**15. Sugar, and low vision**

Complications secondary to diabetes mellitus is the leading cause of blindness in developed countries [6, 40]. According to global estimates, 5% of the 37 million cases of blindness occur secondary to diabetic retinopathy [7]. However, not all cases of diabetic retinopathy results in blindness, some others cause low vision in affected patients.

Low vision as defined by World Health Organization (WHO), is the visual acuity of less than 6/18 in the best-corrected eye of a patient. It can also be defined as the visual field of less than 10 degrees in a patient. There exists a strong relationship between complications resulting from sustained hyperglycaemia as seen in diabetes and low vision. Some of the complications resulting from hyperglycaemia brings about visual changes in sufferers which may eventually lead to low vision. Some visual changes that have been reported by hyperglycaemic patients include changes in Visual acuity, colour vision, contrast sensitivity, reduction in glare tolerance, and visual field all, of which affects a person's quality of life.

## **15.1 Sugar, and visual acuity**

Because visual acuity status is affected by the status of the retina, cornea, lens, and the anterior chamber, visual acuity is one of the visual functions that is heavily affected by hyperglycaemia at different stages of the disease. Visual acuity may be affected by the presence of Diabetic cataract, which reduces the clarity of the lens. Visual acuity may also be affected by the presence of retinopathy which results in irreversible damage in the visual threshold of the patient. Other causes of reduction in visual acuity in a diabetic patients patient may include macular oedema, corneal haze, variations in the refractive status of the eyes due to variations in glycaemic levels, and procedures such as photocoagulation for diabetic macular oedema [49].

### **15.2 Sugar, and colour vision**

Acquired dyschromatopsia has been reported to be common in people living with type 2 diabetes. The Okubo colour study, conducted among type diabetic patients showed that there is an-increased-adjusted-odds (5.89) for the development of colour vision impairment by type 2 diabetic compared with their agematched normal glycaemic peers [2]. Some studies have reported an increase in the incidence of acquired, non-sex-linked blue-yellow colour vision deficit in diabetic patients. According to a study by Melisa et al., the blue-yellow colour deficit is more pronounced as diabetic retinopathy progresses, and is worse among patients who may have undergone laser treatment. The association between colour vision deficit and diabetes may be because diabetes irrespective of stage gradually affects the optic nerve as well as the retina, therefore resulting in abnormalities. Tan et al. also showed that more than 6 duration of type two diabetes may predispose patients to develop colour vision impairment [50].

#### **15.3 Sugar and contrast sensitivity**

Contrast sensitivity is a measure of the amount of contrast required to detect or recognize a visual target. It is a very important visual function in a person. Unfortunately, contrast sensitivity has been reported to decline with sustained hyperglycaemia. This has been attributed to retinal neurosensorial losses which may precede the occurrence of retinopathy in diabetic patients [51]. According to studies by Alberto et al. the occurrence of reduced contrast sensitivity is more in type 1 diabetic patients with retinopathy than with those without retinopathy [52]. Reduced contrast sensitivity can also be found in patients with type 2 diabetes. Safi *et al.* showed that contrast sensitivity decline was aggravated with the progression of retinopathy [53].

#### **15.4 Sugar and visual field**

Visual field defects have been reported as one of the notable low vision abnormalities that can occur in diabetic patients. Patrick and Lavin reported the occurrence of reversible homonymous hemianopia caused by non-ketotic hyperglycaemia in four patients with type 2 diabetes mellitus. [54]. Their report also noted that among the patients, homonymous hemianopia was the first manifestation of diabetes mellitus type 2 in two of the patients. Other factors such cerebrovascular accident, coexisting glaucoma, and pan-retinal photocoagulation has been reported as reasons for visual field defects in diabetic patients [43].

Visual processing disorders may also be seen in diabetic patients following cerebrovascular accident. Processing defects such as visual neglect and extinction has been reported to be partially reversible in these patients following treatment, and interventions.

#### **16. Role of vitreous sugar in the determination of post-mortal interval**

Sugar in the vitreous has found its usefulness in forensic medicine, where it can be used to determine the time of death and possible causes of death. The fact that there are biochemical changes in the blood glucose pathway after death makes the use of blood glucose in the biochemical analysis of the state of a cadaver difficult [55]. However, this difficulty can be overcome if the vitreous humor is used, given that, it is better preserved after death. Use of the concentration of sugar in the vitreous to determine the time of death has gradually gained some level of acceptance in forensic medicine and has been determined to have major advantages over other body fluids. Some of its advantages include its accessibility and the fact that after death it is often protected against putrefaction.

#### **17. Effect of low sugar intake on vision**

Although most of the emphasis of the impact of sugar in the eye is often placed on high sugar level, however low sugar level can also be detrimental to the eye.

**33**

**Author details**

Grace Ogbonna1

\*, Rosemary Ehigbo2

3 Umudike College of Agriculture, Umuahia, Nigeria

2 Specialist Hospital Umuahia, Umuahia, Abia State, Nigeria

\*Address all correspondence to: ogbonnagrace19@gmail.com

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 Mzuzu University, Mzuzu, Malawi

provided the original work is properly cited.

and Ogbonna Hannah3

*Impact of Sugar on Vision*

**18. Conclusions**

**Conflict of interest**

*DOI: http://dx.doi.org/10.5772/intechopen.96325*

can have very negative impact on vision.

The authors declare no conflict of interest.

ity, and central scotomas [56, 57].

The impact of low sugar level includes blurred vision, reduced contrast sensitiv-

Sugar forms a component part of the eye. Its presence at normal concentration is very important for the normal visual function, however when low or high, sugar The impact of low sugar level includes blurred vision, reduced contrast sensitivity, and central scotomas [56, 57].
