Eye examination Study Guide

📖 Core Concepts Eye examination: A series of tests that evaluate visual acuity, focusing ability (far / near), and ocular/visual‑system health. Eight‑point full exam: Visual acuity → Pupil function → Extraocular motility & alignment → Intraocular pressure → Confrontational visual fields → External exam → Slit‑lamp exam → Dilated fundoscopic exam. Visual acuity: Ability to resolve fine detail; expressed as a Snellen fraction (e.g., $20/20$) or LogMAR. Pupil function (PERRLA): Size, shape, reactivity to light, and accommodation. Refraction: Determining the lens power (in diopters) needed to bring the focal point onto the retina; includes objective (retinoscopy/auto‑refractor) and subjective (phoropter) components. Pediatric eye exam: Uses age‑appropriate optotypes, red‑reflex (Bruckner) testing, and cycloplegic refraction because children accommodate strongly. --- 📌 Must Remember Normal visual acuity: $20/20$ (resolves a 1‑minute‑of‑arc pattern at 20 ft). Normal IOP: $10\text{–}21\ \text{mm Hg}$. PERRLA → Pupils Equal, Round, Reactive to Light and Accommodation. Afferent defect (Marcus Gunn pupil): Both pupils dilate when light shines on the affected eye. Efferent defect: Affected pupil stays dilated regardless of light direction. Horner syndrome: Small unilateral pupil + ptosis. Argyll Robertson pupil: Small, irregular, reacts to accommodation but not to light. Common systemic ocular effects: Diabetes → cataract + retinopathy; Hypertension → hypertensive retinopathy or papilledema; Chronic steroids → elevated IOP (glaucoma). Hydroxychloroquine: Annual comprehensive exam after 5 yr of use (baseline required). Fundoscopic red reflex: Symmetric = normal; asymmetry → possible cataract, media opacity, or retinal pathology. --- 🔄 Key Processes Visual Acuity Testing Measure distance VA → then near VA. Test each eye separately, first unaided, then with correction or pinhole. If chart unreadable → use CF, HM, LP, NLP. Swinging‑Flashlight Test Shine light into one eye → observe both pupils constrict. Move light to opposite eye → both pupils should constrict again. Note any dilation when light is on a particular eye (afferent defect). Objective Refraction (Retinoscopy) Project streak of light, move across pupil. Insert trial lenses; neutralize the reflex (movement stops). The lens power that neutralizes = refractive error. Subjective Refraction (Phoropter) Start with objective result. Use “which is clearer?” (better‑eye, worse‑eye, plus/minus) to fine‑tune spherical, cylindrical, and axis values. Confrontational Visual‑Field Testing Patient fixates on examiner’s eye. Examiner moves finger/target into each quadrant; patient counts. Identify scotoma, hemianopia, etc. Cycloplegic Refraction in Children Instill cycloplegic drops (e.g., cyclopentolate). Wait for full cycloplegia (≈30 min). Perform retinoscopy (objective) because accommodation is paralyzed. --- 🔍 Key Comparisons Afferent vs. Efferent Pupillary Defect Afferent: Both pupils dilate when light is on the affected eye (Marcus Gunn). Efferent: Affected pupil stays dilated regardless of light direction. Full vs. Minimal Eye Examination Full: All eight steps, including dilated fundus exam. Minimal: Only visual acuity, pupil function, extraocular motility, and undilated direct ophthalmoscopy. Objective vs. Subjective Refraction Objective: No patient feedback; uses retinoscope or auto‑refractor. Subjective: Patient reports clarity; performed with phoropter/trial lenses. Adult vs. Pediatric Visual‑Acuity Testing Adult: Snellen or LogMAR letters. Child: LEA symbols, tumbling “E”, HOTV, crowded charts. --- ⚠️ Common Misunderstandings “Pupil size ≤ 1 mm difference is abnormal.” – Actually ≤ 1 mm difference is normal. “A Marcus Gunn pupil is an efferent problem.” – It is an afferent defect. “Intraocular pressure > 30 mm Hg is always glaucoma.” – High IOP is a risk factor; diagnosis requires optic‑nerve and visual‑field assessment. “Cycloplegic drops are only for adults.” – They are essential in children to block strong accommodation. “Counting fingers equals 20/200.” – CF, HM, LP are qualitative scales, not precise Snellen equivalents. --- 🧠 Mental Models / Intuition “Light‑and‑dark reflex loop” – Think of the optic nerve (afferent) delivering light information to the pretectal nucleus → bilateral Edinger‑Westphal nuclei (efferent) → both pupils constrict. Break anywhere = abnormal reflex. “Lens‑to‑retina mismatch” – Myopia = eye too long or lens too strong → focus in front of retina. Hyperopia = eye too short or lens too weak → focus behind retina. “Peripheral‑field map” – Imagine the visual field as a clock; each quadrant corresponds to a specific retinal/optic‑nerve region. Loss in a quadrant hints at localized retinal or nerve pathology. --- 🚩 Exceptions & Edge Cases Papilledema: Occurs with malignant hypertension or any intracranial pressure rise – treat as a medical emergency regardless of IOP. Argyll Robertson pupil: Often associated with neurosyphilis; reacts to accommodation but not to light. Small pupil with normal reactivity: May be physiologic anisocoria; only concerning if accompanied by ptosis (Horner). High IOP in a young patient: Consider secondary causes (e.g., steroid‑induced) before primary open‑angle glaucoma. --- 📍 When to Use Which Choose full vs. minimal exam – Full exam for routine comprehensive screening, any visual‑field complaint, or systemic disease risk; minimal exam for quick follow‑up or in resource‑limited settings. Objective vs. subjective refraction – Start with objective to get a baseline; proceed to subjective for final prescription, especially in patients with irregular astigmatism or after cataract surgery. Cycloplegic refraction – Use in children < 7 yr, in suspected latent hyperopia, or when accommodation likely masks true error. Slit‑lamp with fluorescein – Use when corneal abrasion, epithelial defect, or viral keratitis is suspected. Gonioscopy – Required when angle‑closure glaucoma is a concern (e.g., shallow anterior chamber, high IOP). --- 👀 Patterns to Recognize Peripheral field loss pattern → Homonymous hemianopia = post‑chiasmal lesion; Bitemporal hemianopia = optic‑chiasm compression (e.g., pituitary adenoma). Red reflex asymmetry → Media opacity (cataract) or retinal lesion on the side with reduced reflex. Pupil size difference + ptosis → Horner syndrome (sympathetic loss). Irregular, small pupil + accommodation response → Argyll Robertson (neurosyphilis). Glaucomatous optic disc: Cupping, thinning of neuroretinal rim, vertical cup‑disc ratio > 0.6. --- 🗂️ Exam Traps “Marcus Gunn pupil” answer choice – May be paired with “efferent defect”; remember it is afferent. IOP = 22 mm Hg listed as “normal” – The accepted upper limit is 21 mm Hg; 22 mm Hg is borderline/high. “Count fingers = 20/40” – This is a distractor; CF is a qualitative scale, not a precise Snellen value. “Cycloplegic refraction is unnecessary after 12 months of age” – False; strong accommodation persists up to 8 yr; cycloplegia is still indicated when accurate measurement is needed. “A normal swinging‑flashlight test rules out optic nerve disease” – A subtle afferent defect can be missed; a formal RAPD (relative afferent pupillary defect) assessment may be needed. ---