*3.5.1 Inclusion criteria*

People living with T2DM who had follow-up and newly diagnosed T2DM patients in diabetic clinic during study period were included in the study.

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

#### *3.5.2 Exclusion criteria*

People living with T2DM who were seriously ill, pregnant women, and those who had HIV/AIDS, trachoma, acute eye infections (bacterial or viral), trauma to the eye, history of head injury, and history of stroke were excluded from the study.

#### **3.6 Sample size determination and sampling technique**

Sample size was determined using a single population proportion formula by considering the following assumptions:

Prevalence of visual impairment =28.9% [41], 95% confidence interval (zα/2). and 5% margin of error (d = 0.05). Then sample size (n):

$$\mathbf{n} = \frac{(\mathbf{Z}\alpha/2)^2 \mathbf{p}(\mathbf{1} - \mathbf{p})}{\mathbf{d}^2}. \tag{1}$$

$$\mathbf{n} = (\mathbf{1}.\mathbf{96})^2 \times (\mathbf{0}.\mathbf{289}) \times (\mathbf{0}.\mathbf{711})/(\mathbf{0}.\mathbf{05})^2 = \mathbf{316} \tag{2}$$

Adding non-response rate of 5% yielding a final sample size of 332. **Sample size allocation.**

Sample size for each hospitals was allocated by using sample size allocation formula.

$$\mathbf{n}\_{\rangle} = \frac{\mathbf{n}}{\mathbf{N}} \ \mathbf{N}\_{\rangle} \tag{3}$$

Where nj = sample size for each hospitals.

n = total sample size.

Nj = total people living with type 2 diabetes in each hospitals.

N = total people living with type 2 diabetes in all hospitals.

$$\mathbf{n}\_{\rm DRH} = \frac{332}{14000} \ast 10210 = 242\tag{4}$$

$$\mathbf{n}\_{\rm SRH} = \frac{\mathbf{3}\mathbf{3}\mathbf{2}}{\mathbf{1}4000} \ast \mathbf{1}440 = \mathbf{3}\mathbf{4} \tag{5}$$

$$\mathbf{n}\_{\rm{ERH}} = \frac{\mathbf{332}}{\mathbf{14000}} \ast \mathbf{1250} = \mathbf{30} \tag{6}$$

$$\mathbf{n}\_{\rm BRH} = \frac{332}{14000} \ast \mathbf{1} \mathbf{1} \mathbf{1} \mathbf{0} \mathbf{0} = \mathbf{26} \tag{7}$$

Where DRH = Dessie Referral Hospital, SRH=Selam General Hospital, ESH = Ethio General Hospital and BGH=Bati General Hospital (**Figure 2**).

In this study, Dessie Referral Hospital and all private hospitals were included and simple random sampling technique using lottery methods was applied to recruit study participants from those of type 2 DM cases who came to the clinic for follow-up and newly diagnosed T2DM patients during study period.

**Figure 2.**

*Diagrammatic representation of sampling procedure for T2DM at Dessie town Hospitals, Northeast Ethiopia, 2020.*
