Types of Blindness

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Being blind is of course a terrible disability and one that can make life more difficult in a number of ways. For anyone experiencing blindness the situation will be equally difficult and it will be necessary to find a vast range of coping methods to help you to get around and to survive on a day to day basis.

That said however, not all kinds of blindness are the same – and the severity of the condition, as well as the cause and the prognosis, can all vary greatly from individual to individual. The eye and the neural cortex combine to enable us to see and this forms a highly complex system with many different stages – of course this then means that there is also an awful lot that can go wrong at any of these stages. Here we will look at some of the different kinds of blindness that exist and how they differ.

Blindness Caused by Disease

Blindness can be caused by a number of different diseases and conditions. One of the most common (accounting for around 47.9% of blindness caused by disease) is cataracts which is caused by a clouding in the crystalline lens of the eye. This is common in older age (senile cataracts) and can range in severity from slight sight difficulties to complete vision loss. It is slow to progress and can sometimes be reversed through surgery.

Another common condition to cause blindness is glaucoma. Glaucoma is responsible for around 12.3% of disease-related blindness. Here the optic nerve is damaged in a particular pattern which can cause partial damage or complete blindness when untreated. It is usually associated with increased fluid pressure in the eyes.

Macular degeneration usually affects older adults and causes loss of vision in the center of the visual field (AKA the macula). Other causes include corneal opacity and diabetic retinopathy.

Injuries and Abnormalities

Eye injuries can also of course lead to blindness. This is the leading cause of monocular (one eye) blindness in the under 30s. Meanwhile ‘abnormalities’ describe problems such as optic nerve hypoplasia which falls into this category as it affects the optic nerve as opposed to the eye itself. This can be caused by hormone deficiencies, developmental delays and brain malformations and essentially prevents the brain from sending and receiving the correct signals in order to perceive the world around it. Of course chemical poisoning may also cause blindness, either when ingested or when it comes into contact with the eyes. Methanol for instance is mildly toxic, but in the absence of ethanol can be broken down by the body to form formaldehyde and formic acid which may cause to blindness (as well as numerous other conditions).

Of course brain injuries can also lead to blindness or a range of vision problems if they affect the V1 area (visual area 1). Blindsight meanwhile is an interesting condition in which the brain area, nerves and eyes themselves are all undamaged, but where the individual reports being unable to see. However when the patient is presented with stimuli and forced to ‘guess’ where it is in their visual field, they perform better than chance – suggesting that the information is being relayed, but that they are not consciously aware of it.

This will then prevent the brain from interpreting the visual signals it receives and thus prevent normal vision. Damage might also be caused by stroke if it leads to the death of brain cells in the region, or brain tumor.

Genetic

Genetic defects can also lead to vision loss. For instance albinism can often lead to vision problems due to the lack of pigment in the eye (which causes more light to enter). Meanwhile Leber’s congenital amaurosis, a rare inherited eye disease, can lead to complete blindness from birth or childhood, as can Bardet Biedl syndrome – a genetic condition which also leads to obesity, hypogonadism, mental difficulties and renal failure.

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Theodoros Manfredi

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