A hospital-based cross-sectional comparative study was conducted at a glaucoma unit and general out patient clinics of the department of ophthalmology, Menelik II tertiary referral hospital, Ethiopia from October 1, 2019 to November 15, 2019. The source populations for this study were all glaucoma patients who received services at the glaucoma unit and ophthalmic patients attending the general out patient clinics. All glaucoma patients who had follow-up visit and new ophthalmic patients (controls) who came for care during the study period were the study population.
Sample size determination and sampling technique
The sample size was calculated using the formula for comparative studies [16]. Taking the proportion from other similar studies [17], it was assumed that the minimum prevalence of DED among glaucoma patients to be 39% and that of non-glaucoma patients 25%. The significant level was taken as 95% with alpha error set to 5% and power of the study was set at 80%. The ratio of the cases to the control was taken as one. Using these parameters, the required sample size came to be 160 for each group.
Recruitment of study participates
All glaucoma participants were recruited consecutively using their charts during regular scheduled glaucoma unit appointment days. The controls were new patients attending the general ophthalmic outpatient clinics of the department; similarly, they were recruited consecutively using their charts from a triage room. Ophthalmic/general nurses measured both visual acuity and intraocular pressure, and document on the patient’s chart prior getting eye care service form physicians. While the patients were waiting in the waiting area, they were screened for eligibility based on the inclusion and exclusion criteria using their charts, history and examination under slit lump microscope. The selected patients were briefed about the purpose of the study, the questionnaires and the clinical tests, and then requested for willingness to participate. Eye that fulfilled the inclusion criteria was selected, and when both eyes met the inclusion criteria, the right eye was taken.
Inclusion and exclusion criteria
Inclusion criteria for the glaucoma patients were: 1) age above 40, 2) diagnosed with any type of glaucoma and 3) on topical hypotensive medication (s) for three months and above. Exclusion criteria were: 1) use of any non-hypotensive topical drops within the previous 3 months, 2) active or recent ocular infection, 3) presence of immune-compromising disease, 4) lid abnormality such as ectropion, entropion, lagophthalmous, trichiasis and blepharitis, 5) prior lid or ocular surgery and 6) any ocular surface lesions. The controls were also age 40 and above and the exclusion criteria were the same as for the glaucoma patients.
Data collection and analysis
The participants were given OSDI questionnaire to be filled by themselves or by assistant (accompany person or ophthalmic nurse) if they couldn’t do it. The OSDI questionnaire (Allergan Inc., Irvine, CA), which is originally written in English was translated into a national language, Amharic, for the purpose of this study, and was verbally translated for those who speak other languages by accompany persons or others.
When answering the questionnaires if the participant didn’t do any of the activities in the questionnaire, for example doesn’t watch TV, he / she didn’t have to answer the specific question related to watching TV. The score was calculated out of the total questions answered by the participants not by all the questions asked. Each question of OSDI is graded from 0 to 4: 0 indicating none of the time, 1 some of the time 2 half of the time, 3 most of the time, and 4 all of the time.
The participants were also interviewed about their sociodemographic background. For the glaucoma patients, information on hypotensive drops including duration of use, type, number and frequency of drops application was obtained using an interviewer administered structured questionnaire. Patients’ charts were used to retrieve information on the type of medication(s) if patients were not sure during the interview, and the diagnosis and stage of glaucoma. Then patients of both groups under went through the three standard clinical tests. The tests were performed in the following order.
Schirmer I test (without anesthesia)
Each participant was asked to look up and the lower eyelid was drawn gently downward on the temporal side. Rounded bent end of a sterile Schirmer strip (Iscon Surgical Ltd., An ISO 9001, Marudhar, India) was hooked in the inferior fornix over the junction of the temporal and central one third of the lower eyelid margin with care taken to avoid touching the cornea; then the patient was asked to close his/her eyes. After 5 min, the strip of filter paper was removed and the amount of wet filter paper was measured and recorded in millimeters. If the tear front moved unevenly, it was measured from the notch to the middle of the diagonal line. Only whole numbers rounded up to the next whole number were recorded if the tear front is at or greater than the half-millimeter mark.
Tear break up time (TBUT)
One drop of topical anesthesia - tetracaine, was instilled and the patient was asked to close his/ her eyes. After 1 min the patient was instructed to look up to apply a fluorescein sodium ophthalmic strip into the inferior fornix, blink 5 times and then to hold the eyes open. The cornea was scanned with slit lamp microscope using a cobalt blue filter at 10 X magnification. A dry area was indicated by the appearance of a black spot or line. The time in seconds between the last blink and the appearance of black spot was recorded using stopwatch as a tear film break-up-time.
Corneal and conjunctival fluorescein staining
Under slit-lamp microscope with 10X magnification, extent of staining of the conjunctiva and cornea was assessed and graded against the standard Oxford chart [18].
Operational definitions: OSDI questionnaire was graded as normal 0–12, mild to moderate 13–32 and severe 33–100. The value of OSDI was calculated as sum of the severity for all questions answered divided by 4X total number of questions answered.
Schirmer test: normal > = 10 mm, mild to moderate 6-9 mm and severe 0-5 mm. The TBUT graded as normal > = 10 s, mild to moderate 5–9 s and severe < 5 s. Corneal fluorescein staining: normal if 0 (no staining), mild I or II, moderate III and Severe IV or V. Non normal grades were considered as abnormal results.
Data quality control and analysis: At the end of each day, all of the collected data was reviewed and checked for completeness and entered into SPSS (Statistical Package for the Social Science; SPSS Inc., Chicago, IL) version 24 software for data analysis. Descriptive statistics such as frequencies, percentages and mean were used to summarize the demographic data, drug duration, type of medications and OSDI score and results of the three clinical tests. Pearson’s correlation, t-test and one-way ANOVA were utilized for further analysis when indicated. P-value < 0.05 was considered to be statistically significant.
Ethical consideration
The study was carried out in accordance with the tenets of the Declaration of Helsinki, and got ethical approval from the research and publication ethics committee of the Department of Ophthalmology, College of Health Sciences, Addis Ababa University. Written informed consent was obtained from each participant involved in the study. Patients with tests indicating dry eye were informed; the results were documented on their chart to be seen and managed by the treating physicians.
