Prevalence and associated factors of low vision and blindness among patients attending St. Paul’s Hospital Millennium Medical College, Addis Ababa, Ethiopia

An institution based- cross sectional design study was conducted from January to April 2017 at SPHMMC, Tertiary Eye Care and Training Center. The center is well known college with ophthalmic medical service and ophthalmology residency training in the capital city of the country, Addis Ababa. It has been serving more than 16,000 patients with more outpatients and in some cases inpatient services per year. There are sub specialty clinics like retina, glaucoma, pediatric, oculoplasty and optometry clinics within the center. All patients come to the center have been undergoing complete eye examination including diagnostics tests. Medical, optical, laser and surgical service is the routine treatment modalities for the patients at the center. There are also one extra public and two private tertiary eye care centers in the study area. The other 10 public and 15 private secondary and primary eye centers were more focused on treating adnexal eye diseases and major surgeries like cataract and Trabeculectomy, minor surgeries and refractive services.

There was no evidence within the same study setting in which we need to consider in estimating the minimum sample size. Therefore it was considered that 50% proportion of population with visual impairment, 3% error of margin, 95% confidence interval and 10% non- respond rates were used to calculate the sample. Hence a total of 904 sample size was retrieved using single population proportion formula. The study was conducted among persons of all age groups. Study subjects were recruited from registration logbook of the clinic taking every 10th patient, the first being the 7^thmedical record number registered with omission of incomplete records.

Socio-demographic characteristics such as age, sex and address and clinical characteristics like Snellen visual acuity, IOP measured by non-contact air-puff tonometer, slit lamp biomicroscope and Fundus examination results including lists of all ophthalmic diagnosis written on the medical record were retrieved as their respective order. Visual acuity and IOP were measured by ophthalmic nurses while eye examinations were done by senior ophthalmologists. Visual acuity was measured by using retro-illuminated Snellen charts at 6 m and only distance one was considered; and for children less 4 years of age HOTV cards was used. The presenting visual acuity was taken in all cases and for children less than 4 years age appropriate visual acuity equivalent recorded for analysis. Data were recorded on a customized form, and the cause of visual impairment determined from patient cards with primary diagnosis was taken for all participants with a presenting VA of less than 6/18 for each eye separately.

The WHO categories of visual impairment were used to define vision status for study participants. Blindness was defined as a presenting VA of less than 3/60 in the better eye. Low vision was defined as presenting VA of at least 3/60 but less than 6/18 in the better eye. Monocular visual impairment, which is not a WHO definition, was derived to represent participants who had normal or near-normal vision in the better eye (VA of at least 6/18) and visual impairment in the other eye (VA from 6/18 up to 3/60 for low vision and less than 3/60 for blindness) [13].

After the survey, the investigators reviewed the forms and determined the principal disorder responsible for blindness or low vision for the participant, taking into account the main cause for each individual eye. In the instance when different causes had been identified for each eye separately in a given individual, the principal disorder was chosen to be the one that was most readily curable or, if not curable, most easily preventable. The study was conducted in accordance with declaration of Helsinki and approved by institutional review board of SPHMMC according to Ethiopian national research ethics review guideline. The privacy and confidentially of all subject was secured. The department’s usual data quality control is just keeping patients’ clinical profile on log book at each clinic. The data for this study was retrieved from those log-books. Institutional review board of SPHMMC stated that obtaining informed consent for participation is not applicable the study based on the secondary data.

The collected data was entered twice, carefully cleaned and analyzed using SPSS version 23 (www.ibm.com/products/spss-statistics). Descriptive statistics such as frequency distribution and central tendency measures were used to summarize the descriptive part of the study. Pearson X² was used to determine the factors associated with low vision and blindness [14]. P-value less than 0.05 were considered as statistically significant.