Sight Loss: What Causes It And What It Symptom

By Cristiano Antonino Last updated Mar 17, 2023

Decreased vision – the reduction in visual acuity, the ability to see an image clearly, crisply and sharply – is one of the most common visual symptoms experienced by people around the world

Only one eye or both eyes at the same time and with equal or different dioptre loss can suffer a loss of visual acuity

When – in the field of ophthalmology – the term ‘dioptres’ is used, it is referring to the unit of measurement of the power of a lens and, in a broad sense, also the extent of the visual defect that the lens itself corrects.

The human eye is in fact made up of a system (called the dioptric system) of converging lenses with different refractive indices, the purpose of which is to bring light rays to the retina, which focuses them by sending the light stimulus to the brain.

When you experience a decrease in vision, it means that one of the components of the dioptric system has started to malfunction as it should or has undergone changes.

This happens when the eye is affected by a disease, of which decreased vision is one of the first and most important symptoms to take into account.

About Sight Loss: What pathologies lead to declining eyesight?

Decreased vision is a symptom of pathologies or mechanisms that lead either to a different refraction, causing images to no longer reach the retina clearly, or to actual damage to certain eye structures.

Refractive defect

The name ‘refractive defect’ refers to all those visual defects – myopia, presbyopia, hypermetropia, astigmatism – that prevent the correct vision of images entering one’s field of vision.

These visual defects are not necessarily symptoms of an ongoing pathology, they may well be related to the characteristics of the various components of the dioptric system, and thus easily corrected through the use of optical instruments such as spectacles.

Cataracts

A cataract is a phenomenon that consists in the opacification – partial or total – of the crystalline lens, i.e. that part of the eye that is internal and transparent, located between the iris and the vitreous body, which enables the correct visualisation of what appears within the visual field.

The crystalline lens therefore has a fundamental function for the eye: like a camera lens, it has the task of focusing on the retina the light coming from an object, a figure or a landscape that passes the cornea.

Glaucoma

Glaucoma is a chronic disease that affects the optic nerve and can lead to partial or total loss of vision if left untreated.

This disease is related to a sudden rise in intraocular pressure, accompanied – albeit rarely – by a significant reduction in blood flow to the optic nerve, a component of the ocular system responsible for transmitting visual information from the eye to the brain.

When damage to the optic nerve occurs, the visual field is reduced starting with the most peripheral portions, gradually progressing and involving increasingly central portions of the visual field until complete loss of vision.

Keratitis

Keratitis is an inflammatory process that arises from damage to the cornea, the component of the transparent dioptric system that surrounds the eyeball in front, and the first lens in the dioptric pathway that is constantly covered with tear film.

Keratitis can be caused by physical agents, chemical agents, biological agents, traumatic or infectious. It will result in the loss of transparency of the cornea and thus in visual impairment.

Macular degeneration

Macular degeneration is a disease – usually linked to senile age – that manifests itself with a deterioration of the central portion of the retina, the macula, leading to a drastic worsening of visual acuity.

Two main types of macular degeneration can be distinguished: if macular degeneration is dry, this occurs when there is an accumulation of small yellowish glycaemic and protein deposits under the retina or results in a progressive atrophy of the macular region; if macular degeneration is wet, this occurs as a result of the abnormal growth of blood vessels from the choroid at the macula that exude within the retinal layers causing a dramatic decline in vision.

Retinal detachment

Retinal detachment occurs when the inner membrane of the eye – the retina, a thin layer of tissue lining the back of the eye – detaches from the supporting tissues.

Due to pathological phenomena, the retina can lose its adhesion to the tissues with which it usually remains in close contact and – no longer receiving nourishment, blood or support – risks losing its biological functions, leading to necrosis with even permanent damage to the eye.

Detachment of the vitreous body

The vitreous humour is the colourless substance with constant volume that – as a component of the dioptric system – acts as a support for the lens and retina.

With advancing age, the vitreous humour tends to lose its turgid consistency, shrinking and performing less and less of its supporting duty.

If the loss of volume occurs suddenly, almost violently, the elements it supports may suffer trauma, tear or suffer a more or less important injury.

Those just listed are just a few of the eye diseases that can present – among their symptoms – a more or less marked loss of vision, some of which may also be accompanied by eye pain, as in keratitis.

Diagnosing Sight Loss

From the moment the patient begins to experience a noticeable decrease in vision, it is necessary to visit an ophthalmologist for a specialist consultation in order to try – if possible – to correct the disorder or to remedy it if it is a direct consequence of an ongoing disease.

During the specialist examination, the ophthalmologist – after taking a thorough anamnesis to highlight any other pathologies – will immediately proceed with the evaluation of the specialist tests necessary to investigate the origin of the patient’s complaints of decreased vision.

The doctor may use the visual acuity test, and ophthalmoscopy, a specialist test that uses an instrument that – by projecting a beam of light through the pupil onto the retina – is able to provide information about the internal structures of the patient’s eye.

Other specialist tests that could be performed to make an accurate diagnosis could be intraocular pressure measurement and instrumental imaging tests of the internal eye structures.

Sight loss: the most appropriate therapy

In order to eliminate the disorders resulting from a patient’s failing eyesight, it is first necessary to remedy the event or condition that – as a symptom – presents the reduction in visual acuity.

If the loss of eyesight is attributable to a refractive defect, the only thing to be done is to prescribe the patient the appropriate lenses.

If, on the other hand, the loss of vision is a symptom of an ongoing pathology, all the most appropriate therapies – from drug therapy to surgery, if necessary – will have to be implemented in order to first of all treat the ongoing pathology and, consequently, eliminate or mitigate as much as possible the complaints resulting from the loss of vision.

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