam, India. mkharibam@gmail.com
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Received: ,
Accepted: ,
How to cite this article: Kharibam MD, Mansoor SA, Choudhury HK. Observational and non-interventional study to evaluate angle parameters of patients with or without the diagnosis of glaucoma. J Ophthalmic Res Pract 2023;1:19-25.
Abstract
Purpose:
The aim of the study was to assess the different parameters of anterior chamber angle (AA) with anterior segment optical coherence tomography (OCT) in patients with or without the diagnosis of glaucoma.
Methods:
A cross-sectional and observation study of angle parameters for clinically diagnosed, undiagnosed, and suspected patients of angle closure was done. Patients with glaucoma suspect not having angle closure were also included in the study. AAs (nasal and temporal), AC depth (ACD), AC area (ACA), and central corneal thickness (CCT) were assessed using Cirrus high-definition optical coherence tomography.
Results:
Total 349 eyes of 178 patients with mean age of 41.31 ± 13.61 years were analyzed. One hundred and six of them were female (59.55%) and 72 were male (40.45%). The mean values of CCT were 540.85 ± 39.99 µm, 536.44 ± 41.25 µm; ACD were 2.37 ± 0.5 mm, 2.45 ± 0.4 mm, ACA were 17.04 ± 5.20 mm2, 17.48 ± 4.47 mm2, and AC width were 11.10 ± 0.45 mm, 14.13 ± 0.39 mm for the right and left eyes, respectively. The mean AA for the right and left eyes were nasal 22.23° ± 14.57°, 24.14° ± 14.10°; temporal 25.18° ± 14.13°, 25.88° ± 13.55°, respectively.
Conclusion:
The nasal AA was found to be significantly narrower than the temporal angle in both right and left eyes; and the angle asymmetry increases with increasing age.
Keywords
Angle parameters
Anterior segment optical coherence tomography
Cirrus high-definition optical coherence tomography 500
Glaucoma
INTRODUCTION
The global prevalence of glaucoma, the second leading cause of blindness worldwide, for the population aged 40–80 years is 3.54% of which the prevalence of primary open angle glaucoma (POAG) is highest in Africa and that of primary angle closure glaucoma (PACG) is highest in Asia.[1] Angle closure disease according to definition of International Society for geographical and epidemiological ophthalmology is classified as primary angle closure suspect (PACS), primary angle closure (PAC), and PACG.[2] During the COVID-19 pandemic, gonioscopy was recommended to be performed at the discretion of surgeon with appropriate precautions.[3] Hence, the non-contact procedure of anterior segment optical coherence tomography (AS-OCT) was performed alternately. The present study will primarily discuss the anatomic parameters in patients with or without the diagnosis of glaucoma obtained in AS-OCT.
MATERIAL AND METHODS
We conducted an observational cross-sectional study in angle closure suspects, diagnosed and undiagnosed cases of PACG and glaucoma suspects (GS). A person with one or more risk factors that raised the possibility of developing glaucoma later is identified as GS. The risk factors include elevation of intraocular pressure; optic nerve head, retinal nerve fiber layer and visual field abnormalities suggestive of glaucoma; abnormal angles, and family history of glaucoma.[4] Three hundred and forty-nine eyes (total of 178 patients) with at least one eye with PACS, PAC, PACG, and GS were enrolled in the study. The study was conducted at the glaucoma clinic of a tertiary eye care center. The study period was from June 2020 to December 2022. Comprehensive ophthalmic examinations including visual acuity, refraction, slit lamp examination, rebound tonometry, and posterior segment evaluation were done for all patients. The study was conducted in accordance with Declaration of Helsinki. Informed written consent was provided by all patients. Hospital Ethics Committee approval was obtained.
Study device - AS-OCT
AS images can be taken with OCT which is a non-contact and high-resolution imaging method. Cirrus HD OCT Model 500 (Carl Zeiss Meditec, Dublin, CA) is a spectral domain OCT with superluminescent diode laser of 840 nm wavelength and scan speed of 27000–68000 A- scans per second having A- Scan depth of 2 mm. Cirrus HD OCT has axial resolution of 5 µm and transverse resolution of 15 µm.
Definitions of AS-OCT parameters and measurements
By marking the scleral spur and angle recess by the operator, AS-OCT machine automatically measures the angle parameters such as central corneal thickness (CCT), AC area (ACA), and AC angles (AAs) both nasal and temporal. The AA (i.e., the trabecular iris angle) is measured by placing the angle’s apex in the iris recess, its arm at a point on trabecular meshwork 500 µm from the scleral spur and the other arm is placed on the iris at a point perpendicularly opposite to the first point.
AC depth (ACD) is taken as the perpendicular distance between the corneal endothelium at the apex of cornea and anterior surface of lens.
The AC width (ACW) is measured using the built-in chamber tool placing one line horizontally and end points manually adjusting between the opposing scleral spurs.[5] Scans that did not show scleral spur were not included in the study. A single ophthalmic technician performed the measurements in a semi-lit room with patient in seated position.
AS-OCT images were assessed in two quadrants, that is, nasal and temporal. The eyelids were retracted gently during imaging to prevent unintentional pressure on the globe. Image with low signal strength was eliminated. Eyes with corneal pathology, pterygium, post-iridotomy, or poor visualization of scleral spur were excluded from the study. One eye was evaluated for those patients (n = 7).
Statistics
Biometric data were entered in Microsoft Excel (Office 2019) and SPSS software (version 22.0) was used for statistical analysis. Mean ± standard deviation was used to express quantitative variable data. The patients were separated into seven groups based on their age for the ease of statistical analysis, namely, ≤20 years, 21–30 years, 31–40 years, 41–50 years, 51–60 years, 61–70 years, and ≥71 years. AA were divided into five grades as 0°, ≤10°, 11°−20°, 21°−35°, and 36°−45° based on Shaffer grading.[6] Both nasal and temporal angles were included in the study.
RESULTS
Three hundred and forty-nine eyes of 178 patients were analyzed. One hundred and six of them were female (59.55%) and 72 were male (40.45%). The average age of study population was 41.31 ± 13.61 years. [Table 1] shows the parameters of AC measured. [Figures 1-4] shows mean of anterior chamber area, anterior chamber depth, anterior chamber width and central corneal thickness distribution according to age respectively. Among the 698 AA values (including both nasal and temporal angles), 419 (60%) were open angles, 219 (31.37%) were narrow angles and 60 (8.60%) were closed angles. The AA grading according to the Shaffer classification of AA are given in [Table 2] (right eye) and [Table 3] (left eye). [Figure 5] shows the angle distribution according to Shaffer classification of entire study population. Distribution of CCT values, ACD, ACA, and ACW according to age groups for the right and left eyes is given in [Tables 4 and 5], respectively.
| Parameters | Right eye | Left eye |
|---|---|---|
| CCT (µm) | 540.85±39.99 | 536.44±41.25 |
| ACD (mm) | 2.37±0.5 | 2.45±0.4 |
| AC Area (mm2) | 17.04±5.20 | 17.48±4.47 |
| AC Angle nasal (degree) | 22.23±14.57 | 24.14±14.10 |
| AC Angle temporal (degree) | 25.18±14.13 | 25.88±13.55 |
| ACW (in mm) | 11.10±0.45 | 14.13±0.39 |
CCT: Central corneal thickness, ACD: Anterior chamber depth, AC: Anterior chamber, ACW: Anterior chamber width
| Right eye nasal angle | Male | Female | Total | Right eye temporal angle | Male | Female | Total |
|---|---|---|---|---|---|---|---|
| 0° | 5 | 16 | 21 | 0° | 6 | 7 | 13 |
| ≤10° | 2 | 17 | 19 | ≤10° | 2 | 17 | 19 |
| 11–20° | 16 | 26 | 42 | 11–20° | 8 | 24 | 32 |
| 21–35° | 25 | 33 | 58 | 21–35° | 29 | 40 | 69 |
| >35° | 22 | 13 | 35 | >35° | 25 | 17 | 42 |
| Left eye nasal angle | Male | Female | Total | Left eye temporal angle | Male | Female | Total |
|---|---|---|---|---|---|---|---|
| 0° | 4 | 12 | 16 | 0° | 3 | 7 | 10 |
| ≤10° | 5 | 16 | 21 | ≤10° | 4 | 11 | 15 |
| 11–20° | 4 | 28 | 32 | 11–20° | 9 | 30 | 39 |
| 21–35° | 31 | 31 | 62 | 21–35° | 23 | 40 | 63 |
| >35° | 26 | 17 | 43 | >35° | 31 | 16 | 47 |
| CCT in µm | ACD in mm | AC-area in mm2 | AC-nasal in degree | AC-temporal in degree | ACW in mm | |
|---|---|---|---|---|---|---|
| ≤20 years | ||||||
| Male 2 | 544±42.4 | 2.90±0.13 | 22.86±0.07 | 42.5±10.60 | 39.5±2.12 | 11.39±0.06 |
| Female 4 | 539.7±32.10 | 2.64±0.53 | 19.82±0.39 | 31.5±15.45 | 33.25±14.81 | 11.13±0.54 |
| 21–30 | ||||||
| Male 8 | 567±43.27 | 2.76±0.24 | 22.31±3.73 | 36.5±11.09 | 38.75±10.49 | 11.57±0.34 |
| Female 2 | 531±65.76 | 2.87±0.19 | 22.43±1.47 | 39±5.65 | 45±5.65 | 11.42±0.53 |
| 31–40 | ||||||
| Male 13 | 537±41.06 | 2.58±0.38 | 19.79±4.74 | 29.91±19.81 | 29.58±19.44 | 11.24±0.42 |
| Female 15 | 524.1±40.15 | 2.49±0.40 | 18.20±3.49 | 24.61±12.11 | 28.86±9.77 | 11.06±0.40 |
| 41–50 | ||||||
| Male 11 | 527.2±28.6 | 2.47±0.72 | 18.18±7.08 | 23.72±16.48 | 29.27±17.39 | 11.35±0.51 |
| Female 38 | 541.6±28.65 | 2.22±0.43 | 14.95±3.91 | 14.73±10.17 | 18.76±12.10 | 10.98±0.33 |
| 51–60 | ||||||
| Male 21 | 536.3±31.37 | 2.34±0.54 | 16.14±6.00 | 23.33±11.93 | 23.09±13.23 | 11.12±0.59 |
| Female 29 | 544.2±35.61 | 2.24±0.43 | 15.73±4.08 | 17.10±13.64 | 21.50±11.7 | 11.02±0.38 |
| 61–70 | ||||||
| Male 9 | 556.8±78.22 | 2.67±0.31 | 20.82±3.58 | 32.87±12.63 | 33.25±8.43 | 11.45±0.31 |
| Female 17 | 564.5±49.02 | 2.09±0.65 | 14.87±6.19 | 19.82±14.42 | 21.88±13.33 | 10.90±0.49 |
| ≥71 | ||||||
| Male 8 | 518.3±27.28 | 2.35±0.39 | 17.15±5.24 | 23.37±13.92 | 26.25±15.06 | 11.01±0.49 |
| Female 1 | 476 | 2.02 | 12.37 | 0 | 0 | 10.93 |
CCT: Central corneal thickness, ACD: Anterior chamber depth, AC: Anterior chamber, ACW: Anterior chamber width
| CCT in µm | ACD in mm | AC-area in mm2 | AC-nasal in degree | AC-temporal in degree | ACW in mm | |
|---|---|---|---|---|---|---|
| ≤20 years | ||||||
| Male 2 | 546±11.3 | 2.83±0.07 | 21.85±0.31 | 40±9.8 | 32.5±9.19 | 11.52±0.02 |
| Female 4 | 534.5±36.29 | 2.68±0.39 | 19.79±3.64 | 36.75±26.99 | 39.5±15.84 | 10.77±0.71 |
| 21–30 | ||||||
| Male 8 | 558.7±43.27 | 2.71±0.22 | 21.42±1.77 | 38.57±9.48 | 38.14±10.15 | 11.52±0.35 |
| Female 2 | 536±29.69 | 2.94±0.19 | 22.93±1.03 | 46±8.48 | 41.5±12.02 | 11.09±0.12 |
| 31–40 | ||||||
| Male 13 | 534.5±37.77 | 2.69±0.31 | 20.27±3.87 | 31.46±14.4 | 32.07±14.48 | 11.25±0.38 |
| Female 15 | 536.8±91.91 | 2.43±0.37 | 16.80±4.46 | 20.4±13.31 | 26.06±7.56 | 11.04±0.38 |
| 41–50 | ||||||
| Male 11 | 519.1±29.06 | 2.62±0.46 | 19.36±5.40 | 23.45±16.89 | 27.18±19.36 | 11.35±0.54 |
| Female 38 | 536.4±28.69 | 2.27±0.37 | 14.88±3.53 | 16.05±11.22 | 17.21±15.5 | 11.03±0.40 |
| 51–60 | ||||||
| Male 21 | 532.7±30.32 | 2.42±0.51 | 17.41±4.86 | 24.57±11.90 | 27.23±12.89 | 11.02±0.78 |
| Female 29 | 538.8±29.20 | 2.32±0.37 | 16.28±4.04 | 19.39±11.77 | 21.42±10.97 | 11.04±0.49 |
| 61–70 | ||||||
| Male 9 | 548.7±50.33 | 2.62±0.41 | 19.38±4.54 | 32.22±12.23 | 30.77±12.23 | 11.41±0.33 |
| Female 17 | 547.3±29.76 | 2.40±0.39 | 17.25±3.99 | 19.82±14.42 | 27.93±11.31 | 10.93±0.45 |
| ≥71 | ||||||
| Male 8 | 512.2±31.66 | 2.54±0.35 | 19.54±4.14 | 33.28±10.90 | 30.57±10.93 | 9.49±3.80 |
| Female 1 | 459 | 1.93 | 7.57 | 0 | 0 | 10.87 |
CCT: Central corneal thickness, ACD: Anterior chamber depth, AC: Anterior chamber, ACW: Anterior chamber width
- Mean of anterior chamber area distribution according to age.
- Mean of anterior chamber depth distribution according to age.
- Mean of anterior chamber width distribution according to age.
- Mean of central corneal thickness distribution according to age.
- Pie chart of angle distribution.
The mean angles in PACG and PAC, PACS, POAG, and GS in our study are 3.73° ± 3.9°, 6.76° ± 2.66°, 33.59° ± 9.15°, and 22.66° ± 9.46°, respectively. [Figure 6] shows AS-OCT image of a closed angle. [Figure 7] shows AS-OCT image of a narrow angle with ruler showing CCT (513 µm), ACD (1.85 mm), Lens Vault (1115 µm) and ACW (11.14 mm). [Figure 8] shows AS-OCT image of an open angle with angle parameters.
- Image depicting angle closure.
- Image depicting narrow-angle.
- Wide-angle with angle parameters.
While analyzing the nasal and temporal angles in both eyes, the nasal angle was found to be narrower than the temporal angle. The mean nasal angle in the right eye was 22.23° ± 14.57° and temporal angle was 25.18° ± 14.14° (P < 0.001) and in the left eye, the nasal was 24.14° ± 14.10° versus temporal 25.88° ± 13.55° (P < 0.05). [Figures 9 and 10] shows the mean anterior chamber angle distribution according to age of left and right eye respectively. The study also revealed that the difference between nasal and temporal angles was more in older age groups, that is, >50 years (5.78° ± 5.64° for the right eye and 5.16° ± 4.22° for the left eye) as compared to younger age groups, that is, <50 years (5.32° ± 4.82° for the right eye and 4.77° ± 4.92° for the left eye).
- Mean of the left eye anterior chamber angle distribution according to age.
- Mean of the right eye anterior chamber angle distribution according to age.
DISCUSSION
Identifying the scleral spur is critical for proper angle biometry assessment, as the angle measurement is dependent on it entirely.[7] To measure the angle parameters, the angle recess and scleral spur are manually marked by the observer. A scleral spur is a point where sclera protrudes inward and the inner surface of sclera changes in curvature.
Several techniques, including Van Herrick assessment, gonioscopy, ultrasound biomicroscopy, and AS-OCT, have been described for population-based screening of Primary angle closure disease (PACD).[8-10] A community-based ASOCT imaging study found that in 22.8% of angles, the scleral spur could not be clearly distinguished.[11] Angle assessment in case of angle closure is widely being done using various types of AS-OCT.[11,12] In this study, we are using Cirrus HD OCT 500 to study the angle parameters.
The mean age of our study population was 41.31 ± 13.61 years lesser than that reported by Angmo et al.[7] (59.48 ± 7.95 years), Radhakrishnan et al.[13] (60.8 ± 9.8 years), and Lin et al.[11] (55.5 ± 9.0 years).
The mean CCT value in our study was 549 ± 41.01 µm which was more than that reported by Angmo et al.[7] (522.5 ± 34.75 µm and 539.55 ± 29.56 µm), Malhotra et al.[14] (505.97 ± 30.12 µm), Yazici et al.[15] (529 ± 30.5 µm), and similar to Bechmann et al.[16] (530 ± 32 µm).
The ACD in our study was found to be 2.28 ± 0.34 mm, similar to that reported by Angmo et al.[7] (2.144 ± 0.38 mm and 2.133 ± 0.39 mm) and lesser than that of Moghimi et al.[12] (2.53 ± 0.28 mm) and Yazici et al.[15] (2.94 ± 0.34 mm).
The mean ACA value was found as 15.61 ± 8.17 mm2 in the present study, lesser than that reported by Wu et al.[17] (20.1 mm2). The mean ACW was 11.29 ± 0.72 mm in our study, similar to Xu et al.[18] (11.6 ± 0.39) mm and lesser than Goldsmith et al.[19] (12.53 ± 0.47 mm). The study done by Nongpiur et al. has reported that when compared with eyes having wide angle, the mean ACW was lesser in eyes with narrow angle (11.80 mm vs. 11.60 mm, P < 0.001).[5]
In this study, we have found out that the nasal AA was significantly narrower than the temporal angle in both right and left eyes. Till date, no study has reported AA being narrower nasally than temporally.
Limitation of our study was correlation between the various parameters of AC and AA was not done. The angles were manually measured, which can be a cause of error.
CONCLUSION
In this study, in general non randomized population, it was found that the nasal AA is significantly narrower than the temporal angle in both right and left eyes. It was also observed that the angle asymmetry increases with age in general population.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent.
Conflicts of interest
There are no conflicts of interest.
Financial support and sponsorship
Nil.
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