Low vision is a particular condition caused by a central, peripheral or mixed visual impairment that results in a person’s inability to carry out normal activities of daily living, limiting their social, private and work sphere

Low vision is defined as irreversible bilateral visual impairment that cannot be resolved with surgical therapy and/or optical correction

Who is visually impaired

The visually impaired are those who have

• visual acuity of no more than 3/10 in both eyes or in the better eye despite the best optical correction
• binocular perimetric residual of less than 60 per cent.

Data from 2016 speak of approximately 246 million visually impaired people worldwide and more than 1.2 million in Italy alone (source: IAPB).

The causes of low vision

When dealing with low vision, from a medical point of view, it is necessary to go straight to identifying the causes, i.e. what led the person to gradually lose part of their sight.

Low vision ranks third, after arthritis and cardiovascular diseases, among the causes of loss of autonomy and the need for assistance in daily activities.

The causes vary from country to country and depend on economic conditions and the efficiency of the health service.

The main causes in the western world are divided into:

• age-related macular degeneration (AMD);
• diabetic retinopathy (DR);
• retinitis pigmentosa (RP);
• glaucoma.

In underdeveloped countries, in addition to those mentioned above, the main cause of low vision is cataracts, which have been successfully treated for years in the western world, followed by

• uncorrected refractive defects;
• trachoma: infection sustained by the micro-organism Chlamydia Trachomatis;
• onchocerciasis: also called ‘river blindness’, caused by a small insect;
• xerophthalmia: avitaminosis A).

Individuals over 65 years of age, who make up approximately 80% of these patients, are most affected by low vision; in Italy, the incidence of low vision is close to 2-3%.

Symptoms

According to the GISI (Gruppo Italiano Studio Ipovisione) classification, low vision can be linked to the loss of 2 types of vision

• Central vision: the reduction in vision occurs in the central part of vision and is based on the assessment of visual acuity with the best optical correction (BCVA). Patients report that they can no longer distinguish people’s faces, read or perform the simplest everyday actions. The causes are related to retinal diseases, such as macular degeneration, diabetic retinopathy;
• peripheral vision: the reduction in vision occurs in the peripheral part of vision, which is assessed by the visual field examination (Esterman or Zingirian-Gandolfo percentage). Patients report not being able to see objects or people sideways, difficulty in walking independently. Causes are related to optic nerve diseases, such as glaucoma, Leber syndrome.

Several figures are involved in the diagnosis and rehabilitation of the visually impaired patient, including:

• ophthalmologist;
• orthoptist;
• psychologist;
• educator;
• orientation and mobility instructor.

Specifically, the ophthalmologist deals with the cause of the condition; the orthoptist with the patient’s rehabilitation.

Diagnosis of low vision 

In order to make a correct diagnosis of low vision, depending on the type of visual impairment, it is necessary to undergo specific instrumental examinations:

• OCT (Computerized Optical Tomography), useful in the diagnosis of diseases of the central retina and optic nerve;
• fluorangiography (FAG), useful in the assessment and diagnosis of inflammatory and vascular retinal diseases;
• microperimetry, defines the anatomical damage and identifies the best point of retinal fixation;
• visual field, calculates the peripheral visual residual;
• VEP (Visual Evoked Potentials), useful in assessing the functional integrity of the visual pathways.

How low vision is treated 

With regard to treatment, from a medical point of view, it is necessary to identify and treat the cause, i.e. the pathology.

In the case of myopic or age-related maculopathy, intravitreal injections (IVT) are often used.

In the case of retinal detachment, argon laser treatment or vitrectomy is used.

In the presence of glaucoma, it is possible to intervene either with medication or surgery to control and lower the pressure in the eye.

In addition, again on indication of the ophthalmologist, great help is provided by orthoptists who play a very important role in visual rehabilitation, performing diagnostic-instrumental examinations and teaching the patient to exploit his visual residual through the use of optical aids and visual training.

Indeed, while in the blind patient recovery of visual function is no longer possible, in the visually impaired it is possible to exploit areas of the retina that are still healthy in order to improve the patient’s quality of life as far as possible.

In this regard, the ophthalmologist can prescribe visual aids:

• optical aids for near vision: video magnifier, hypercorrective optical aid;
• optical aids for distance: Galilean telescope, selective filters.

How to prevent low vision 

From a prevention point of view, it is certainly possible to do something.

It is already necessary to intervene on the young population through the intake of specific antioxidant supplements based on vitamin A, vitamin E, selenium, zinc, copper, capable of safeguarding those trace elements and vitamins that become deficient with advancing age, such as Zeaxanthin or Lutein.

Very important, finally, is also the:

• correction of risk factors, e.g:
• following a healthy diet;
• practising physical activity;
• not smoking;
• phototoxic protection from ultraviolet rays, i.e. protection against skin reactions caused by sun exposure, which must always be taken care of by wearing sunglasses.

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Source:

GSD