Central Visual Acuity — Visometry and Examination Method

1. Definition and Physiological Basis

2. Visometry — Notation Systems

a. Snellen Notation (fraction notation)

Distance patient reads the chart / Distance at which a normal observer reads the same line

• 6/6 (metric) = 20/20 (feet) = normal acuity
• 6/12 (20/40) = the patient reads at 6 m what normals read at 12 m
• 6/60 (20/200) = threshold for legal blindness

b. Decimal Notation

c. LogMAR Notation

d. Near VA — Jaeger System

• J1 ≈ 20/20
• J7 ≈ 20/50
• J13 ≈ 20/100
• J16 ≈ 20/200

3. Examination Method

Equipment

• Snellen chart — wall-mounted at 6 m (20 ft); illuminated
• Rosenbaum card — portable near card held at 36 cm (14 in); useful at bedside
• Pinhole occluder — opaque disc with ~1 mm hole(s) (Fig. 1.2 in Kanski)
• ETDRS / Bailey-Lovie chart — for research-grade measurement

Snellen visual acuity chart — Kanski's Clinical Ophthalmology

Step-by-Step Procedure

1. Refractive correction: Test first with the patient's habitual correction (glasses or contact lenses). Unaided acuity may also be recorded separately.
2. Monocular testing: Test each eye individually — the worse eye first, with the fellow eye fully occluded.
3. Distance testing: Patient stands 6 m (20 ft) from the chart; reads the smallest line possible. Push the patient to attempt every letter.
4. Record acuity: Note the smallest line where the majority of letters are read correctly.
5. Pinhole test: If VA < 6/6, repeat with a pinhole aperture over the tested eye.
   • Improvement with pinhole → refractive error or anterior media opacity (cornea, lens, aqueous, vitreous) — optical cause
   • No improvement → suggests retinal or neural disease (macular, optic nerve)
   • Note: pinhole may worsen acuity in macular disease and posterior lens opacity
6. Binocular VA: Usually equals or exceeds the better monocular VA when both eyes are roughly equal.

For Very Poor Vision (Below Chart Level)

Legal and Regulatory Thresholds

• Legal blindness: best-corrected VA ≤ 6/60 (20/200) in the better eye, OR visual field ≤ 20°
• Driving (most jurisdictions): corrected VA ≥ 6/12 (20/40) in at least one eye
• Homonymous hemianopia is an independent contraindication to driving regardless of acuity. (Harrison's Principles of Internal Medicine, 22nd ed.)

Testing in Preverbal Children

• Fixation and following response (face or bright targets)
• Preferential looking (Teller/Keeler acuity cards, Cardiff acuity cards): infants prefer patterned over homogeneous stimuli; finest grating resolved = VA estimate
• 10Δ prism test and rotation test assess inter-eye equality
• Note: grating acuity may overestimate Snellen acuity in amblyopia. (Kanski's Clinical Ophthalmology)

4. Summary Table: VA Notation Equivalents

Eyelid Diseases: Blepharitis, Hordeolum (Stye), and Chalazion

I. BLEPHARITIS

Definition

Classification and Etiology

Risk Factors

• Seborrhoeic dermatitis / dandruff
• Acne rosacea
• Atopic dermatitis / eczema
• Demodex infestation (especially in older patients)
• Contact lens wear
• Immunosuppression
• Dry eye syndrome (bidirectional relationship)

Clinical Features

• Burning, itching, grittiness, mild photophobia
• Crusting and redness of the lid margins
• Morning crusting / lashes stuck together on waking
• Tearing; contact lens intolerance
• Remissions and exacerbations (chronically relapsing course)
• Stinging more common in posterior disease; dry eye symptoms worsen through the day

Blepharitis with lash collarettes — Wills Eye Manual

Diagnostics

• Clinical diagnosis — slit-lamp examination of lid margins, lash bases, meibomian gland orifices
• Evert eyelid: assess meibomian gland inspissation
• Microscopic examination of epilated eyelashes — if Demodex suspected (cylindrical sleeves confirm)
• Culture if bacterial superinfection suspected
• Look for associated skin disease (rosacea, seborrhoeic dermatitis, atopic dermatitis)
• Important to exclude sebaceous gland carcinoma in chronic unilateral blepharitis, recurrent chalazia, or madarosis in older patients

Treatment

• Warm compresses 5–10 min, 2–4× daily → softens crusts and meibum
• Lid scrubs 2× daily with commercial scrub pads or diluted mild shampoo on a washcloth → removes debris, reduces bacterial load
• Meibomian gland expression: roll finger anteriorly over lid margin when significant MGD is present
• Frequency can be reduced once controlled

• Topical: sodium fusidic acid, erythromycin ointment, azithromycin gel-drop, bacitracin, chloramphenicol — applied to lid margins at bedtime (q.h.s.) after lid hygiene

• Doxycycline 50–100 mg twice daily × 1 week → taper to 50 mg daily × 6–24 weeks (reduces lipase production; anti-inflammatory)
• Lymecycline 408 mg daily up to 3 months
• Azithromycin 500 mg daily × 3 days for 3 cycles at 1-week intervals (preferred for anterior disease)
• Erythromycin 250 mg 1–2× daily (alternative; safe in children and pregnancy)
• ⚠️ Tetracyclines contraindicated in children <12 years and pregnancy/breastfeeding

• Topical steroid (fluorometholone 0.1% or loteprednol 4× daily × 1 week) for active inflammation or papillary conjunctivitis; occasionally higher-strength preparations
• Cyclosporine 0.05% / 0.09% or lifitegrast 5% drops b.i.d. for immune-mediated component
• Topical antibiotic-steroid combination (e.g., tobramycin/dexamethasone) for unresponsive meibomitis

• Omega-3 fatty acid supplementation (fish/plant oil supplements show substantial benefit)
• Tea tree oil (50% scrub + 5% ointment; or terpinen-4-ol 2.5% wipes) — anti-Demodex activity
• Topical permethrin, oral ivermectin (200 µg/kg × 2 doses, 1 week apart)
• Lotilaner 0.25% (TP-03) ophthalmic solution — novel, effective at reducing collarettes and Demodex density within 4 weeks
• Preservative-free artificial tears for dry eye component
• Novel devices (e.g., LipiFlow) — thermal pulsation to heat and express meibomian glands

II. HORDEOLUM (STYE — "Barley")

Definition

• External hordeolum (stye): abscess of the gland of Zeis (sebaceous gland of a lash follicle) or Moll's gland — appears at the eyelid margin
• Internal hordeolum: abscess of the meibomian gland — points toward the conjunctival surface

Etiology

• Causative organism: Staphylococcus aureus (most common); occasionally other Staphylococcus species
• May evolve from or coexist with a chalazion

Risk Factors

• Blepharitis (most important predisposing condition)
• Poor eyelid hygiene
• Rosacea
• Immunocompromise / diabetes
• Contact lens wear

Clinical Features

• Acute onset of painful, red, tender, localized swelling at the eyelid margin (external) or within the tarsal plate (internal)
• Erythema, oedema of surrounding lid
• May point and drain mucopurulent material spontaneously
• May progress to preseptal cellulitis if untreated

Diagnostics

• Clinical — history and external examination
• Palpate lid for nodule; evert eyelid
• Slit-lamp assessment for associated blepharitis/meibomitis
• Culture only if recurrent or cellulitis develops

Treatment

1. Warm compresses ≥10 minutes, 4× daily — promotes spontaneous drainage
2. Topical antibiotic (bacitracin, tobramycin, or erythromycin ointment b.i.d. × 1–2 weeks)
3. If worsening → incision and drainage (I&D); manage secondary preseptal cellulitis with systemic antibiotics
4. Systemic antibiotics (e.g., oral penicillinase-resistant antibiotic or trimethoprim-sulfamethoxazole for MRSA) if cellulitis develops

III. CHALAZION (Meibomian Cyst)

Definition

Etiology and Pathogenesis

• Obstruction of meibomian gland duct → retained lipid secretions → lipogranulomatous chronic inflammatory reaction
• Histopathology: extracellular fat deposits surrounded by lipid-laden epithelioid cells, multinucleated giant cells, and lymphocytes
• Not primarily infectious (though may become secondarily infected → internal hordeolum)
• Bortezomib (proteasome inhibitor for multiple myeloma) predisposes to chalazia within 3 months of initiation

Risk Factors

• Chronic blepharitis / MGD
• Acne rosacea (associated with multiple and recurrent chalazia)
• Seborrhoeic dermatitis
• Systemic retinoids
• Bortezomib therapy
• Immunosuppression

Clinical Features

• Gradually enlarging, painless, well-defined, firm, rounded nodule within the tarsal plate — visible or palpable
• Upper lid more commonly affected than lower
• Bulging inspissated secretions may be visible at the meibomian gland orifice
• Associated conjunctival granuloma may form on the inner surface of the everted lid

• Localized cellulitis, pain, erythema if secondarily infected (internal hordeolum)

Chalazion — Kanski's Clinical Ophthalmology

Diagnostics

1. History: previous chalazia, eyelid lesions, ocular surgery, systemic medications (bortezomib, retinoids), rosacea
2. External examination: palpate eyelid for nodule; inspect for rosacea
3. Slit-lamp examination: evert eyelid — assess meibomian glands for inspissation; look for madarosis, poliosis, ulceration (to exclude malignancy)
4. Differential diagnosis to exclude:
   • Sebaceous gland carcinoma — suspect in older patients with recurrent chalazia in the same position, eyelid thickening, madarosis, or chronic unilateral blepharitis → biopsy
   • Preseptal cellulitis
   • Pyogenic granuloma
5. Rule: All excised chalazia (especially recurrent or atypical) should be sent for histopathology

Treatment

• Warm compresses ≥10 minutes, 4× daily + gentle massage over the lesion
• At least one-third of chalazia resolve spontaneously → observation appropriate if improving

• Topical antibiotic-steroid ointment (e.g., neomycin/polymyxin B/dexamethasone b.i.d. × 1–2 weeks) — for chalazion
• Oral doxycycline 20–50 mg daily–b.i.d. (low-dose, anti-inflammatory) — for multiple or recurrent chalazia, especially with rosacea
• Systemic antibiotics only if significant bacterial infection present

• Triamcinolone acetonide 40 mg/mL diluted 1:1 with 2% lidocaine/epinephrine, 0.2–1.0 mL, 27- or 30-gauge needle
• Success rate ~80% after one injection; second injection possible after 1–2 weeks
• Preferred for marginal lesions or those near the lacrimal punctum
• ⚠️ Risks: skin depigmentation (especially dark-skinned individuals), fat atrophy, rare retinal vascular occlusion — use conjunctival approach to minimize depigmentation risk

1. Local anaesthesia infiltration
2. Eyelid everted with a chalazion clamp
3. Vertical incision through the tarsal plate (conjunctival surface)
4. Contents curetted; solid inflammatory material excised with fine scissors and sent for histopathology
5. No sutures required
6. Topical antibiotic 3× daily for 5 days post-procedure

• Marginal lesions: intralesional steroid, or horizontal incision on conjunctival surface, or vertical incision through the grey line

• Daily lid hygiene regimen (treat underlying blepharitis)
• Systemic tetracycline (long-term, low-dose) for recurrent chalazia with acne rosacea

Comparison Summary

Eyelid Diseases: Blepharitis, Hordeolum (Stye), Chalazion

BLEPHARITIS

Definition

Etiology

Risk Factors

Clinical Features

Diagnostics

• Clinical slit-lamp examination of lid margins and meibomian orifices
• Eyelid eversion: meibomian gland inspissation
• Epilated lash microscopy: Demodex mites/eggs
• Culture if bacterial superinfection suspected
• Exclude sebaceous carcinoma in chronic unilateral blepharitis with madarosis (especially older patients)

Treatment

1. Lid hygiene (cornerstone): warm compresses 5–10 min b.i.d.–q.i.d. + eyelid scrubs (commercial pads or diluted mild shampoo) 2×/day; meibomian gland expression for MGD
2. Topical antibiotics (anterior disease): erythromycin, bacitracin, azithromycin gel, fusidic acid — rubbed onto lid margins at bedtime
3. Oral antibiotics (posterior/MGD or rosacea):
   • Doxycycline 50–100 mg b.i.d. × 1 week → taper to 50 mg daily × 6–24 weeks
   • Azithromycin 500 mg daily × 3 days for 3 cycles (preferred for anterior)
   • Erythromycin 250 mg 1–2×/day (safe in children and pregnancy)
   • ⚠️ Tetracyclines contraindicated <12 years, pregnancy, breastfeeding
4. Topical steroids: fluorometholone 0.1% or loteprednol q.i.d. × 1 week for active inflammation
5. Immunomodulators: cyclosporine 0.05–0.09% or lifitegrast 5% b.i.d.
6. Demodex-specific: tea tree oil (50% scrub + 5% ointment) or terpinen-4-ol 2.5% wipes; oral ivermectin 200 µg/kg × 2 doses 1 week apart; lotilaner 0.25% ophthalmic solution
7. Omega-3 supplements, preservative-free artificial tears, LipiFlow thermal pulsation device (for MGD)

HORDEOLUM ("BARLEY" / STYE)

Definition

• External hordeolum: abscess of the gland of Zeis (sebaceous, at lash base) or Moll's gland — visible at the lid margin
• Internal hordeolum: abscess of the meibomian gland — points toward the conjunctival surface; more deeply seated

Etiology

Risk Factors

Clinical Features

• Rapid onset (hours to days) of painful, tender, erythematous, localized swelling
• External: at the lid margin, often with a visible pointing abscess or pustule
• Internal: within the tarsal plate, palpable tender nodule; conjunctival surface may show yellow spot
• Surrounding lid oedema and erythema
• May drain spontaneously (mucopurulent discharge)
• ⚠️ Can progress to preseptal (periorbital) cellulitis if untreated

Diagnostics

• Clinical diagnosis: history and external examination
• Palpate involved lid; evert eyelid
• Slit-lamp: assess for associated blepharitis/meibomitis
• Culture only if recurrent or cellulitis develops

Treatment

1. Warm compresses ≥10 min, q.i.d. (promotes spontaneous drainage — first-line)
2. Topical antibiotic: bacitracin, tobramycin, or erythromycin ointment b.i.d. × 1–2 weeks
3. If worsening or no resolution: Incision and drainage (I&D)
4. If preseptal cellulitis develops: systemic antibiotics (oral or IV depending on severity)

CHALAZION (Meibomian Cyst)

Definition

Etiology / Pathogenesis

• Obstruction of meibomian duct → stagnant lipid secretions → lipogranulomatous reaction
• Histopathology: extracellular fat deposits surrounded by lipid-laden epithelioid cells, multinucleated giant cells, lymphocytes
• Associated conditions: blepharitis, acne rosacea, seborrhoeic dermatitis
• Drug-associated: bortezomib (proteasome inhibitor) predisposes within 3 months of initiation

Risk Factors

Clinical Features

• Gradual, painless, well-defined, firm, rounded nodule within the tarsal plate
• Upper lid > lower lid
• No acute tenderness; may cause cosmetic deformity or visual blurring if large (induced astigmatism)
• Inspissated secretions visible at gland orifice
• Associated conjunctival granuloma (visible on everted lid)

• Secondarily infected → internal hordeolum: painful, erythematous, tender lid swelling

Chalazion — Kanski's Clinical Ophthalmology

Diagnostics

1. History: previous chalazia, medications (bortezomib, retinoids), rosacea
2. External examination: palpate nodule; inspect for rosacea
3. Slit-lamp + lid eversion: assess meibomian glands, look for madarosis/poliosis/ulceration
4. Differential: preseptal cellulitis, sebaceous carcinoma, pyogenic granuloma, forniceal foreign body
5. ⚠️ Recurrent chalazion in same position in older patient → biopsy to exclude sebaceous gland carcinoma
6. All excised specimens sent for histopathology

Treatment

• Warm compresses ≥10 min q.i.d. + gentle massage
• ~1/3 resolve spontaneously; observation appropriate if improving

• Topical antibiotic-steroid ointment (neomycin/polymyxin B/dexamethasone b.i.d. × 1–2 weeks)
• Oral doxycycline 20–50 mg daily (low-dose anti-inflammatory) for recurrent/multiple chalazia or rosacea

• Triamcinolone acetonide 40 mg/mL diluted 1:1 with 2% lidocaine/epinephrine, 0.2–1.0 mL
• Success ~80% after first injection; repeat at 1–2 weeks if needed
• Preferred for marginal lesions near the lacrimal punctum
• ⚠️ Risks: skin depigmentation (especially dark skin), fat atrophy, rare retinal artery occlusion

• Indications: failed medical therapy + patient request
• Technique: local anaesthesia → eyelid everted with chalazion clamp → vertical incision through tarsal plate (conjunctival surface) → curette contents → no suture → topical antibiotic 3× daily × 5 days
• Send contents for histopathology

• Daily lid hygiene (treats underlying blepharitis)
• Long-term low-dose tetracycline if recurrent chalazia with rosacea

At-a-Glance Comparison