Eye Anatomy and Physiology

• Study notes on the anatomy, physiology, development, common conditions, and assessments of the eye.

Eye Anatomy

• The palpebral fissure is the open space between the eyelids.
• The canthus refers to the corner of the eye.
• Tarsal plates are connective tissue within the eyelids that contain meibomian glands.
• Meibomian glands are modified sebaceous glands that secrete an oily lubricating material onto the eyelids.
• The conjunctiva is a transparent protective covering of the eye.
• The lacrimal apparatus consists of lacrimal glands and ducts.
• Six muscles attach the eyeball to its orbit.
• The three layers of the eye are the sclera, choroid, and retina.
• The sclera is the white of the eye.
• The cornea is the clear outer layer of the eye that bends incoming light rays to focus on the retina.
• The choroid prevents extra light from entering and reflecting internally, and delivers blood to the retina.
• The iris dilates and constricts the pupil.
• Pupil size is determined by the parasympathetic and sympathetic nervous systems and should be round and regular.
• The lens is a biconvex disc posterior to the pupil that acts as a refracting medium.
• The retina is the visual receptive layer of the eye where light waves change into nerve impulses.
• Retinal structures visible through an ophthalmoscope include the optic disc, retinal vessels, general background, and macula.
• The optic disc is where fibers from the retina converge to form the optic nerve.
• Retinal vessels consist of paired arteries and veins extending to each quadrant, with a normal artery-to-vein ratio (AVR) of 2:3.
• The macula, located on the temporal side of the fundus, is a slightly darker region surrounding the fovea centralis that receives and transduces light from the center of the visual field.

Eye Function and Development

• The pupillary light reflex is the normal constriction of pupils when bright light shines on the retina.
• Fixation refers to focusing on a single object.
• Accommodation describes how pupils dilate when focusing on something farther away and constrict when focusing on something up close.
• Convergence is the movement of eyeballs towards the midline.
• Peripheral vision is intact in newborns, but the macula is absent at birth and matures by 8 months.
• Binocularity is established by 3-4 months.
• The lens is spherical at birth with a "soft plastic" consistency.

Aging and Eye Conditions

• Pupil size decreases with age.
• Presbyopia is a common age-related vision change.
• Visual acuity gradually decreases after age 50, and more so after age 70.
• Cataracts can begin to form by age 70.
• Common causes of decreased visual function in older adults include cataracts, glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy.
• Cataracts are the clouding of the lens due to protein clumping.
• Glaucoma is increased intraocular pressure with a strong genetic link; African Americans are 3-6 times more likely to develop it than Caucasian Americans.
• Age-related macular degeneration (AMD) involves the breakdown of cells in the macula, leading to loss of central vision and is more prevalent in Caucasians.
• Risk factors for AMD include family history, smoking, hyperopia, light iris color, hypertension, hypercholesterolemia, and being female.
• Diabetic retinopathy is damage to blood vessels in the retina due to diabetes and is a leading cause of blindness in adults ages 25-74.
• Visual impairment (VI) is defined as not being able to see letters on the eye chart at line 20/50 or below and is most prevalent in Caucasian women and older adults.
• Strabismus is a wandering or lazy eye.
• Diplopia is double vision.
• Nystagmus is rapid side-to-side eye movement, which can be an indication of drug intoxication.

Eye Assessment

• COCA is an acronym for color, odor, consistency, amount, used in eye assessment.
• The confrontation test assesses peripheral vision and tests cranial nerve (CN) II.
• The corneal light reflex (Hirschberg) test assesses that the reflection of the light on the corneas should be in the exact same spot on each eye.
• The 6 cardinal fields of gaze test assesses for potential extraocular movement (EOM) muscle weakness, nystagmus, or lid lag.
• A normal optic disc appearance is creamy yellow-orange to pink with a round/oval shape and distinct margins.
• Normal retinal vessels have arteries that are brighter and thicker than veins, a normal AV ratio of 2:3 or 4:5, and a normal decrease in caliber as they extend to the periphery.
• A normal fundus appearance is light red to dark brown/red, clear, with no lesions obstructing retinal structures.

Eye Conditions

• Periorbital edema is edema around the eyes.
• Exophthalmos is protruding eyes.
• Enophthalmos is sunken eyes, which can result from trauma/fractures.
• Ptosis is drooping of the upper eyelid.
• Blepharitis is eyelid inflammation.
• A chalazion is inflammation from an oil gland.
• A stye (hordeolum) is inflammation from an eyelash.
• Ectropion is the lower lid rolling out.
• Entropion is the lower lid rolling in.
• Anisocoria is unequal pupil size.
• Monocular blindness is blindness in one eye.
• Miosis is constricted and fixed pupils caused by misuse of eye drops, drugs, or trauma.
• Mydriasis is dilated and fixed pupils caused by misuse of eye drops, drugs, or trauma.
• Horner's syndrome includes anisocoria and eyelid drooping and can be genetic.
• Conjunctivitis is inflammation of the conjunctiva (pink eye), which is highly contagious.
• Iritis (circumcorneal redness) is a deep, dull red halo around the iris and cornea and requires immediate medical attention because the patient experience deep eye pain.
• Subconjunctival hemorrhage is a burst capillary.
• A pterygium is a winglike growth of conjunctival tissue extending to the cornea.
• A shallow anterior chamber is often due to blunt trauma causing increased intraocular pressure (IOP).
• Hyphema is blood in the anterior chamber of the eye.
• Hypopyon is pus in the anterior chamber of the eye.
• Optic atrophy is disc pallor.
• Papilledema is a choked disk.

Study notes covering eye anatomy, physiology, and common conditions. Key areas include the palpebral fissure, canthus, tarsal plates, and meibomian glands. Also covered are the conjunctiva, lacrimal apparatus, eye muscles, and the sclera, choroid, and retina layers.