Conditions of the Eye
Myopia, Hyperopia and Cataracts affect vision.
Description - Myopia commonly known as short sightedness, usually results from an elongated eyeball. Close objects can be viewed with no difficulty due to accommodation by the lens. However, distant objects appear to be blurred due to the light rays being refracted infront of the retina.
Treatment - To correct this condition a concave lens is used either as spectacles or contact lenses. As you can see to the right the diagram depicts myopia, as the light is focused before the retina. Through the use of the concave lens, which diverges the light rays, the focal point hits the right spot on the retina (Fovea).
Description - Hyperopia is commonly known as long sightedness. The condition occurs from either a short eyeball or poor accommodation ability by the lens. Distant objects can be viewed easily where as close objects appear blurry. This is due to thethe focal point for close objects is behind the retina, .
Treatment - To correct this convergent or convex lenses are used in the form of spectacles or contact lenses.
Other technologies used to correct myopia and Hyperopia
Other technologies that are used to correct myopia and hyperopia include:
- radial keratotomy - fine surgical instruments shave small amounts of corneal tissue off the eye.
- photo-refractive keratectomy - a computer controlled laser is used to remove thin slices of corneal tissue.
Both of these technologies involve a surgical procedure which reshapes the cornea.
What is a cataract?
A normal human adult lens should be transparent to allow light to flow through to the retina. The transparency is due to structural and biochemical factors. The lens consists of many folded fibres called crystallins. The way these fibres are arranged makes the lens transparent. Lens fibres are capable of producing energy for the lens. Like all fibres and tissue, lens fibres need to be replaced making the lens become thicker and less elastic over time.
When the lens thickens or becomes cloudy the vision of the person decreases. This condition is known as cataracts. It is believed that the cause of cataracts is the insufficient nutrients in the lens fibres due to the density of these fibres. The crystallin proteins are then oxidised which then in turn causes the fibres to clump together producing a cloudy thickened lens.
What technology exists to prevent or treat blindness from cataracts?
There exist some simple measures to prevent the development of cataracts:
- Sunglasses to prevent U.V. light damaging the lens and
- An adequate diet high in anti–oxidants which destroy free radicals.
Surgical procedures - in some circumstances the cataracts are well developed causing blindness to the patient. In this case a surgical procedure known as phacoemulsification must take place.
- A small chisel–like instrument is inserted into the lens.
- The content of the lens is sucked out
- The lens cavity is filled with a fluid to prevent damage to the cavity and loss of vitreous humor which will cause the retina to detach from the eyeball.
- A contact lens is then placed in the lens cavity. This is performed by folding the contact lens and inserting it into the eye via a straw.
Once inside the cavity the lens unfolds and remains there for the rest of the patient’s life restoring their vision. The contact lens is known as an interocular lens (IOL) which resists U.V. light and is accepted by the body due to its plastic nature.
Implications for society
Phacoemulsification is a surgical technique which has greatly impacted society.
Key benefits of the technology:
- The procedure itself takes very little time,
- is performed under a local anaesthetic
- can be performed almost anywhere around the world.
Phacoemulsification has revolutionised how doctors treat cataracts as it prevents unnecessary blindness especially in third–world countries. Phacoemulsification is a safe, precise and successful technique available to thousands of people in developed and developing countries.
The late Fred Hollows, who was responsible for restoring sight to many people in third world countries, set up a factory which made interocular lenses for only 10 cents. This made the process even affordable for the poor. It is through phacoemulsification, a huge advance in technology, cataracts are easily and successfully treated.