Dry Eye Disease & Conjunctival Disorders

A high-yield cluster spanning the tear film, the lacrimal functional unit and the conjunctiva. Dry eye disease (DED) is one of the commonest reasons patients present to an ophthalmology OPD, and the conjunctival disorders here — from a banal pinguecula to sight-threatening xerophthalmia — are perennial NEET PG MCQ fodder, especially Schirmer's cut-offs and Bitot's spots.

The tear film & lacrimal functional unit

The pre-corneal tear film is classically described as trilaminar, though modern thinking favours a gel-like continuum. From superficial to deep:

Layer	Source	Thickness	Function
Lipid (oily)	Meibomian glands (holocrine)	~0.1 µm	Retards evaporation, stabilises film
Aqueous	Main lacrimal gland (reflex) + accessory glands of Krause & Wolfring (basal)	~7 µm	Bulk volume, oxygen, antibacterials (lysozyme, lactoferrin, IgA)
Mucin	Conjunctival goblet cells + corneal epithelial glycocalyx	~0.8 µm	Converts hydrophobic epithelium to hydrophilic; anchors film

High-yield: The main lacrimal gland supplies reflex tearing; the accessory glands of Krause and Wolfring supply basal secretion. Schirmer's test without anaesthesia measures reflex + basal; with anaesthesia it isolates basal secretion.

The lacrimal functional unit = ocular surface (cornea, conjunctiva, meibomian glands) + lacrimal glands + interconnecting sensory (V1, nasociliary) and autonomic (mainly parasympathetic) nerves. Disruption anywhere drives DED.

Dry eye disease — definition & classification

DED (keratoconjunctivitis sicca) is a multifactorial disease of the ocular surface characterised by loss of tear-film homeostasis, with tear-film instability and hyperosmolarity, ocular surface inflammation/damage and neurosensory abnormalities as the central mechanisms (TFOS DEWS II, 2017 definition). Tear hyperosmolarity and instability form the core vicious cycle.

The DEWS II aetiological classification:

Type	Mechanism	Key examples
Aqueous-deficient	Reduced lacrimal secretion	Sjögren syndrome (primary/secondary), age, lacrimal gland disease, sarcoid, lymphoma, post-radiation, anticholinergic drugs
Evaporative (more common)	Excess tear loss	Meibomian gland dysfunction (MGD) — the leading cause, blepharitis, lagophthalmos, low blink rate (screens), contact lenses, vitamin A deficiency

High-yield: Evaporative dry eye due to MGD is the single commonest cause of DED. Aqueous-deficient + evaporative frequently coexist.

Sjögren syndrome: autoimmune lymphocytic destruction of lacrimal and salivary glands → dry eyes (xerophthalmia) + dry mouth (xerostomia). Primary = isolated; secondary = with another connective tissue disease (rheumatoid arthritis most common, also SLE). Anti-Ro/SSA and anti-La/SSB antibodies; minor salivary gland (labial) biopsy is confirmatory.

Pathophysiology — the vicious cycle

Tear instability / hyperosmolarity → activates stress kinases (MAPK) and NF-κB in epithelium → release of inflammatory cytokines (IL-1, IL-6, TNF-α) and matrix metalloproteinase-9 (MMP-9) → epithelial damage + goblet cell loss → further mucin deficiency → more instability.

Stepwise flow: Reduced/poor-quality tears → tear hyperosmolarity → epithelial stress + inflammation (MMP-9, cytokines) → goblet cell & epithelial loss → tear-film instability → ↑ osmolarity (loop closes).

This self-perpetuating inflammatory loop is why anti-inflammatory therapy (cyclosporine, lifitegrast, short pulse steroids) works, not just lubricants.

Clinical features

• Symptoms: foreign-body/grittiness sensation, burning, redness, fluctuating blurred vision that clears on blinking, photophobia, and — paradoxically — reflex watering/epiphora (cornea irritation triggers reflex tearing).
• Symptoms classically worse in the evening, in air-conditioning, with prolonged screen use, in low-humidity environments.
• Signs: reduced tear meniscus height (<0.2 mm), debris in tear film, punctate epithelial erosions (interpalpebral, inferior cornea), conjunctival staining, filaments (filamentary keratitis in severe cases), MGD signs (capped/inspissated meibomian orifices, frothy lid-margin secretions).

High-yield: Discordance between severe symptoms and minimal signs (or vice versa) is characteristic of DED owing to its neurosensory component.

Diagnosis & investigations

A logical, least-invasive-first order is essential (each test alters the next).

Recommended sequence → Symptom questionnaire (OSDI/DEQ-5) → Tear breakup time → Ocular surface staining → Schirmer's test (most invasive, last).

Tear breakup time (TBUT)

Fluorescein instilled; patient blinks then stares; time to first dry spot (black spot in the green film) is measured at slit lamp with cobalt-blue filter.

High-yield: Normal TBUT > 10 seconds. TBUT < 10 s indicates tear-film instability; < 5 s is markedly abnormal. Non-invasive TBUT (NIBUT) avoids fluorescein artefact.

Schirmer's test (the perennial favourite)

Whatman No. 41 filter paper strip (5 mm × 35 mm), bent end placed at the junction of lateral 1/3 and medial 2/3 of the lower fornix; wetting read at 5 minutes.

Test	What it measures	Normal	Abnormal
Schirmer I (no anaesthesia)	Basal + reflex secretion	> 15 mm / 5 min	< 15 mm; < 5.5 mm = definite dry eye
Schirmer I with anaesthesia (basal)	Basal secretion only	> 10 mm	< 10 mm
Schirmer II	Reflex secretion (nasal mucosa stimulation with cotton bud)	> 15 mm	Tests reflex/lacrimal reserve

High-yield: Remember the numbers — Schirmer's < 5.5 mm in 5 min strongly suggests aqueous-deficient dry eye; normal Schirmer I > 15 mm. A common MCQ stem.

Ocular surface staining

• Fluorescein → stains areas of epithelial loss / disrupted tight junctions (cornea); viewed with cobalt blue.
• Rose bengal → stains devitalised/dead epithelial cells AND mucin-deficient areas that lack a protective mucin coat; classically stains the interpalpebral conjunctiva in a triangular pattern (van Bijsterveld scoring). Note: rose bengal is irritating/stings — instil after anaesthesia.
• Lissamine green → stains devitalised cells like rose bengal but is far better tolerated, hence now preferred.

High-yield: Rose bengal stains dead and degenerate cells and mucin-poor areas; fluorescein stains epithelial defects. This staining distinction is heavily tested.

Other tests

• Tear osmolarity — most objective single test; > 308 mOsm/L suggestive, > 316 mOsm/L diagnostic; inter-eye variability > 8 mOsm/L indicates instability.
• Tear-film MMP-9 (InflammaDry) — point-of-care marker of ocular surface inflammation (positive ≥ 40 ng/mL).
• Meibography for MGD; tear-film lipid layer interferometry.

Management

A stepwise (DEWS II) ladder:

1. Patient education + environment — humidifiers, reduce screen time, conscious blinking, avoid air drafts/fans, omega-3 supplements, lid hygiene + warm compresses (for MGD), review systemic anticholinergics.
2. Ocular lubricants — preservative-free artificial tears for frequent dosing; gels/ointments at night. Avoid benzalkonium chloride (BAK) preservative with frequent use (it is itself surface-toxic).
3. Anti-inflammatory — topical ciclosporin 0.05% (DOC for chronic moderate DED — restores tear production, reduces inflammation), lifitegrast 5% (LFA-1 antagonist), short pulse of topical steroids for flares, topical autologous serum for severe cases.
4. Tear conservation — punctal plugs / punctal occlusion (silicone plugs first, then cautery) to retain tears.
5. Severe/refractory — secretagogues (oral pilocarpine for Sjögren), therapeutic/scleral contact lenses, amniotic membrane, tarsorrhaphy.

High-yield: Topical ciclosporin (0.05%) is the drug of choice for chronic moderate-to-severe DED — it targets the underlying inflammatory loop. Punctal occlusion conserves tears in aqueous-deficient DED.

For MGD specifically: warm compresses + lid massage + lid hygiene ± oral doxycycline/azithromycin (anti-inflammatory + improves meibum quality) and omega-3.

Complications of DED

Filamentary keratitis, persistent epithelial defects, corneal melting/ulceration and perforation (severe Sjögren), microbial keratitis, corneal scarring/neovascularisation, and chronic visual disability.

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Conjunctival degenerations & disorders

Pinguecula

A yellowish-white, triangular, elevated subepithelial nodule on the bulbar conjunctiva, typically on the nasal side, not crossing the limbus. Histology: elastotic degeneration of subepithelial collagen (basophilic, hyalinised). Due to chronic UV/dust/wind exposure. Usually asymptomatic → reassurance; excise only if cosmetically/recurrently inflamed (pingueculitis).

Pterygium

A triangular fibrovascular wing of conjunctiva that DOES encroach onto the cornea (the key difference from pinguecula), again nasal > temporal, related to UV exposure (think tropical/outdoor workers — "surfer's/farmer's eye").

Feature	Pinguecula	Pterygium
Crosses limbus onto cornea?	No	Yes
Shape	Nodular, raised	Triangular wing
Site	Nasal bulbar conjunctiva	Nasal (mostly)
Vision threat	Nil	Yes (astigmatism, axis encroachment)
Treatment	Observe	Excision + conjunctival autograft (lowest recurrence)

High-yield: Pinguecula does NOT cross the limbus; pterygium DOES. Pterygium parts = cap (Fuchs' islets) → head → neck → body; Stocker's line = iron deposit at the advancing head.

Concretions

Hard yellow-white deposits in the palpebral conjunctiva (epithelial debris + mucin in degenerated crypts), common in elderly/chronic conjunctivitis; cause foreign-body sensation → removed with a needle.

Symblepharon

Adhesion between the palpebral conjunctiva of the lid and the bulbar conjunctiva (or cornea), caused by raw, denuded surfaces healing together.

• Causes: chemical burns (especially alkali — worse than acid as alkali penetrates deeper), Stevens-Johnson syndrome / toxic epidermal necrolysis, ocular cicatricial pemphigoid, trachoma, thermal burns, surgery.
• Types: anterior, posterior, total. Complications: restricted ocular motility (diplopia), lagophthalmos, exposure, cosmetic disfigurement.
• Management: prevention is key — in chemical burns, sweep the fornices with a glass rod and use symblepharon ring; established cases need surgical division + amniotic membrane/mucous membrane graft.

High-yield: Alkali burns are more dangerous than acid burns (liquefactive necrosis, deeper penetration) and a leading cause of symblepharon. First aid for any ocular chemical burn = copious immediate irrigation before anything else.

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Xerophthalmia & Vitamin A deficiency

Vitamin A (retinol) is essential for conjunctival/corneal epithelial integrity and goblet cell maintenance (and for rhodopsin in rods). Deficiency → xerophthalmia, the leading cause of preventable childhood blindness in developing countries. A favourite NEET PG and community-medicine overlap topic.

WHO classification of xerophthalmia

Code	Sign	Note
XN	Night blindness (nyctalopia)	Earliest symptom
X1A	Conjunctival xerosis	Dry, non-wettable conjunctiva
X1B	Bitot's spot	Triangular foamy/cheesy patch (interpalpebral, temporal bulbar conjunctiva)
X2	Corneal xerosis	Hazy, dry, lustreless cornea
X3A	Corneal ulceration/keratomalacia < 1/3 cornea
X3B	Keratomalacia ≥ 1/3 cornea	Liquefactive corneal necrosis
XS	Corneal scar
XF	Xerophthalmic fundus	Retinal changes

High-yield: Bitot's spot = triangular, foamy/silvery-white patch on the temporal interpalpebral bulbar conjunctiva, made of keratinised epithelium + saprophytic bacilli (Corynebacterium xerosis) + gas. Bitot's spots in young children indicate active vit A deficiency; in older children/adults they may be inactive residue.

High-yield: Night blindness (XN) is the EARLIEST sign; keratomalacia (X3B) is the most severe/blinding. Bitot's spot is X1B.

Treatment (WHO/IAP vitamin A schedule)

High-dose oral vitamin A:

• Age > 1 year: 2,00,000 IU orally on Day 1, Day 2, and Day 14.
• Age 6–12 months: 1,00,000 IU; < 6 months: 50,000 IU (same 3-dose schedule).

Prophylaxis (Indian National Programme): 1,00,000 IU at 9 months (with measles vaccine), then 2,00,000 IU every 6 months up to 5 years (total 9 doses).

High-yield: Memorise 2,00,000 IU on days 1, 2 and 14 for therapeutic vitamin A in a child > 1 year. Keratomalacia is an ophthalmic emergency — treat empirically without waiting for confirmation.

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Key differentials

• Watering eye: DED (reflex) vs nasolacrimal duct obstruction (true epiphora — do regurgitation/syringing test; ROPLAS positive in dacryocystitis) vs trichiasis/entropion.
• Red gritty eye: DED vs blepharitis (lid margin involvement) vs allergic conjunctivitis (itch, papillae) vs infective conjunctivitis (discharge).
• White conjunctival lesion: pinguecula vs pterygium vs Bitot's spot vs conjunctival intraepithelial neoplasia/limbal dermoid (consider in atypical/unilateral lesions).
• Filamentary keratitis: DED vs superior limbic keratoconjunctivitis vs recurrent erosion.

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Recently asked / exam angle

• Schirmer's test cut-off: "Normal value of Schirmer I" → > 15 mm in 5 min; abnormal < 5.5 mm. Strip length 35 mm placed in lower fornix.
• TBUT normal → > 10 seconds; tests tear-film stability.
• Rose bengal stains → dead/devitalised epithelial cells and mucin-deficient areas (vs fluorescein → epithelial defects).
• Earliest sign of vitamin A deficiency → night blindness; Bitot's spot = X1B, located on temporal bulbar conjunctiva.
• Vitamin A therapeutic dose in child >1 yr → 2,00,000 IU on days 1, 2, 14.
• Pinguecula vs pterygium → only pterygium crosses the limbus; pinguecula shows elastotic degeneration.
• Commonest cause of dry eye → MGD/evaporative.
• DOC for chronic dry eye → topical ciclosporin 0.05%.
• Sjögren antibodies → anti-Ro (SSA) / anti-La (SSB).
• Stocker's line associated with pterygium; Fuchs' islets in the cap.
• Symblepharon classically follows alkali chemical burns / SJS / ocular cicatricial pemphigoid.

Rapid revision

1. Tear film: lipid (meibomian) → aqueous (lacrimal) → mucin (goblet cells); mucin makes the surface wettable.
2. Accessory glands (Krause, Wolfring) = basal secretion; main lacrimal gland = reflex.
3. Schirmer I normal > 15 mm/5 min; < 5.5 mm = dry eye; with anaesthesia (basal) normal > 10 mm.
4. TBUT > 10 s normal; < 10 s = unstable tear film.
5. Fluorescein stains epithelial defects; rose bengal/lissamine green stain dead cells & mucin-poor areas (lissamine better tolerated).
6. Evaporative/MGD is the commonest dry eye; topical ciclosporin 0.05% is DOC for chronic DED; punctal plugs conserve tears.
7. Core DED mechanism = tear hyperosmolarity + instability → inflammation (MMP-9).
8. Pinguecula does NOT cross limbus (elastotic degeneration); pterygium DOES — treat with excision + conjunctival autograft.
9. Symblepharon = lid-to-globe adhesion; commonest after alkali burns/SJS/pemphigoid; prevent with symblepharon ring.
10. Night blindness = earliest vit A deficiency sign; keratomalacia = most severe; Bitot's spot (X1B) on temporal conjunctiva.
11. Vitamin A therapeutic: 2,00,000 IU on days 1, 2, 14 (>1 yr); prophylaxis 2,00,000 IU 6-monthly to age 5.
12. Sjögren = dry eye + dry mouth; anti-Ro/anti-La, labial salivary gland biopsy confirms; pilocarpine for secretagogue effect.