Study area and period
The study was carried out in Debre Tabor Comprehensive specialized hospital from September 1/2020 to February 30/2021. Debre Tabor is located North West of the Amhara Region of Ethiopia, 103 km from Bahir Dar (Regional Capital), and 666Km from Addis Ababa (Capital city of Ethiopia). It is one of the oldest hospitals in the Amhara region, which provides services for about 5 million populations. The hospital is currently used as a referral center for district hospitals in the zone and a teaching hospital for medical and health science students of Debre Tabor University. The ophthalmic clinic is one department of the hospital with its minor and major operating units.
Study design and population characteristics
An institution-based cross-sectional study design was implemented. All patients, aged 40 and above years old who visited the ophthalmic outpatient department of Debre Tabor Comprehensive specialized hospital were the source population, and patients aged 40 and above years old visited the ophthalmic outpatient department of Debre Tabor Comprehensive specialized hospital during the time of data collection were the study populations.
All patients, 40 years of age and above were eligible to participate in this study while patients who were failed to communicate because of severe illness were excluded from this study.
Sample size determination
The sample size was determined using a single population proportion formula (n = Z 2 * p (1-P) /d2) for a crossectional survey based on the following assumptions: the prevalence of glaucoma (p) (9.79%) at the University of Gondar Tertiary Eye Care and Training Center, Ethiopia  with 95% level of confidence and 3% tolerable margin of error, the sample size required was 376. Adjustment using the correction formula was made to calculate the exact sample size since the total source population (N) was below 10,000. Therefore, the final required sample size was 279 by considering a non-response rate of 5%.
A systematic random sampling technique was used to select the study participants. A total of 956 patients were visiting the ophthalmic outpatient department over the last six-month period. Therefore, we calculated the sampling interval (k = N/n = 956/279 ≈ 3). Then the lottery method was used to get the random starter number which was 2. The first individual was taken as nth and the next was by sampling fraction (k = 3). And then every 3 patients were interviewed until the allocated sample size was achieved.
Data collection procedure
The questionnaire was developed after reviewing different kinds of literature [3, 11, 13, 17, 18]. The questionnaire consisted of demographic data, socioeconomic information, clinical and behavioral characteristics of patients. It was first prepared in English and then translated to Amharic (local language) to facilitate communication. Pretest was conducted outside the study hospital and modification was made before the actual data collection. Data collectors have obtained permission to proceed with interviewing. The data was collected by the trained two BSC nurses.
Data quality control measure
To ensure the quality of the data every day after data collection, the questioner was reviewed for completeness, accuracy, and clarity by the data collectors.
Data processing and analysis
The collected data was cleaned, entered, and analyzed using SPSS version 23. To explain the study population concerning relevant variables, data were described using summary measures (frequency, proportion means). Proportions estimated along with 95% CI level. Both bivariate and multivariable logistic regression analyses were carried out. Variables with a p-value < 0.25 in the bivariate analysis were fitted into the multivariable logistic regression model for the prediction of determinants . The Hosmer-Lemeshow goodness-of-fit statistics were used to assess whether the necessary assumptions for the application of multiple logistic regression were fulfilled and it was non-significant (p = 0.76). Crude and adjusted odds ratio with 95% confidence interval was computed. The Adjusted Odds ratio with a 95% confidence interval is used to measure the strength of association and the actual predictors of the outcome variables. P-values less than 0.05 were used as a cutoff point for declaring statistically significant.
socio-demographic, socioeconomic, clinical, and behavioral factors.
Measurement of Intra-Ocular-Pressure (IOP)
By using trans- palpebral tonometry: Appling topical anesthetic and dilating drops then we have instructed the patient to position their head into a device called the slit lamp. After that, a small tip gently touches the surface of the eye by using tonometry, and the eye pressure was measured. The eye pressure is measured based on the force required to gently flatten a fixed area of the cornea.
Visual acuity measurement
Visual acuity is a measure of the ability of the eye to distinguish the details of objects. Visual acuity testing is part of every eye examination. We measured by using the following equipment; Multi-letter Snellen chart and Plain occluder, card, or tissue.
After explaining the procedure and ensuring good natural light or illumination on the chart.
Positioned the patient, sitting or standing, six meters away from the 6-m Snellen or tumbling E chart (or 3 m away from the 3-m Snellen or E chart). Testing and recording visual acuity. Test the eyes one at a time, usually starting with the right eye, without any spectacles.
Ask the patient to cover the left eye with the plain occluder, card, or tissue.
Visual field measurement
We have measured the visual field in degrees from the central fixation in four quadrants: temporal (toward patient’s ear), nasal (toward patient’s nose), superior (upper, or above center), and inferior (lower, or below center).
In this study, the diagnosis and classification of glaucoma were based on the criteria defined by the International Society for Geographical and Epidemiological Ophthalmology (ISGEO) .
Cases were classified as category 3 according to the ISGEO scheme and made by: Visual acuity < 3/60 and IOP > 99.5th percentile (> 21 mmHg) OR Visual acuity < 3/60 and the eye had evidence of glaucoma filtering surgery or medical records were available confirming glaucomatous morbidity .
Primary open angle
An eye that does not have evidence of angle-closure on Gonioscopy, and where there is no identifiable secondary cause.
Primary closed angle
An eye with an occludable drainage angle and where there is no identifiable secondary cause.