Published on March 5, 2014
Learning Objectives The Human Eye The Important Parts of The Eye Power of Accommodation Defects of vision and their correction Myopia or Near-sightedness, Hypermetropia or Farsightedness Presbyopia
The Important Parts of The Eye Cornea Cornea: The front part of the eye is covered by transparent spherical membrane called cornea.
The Important Parts of The Eye Cornea Iris Iris: Just behind the cornea is a dark coloured muscular diaphragm which has a small circular opening in the middle.
The Important Parts of The Eye Cornea Pupil Iris Pupil: Pupil is the small circular opening of iris. The pupil appears black because no light is reflected from it.
The Important Parts of The Eye Cornea Pupil Iris Eye Lens Eye Lens: The eye lens is a convex lens made of a transparent jelly like proteinaceous material.
The Important Parts of The Eye Ciliary muscles Cornea Pupil Iris Eye Lens Ciliary muscles: The eye lens is held in position by ciliary muscles. The ciliary muscles help in changing the curvature and focal length of the eye lens.
The Important Parts of The Eye Ciliary muscles Cornea Pupil Iris Eye Lens Retina Retina: The inner back surface of the eye ball is called retina. It is a semi-transparent membrane which is light sensitive and is equivalent to the screen of a camera.
The Important Parts of The Eye Ciliary muscles Vitreous humour Cornea Pupil Iris Eye Lens Retina Vitreous humour: The space between the retina and eye lens is filled with another fluid called vitreous humour.
The Important Parts of The Eye Ciliary muscles Vitreous humour Cornea Blind spot Pupil Optic Nerve Iris Eye Lens Retina Blind Spot: It is a spot at which the optic nerve enters the eye and is insensitive to light and hence the name.
Power of Accommodation Near object Far object Power of Accommodation: The ability of the eye to focus objects lying at different distances is called the power of accommodation of the eye.
Power of Accommodation Ciliary muscles Thin Eye Lens Thick Eye Lens When the ciliary muscles are relaxed, the eye lens becomes thin. Thus, its focal length increases and we see the distant objects clearly. When the ciliary muscles are contract, then the curvature of the eye lens is increases and the eye lens becomes thick. Thus, its focal length decreases and we see the nearby objects.
Power of Accommodation Near Point of the Eye Far Point of The Eye 25 cm Near point or least distance of distinct vision is the point nearest to the eye at which an object is visible distinctly. Far point of the eye is the maximum distance up to which the normal eye can see things clearly. It is infinity for a normal eye.
Defects of Vision and Their Correction
Myopia or Near-sightedness Myopic Eye Correction Concave Lens Myopia :The light from a distant object arriving at the eye lens may get converged at a point in front of the retina in the vitreous body. Correction for myopia: To compensate this, we interpose a concave lens between the eye and the object, with the diverging effect desired to get the image focused on the retina.
Hypermetropia or Farsightedness Hypermetropic Eye Hypermetropia: If the eye-lens focuses the incoming light at a point behind the retina, this defect is called far sightedness or hypermetropia. Correction Convex Lens Correction for hypermetropic eye: A convergent lens(convex lens) is needed to compensate for the defect in vision.
Presbyopia Presbyopia is a common type of vision disorder that occurs as you age. It is often referred to as the aging eye condition. Presbyopia results in the inability to focus up close, a problem associated with refraction in the eye.
Cataract Milky and Cloudy Eye Cataract: The crystalline lens of people at old age becomes milky and cloudy. This condition is called cataract. This causes partial or complete loss of vision. It is possible to restore vision through a cataract surgery.
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