Eye Functions and Clear Vision

Eye Functions for Clear Vision

• Four key functions ensure clear vision: refraction, pupillary constriction, accommodation, and convergence.

Refraction

• Refraction involves bending light outside and into the eye through a curved surface and into the retina.

Pupillary Constriction

• Pupillary constriction regulates the amount of light entering the eye by constriction and dilation.

Accommodation

• Accommodation is focusing on objects through the retina, whether they are close or far away.

Convergence

• Convergence is the ability to turn both eyes inward toward the nose at the same time.

Coordinated Eye Movement

• Coordinated eye movement ensures that both eyes receive the same image at the same time, resulting in a single, unified image.

Eye Muscle Innervation

• Cranial nerves 3 (oculomotor), 4 (trochlear), and 6 (abducens) innervate the muscles around the eyes, controlling eye movement.

Optic Nerve (CN II)

• The optic nerve (CN II) is responsible for sight, connecting the optic disc to the brain.

Trigeminal Nerve (CN V)

• The trigeminal nerve (CN V) stimulates the blinking reflex when the cornea is touched.

Facial Nerve (CN VII)

• The facial nerve (CN VII) innervates the lacrimal glands and muscles responsible for eyelid closure.

Assessing Cardinal Fields of Vision

• Assessment involves having the patient follow a finger in six directions, forming an "X" pattern.
• Inability to turn the eye in a particular direction indicates muscle weakness or nerve damage.

Vision Testing

• Visual acuity tests measure distance and near vision.

Snellen Chart

• The Snellen chart assesses distance vision.

Rosenbaum Pocket Vision Screener

• The Rosenbaum pocket vision screener assesses near vision.

Visual Acuity Interpretation

• 20/50 vision means a person can see at 20 feet what a healthy person can see at 50 feet.

Age-Related Vision Changes

• Age-related changes include arcus senilis, presbyopia, structural changes, ectropion, clarity and shape changes, and decreased iris dilation.

Arcus Senilis

• Arcus senilis is a blue ring around the eye due to fatty deposits and does not affect sight.

Presbyopia

• Presbyopia is the age-related decline in near vision, requiring objects to be held farther away to be seen clearly, especially reading material.

Structural Eye Changes with Age

• Eye muscle tone decreases with age, reducing the ability to gaze or focus on a single object.

Ectropion

• Ectropion is the relaxation of the lower eyelid, leading to dry eye.

Clarity and Shape Changes with Age

• The cornea flattens and becomes irregular, causing astigmatism and blurry vision.

Iris Changes with Age

• The iris's ability to dilate decreases, making it harder to adapt to dark environments and increasing the risk of injury at night.

Refraction Factors

• Refraction depends on eye length and the refractive power of the lens system.

Refractory Errors

• Refractory errors are caused by problems in eye length or refraction.

Types of Refraction

• Emmetropia, hyperopia, myopia, and astigmatism are the four types of refraction.

Emmetropia

• Emmetropia is perfect refraction, where distant images focus sharply on the retina.

Presbyopia Outcome

• In Presbyopia, images fall behind the retina (also called hyperopia, or far-sightedness)

Presbyopia Onset

• Presbyopia typically begins in the 40s.

Hyperopia

• Hyperopia (farsightedness) occurs when the eye does not refract enough, causing images to converge behind the retina.
• Distant vision is normal, but near vision is poor.
• Convex glasses/contacts treat hyperopia.

Myopia

• Myopia (nearsightedness) occurs when light overextends, causing images to converge in front of the retina.
• Near vision is normal, but distant vision is poor.
• Biconcave glasses/contacts treat myopia.

Astigmatism

• Astigmatism is a refractive error caused by unevenly curved surfaces in the eye, especially the cornea, leading to distorted vision.
• Eyeglasses, contacts, LASIK, or PRK surgery can correct astigmatism.

LASIK and PRK

• LASIK and PRK are laser procedures that reshape corneal layers to correct nearsightedness, farsightedness, and astigmatism.
• Vision increases within 1 hour post-op, and complete healing occurs within 4 weeks.

Blindness

• Blindness ranges from 20/400 vision to no light perception.

Legal Blindness

• Legal blindness is defined as 20/200 vision or less with corrective lenses in the better eye or a visual field of 20 degrees or less.
• Blindness can occur in one or both eyes.

Common Causes of Blindness

• Diabetic retinopathy, macular degeneration, glaucoma, and cataracts are common causes of blindness.

Nursing Interventions for Blindness

• Interventions focus on communication, safety, ambulation, maintaining self-care, and providing support.
• Knocking and announcing oneself before entering the room is essential.
• Reduced vision should be noted in the medical record, communicated to staff, and identified on the door. -Ensure all members of the healthcare team also knock and introduce themselves
• Determine the degree of blindness
• Orient the patient to