**1. Introduction**

### **1.1 Statement of the problem**

Type-2 diabetes mellitus (T2DM) is a global metabolic disease, mainly seen in developing countries [1]. Patients with T2DM are highly prone to have cardiovascular disease, renal failure, neurological problems, and retinopathy [2, 3]. If the vision of an individual has been lost once due to diabetic retinopathy, usually it could not be restored, despite some forms that probably may be treated by complex vitreoretinal surgery [1–3].

Visually impaired people (VI) could not maintain employment, productivity, independence, their medical expense, or they may not be able to legally licensed to drive, they get difficulties in reading and fail to work inorder to obtain wages to their family and execute their social responsibilities as a whole [4, 5]. It also has been linked to falls, injury, and worsened status in spanning mental health, cognition, social function, and educational attainment [6]. People developing visual impairment(s) encounter a significant challenge. They experience major life changes, such as general health limitations or loss of nearby family member [1, 6]. They also are at higher risk of violence and abuse, which limit them from participating in and contributing to their families and societies on an equal basis with others [7].

Globally, prevalence of visual impairment increased sharply from 441.1 million [8] to 2.2 billion [4]. Of which at least 1 billion of VI could have been prevented. Among the causes of visual impairment, 1% was associated with diabetic retinopathy [9]. Diabetic retinopathy is damage to blood vessels in the retina, swelling in the central part of the retina, and abnormal blood vessels formation, which can lead to bleed or cause scarring of the retina that results in visual impairment [10].

Sub-Saharan Africa report on visual impairment figures out that the prevalence of visual impairment was 29.7% among diabetes mellitus [11]. Cataract, diabetic retinopathy, glaucoma, and maculopathy were the causes of visual impairment. Ethiopian systematic review and meta-analysis report revealed that the prevalence of diabetic retinopathy among diabetes mellitus patients was 19.48%, which is one cause of preventable visual impairment among middle-age and elderly populations [12].

In Ethiopia, no research is done on visual impairment among diabetes mellitus patients. But one previous study at the same setting found that visual disturbance was the second major chronic complication among newly diagnosed diabetes mellitus patients that was detected by clinical findings and questionnaire-based approaches. Moreover, specific associated factors for developing visual impairment had not been assessed. In parallel to rapid increment of DM, visual impairment is still public health challenge due to its chronic impacts.

Therefore, this study is designed to assess the magnitude and associated factors of long-term complication of DM, particularly vision impairments among both newly diagnosed and old type 2 diabetes mellitus patients having follow-up in Dessie town hospitals, northeastern Ethiopia, using ocular examinations and ocular tests. Since diabetes mellitus is a lifelong disease, the findings of this study will be used as input for all stakeholders such as governments, healthcare providers, people living with DM, civil society, food producers, and manufacturers and suppliers of medicines and technology. Collectively, they can make a significant contribution to halt the most serious and feared diabetes mellitus complication, (i.e., vision loss) and improve their lives as well.

*Visual Impairment and Its Associated Factors among People Living with Type-2 Diabetes… DOI: http://dx.doi.org/10.5772/intechopen.105793*

#### **1.2 Literature review**

#### *1.2.1 Definition and classification of visual impairment*

Visual impairment (VI) is a functional limitation of the eye(s) due to a disorder or disease that results in reduced visual acuity, visual field loss, photophobia, diplopia, visual distortion, visual perceptual difficulties, or any combination of the above [13]. Visual impairment is also often defined as presented visual acuity of worse than either 20/40 0r 20/60 to no light perception (NLP) in either or both eyes [14].

Visual impairment can be congenital or hereditary. Other main causes of VI incude refractive error, cataract, glaucoma, corneal opacity, age-related macular degeneration, and diabetic retinopathy [4, 13, 15–17]. It is also linked to ocular infection or disease, trauma, and systemic diseases such as hyperthyroidism [18], rheumatoid arthritis, HIV/AIDS, and hypertension [19].

Visual impairment in category Inernational Classification of Disease code H54 (H54) comprises from category 0 to 9 based on presenting distance on visual acuity test and classified as low vision (mild, moderate, and severe visual impairments) and blindness [4, 20] (annex VI).

#### *1.2.2 Pathogenesis of visual impairment due to diabetes mellitus*

Chronic hyperglycemia following long-standing DM is claimed to cause visual impairment via the production of inflammatory factors, which lead to inflammation of endothelium that in turn reduces the integrity of the blood retinal barrier in diabetic eyes [21, 22]. These are attributed to decreased in the activity of nitric oxide, increased in the activity of angiotensin II, endothelin-1, and vascular endothelial growth factor (VEGF) [3]. Besides, there is slow growth of new blood vessels in the iris and trabecular meshwork, which inhibits outflow of the aqueous humor fluid that causes irreversible damage to the optic nerve, eventually leading to blindness [21]. Disruption of the blood retinal barrier is responsible for developing retinovascular diseases including diabetic retinopathy (DR). Henceforth, DR causes vascular leakage and macular edema. If timely management is not tailored, there will be reduced vision and eventually blindness [2, 23].

Diabetes-associated glucose toxicity leads to biochemical changes due to polyol pathway and activation of protein kinase C (PKC) [24]. The polyol pathway is started by the conversion of glucose to sorbitol by the aldose reductase, and then sorbitol is changed into fructose by sorbitol dehydrogenase [25]. Accumulation of sorbitol leads to osmotic changes resulting in hydropic lens fibers that degenerate lens and form sugar cataracts [26]. Both polyol pathway and PKC result in increased oxidative stress, inflammation, and vascular incompetence. Oxidative stress and inflammation cause upregulation of growth factors that play a role in the breakdown of the blood retinal barrier and development of macular edema [26, 27]. Chronic hyperglycemia also increases diacylglycerol (DAG) that leads to the activation of protein PKC. Then PKC increases vascular permeability and upregulation of retinal vascular endothelial growth factors. Diacylglycerol and PKC pathways progressively affect inflammation, neovascularization, and retinal blood flow, which ends up with DR and progressively visual impairment [27, 28].

#### *1.2.3 Prevalence of visual impairment among type-2 diabetic mellitus patients*

Pandemicity of T2DM is rising rapidly probably due to increasing obesity, reduced physical exercise as countries become more industrialized and aging of the population [6]. Between 2010 and 2030, a 20% increase DM cases in developed countries and a 69% increase in developing countries have been predicted [29]. According to WHO report, currently global prevalence of visually impaired people is estimated to be 2.2 billion. Of these, at least 1 billion visual impairment is preventable or has yet to be addressed [4].

Many studies were conducted in different countries on the prevalence of visual impairment among T2DM. VI among T2DM in Sankara Nethralaya was 4% [30], Peru 26.3% [31], China 10% [16], Jordan 17.7% [32], Turkey 16.2% [33], and Yemenian 76.5% [34].

Studies in Africa reported different magnitude of VI. The prevalence of unilateral visual impairment among DM patients was 78.25% in South Africa [35], 17.1% in Zambia [36], and 18.4% in Kumasi, Ghana [37]. In Nigerian, 24.1% of T2DM cases had visual impairment [38]. Moreover observational studies in Tunisia [39] and Cameron [40] revealed 22.2% and 22.6% prevalence of VI among DM patients, respectively.

In Ethiopia, there is no visual impairment study done among diabetes mellitus patients, but in a study at St. Paul's Hospital, visual impairment was 17.6% among all ophthalmic cases. Of this, 58.7% had low vision and 41.3% had blindness [23] and that of Dessie referral Hospital, the prevalence of visual disturbance among diabetes mellitus patients was 28.9% [41].

#### *1.2.4 Associated factors of visual impairment among T2DM patients*

Factors associated for developing visual impairment vary among different studies. A study done in China, Jordan, and Yemen revealed that visual impairment was statistically associated to patients' age, duration of diabetes, body mass index (23.4 3.9), education level (≤ primary education), and insulin as treatment option [16, 32, 42].

Finding from Sankara Nethralaya showed that visual impairment was higher among diabetes patients age > 60 years and low socioeconomic status [30]. In Peruvian population, hypertension, hemoglobin A1c, and use of insulin or sulfonylurase as diabetic treatment were associated to visual impairment [31]. Diabetes and visual impairment study in sub-Saharan Africa (evidence from Cameroon) revealed that factors such as age (≥ 50), duration (≥10 years), and hypertension were associated with severe visual impairment [11]. A study from Zambia, Turkey, and Tunisia findings indicated that age, overweight, duration of diabetes, high random blood sugar, high systolic blood pressure, and insulin as diabetic treatment were significantly associated to visual impairment [33, 36, 39].

In Arbaminch Referral Hospital, baseline age (≥ 60), duration of diabetes (≥6), baseline systolic BP level (>140) were significantly associated to DR [43] while in Dessie, patients' age, drug regimen, and specific medications taken were associated with diabetic complication (**Figure 1**) [41].

*Visual Impairment and Its Associated Factors among People Living with Type-2 Diabetes… DOI: http://dx.doi.org/10.5772/intechopen.105793*

#### *1.2.5 Developed conceptual framework*

#### **Figure 1.**

*Conceptual framework adapted from different literatures illustrating possible factors affecting visual impairment among people living with T2DM at Dessie, Northeast Ethiopia, 2020 [11, 16, 31, 32, 36, 39, 43].*

#### **1.3 Justification of the study**

To the best of my knowledge, there was no study conducted in Ethiopia to determine the prevalence of VI and its associated factors among people living with T2DM. Vision loss is the most serious and feared outcome of DM-associated complication. After completion, this study will provide an in-depth and comprehensive information on the prevalence of VI and identify associated factors among people living with T2DM. The findings of this study will enable DM patients to implement preventive strategies and adhere to self-care management and medication to improve glycemic control and hence preventing VI by targeting associated factors. Preventive strategies include screening for DR, provision of follow-up care, and ensuring the follow-up techniques that meet the standard clinical guidelines. Making available an adequate referral mechanism allows all patients to screen and diagnose DM early so that possible ensuring eye complications are detected. Indeed, it will create an effort to develop effective health service programs and policies for better management of DM and costeffective strategies in Ethiopian context as well as a baseline for the coming researchers and stakeholders at higher level.
