The Human Eye

IntroductionThe human eye is the only organ which senses light and it helps us have a live relay of what’s happening around us. We would not be able to see anything if there is no eyes. The eyes also has some defects and conditions so that it does not get affected.

PARTS OF THE HUMAN EYE

CORNEA

The cornea is the part which allows light to enter our eyes. The diameterof our eye is approximately 2.3 cm in size. It is cylindrical and dome shaped in shape.

IRISIris is the organ which regulates the amount of light entering our eyes. It is coloured in black, brown, red, green etc.For eg: when we enter a dark room it takes some time for us to see objects. This is because there is no adequate amount of light entering our eyes. And the illumination process is slow and it takes some time for us to see objects in dim room.

PUPIL

The pupil is the hole in the center of the iris that light passes through. When we focus and see an object the pupil expands. Such as revertibly when we do not focus an object the pupil gets shrink. This also makes the optic nerve to change its size.

Ciliary MuscleThis part helps to adjust the focal length of our eyes according to our eyes. While ageing this part loses the flexibility of it and it arises as Presbyopia.

EYELENS

It is made of a transparent and flexible material like a jelly made of proteins. It forms of a real image of the objects on the retina of the eye

Power Of Accommodation

It is the ability of our eye lens to adjust the focal length according to the distance of the object from our eyes. In ageing the power of accomodation of our eyes decreases. And the ciliary muscles loses the flexibility.

The range of our eyes:Our eyes can see objects ranging from (25

cm to infinity.)

RETINA

The retina receives the light on it to get a clear vision. It converts light rays into electrical signals and sends them to the brain through the optic nerve. The retina is where most problems leading to vision loss occur.

OPTIC NERVE

Each optic nerve has about 1.2 million nerve fibers. This is the cable connecting the eye to the brain. And it receives signals and sends information to the brain.

VITREOUS HUMOUR

The vitreous humour or vitreous humor is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. The vitreous is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye. It is produced by certain retinal cells. It contains very few, no blood vessels, and 98-99% of its volume is water with salts, sugars, vitrosin, and a wide array of proteins in micro amounts.

AQUEOUS HUMOUR

The aqueous humour is a clear, gelatinous fluid similar to plasma, but containing low-protein concentrations. It is secreted from the ciliary epithelium, a structure supporting the lens.It is located in, the space between the lens and the cornea.

Defects To The Eye

MYOPIAMyopia is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it. This causes the image that one sees when looking at a distant object to be out of focus but in focus when looking at a close object.Myopia presents with blurry distance vision, but generally gives good near vision. In high myopia, even near vision is affected, and patients cannot read without their glasses for distance.

CAUSES

Most nearsightedness is caused by a natural change in the shape of the eyeball.Other than the natural change in the shape of the eyeball, there are a few rare causes of nearsightedness. These are:• Elongation of eye balls.• Excessive curvature of eye balls.

• Pathological myopia, in which the back of the eyeball continues to grow longer after reaching normal adult size.

• Secondary myopia, which may develop as a result of many conditions, including premature birth and a number of eye diseases.

• In some cases, nearsightedness may be caused by eye problems such as cataracts,etc.

TREATMENT

There is no universally accepted method of preventing myopia. Commonly attempted preventive methods include wearing reading glasses, eye drops and participating in more outdoor activities. Concave lens are used to treat this.

HYPERMETROPIA

Hypermetropia, is a defect of vision caused by an imperfection in the eye causing difficulty focusing on near objects. Farsightedness occurs when light entering the eye through the lens is focused behind the retina instead of directly on it.

CAUSES

Hypermetropia can be caused by infections, injuries, migraines, aging or genetics. This is caused by an eye that is too short, whose cornea is not curved enough, or whose lens sits farther back in the eye than normal. Farsightedness is also Inherited.

TREATMENT

Minor amounts of hyperopia are sometimes left uncorrected. However, larger amounts may be corrected with convex lenses in eyeglasses or contact lenses. Convex lenses have a positive dioptric value, which causes the light to focus closer than its normal range.

PRESBYOPIA

Presbyopia is a condition where the eye exhibits a progressively diminished ability to focus on near objects with age. Presbyopia’s exact mechanisms are not known with certainty; the research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens’s curvature from continual growth and loss of power of the ciliary muscles (the muscles that bend and straighten the lens) have also been considered as its cause.

SYMPTOMS OF PRESBYOPIA

The first symptoms most people notice are difficulty reading fine print, particularly in low light conditions, eyestrain when reading for long periods, blur at near or momentarily blurred vision when transitioning between viewing distances .These symptoms are usually first noticed between the ages of 40 and 50.

TREATMENT

Corrective lenses such as bi-focal lens can be used to correct this defect. The upper part of the glass is concave and the down part is convex.