How Light Affects your Eyes

 

Of all the organs in the body, the eyes might be one of the most complex; especially considering their incredible importance despite their size.

Eyes are particularly vulnerable to a number of agents. Occasionally, light is one of them.

In this article, we’re going to examine how the eye functions and how it reacts to different levels of light, as well as the dangers of over-exposure to light and potential treatments.

How your eyes work

When you look at an object, the first part of the eye to be called into action is the cornea.

The cornea is the transparent front part of the eye which provides a protective window between the rest of the eye and the outside world.

When light rays meet the cornea, its refractive power manipulates and bends them in such a way that they pass through the pupil (the hole located in the centre of the iris), allowing them to enter the eye.

The iris is the circular structure in the eye surrounding the pupil, and it is responsible for reducing and enlarging the size of the pupil.

In doing so, it helps to adjust how much light reaches the retina at the back of the eye.

When the light rays pass through the pupil, they also pass through the eye’s lens. This is a transparent, flexible structure that helps to refract light.

The lens is able to change the focal distance of the eye, allowing it to focus on objects at various distances. It does this by changing shape - shortening or lengthening its width.

The rays then pass through a clear, dense gel-like substance, known as the vitreous. The main function of the vitreous is to transmit light to the retina and to exert enough pressure to enable the retina layers pressed together tightly. This pressure helps maintain the eye's spherical shape.

Once through the vitreous, light rays arrive at the retina.

The retina is a light sensitive layer of tissue, responsible for converting light rays into images. It operates similarly to the film in a camera, in that it processes the light rays into electrical impulses.

It then sends these impulses to the optic nerve via over a million nerve fibres.

 

How eyes react to different light intensities

The iris acts as the main guardian of the eye from extreme light intensities - its job is to adjust the size of the pupil.

The process is known as the pupillary light reflex, where the iris controls the diameter of the pupil in response to the light intensity that falls upon the eye.

The eye requires a certain level of light intensity for the retina to process into images. It is fundamental for the iris to moderate the amount of light that enters the eye because an excessive amount would cause the retina to struggle to process images, or even harm it.

A greater intensity of light will cause the iris to constrict the pupil, thus allowing less light in. A low level of light intensity will result in the pupil dilating and allowing more light in.

As another light-refracting structure, the lens also contributes to protecting the retina from extreme light intensities.

The change in shape of the lens is controlled by ciliary muscles which surround it, attached via the zonules. These muscles, similarly to the iris, will contract and relax in response to focus on objects at different distances from the eye.

 

Can excessive light damage your eyes?

The short answer to this is yes. When the retina’s light-sensing cells become over stimulated, they release signaling chemicals in mass amounts.

If the retina were to release too many of these chemicals at a time – say for instance, if you were to look directly into the sun, this can damage the back of the eye[1].

Extended exposure to the sun’s ultraviolet (UV) rays can also damage the eye. In particular, it is known to damage the macula, which is the part of the retina that is responsible for the central vision.

Central vision refers to what you see directly in front of you in sharp focus and is required for tasks such as reading and driving.

While the pupil will naturally contract when exposed to bright light, the amount of light still entering the eye will be concentrated on the macula tissue, damaging it in the process.

Extended exposure to ultraviolet (UV) rays can cause damage to the cornea. Corneal flash burns can be considered sunburn of the eye surface and can come from various sources, such as sunlight, sun lamps in tanning salons and the reflection of sunlight off water.

As well as being painful, they can cause blurry vision and loss of vision. UV ray exposure has even been linked to various forms of eye damage, including a particular type of cataracts and macular degeneration.

A cataract is a clouding of the lens within the eye. The lens mostly consists of water and protein which is arranged in a precise way in order to keep the lens clear.

However, for reasons that are unclear, the protein in the eyes of some people will gather together and cloud the surface of the lens.

Initially it will have relatively little impact on a person’s vision, although it may cause things to appear slightly blurry.

Additionally, forms of light, such as those from the sun or car headlights, may appear more glaring. If left untreated, the condition is likely to worsen and can in more extreme cases lead to blindness.

Macular degeneration is, unsurprisingly, degeneration of the macula. If this process occurs, it impacts central vision and can cause blind spots in this area.

Age-related macular degeneration (AMD) occurs when deposits known as drusen (build-up of mainly protein and fat containing deposits) build up in the macula.

 

How can I treat and prevent eye problems resulting from light exposure?

First of all, it must be emphasised that because the eyes are very sensitive to damage and disease, you must seek medical care from a healthcare professional if you are experiencing any form of discomfort following light exposure.

Should you be suffering from altered or blurry vision you should go to a hospital’s accident and emergency department for an evaluation.

For any light-sensitivity issues as a result of over-exposure, wearing sunglasses on a regular basis to reduce sensitivity is suggested. Naturally, you are also advised to avoid further exposure to bright lights.

The use of contact lenses is not advised for anybody experiencing any form of eye pain, whether it’s due to over-exposure to light or some other cause, as they can restrict the amount of oxygen reaching the cornea and can be a breeding ground for bacteria if not sterilised sufficiently

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