Eye Structure and Function

• Vision is essential for clear sight and the eye converts light to electrical signals for the brain.
• Vision allows environmental perception, threat recognition, and aesthetic appreciation.
• The eye has internal and external structures and the adult eyeball has three layers.
• The sclera is the tough, protective outer layer of the eye.
• The uvea, the middle layer, includes the choroid, ciliary body, and iris.
• The retina, the inner layer, converts light waves into nerve signals:
• Intraocular pressure is needed to keep the eyeball inflated.

Internal Eye Structures

• Aqueous humor is a clear fluid in the front of the eye that maintains pressure, nourishes the cornea and lens, and drains through the canals of Schlemm.
• The canals of Schlemm, around the iris, drain aqueous fluid into the bloodstream and the meshwork regulates eye pressure.
• Blockage of the canals of Schlemm can lead to glaucoma and optic nerve damage.
• The choroid is a layer of blood vessels between the retina and sclera that feeds the retina.
• Abnormal blood vessel growth in the choroid can harm the macula, leading to macular degeneration and vision loss.

Ciliary body Functions

• Pupillary constriction (changing the lens for eye focus).
• Aqueous humor production.
• Maintenance of lens zonules (fibers that hold the lens).
• Ciliary muscles change the lens shape to focus on images at different distances.
• The ciliary muscles relax and flatten the lens for distance vision.
• Presbyopia: ciliary muscles and lens lose elasticity with age, often resulting in the need for reading glasses after 40.

Other Eye Components

• Conjunctivae lubricate the front of the eye and eyelids and function as the first defense against eye infections.
• Conjunctivitis is the inflammation of the conjunctivae.
• The cornea is a transparent dome over the iris with no blood vessels and serves as the most powerful lens in the eye's optical system.
• The fovea is the central part of the macula and provides the sharpest vision.
• The iris is a ring of muscle fibers behind the cornea that contracts to control pupil size, protecting the retina.
• Lenses, located behind the cornea, are circular and convex and keep images in focus on the retina.
• The lenses bulge for near objects and flatten for distant objects.
• The macula is the most sensitive part of the retina and provides detailed vision needed for tasks like reading.
• Macular degeneration can severely reduce eyesight.
• The optic disc is where the optic nerve exits the eye, creating a blind spot.
• The optic nerve (cranial nerve II) connects the eye to the brain, transmitting visual signals.

Eye Muscles

• Six orbital muscles control eye movements and four manage eye movement when the head is twisted.
• Dysfunction in these muscles can cause nystagmus or amblyopia.
• The pupil allows light to enter the eye and muscles within the iris regulate pupil size.
• The retina turns light into electrical signals and sends them to the brain via the optic nerve.
• Peripheral vision is handled by the sides of the retina, whereas the macula processes central vision.
• Retinal blood vessels, located in the choroid, nourish the eye with oxygen.
• Blood vessel abnormalities can cause vision loss like diabetic neuropathy and macular degeneration.
• The sclera, the white outer layer of the eyeball, is covered by conjunctival tissue.
• Blood vessel discoloration in the sclera can indicate health issues.
• Vitreous humor, maintain the shape of the eye and liquefies with age, causing floaters and dark spots in vision.
• Eyelashes and eyebrows protect the eyes from dust and particles.
• Eyelashes act as a screen against harmful particles and touching the eyelashes causes blinking.
• Eyelids protect and lubricate the eyes and oil glands mix oils with tears to keep the eyes moist.
• Lacriminal sacs drain tears and debris from the eye through the nasolacrimal duct into the nose, keeping the nasal lining moist.
• Lacrimal glands lubricate the cornea and prevent dehydration and continuously release tears and protective enzymes.

Vision Nerves

• 4 cranial nerves are involved in vision and accurate eye function.
• Light enters the pupil and hits the lens, where ciliary muscles adjust the lens shape for near or far focus and light on the retina turns into signals for the brain.
• Nerve II (Optic) transports visual information from the retina to the brain.
• Nerve III (Oculomotor) controls pupil constriction, eyelid and eyeball movement.
• Nerve IV (Trochlear) controls downward and lateral eye movement.
• Nerve VI (Abducens) controls lateral eye movement.
• Accommodation is the eye's ability to adjust vision when switching focus.
• Convergence is when both eyes move inward to focus on a close object.

Assessment

• Gathering a comprehensive health history is essential including living conditions, occupation, medications, allergies, injuries, illnesses, and surgeries.
• Personal and family history of eye problems helps determine potential genetic risks.
• Lutein and beta-carotene support retinal function and deficiencies in vitamin A can cause dry eyes and blindness.
• Vitamins C and E are antioxidants that protect against free-radical damage.
• A history of eye trauma helps identify potential pathologies.
• Assessment of protective equipment use is important for preventing injuries.
• Occupational hazards can cause rust rings and corneal erosion if protective goggles are not worn.

Eye Protection

• Wear protective eyewear for sports and occupations.
• Wear ultraviolet protective eyewear for sun exposure.
• Use a face shield with safety goggles for needed protection.
• Wear eye goggles for grass cutting, weed whacking, wood chopping, and when using caustic substances.

Inspection

• Explain the examination process to the patient and hand washing/glove use are required.
• Check the symmetry of the eyes and any unusual bulging (exophthalmos) or sinking and check eyebrow alignment with the top of the ears.

Eye Structures

• Eyebrows: Check hair distribution, symmetry, and alignment with the ears.
• Eyelashes: Check distribution, curl, and projection.
• Eyelids: Check surface, blinking ability and frequency, drooping, swelling, discoloration, and lesions.
• Conjunctiva: Check color and texture by retracting the eyelids and having the patient look in different directions.
• A pale conjunctiva can indicate low red blood cell count.
• Iris: Check color, symmetry, size, and pupil shape.
• Anisocoria, a noticeable difference in pupil size, is normal in about 5% of people and normal pupil size is between 3 and 5 mm.
• The Snellen chart, or "eye chart," tests distance vision and has 11 rows of capital letters that get smaller down the chart.
• The corneal light reflex assesses extraocular muscle function, evaluating cranial nerves III, IV, and VI.

Corneal Light Reflex

• The test checks eye alignment.
• With proper alignment, light reflects in the same position in both pupils, whereas misalignment causes off-center reflection
• The patient stares ahead as the provider shines a penlight on both corneas from 12-15 inches away.
• Symmetrical light reflection indicates proper alignment and asymmetry suggests muscle imbalance.
• Assessment of Six Ocular Movements:
• Check eye alignment and coordination in patients older than 6.
• The patient keeps their head still and follows a penlight with their eyes as it moves slowly.
• Movement is periodically stopped to check for nystagmus.
• Pupillary light reflex is the normal constriction of the pupil when exposed to bright light.
• Cranial nerve II (optic nerve) detects incoming light, and cranial nerve III (oculomotor nerve) causes pupillary constriction.
• A direct light reflex is pupil constriction in the eye exposed to light, and a consensual light reflex is simultaneous constriction in the other pupil.
• The test is performed in a darkened room where the provider shines light from the side, eliciting constriction in both pupils.
• Ophthalmic Examination: Typically done by an MD or APRN in an office or clinic.
• Specialists include ophthalmologists and optometrists.

Ophthalmoscope Use

• Allows viewing of the retina, vessels, and other eye structures with better visualization by dilating by examining in a darkened room.
• The patient stares straight ahead, and the provider uses the same eye as the patient's eye being examined, using a hand for steady distance.
• A red reflex should be visible, indicating light reflecting off the retina; absence may indicate lens opacity or cloudiness.
• Once the retina is visible, the optic disc, vessels, fovea, and macula should be visible.
• The provider explains the exam before suspending the exam if the patient is combative.

Diagnostic tools

• CT scans help diagnose eye diseases by examining blood vessels, eye muscles, optic nerve, abscesses, fractures, and foreign bodies with or without contrast.
• MRI provides detailed soft tissue views without bone or air contrast and is useful for detecting tumors, infections, chronic diseases, fractures, optic nerve changes, and enlarged eye muscles.
• Ultrasonography uses high-frequency sound waves to image soft tissues when direct visualization is difficult and can be performed in the office and is useful for detecting vitreous hemorrhage and tumors.

Nursing Implications for eye exams

• Complete pre-procedure teaching and checklist.
• Ensure informed consent is signed and witnessed.
• Assess allergies if dye/contrast is used.
• Obtain IV access for dye/contrast administration.
• Check BUN/creatinine levels to prevent kidney injury from dye/contrast.
• Assess patient allergies and use anesthetic eye drops to minimize discomfort and instruct the patient not to rub their eyes after the procedure until the anesthetic wears off.
• Radioisotope Scanning:
• Involves injecting small amounts of radioactive substances to differentiate between normal and malignant tissues, often used to identify tumors and ocular melanomas.
• Complete pre-procedure teaching and checklist, ensure sign consent, check allergies, check IV, inform about radioisotope drops.
• Implement radiation safety, remove dye/contrasts, remove metal objects, notify technician of metal objects, check NPO status, confirm sedation for claustrophobic patients

Slit Lamp

• It is often part of a routine eye exam and it can view posterior eye structures like the optic nerve and retina.
• It aids in diagnosing cataracts, conjunctivitis, glaucoma, macular degeneration, and foreign bodies and uses high-intensity light magnification for 3D imaging.
• Anesthetic eye drops may be tested and patients must remove glasses or contacts.

Examination points

• Complete pre-procedure teaching.
• Assess allergies if using anesthetic drops; instruct patients not to rub their eyes until the anesthetic wears off.
• A tonometer measures the pressure inside the eyeball, with a normal range of 10 to 21 mm Hg.
• Elevated pressure can reduce blood flow and cause visual problems, often due to overproduction of aqueous humor or inadequate drainage through the canals of Schlemm.
• The test may involve anesthetic drops and fluorescein dye to enhance visualization.
• The patient rests their chin and stares into the instrument while the provider shines a light and gently touches the probe to the eye to get a pressure reading.
• Patients must remove glasses or contacts and limit fluid intake before the test and avoid rubbing their eyes after the test until sensation returns to prevent injury.

Tests

• Provide pre-procedure teaching and assess allergies to anesthetic eye drops.
• Instruct patients not to rub their eyes until the anesthetic wears off.
• The corneal staining test uses fluorescein dye to detect foreign bodies or scratches on the cornea.
• The dye is applied as a drop or with blotting paper, and the patient blinks to spread it.
• A blue light is used in a darkened room to visualize any corneal issues, and anesthetic may be used for comfort.
• Patients should be informed about the test and the dye's temporary discoloration.
• Postprocedure instructions include changes in skin color (slightly yellow) and urine (slightly green/yellow) for a couple of hours after the procedure.

Eye protection

• Do not use if allergic to pain-numbing medications.
• May cause initial stinging/discomfort.
• Do not rub eyes to prevent injury.
• Wear protective glass lenses until eye sensitivity returns.
• Wearing protective goggles during high-risk activities at work and home is essential.
• Everyday activities can also cause injuries and sunglasses are important but often and often and it is oftne overlooked
• Sun exposure to UV-B light can damage the eyes and lead to cataracts and regular hand washing prevents the transfer of harmful substances.

Age related eye changes

• Deposits in the vitreous humor can lead to floaters.
• The conjunctiva becomes more prone to chronic inflammation and dryness due to hormonal changes, and tear glands and conjunctiva may lose the ability to lubricate the eye.
• Retinal arteries and veins narrow, causing a less responsive light reflex.
• Eyelids lose elasticity, causing ptosis (drooping).

Explore the anatomy and physiology of the human eye. Learn about the key structures, including the sclera, uvea, retina, and their respective functions in vision. Understand how intraocular pressure and the aqueous humor maintain eye health and how disruptions can lead to conditions like glaucoma.