N109: Foundations in Nursing Practice

N109: Foundations in Nursing Practice Study Guide Structure and functions of the eye: Eye Structure Function Conjunctiva The layer of epithelial cells that covers the cornea and protects it against damage. Cornea The transparent front of the eye, which helps to converge light rays as they enter the eye. Sclera The opaque outer structure that provides protection and attachment surfaces for eye muscles. Choroid Served by a network of blood vessels, it provides the means to supply nutrients to the eye and remove waste from the eye. Iris This muscular structure that helps to control the amount of light entering the eye. Pupil The hole in the middle of the iris where light enters the eye. It will normally constrict in bright light and dilate indim light. Lens The flexible, curved structure in the eye that changes shape to focus light rays onto the retina. Retina A layer of sensory neurons (rods and cones) and relay neurons that respond to light and pass the impulses to the optic nerve. Optic Nerve Cranial nerve 2, which transmits from the retina to the brain. Fovea A part of the retina that contains only cone cells, and is primarily responsible for visual acuity. Aqueous Humour Helps to maintain the shape of the anterior chamber of the eyeball. Vitreous Humour The jelly-like mass located behind the lens that supports and protects the lens, and helps maintain the shape of the posterior chamber. 5.3 Problems Causing Visual Impairment Problems causing visual impairment can occur at any age and can vary in intensity. Some common problems that can cause visual impairment include: • Absolute blindness: This is defined as the absence of light perception. The best corrected visual acuity (BCVA) can range from 20/400 to no light perception (NLP) at all. In legal blindness, the BCVA does not exceed 20/200 in the better eye and the widest visual field diameter is 20 degrees or less. If a person meets the criteria for legal blindness, they may be eligible for government financial assistance. • Age-related Macular Degeneration (AMD): This is a disease associated with aging that gradually destroys sharp, central vision. Central vision is needed for seeing objects clearly and for common daily tasks, such as reading and driving. AMD causes no pain and may advance so slowly that people notice little change in their vision. In others, the disease progresses faster

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