Abstract

Baground

Cataract is a major public health concern and the leading cause of blindness and low vision in Ethiopia. However, no studies have been conducted to assess the prevalence of cataract and associated factors among adult diabetic patients in the study area. Therefore, this study aimed to assess the prevalence of cataract and associated factors among adult diabetic patients in Northwest Ethiopia.

Methods

A multicenter cross-sectional study was conducted in Northwest Ethiopia from May 8 to June 8, 2023. A systematic random sampling technique was used to select study subjects. Data were collected through an in-person interview and physical examination. The data were imported to Kobo Toolbox version 2022 4.4 and exported to Stata version 14. A binary logistic regression was carried out to identify factors associated with cataract, and the strength of association was determined by adjusted odds ratio. A variable with a P-value of < 0.05 at a 95% confidence interval was considered a significant factor for cataract.

Results

The study included 1100 study subjects with a median age of 52 years. The prevalence of cataract was 42.2% (95%CI: 39.1-45.1%). Older age (AOR = 9.73, 95% CI: 5.53–17.13), ≥ 10 years duration of diabetic mellitus (AOR = 2.77, 95% CI: 1.96–3.90), poor glycemic control (AOR = 1.96, 95% CI: 1.40–2.74), and proliferative diabetic retinopathy (AOR = 4.14, 95% CI: 2.04–8.40), were factors significantly associated with cataract.

Conclusions

This study revealed a high prevalence of cataract among adult diabetic patients. Older age, longer duration of diabetes mellitus, poor glycemic control, diabetic retinopathy, and proliferative diabetic retinopathy had statistically significant associations with cataract. Therefore better controlling blood sugar levels will reduce the development of cataract. Regular screening of their eye will be also recommended to reduce visual impairment and blindness due cataract.

Baground

Cataract is characterized by a gradual loss of transparency in the crystalline lens of the eye and is classified into three types: nuclear, cortical, and posterior sub-capsular cataract [1]. It is a leading cause of blindness worldwide, accounting for 47.8% of cases in both the general and diabetic population [2]. In Ethiopia, around half million people are blind, and 1.2Ìýmillion suffer from severe visual impairment due to cataract [3, 4].

Globally, the prevalence of diabetic cataract has been increasing due to the rise in the number of diabetic patients [5, 6]. Preventing the development of cataract in diabetic patients remains a challenge, even though cataract surgery is the most effective treatment options of cataract in the worldwide [7]. Patients with diabetes mellitus are at a higher risk of post-surgery complications [8]. Furthermore, lack of awareness about cataract and the treatment options available, as well as the high cost of surgery are the most common barriers to uptake of cataract surgery [9]. Diabetes and diabetic-related cataract are significant health and economic burdens, especially in developing countries where access to diabetes treatment and cataract surgery is limited [7, 10]. An estimated investment of $5733Ìýmillion from 2010 to 2020 is required to eliminate blindness caused by cataract [3].

Studies has shown that factors such as age, sex, duration of diabetes, fasting blood sugar, high density lipoprotein, low density lipoprotein, creatinine, and hypertension have a significant association with cataract development [1, 3, 11,12,13].

Cataract is a major public health issue in Ethiopia [9], and was prioritized in the VISION 2020 program by the WHO [14]. However, there is a lack of evidence regarding the magnitude of cataract and associated factors among diabetic patients in Ethiopia, particularly in the study area.

Therefore, it is crucial to provide updated evidence on the prevalence of cataract in diabetic patients and associated risk factors to design appropriate intervention methods, particularly in modifying the risk factors of cataract. This study aimed to determine prevalence of cataract and associated factors among adult diabetic patients in Northwest Ethiopia.

Methods and materials

Study design, area and period

An institution based cross-sectional study was conducted across five Comprehensive Specialized Hospitals at diabetic clinics in northwest Ethiopia namely: University of Gondar, Felege Hiwot Hospital, Tibebe Gion Hospital, Debre Tabor Hospital and Debre Markos Hospital. This study took place at the diabetic care clinics of these hospitals from May 8, 2023, to June 8, 2023. Each hospital also offer separate areas for eye care services. The diabetic patients were cared for by internists, general practitioners, and nurses, while the ophthalmic department in each hospital provided comprehensive eye care services for the surrounding community, staffed by ophthalmologists, optometrists, and ophthalmic nurses.

Study population and eligibility criteria

All adult diabetic patients aged ≥ 18 years who visited five Comprehensive Specialized Hospitals in Northwest Ethiopia during the data collection period were included in the study. However, adult diabetic patients who had aphakia or psedophakia, dense central corneal opacity, and mental health problems or severe illness were excluded from the study.

Sample size determination and Sampling Procedure

The sample size was calculated using the single population proportion formula.

$n = \:\frac{{{{\left( {Z{\raise0.7ex\hbox{$\alpha $} \!\mathord{\left/{\vphantom {\alpha 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}} \right)}^2}x\:P\:\left( {1 - P} \right)}}{{\begin{array}{*{20}{c}}{{d^2}} \end{array}}}$, with the expected proportion of cataract (P) assumed to be 50%, as no previous studies had been conducted among diabetic patients in Ethiopia. The calculation was made at a 95% confidence level with a 3% margin of error (d). Based on this, the calculated sample size was 1,068. After accounting for a 5% non-response rate, the final sample size was determined to be 1,121.

Over a five-week period, a total of 2,660 new and follow-up diabetic patients received care at these hospitals. The sample size was proportionally allocated across five comprehensive specialized hospitals. The allocation was based on the population size of each hospital compared to the total population sized.

The formula used is:

$$\:\:Proportion{\text{ }}allocation{\text{ }} = n\frac{{Nh}}{N}$$

Where, n = is the total sample size, N = total population size, Nh = size of population in each hospital (Fig.Ìý1).

Fig. 1

This flow diagram shows the sampling procedure to assess the magnitude and associated factors of cataract among adult diabetic patients in Northwest Ethiopia, 2023

To select study participants, we employed a systematic random sampling technique with an interval of 2. This interval was determined using the formula, $\:K=\:\frac{N}{n}$, where, N represents the total population size and n denotes the desired sample size.

Operational definition

Cataract

The presence of nuclear or cortical or posterior capsular cataract or mixed in either of the eye [15].

Grading of cataract

Based on the LOCS III systemic method of grading the severity of lens opacities comparing with LOCS III standard photographs [16]. Thus, nuclear cataract was diagnosed if a LOCS III score of 4 or more, and cortical and posterior capsular cataract was diagnosed if a LOCS III score of 2 or more [16].

Proliferative Diabetic Retinopathy(PDR)

Is defined as the presence of neovascularization of the retina or optic disk, tractional retinal detachment, or a known history of PDR in at least one eye [17].

Poor glycemic control

A fasting blood glucose levels > 130Ìýmg/dl at the time of data collection [18].

Eye checkup practices

Participants who underwent an ophthalmic examination within the past one year are considered to have good eye check-up practices, while those who haven’t had an ophthalmic examination within the past one year are considered to have poor eye check-up practices [19].

Medication adherence

Participants who responded below the median value (6) of self-reported diabetic medication adherence questions have considered as poor adherence to diabetic medication, otherwise, having good medication adherence [18].

Data collection tool and procedure

The eligible participants were interviewed through an interviewer-administered questionnaire after taking informed written consent. The questionnaire collected demographic information, ocular, systemic and clinical data. Data was collected by ten well-trained data collectors, comprising five nurses and five optometrists. Nurses selected study participants at the diabetic clinic based on eligibility criteria and referred them to eye care clinics for comprehensive ocular examinations. At the eye care clinics, each participant’s initial distance visual acuity was assessed under optimal lighting conditions at a distance of six meters.

Both anterior and posterior eye examinations were conducted by the optometrist using a slit lamp and a + 90 Volk lens, following pupillary dilation with 1% tropicamide eye drops. After the eye examinations, participants underwent a face-to-face interview. Additionally, fasting blood sugar levels were measured using the HemoCue Glucose B-201+, which requires a sample of 5Ìýµl of capillary whole blood. Body mass index (BMI) was assessed using a standiometer. Furthermore, the duration of diabetes mellitus (DM) and any associated systemic comorbidities were documented by reviewing each patient’s medical chart. A patient diagnosed with cataract was linked to ophthalmologists for further evaluation and management.

The data collection process was supervised by the principal investigator (PI), who provided a full day of training to the data collectors on proper data collection techniques, instrument usage, and maintaining ethical standards. A pretest was conducted on 5% (57) of the sample size at Debark General Hospital prior to the actual data collection to ensure completeness, appropriateness, and mutual understanding. Necessary modifications were made based on the pretest results. To ensure data quality, the PI closely supervised the data collection process daily. A field review was conducted to verify the completeness of the questionnaires, and any needed corrections were made on-site. The data was subsequently coded for management, and data cleaning and cross-checking were performed before analysis.

Data processing and analysis

The data collected was exported to Stata version 14 for analysis. Descriptive statistics, such as frequency and percentage, were used to summarize the data. To check the multicollinearity of variables, the variance inflation factor and the tolerance test were used. To determine the factors associated with cataract, binary logistic regression was applied. Variables with a P value of less than 0.2 in the Bivariable analysis were included in the multivariable regression analysis. The goodness of the model fit was tested using the Hosmer–Lemeshow test. Variables with a P value of less than 0.05 in the multivariable logistic regression analysis were considered statistically significant at the 95% confidence interval.

Result

Socio demographic characteristics of the study participants

A total of 1,100 study participants took part in this research, resulting in a response rate of 98%. The median age of the participants was 52 years, with an interquartile range of ± 24 years. Among the total participants, 601 (54.6%) were male, and 776 (70.5%) lived in urban areas (TableÌý1).

Table 1 Socio-demographic characteristics of adult diabetic patients in Northwest Ethiopian in 2023 (n = 1100)

Clinical characteristics of the study participants

Out of the total study subjects, 840 (76.4%) had type II diabetes, 807 (73.4%) had poor glycemic control, and nearly 42% showed poor adherence to diabetic medication and eye check-up practices (TablesÌý2 and 3).

Table 2 Clinical characteristics of adult diabetic patients in Northwest Ethiopia, 2023 (n = 1100)

Table 3 Prevalence of cataract and others ocular comorbidity among adult Diabetic patients in Northwest, Ethiopia, 2023 (n = 1100)

Prevalence of cataract and others ocular comorbidity

In this study, the prevalence of cataract among diabetic patients was found to be 42.2% (95% CI: 39.1-45.1%). The most common type of cataract reported was posterior capsule cataract, accounting for 17.5%, followed by nuclear cataract at 13%. Out of 1,100 participants in the study, 259 (23.5%) experienced moderate visual impairment, and 41.8% had poor eye checkup practices (TableÌý3).

Factors associated with cataract among adult diabetic patients

In a Bivariable binary logistic regression analysis, several factors were found to be associated with cataract at a significance level of p < 0.25. These factors include older age, family history of diabetes, occupational status, hypertensions, duration of diabetes, proliferative diabetic retinopathy, glaucoma, eye checkup practices, glycemic control, and diabetes treatment. Subsequently, a multivariable binary logistic regression was conducted to evaluate the relative effects of these independent variables on the outcome of cataract development. The results from the multivariable analysis revealed that older age, proliferative diabetic retinopathy, glycemic control, and duration of diabetes had a significant association with cataract.

Participants with aged greater than 58 years were 9.73 times more likely to have cataract as compared to participants with age less than 27 years (AOR = 9.73, 95% CI: 5.53–17.13). The odd of developing cataract was 4.14 times higher among participants with proliferative diabetic retinopathy than participants without proliferative diabetic retinopathy (AOR = 4.14, 95% CI: 2.04–8.40).

Participants who had poor glycemic control had 1.96 times more likely to develop cataract than their counterparts (AOR = 1.96, 95%CI: 1.40–2.74). The odds of having cataract in participants with a diabetes duration of 10 years or more were 2.43 times higher than participants with a diabetes duration of less than 10 years (AOR = 2.77,95%CI: 1.96–3.90) (TableÌý4).

Table 4 Factors associated with cataract among adult diabetic patients in Northwest Ethiopia (n = 1100)

Discussion

The prevalence of cataract among adult diabetic patients in this study was 42.2% (95%CI: 39.1-45.1%) which was in line with a study done in Helsinki (42%) [20], and Western Africa (44.3%) [21]. However, the result of this study was lower than studies conducted in Palestine 47.8% [22], and Korea (50%) [12]. This discrepancy may be due to variations in socio-demographic characteristics and study populations. For example, studies conducted in the Island and Korea included only type II diabetes patients who are more likely to develop cataract.

In contrast, the prevalence of cataract in this study was higher compared to studies conducted in Russia (30.6%).¹³ This discrepancy may be attributed to socio-demographic differences. For instance, in Russia, cataract was more frequently observed among patients with type 1 diabetes mellitus (DM). Moreover, among patients with type 2 DM, a larger proportion had a shorter duration of the disease. In our study, however, we found that patients with type 2 DM who had a longer duration of the disease were at a higher risk of developing cataract. Another possible explanation for this difference is that living in a developed country can result in better diabetes management and greater access to cataract surgery, which may help reduce the severity of cataract.

In this study age greater than 58 years were ten times higher the occurrence of cataract as compared to participants with age less than 27 years. This finding was in line with a studies conducted on Helsinki [11, 20] and Australia [23]. The probable reason for this positive association might be related to type 2 DM. As several researchers found that older age as a significant factors for the occurrence of diabetic cataract among individuals with type 2 DM [20]. Our study found that a number of patients with type 2 diabetes had cataract. The possible reason for this result might be due to the metabolic changes and complications associated with diabetes over time, which can significantly contribute to the development of diabetic cataract in older individuals. Additionally, as individual’s aged, they become more susceptible to age-related diseases like glaucoma, which can facilitate the formation of cataract. Moreover, the lens itself becomes hardened due to age, which further contributes to the formation of cataract [24].

Having duration of DM greater than 10 years was twice times high the odds of developing cataract as compared to duration of DM less than 10 years. There was similar evidence in studies conducted in Korea [25], Russia [26], and United Kingdom [1]. It has been observed that there is a positive relationship between the duration of diabetes mellitus (DM) and metabolic changes in the body. As the duration of DM increases, the pancreatic beta cells become degenerate, which results in poor glycemic control in both the blood vessels and the aqueous. The enzymes present in the cornea convert glucose into sorbitol, which can cause the lens to distort and become opaque if the blood sugar level remains elevated for a prolonged period [1, 12, 20]. Therefore, to reduce the risk of developing cataract, effective management of blood sugar levels is important for individuals with diabetes.

Moreover, this study found that the odd of developing cataract was twice times higher the study subject having poor glycemic control as compared to good glycemic control. This study was aligns with a studies done in United Kingdom [1] and Australia [23]. This relationship between poor glycemic control and cataract may be due to elevated blood sugar damaging blood vessels throughout the body, including the eyes, leading to cataract. In diabetes, high blood sugar levels in aqueous humor can cause the lens to swell and lead to blurred vision. Furthermore, uncontrolled blood sugar can result in the convention of glucose to sorbitol in the lens, contributing to cloudy vision characterized of cataract [27].

The odd of cataract development was four times higher among proliferative diabetic study subjects as compared to non-proliferative diabetic retinopathy participants. This study was in line with in Taiwan [28]. This might be due to uncontrolled high blood sugar levels, vascular endothelial growth factors (VEGF) and anti-VEGF therapy. Cataract may progress more rapidly in people with diabetes, including those with PDR, due to the impact of high blood sugar on the eyes, leading to depositing sorbitol and absorbing water leads to changes lens swelling and clouding [29]. Researchers suggest that VEGF is not directly linked to the development cataract but rather plays a significant role for develop transient nuclear cataract due to hypoxia incision developing aberrant new blood vessels in the cilliary body and lenses become hardened leading to swelling and opacity [30].

The strength and limitation of the study

This study was better representation to the general population by including a diverse range of ages and geographical locations. Additionally, it was conducted across multi-centers. However, there was some limitation in this study. One limitation was the assessment of glycemic control was by fasting blood sugar levels due to hemoglobin A1C testing was not available in the study area. Furthermore, the evaluation of income did not utilize a wealth index, which may have resulted in estimation errors related to participants income levels. Additionally, this study was done in hospital based so missed undiagnosed diabetic population found in the community.

Conclusion

In this study, the prevalence of cataract among adult diabetic patients was higher. Besides, older age, long duration of DM, poor glycemic control and PDR had statistically significant association factors with cataract. Therefore better controlling blood sugar levels and preventing the development of PDR will reduce the development of cataract. Indeed, as the duration increases, regular screening of their eye will be recommended to reduce visual impairment and blindness due cataract.