Science Chapter 10: The Human Eye

The Human Eye

• The human eye functions like a camera, using a lens system to form images on the retina.
• Light enters the eye through the cornea, which is a transparent bulge at the front of the eyeball.
• The diameter of the eyeball is approximately 2.3 cm; most refraction occurs at the cornea's outer surface.
• The eye lens fine-tunes the focal length for focusing on objects at various distances.
• The iris, located behind the cornea, controls the size of the pupil, regulating the amount of light entering the eye.
• The eye lens creates an inverted real image on the retina, which contains light-sensitive cells.
• These cells convert light into electrical signals sent to the brain via optic nerves; the brain interprets these signals for perception of objects.

Power of Accommodation

• The eye lens is made of a fibrous jelly-like material and its curvature can be adjusted by ciliary muscles.
• When relaxed, the lens becomes thinner, increasing its focal length, allowing clear vision of distant objects.
• When focusing on nearby objects, the ciliary muscles contract, thickening the lens and decreasing focal length.
• Accommodation refers to the lens's ability to adjust its focal length; it has a minimum limit for focus.
• The least distance of distinct vision, or near point, is about 25 cm for a young adult with normal vision.
• The far point is infinity for a normal eye, meaning clear vision is possible from 25 cm to infinity.
• Cataracts occur when the lens becomes cloudy, causing vision loss, which can be treated with surgery.

Defects of Vision

• Refractive defects of the eye can lead to blurred vision and difficulty in focusing on objects.
• Common refractive defects include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism.
• Glasses or contact lenses are used to correct these vision defects, allowing light to focus correctly on the retina.

The Human Eye

• The human eye functions like a camera, using a lens system to form images on the retina.
• Light enters the eye through the cornea, which is a transparent bulge at the front of the eyeball.
• The diameter of the eyeball is approximately 2.3 cm; most refraction occurs at the cornea's outer surface.
• The eye lens fine-tunes the focal length for focusing on objects at various distances.
• The iris, located behind the cornea, controls the size of the pupil, regulating the amount of light entering the eye.
• The eye lens creates an inverted real image on the retina, which contains light-sensitive cells.
• These cells convert light into electrical signals sent to the brain via optic nerves; the brain interprets these signals for perception of objects.

Power of Accommodation

• The eye lens is made of a fibrous jelly-like material and its curvature can be adjusted by ciliary muscles.
• When relaxed, the lens becomes thinner, increasing its focal length, allowing clear vision of distant objects.
• When focusing on nearby objects, the ciliary muscles contract, thickening the lens and decreasing focal length.
• Accommodation refers to the lens's ability to adjust its focal length; it has a minimum limit for focus.
• The least distance of distinct vision, or near point, is about 25 cm for a young adult with normal vision.
• The far point is infinity for a normal eye, meaning clear vision is possible from 25 cm to infinity.
• Cataracts occur when the lens becomes cloudy, causing vision loss, which can be treated with surgery.

Defects of Vision

• Refractive defects of the eye can lead to blurred vision and difficulty in focusing on objects.
• Common refractive defects include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism.
• Glasses or contact lenses are used to correct these vision defects, allowing light to focus correctly on the retina.