Optometry Terms: C
Cataract: Cloudiness which forms on the lens of the eye or on the envelope which can cause from mild to severe sight impairment by inhibiting enough light from reaching the eye.
Central retinal artery: Also called just Retinal Artery, it is branched from the ophthalmic artery and running along the optic nerve within the dural sheath of the nerve until it reaches the eyeball.
Central Retinal Vein: This is a short vein which drains the blood as it leaves the capillaries of the retina, entering the larger veins found outside the eye.
Central Vision: What you see when you look straight ahead is known as ‘central vision.’ Central vision is what we use when we read, drive, or look at something straight on; all the activities that require sharp, focused sight. Central vision is different than “peripheral vision.”
Chalazion: Sometimes referred to as a ‘stye’ a chalazion is a small lump referring to a swelling in the eyelid. It is caused by an inflammation in one of the small oil producing glands found in the upper and lower eyelids. Its symptoms include blurred vision, swelling and tenderness, and a lump.
Choroid : One of the three main layers found in the eye of vertebrate. This central layer, between the retina and the sclera contains the connective tissue as well as the vascular system, keeping the eye nourished and oxygenated.
Color Blindness: Color Blindness refers to the diminished ability to distinguish between certain colors. Usually genetic in origin, linked to the Y-chromosome, but it can also be caused by injury or exposure to some chemicals.
Cone: The cells of the eye which receive the information about light rays and interpret them as colors, are known as the cones. The cones need large amounts of light to function, as opposed to the rods, which can function in low levels of light, explaining why human eyes do not distinguish colors well in dark environments.
Conjunctiva: The conjunctiva is the outer, mucous layer of the eye covering the inner surface of the eyelid and the sclera, (white) of the eye.
Conjunctivitis: Inflammation of the conjunctiva, the outer, mucous layer of the eye. Sometimes called ‘pink eye’ or ‘madras eye.’
Convergence: The movement of both eyes together towards each other is known as convergence. The eyes will converge in order to visualize objects at very close range.
Cornea: The cornea is the clear, front part of the eye which covers the pupil, iris and inner chamber of the eye. The cornea, together with the lens, refracts light and is responsible for about 65% of the eye’s total optical power.
Cross-eyed: When the eyes do not properly align the eyes appear ‘cross-eyed.’ The condition is called Strabismus and can cause the eyes to point inwards, towards the nose, or outwards, away from the nose.
Crystalline lens: another name for the lens, which is a transparent, structure which is biconvex, that, paired with the cornea, refracts incoming light so that it is focused on the retina. The lens is able to change shape, thereby focusing on objects at varying distances.
Cycloplegic refraction: This is a procedure which is used to elucidate the true prescription (refractive error) of a patient needing corrective lenses. It is done by administering atropine or cyclogel to temporarily paralyze the muscles used in focusing.