Human Eye – Anatomy, Assessment & Common Disorders

Anatomy of the Human Eye

  • External components

    • Eyelids

    • Protect anterior globe; abnormalities: ptosis (droop), ectropion (eversion), entropion (inversion), lid retraction & exophthalmos (often in hyper-thyroidism)

    • Conjunctiva

    • Thin mucous membrane covering sclera & inner eyelids; should appear clear, free of edema or exudate

    • Sclera

    • Tough fibrous outer coat ("white of eye"); normal color white—yellowing indicates jaundice, dark spots may be racial variant

    • Cornea

    • Transparent anterior continuation of sclera; main refractive surface; highly innervated & avascular

    • Lacrimal apparatus

    • Lacrimal caruncle, puncta, canaliculi, sac & nasolacrimal duct—produce & drain tears

  • Globe & internal structures

    • Three tunics

    • Fibrous (sclera + cornea)

    • Vascular (choroid + ciliary body + iris)

    • Neural (retina)

    • Chambers

    • Anterior chamber (between cornea & iris) – filled with aqueous humour

    • Posterior chamber (between iris & lens) – aqueous humour

    • Vitreous chamber (behind lens to retina) – vitreous humour

    • Lens

    • Biconvex, avascular; changes curvature via ciliary muscle for accommodation

    • Iris & pupil

    • Iris controls pupillary aperture; sympathetic input dilates, parasympathetic constricts. Central opening = pupil

    • Retina

    • Ten layered neural tissue containing photoreceptors (rods, cones)

    • Specialized regions:

      • Macula lutea – high cone density → central vision

      • Fovea centralis – highest visual acuity

      • Optic disc – entry of optic nerve & vessels; physiologic blind spot; central depression = optic cup

    • Optic nerve (CN II)

    • Conveys visual impulses to brain

Functional Summary of Major Ocular Structures

  • Cornea – refracts incoming light & serves as protective barrier

  • Aqueous humour – nourishes cornea/lens, maintains intra-ocular pressure (IOP)

  • Lens – fine focusing of light on retina

  • Ciliary muscles – adjust lens curvature for accommodation

  • Vitreous humour – maintains globe shape and retinal attachment

  • Retina – phototransduction (rods for dim light & peripheral vision, cones for color & acuity)

  • Fovea – area of highest cone density → sharp vision

  • Sclera – protective outer coat and attachment site for extra-ocular muscles

  • Optic nerve – transmits electrical impulses to visual cortex

  • Pupil – variable aperture regulating light entry

Eye Chambers & Spatial Relationships

  • Ordered anterior → posterior: Cornea → Anterior chamber → Iris/Pupil → Posterior chamber → Lens → Vitreous chamber → Retina

  • Relative volumes: Vitreous chamber ≈ 4/54/5 of globe volume

Nursing Assessment of the Eye

  • History

    • Onset, duration, severity of visual changes; pain, diplopia, halos, floaters, trauma, systemic diseases (e.g., DM, HTN)

  • External inspection

    • Symmetry of palpebral fissures, lashes, brows, globe position

    • Conjunctiva & sclera color/vascular pattern (depress lower lids while patient looks up)

    • Iris—uniform pigmentation, free of lesions

    • Pupil size/shape (record as PERRLA – Pupils Equal, Round, Reactive to Light & Accommodation)

  • Pupillary light reflex

    • Dark → dilation; bright → constriction. Use pen-light from temporal side; note direct & consensual response

  • Accommodation test

    • Ask patient to fixate on distant object then near target (≈10 cm); observe convergence & pupillary constriction

    • Pathologic finding: Argyll-Robertson pupil – reacts to accommodation but not to light (bilateral miotic, irregular)

  • Visual acuity (distance)

    • Snellen chart at 6 m (20 ft)

    • Cover one eye (test worse eye first) then the other, then both

    • Record smallest line read with ≤2 errors, e.g. 20/3020/30

    • Legal blindness: ≤20/20020/200 with correction OR visual field <20∘20^{\circ}

    • Near acuity – read newsprint at 35–40 cm

  • Color vision – Ishihara pseudo-isochromatic plates (red-green deficiencies)

  • Visual fields (confrontation)

    • Patient & examiner at eye level, 60–90 cm apart; compare patient’s peripheral vision to examiner’s

    • Normal limits: 90∘90^{\circ} temporally, 60∘60^{\circ} nasally, 50∘50^{\circ} superiorly, 70∘70^{\circ} inferiorly

    • Patterns: bitemporal hemianopia, homonymous hemianopia, quadrantanopias

  • Extra-ocular muscle function

    • Six cardinal positions of gaze – “H” pattern

    • Muscles/Nerves: LR6, SO4, all others 3

    • Note nystagmus, diplopia, or palsies (e.g., CN VI palsy – inability to abduct; trapped inferior rectus – vertical deficit)

Ophthalmoscopic Examination

  • Equipment parts: brow rest, viewing window, diopter dial, filters, rheostat

  • Technique

    • Darken room, set lens dial to 00, right eye to right eye at 15° temporal angle ≈3–5 cm away, move in toward pupil

    • Inspect

    • Red reflex

    • Optic disc: color (yellow-orange to pink), margins (sharp), cup:disc ratio (<0.50.5)

    • Vessels: arteries narrower & brighter than veins; follow to periphery

    • Macula/fovea – ask patient to look at light for direct view

  • Abnormal findings

    • Papilledema – swollen hyperemic disc with blurred margins due to raised ICP

    • Glaucomatous cupping – enlarged pale cup from elevated IOP

    • Optic atrophy – white disc, loss of vessels

    • Hypertensive retinopathy – flame hemorrhages, cotton-wool spots, hard exudates

Disorders of Vision & Refraction

  • Blindness / Near-blindness

    • Range: partial loss → no light perception (functional blindness = light perception without usable vision)

    • Causes

    • Congenital: genetic defects, maternal rubella

    • Acquired: diabetic retinopathy, glaucoma, cataract, retinal degeneration, trauma

    • Clinical cues: diplopia, halos, floaters, peripheral loss, pain, bulging, emotional distress

    • Management

    • Corrective lenses, assistive devices (cane, guide dog, magnifiers), surgery

    • Nursing: assess onset/severity, observe coping & self-care; diagnoses – Risk for Injury, Disturbed Sensory Perception, Ineffective Coping, Self-Care Deficit

  • Refractive errors (light fails to focus on retina)

    • Myopia (nearsighted)

    • Globe elongated; light converges anterior to retina → blurred distance vision

    • Snellen confirmation; new glasses ~q2 y; surgical options: keratorefractive (PRK, LASIK)

    • Pre-op: discontinue hard contacts 1–21–2 days prior; explain postoperative drop regimen

    • Hyperopia (farsighted)

    • Globe too short; focus posterior to retina → blurred near vision

    • Astigmatism

    • Unequal corneal curvature → multiple focal points

    • S/S: blurred vision without discomfort; Dx: ophthalmoscopy, retinoscopy, refraction

    • Tx: cylindrical lenses, possible corneal surgery

    • Strabismus

    • Eyes unable to align on one object; may cause amblyopia if untreated

Inflammatory Disorders of Eyelid & Conjunctiva

  • Blepharitis

    • Ulcerative (staphylococcal) vs non-ulcerative (seborrheic, psoriatic, allergic)

    • S/S: lid erythema, crusting at lash base, itching, photophobia, lids sticking on waking

    • Tx: ophthalmic antibiotic ointment (erythromycin), gentle cleansing with diluted baby shampoo

    • Nursing: hand hygiene, avoid makeup until healed; then purchase new cosmetics

  • Conjunctivitis ("pink eye")

    • Bacterial (strep, staph, gonococcus, pneumococcus, chlamydia)

    • Highly contagious; transmitted via hands

    • S/S: red conjunctiva, gritty feeling, lid edema, mucopurulent discharge/crusting

    • Tx: warm compresses 2–4×/day2–4\times/day, topical antibiotics (gentamicin, tobramycin, erythromycin, ciprofloxacin); cleanse lids with NS

    • Viral (HSV-1, herpes zoster, Chlamydia trachomatis)

    • Watery discharge, punctate grey/white lesions; HSV treated with antivirals (acyclovir)

    • Nursing: gloves, individual linens, avoid contacts, smoke, fumes

  • Keratitis

    • Corneal inflammation (bacterial, viral, fungal, allergic, traumatic)

    • Common pathogens: pneumococcus, staph, strep, pseudomonas; HSV is leading viral

    • S/S: severe pain, photophobia, tearing, corneal edema, vision reduction

    • Tx: topical ± systemic antimicrobial, analgesia, warm/cold compress, pressure patch, epithelial debridement, keratoplasty for scarring

    • Nursing: pain control, medication instruction, safety, recognition of complications

Lens Disorder

  • Cataracts

    • Non-infectious lens opacity; types: congenital (rubella), acquired (disease, toxins, trauma), senile (age-related)

    • S/S: gradual blurred/cloudy vision, glare, decreased night vision, diplopia, halos, abnormal color perception, central opacity on exam

    • Dx: ophthalmoscope or slit-lamp

    • Tx: monitor until ADL impaired → phacoemulsification with intra-ocular lens (IOL) implant

    • Complications: vitreous loss, hemorrhage, wound dehiscence

    • Post-op care

    • Discharge after few hours; use antibiotic & steroid drops, night shield

    • Avoid bending, stooping, coughing, lifting; report pain, erythema, drainage, or sudden vision change; protect from direct sunlight

Retinal Disorder

  • Diabetic Retinopathy

    • Microvascular complication of chronic hyperglycemia

    • Pathology: capillary micro-aneurysms, intraretinal hemorrhages, hard exudates, cotton-wool spots, neovascularization & fibrous tissue

    • S/S: floaters, progressive vision loss; ophthalmoscopy shows dilated/tortuous vessels

    • Tx: laser photocoagulation (seals leaky vessels), cryotherapy (freezes neovascular areas); control blood glucose & BP

Extra Points & Real-World Connections

  • Hyperthyroidism (Graves) → lid lag & exophthalmos due to T-cell autoimmunity; monitor heart rate >9090 bpm, tremor, moist skin

  • Visual field defects assist localization of neuro-lesions (e.g., bitemporal hemianopia → optic chiasm compression by pituitary macro-adenoma)

  • Legal and ethical aspects

    • Blindness classification impacts disability benefits; nurses must promote autonomy while ensuring safety

    • Infection control crucial to prevent outbreaks of bacterial conjunctivitis in communal settings

Key Numerical / Formula References

  • Distance visual acuity standards: 20/2020/20 normal, 20/20020/200 legal blindness

  • Normal visual field extent: 90∘90^{\circ} temporal, 60∘60^{\circ} nasal, 50∘50^{\circ} superior, 70∘70^{\circ} inferior

  • Optic cup : disc ratio <0.50.5; values >0.60.6 suggest glaucomatous cupping

  • Snellen testing distance: 6 m6\,\text{m} (or 20 ft20\,\text{ft})