👁️ Visual acuity must always be assessed at the bedside during any eye examination.
It provides a crucial baseline for both ocular and systemic conditions, and can guide urgency of referral.
📍 About
- Visual acuity depends on the integrity of the entire optic pathway - from the eye to the occipital cortex.
🌟 Perfect Vision Requires:
- Clear focusing of light by the cornea & lens onto the retina.
- Unobstructed optical media (cornea, aqueous, lens, vitreous).
- Healthy retina with functioning photoreceptors.
- Intact optic nerve to carry signals to the brain.
- Normal neural pathways (optic chiasm → tracts → radiations → occipital cortex).
- Testing each eye separately avoids masking of unilateral pathology by binocular vision.
🩺 Clinical Assessment of Visual Acuity
- Importance: Detects refractive errors, retinal disease, optic neuropathies, or cortical dysfunction.
- Techniques:
- Always test with corrective lenses (or pinhole) to exclude refractive error.
- Assess each eye independently (cover–uncover method).
- Methods:
- Bedside: Use printed material or standard near-vision cards if a Snellen chart is unavailable.
- Snellen Chart:
- Standard at 6 m distance (20 feet in US) or near card at ~14 inches.
- Results expressed as a fraction - e.g. 6/6 (normal), 6/60 (severe impairment).
- Pinhole test: Improves vision in refractive error but not in retinal/optic nerve disease.
🔬 Investigations
- If vision is reduced, further evaluation may include:
- Fundoscopy - retinal & optic disc assessment.
- Slit-lamp - anterior segment and lens.
- Visual fields - glaucoma, stroke, retinal lesions.
- OCT - macula & retinal nerve fibre layer.
- MRI/CT - optic nerve or cortical pathology.
💊 Management
- Refractive errors: Correct with glasses/contact lenses.
- Ocular disease: Ophthalmology referral for cataract, macular degeneration, diabetic retinopathy, glaucoma.
- Acute vision loss: Urgent referral - consider central retinal artery occlusion (CRAO), retinal detachment, optic neuritis, or temporal arteritis.
- Chronic disease: Manage systemic causes (diabetes, hypertension) and monitor progression.
📌 Exam Tip
🔑 Always document visual acuity in both eyes with and without correction.
If vision improves with pinhole → refractive error.
If not → consider retinal, optic nerve, or cortical pathology.
