Eye Anatomy

Anatomy of the Eye

• The cornea is a transparent, avascular, dome-like structure
• It serves as the main refracting surface of the eye
• Aqueous humor is produced by the ciliary body and nourishes the cornea
• The uvea consists of the iris, ciliary body, and choroid
• The iris is the colored part of the eye
• The pupil is a space that dilates and constricts in response to light
• The lens is a colorless and biconvex structure
• Allows focusing for near vision and refocusing for distance vision (accommodation)
• A choroid is a vascular tissue
• It supplies blood to the portion of the sensory retina closest to it
• Vitreous humor occupies 2/3 of the eye's volume
• Helps maintain the shape of the eye
• The retina is composed of 10 microscopic layers
• It is a neural tissue and an extension of the optic nerve
• The macula is the part of the retina and is responsible for central vision
• Rods are responsible for night vision
• Cones are responsible for bright light and color vision

Testing vision

• The Snellen chart consists of progressively smaller rows of letters
• Used to test distance vision
• 20/20 vision is considered the standard of normal vision
• A person with 20/200 vision can see an object from 20 feet away that a person with 20/20 vision can see from 200 feet away
• An ophthalmoscope examines the fundus, optic cup, periphery of the retina, and macula
• A slit lamp is a binocular microscope
• It examines the eye with magnification of 10 to 40 times the real image
• A tonometer measures IOP
• It determines the pressure necessary to indent or flatten a small anterior area of the eye
• Normal IOP is 10-21 mmHg
• Perimetry evaluates the field of vision, the area, or the extent of physical space visible to an eye in a given position
• The ishihara color plate test identifies color vision deficits/color-blindness
• Dots of primary colors are integrated into a background of secondary colors, arranged in patterns like numbers or shapes
• An amsler grid tests patients with macular problems such as macular degeneration
• It consists of a geometric grid of identical squares with a central fixation point
• The patient stares at the central fixation spot
• Some squares may look faded, or the lines may be wavy for patients with macular problems

Eye-related Terms

• Aphakia is without a lens
• Astigmatism is the irregularity in the curve of the cornea
• Blindness visual acuity with best correction (BCVA) ranges from 20/400
• Legal blindness has a BCVA that does not exceed 20/200
• Diplopia is double vision
• Emmetropia is normal vision
• Hyperopia is far-sightedness
• Myopia is near-sightedness
• Hyperemia translates to red eye
• Nystagmus is the involuntary oscillation of the eyeball
• Proptosis is the downward displacement of the eyeball
• Ptosis is a drooping eyelid
• Papilledema is swelling of the optic disc
• Strabismus is a condition in which there is deviation from perfect ocular alignment
• An enucleation is the removal of the entire eye and the part of the optic nerve
• Evisceration involves the surgical removal of the intraocular contents
• This is achieved through an incision or opening in the cornea or sclera
• Exenteration is the removal of the eyelids, the eye, and various amounts of orbital contents

Conditions of the Eyelids and Conjunctiva

• Blepharitis is an inflammatory reaction of the eyelid margin, or seborrheic skin condition
• It is commonly caused by Staphylococcus aureus
• Manifestations include flaking, redness, irritation and recurrent styes
• If bacterium S. aureus is likely, use antibiotic ointment
• Scrub the margin of eyelid with cotton swab
• Apply ointment with cotton swab as directed
• Hordeolum (stye) refers to an inflammation/infection of glands and follicles of the eyelid margin
• External hordeolum impacts the hair follicles of the lashes
• Chalazion is a granulomatous, chronic infection of meibomian glands
• Etiological factors are the bacterium staphylococcus and seborrhea
• Manifestations include pain, redness, foreign body sensation and possible pustule
• Warm soaks, good handwashing, eyelid hygiene, and antibiotic ointment can assist
• Conjunctivitis is an inflammation or infection of the bulbar (covering the cornea and sclera) or palpebral (lining the eyelids) conjunctiva
• Pink eye is usually referring to infectious conjunctivitis
• Causes of bacterial conjunctivitis are Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus
• Adenovirus and herpes simplex virus cause viral conjunctivitis
• Allergic conjunctivitis is caused by hypersensitivity reaction in allergic rhinitis or environmental pollutants/allergens
• Manifestations are foreign body sensation, scratching or burning, itching, and light sensitivity (photophobia)
• Warm soaks are used with crusting/drainage, cold compress is used in viral cases of conjunctivitis
• Bacterial conjunctivitis needs topical antibiotics
• Allergic conjunctivitis needs topical or oral antihistamines, vasoconstrictors, and mast cell stabilizers
• Corneal abrasion/ulceration (Keratitis) happens when the layers of cornea are lost due to contact lens overwearing or trauma
• This may lead to corneal ulcer and secondary infection into cornea (keratitis) possibly resulting in blindness
• Manifestations are pain, redness, foreign body sensation, photophobia, increased tearing and difficulty opening the eye
• Fluorescein staining and woods lamp or slit lamp are diagnostic procedures
• Treatment is urgent
• Potent antibiotic eyedrops and eye patching should be done in first 24 hours
• Manage pain with cycloplegics
• See an ophthalmologist for ulceration
• Ensure the patch is secure
• Review safety practices (eye sheild use, hand washing)
• Iritis/Uveitis is inflammation of the intraocular structure
• This may involve the anterior uvea such as the iris (iritis) or the iris and ciliary body (iridocyclitis)
• It can also involve intermediate uveitis structures such as parts posterior to the lens (pars plantis or peripheral uveitis)
• The choroid (choroiditis), or the retina (retinitis), or vitreous near the optic nerve and macula of posterior uveitis can be involved
• Anterior uveitis is usually unilateral
• Posterior uveitis is often bilateral
• Etiologies are immune disorders or even idiopathic causes
• Can be from other conditions like ankylosing spondylitis, Crohn's, Reiter's syndrome, lupus or even trauma
• Acute onset with deep eye pain, light hypersensitivity, conjunctival redness and a pupil that does not respond briskly are manifestations
• Ophthalmology and intervention needed
• Corticosterioids and cycloplegic agents will treat inflammation

Disorders of the eyes

• Cataracts are clouding/opacity of the crystalline lens which impairs vision
• Etiologies are aging, congenital issues or trauma
• Risk factors are diabetes, UV light, high-dose radiation/corticosteroids, etc.
• Blurred central vision, glare from bright lights, gradual & painless vision loss, milky pupils are manifestations
• Diagnosed using slit-lamp examination, ophthalmoscopy, perimetry and visual acuity tests
• Surgical removal of the lens can be done, usually under local anesthetics
• Preoperative eyedrops lessen motor activity
• Postoperative oral medications drop intraocular pressure
• intraocular lens (IOL) implants replace the thick eye glasses with suboptimal refraction
• Otherwise, a contact lens/spectacles can correct refraction
• Two types of cataract extractions exist
• Intracapsular extraction requires removing lens and capsule via small cut
• Extracapsular extraction cuts the lens capsule and extracts the nucleus/cortex/anterior capsules
• The posterior capsule is usually kept in place and is the base where and IOL is implanted
• Cryosugery is a procedure where supercooled instrument freezes the exposed lens lifting the lens out
• In Phacoemulsification, a section of the anterior capsule is removed, and a device liquefies the nucleus and cortex
• After liquefaction, the nucleus and cortex is suctioned through a tube
• Orient and explain the procedure to drop anxiety
• Instruct avoiding touching eyes to decrease contamination
• Obtain conjunctival cultures, if requested, using aseptic technique
• Administer preoperative eye drops, antibiotic, mydriatic-cycloplegic and etc
• I.V. sedative, antiemetic, and opioids may be needed
• post-operative drugs mitigate pain and prevent nausea/vomiting
• Sudden pain coupled with with restlessness and increased pulse, and with fever is alarming
• Coughing and rapid movements can prevent increased IOP
• Prevent complications; sit upright with head elevated, ambulate but move gently
• Glasses and eye shields may b need at all times
• Wipe the postoperative eye with a tissue outwards
• Lens replacements include aphakic eyeglasses, contacts or IOL implants
• Aphakic causes objects to appear magnified
• Contacts allow almost normal vision
• IOL usual option for lens replacement
• IOLs can be single-focus/monofocal, multifocal or accomodative
• Acute (close angle) glaucoma is defined by an obstruction occurs at the meshwork and the Canal of Schlemm
• It is often progressive visual field loss, leading to eventual blindness
• Rapidly declining eyesight should be clinical indication of of Angle-Closure Glaucoma
• Expect intense periocular ache, conjunctival hyperemia/congestion, nausea/vomiting, bradycardia, peripheral visual loss
• Pupil that is vertically oval, may not react to light/accomodate
• Can be diagnosed with tonometry, ophthalmoscopy, gonioscopy and perimetry
• Should be medically treated with hyperosmotic drugs, hypotensives and through surgical procedure
• Patients should adhere to drug regimen and maintain appointments
• Remind health condition and remind when signs return
• Chronic open angle glaucoma:
• IOP rises from within.
• Loss field.
• Causes: Age, heredity, and ethnicity.
• Symptoms: Headache, blurred vision, halos, pain.
• Nursing intervention: Prescribed medications, exercise.

Retinal detachment

• Involves the sensory region detaching from the pigmented epithelium
• a break in the retina leads to the detachment
• Trauma and inflammation can lead to spontaneous detachment, which is when degenerative changes in the vitreous/retina lead to detachment
• The patient notes visual sensations where there are particles where the eyes look
• There is a sensation of a veil in the fields of eyesight
• Legal blindness occurs if holes are not filled and sealed
• Perform indirect ophthalmoscopy to confirm the detachment
• Perform a slit-lamp exam, as well as optical coherence tomograph
• Perform scleral buckling, where the retina is pulled to correct the detachment
• Inject silicone oil into the vitreous to push the retina
• Perform cryosurgery by using a freezing agent to cause scaring to adhere the retina
• To avoid complications, the bumping of the head must be avoided
• Prevent actions that can raise the eye pressure
• Encourage mobility as needed and ambulation
• Analgesics, sedatives and radio will help treatment

Macular Degeneration

• Common cause for vision loss in people over 60
• Slow breakdown of outer retina (dry form); abrupt onset with wet version
• Amsler grids should be used to monitor patient vision
• Injuries lead to tissue traumas
• Injuries that cause the soft tissue is from injury to the optic nerve
• Surgical action is needed right away
• Inspection causes: lid issues, hemorrhaging.
• Actions: Inspection, and thorough cleanings.
• Medical intervention: Antibiotics.

Other Information

• Muscles, fat and fascia in nerves may be caught
• Diagnose muscle entrapment with CT
• Operate on fractures; conduct surgical repair
• A metal shield can be used if bleeding is a concern
• Avoid injuries to the eyes
• Damage to the tympanic structure can impact the hearing
• Cerumen and foreign blockages can impact the ear
• Irrigation with the ear dislodges them
• Use suction or tools as a last resort

Concise review of the anatomy of the human eye. Covers the cornea, aqueous humor, uvea, lens, choroid, vitreous humor, retina, macula, rods, and cones providing key function of each component.