---

Tear Film Instability - Comprehensive MS Ophthalmology Examination Notes

---

1. DEFINITIONS

"Dry eye disease is a multifactorial disease of the ocular surface and tear film accompanied by increased osmolarity of the tear film and inflammation of the ocular surface." - Kanski's Clinical Ophthalmology, 10th ed.

---

2. TEAR FILM PHYSIOLOGY

2.1 Three-Layer Structure

• Outer lipid: polar phase (phospholipids adjacent to aqueous-mucin) + non-polar phase (waxes, cholesterol esters, triglycerides)
• Polar lipids bound to lipocalins (small secretory proteins) within the aqueous layer
• Lid movement during blinking releases lipids from glands
• Deficiency → evaporative dry eye

• Mucins are high-molecular-weight glycoproteins: transmembrane or secretory (gel-forming / soluble)
• Rose Bengal staining of diseased epithelium indicates absence of transmembrane and gel mucous layers
• Goblet cell loss occurs with cicatrizing conjunctivitis, vitamin A deficiency, chemical burns, medication toxicity

2.2 Tear Film Spread

1. Normal blink reflex
2. Contact between external ocular surface and eyelids
3. Normal corneal epithelium

2.3 Hormonal Regulation

• Androgens: prime hormones for regulation of lipid production
• Oestrogens and progesterone receptors in conjunctiva and lacrimal glands
• Neural fibres adjacent to lacrimal glands and goblet cells stimulate aqueous and mucus secretion

---

3. PATHOPHYSIOLOGY / MECHANISM OF DISEASE

Tear Instability
      ↓
Tear Hyperosmolarity ←→ Inflammation ←→ Ocular Surface Damage
      ↑_________________________________↑

• Inflammation in conjunctiva and accessory glands is present in 80% of KCS patients and may be both a cause AND consequence of dry eye (self-perpetuating cycle)
• Strong association between dry eye syndrome and reduced levels of systemic androsterone sulphate and epiandrosterone sulphate
• Tear instability → exposure of ocular surface epithelium → release of inflammatory mediators (IL-1, TNF-α) → T-cell mediated inflammation → goblet cell and epithelial damage → worsens instability

---

4. CLASSIFICATION

Primary Classification

DRY EYE DISEASE
├── AQUEOUS-DEFICIENT
│   ├── Sjögren syndrome dry eye (primary or secondary)
│   └── Non-Sjögren syndrome dry eye
│       ├── Lacrimal deficiency (primary or secondary)
│       ├── Lacrimal gland duct obstruction
│       └── Reflex hyposecretion
└── EVAPORATIVE
    ├── Intrinsic (meibomian gland dysfunction, blink-related)
    └── Extrinsic (vitamin A deficiency, contact lens, medication)

4.1 Aqueous-Deficient Dry Eye

• Primary (sicca complex: dry eyes + dry mouth)
• Secondary (associated with RA, SLE, other connective tissue disease)

• Primary: age-related dry eye, congenital alacrima, familial dysautonomia
• Secondary lacrimal deficiency: inflammatory/neoplastic lacrimal gland infiltration, AIDS, graft-versus-host disease, lacrimal gland/nerve ablation
• Lacrimal duct obstruction: trachoma, cicatricial pemphigoid, chemical injury, Stevens-Johnson syndrome
• Reflex hyposecretion - sensory block: contact lens wear, diabetes, refractive surgery, neurotrophic keratitis
• Reflex hyposecretion - motor block: CN VII damage, systemic drugs

4.2 Evaporative Dry Eye

• Meibomian gland dysfunction (MGD) - most common cause of evaporative dry eye
• Lid-related: low blink rate (prolonged computer use), incomplete blink, lid aperture disorders
• Drug-related (systemic retinoids reduce meibomian gland function)

• Vitamin A deficiency (goblet cell loss)
• Contact lens wear
• Ocular surface disease (allergy, preservative toxicity)

---

5. SYMPTOMS

• Burning, stinging, dryness
• Foreign body / gritty sensation
• Itching
• Excess tearing (paradoxical reflex tearing)
• Mildly to moderately decreased / fluctuating vision
• Eye fatigue

• Aqueous deficiency: symptoms worse later in the day
• Evaporative (MGD): symptoms worse in the morning

---

6. CLINICAL SIGNS (DYNAMIC FEATURES)

6.1 Tear Meniscus

• Normal inferior tear meniscus: at least 0.5 mm in height with a convex shape
• Dry eye: scanty, concave, or absent tear meniscus
• Evaluate before instillation of any drops

6.2 Tear Film Break-up (Dynamic Assessment)

• Measure time from complete blink to first appearance of a dark spot (dry area) in the tear film
• Normal TBUT: >10 seconds
• Abnormal: <10 seconds (indicates tear film instability)
• Caution: Tear film defects must be randomly located - isolated early break-up at the same spot may indicate a focal corneal surface irregularity

6.3 Corneal and Conjunctival Staining

• Interpalpebral (cornea + conjunctiva): aqueous tear deficiency
• Superior conjunctival: superior limbic keratoconjunctivitis
• Inferior corneal + conjunctival: blepharitis or exposure keratopathy

6.4 Other Slit-Lamp Signs

• Mucous debris in tear film (Fig. 5.5A)
• Excess mucus threads or filaments on cornea (severe cases)
• Punctate corneal epithelial erosions (interpalpebral zone)
• Corneal filaments: degenerated epithelial cells + mucus core adherent to corneal surface (filamentary keratitis)
• Mucous plaque formation (severe)

6.5 Severe Corneal Complications

• Corneal melting (keratolysis)
• Corneal perforation with iris plugging
• Secondary bacterial infection

---

7. DIAGNOSIS

7.1 Diagnostic Tests (Order of Performance)

A. Tear Film Break-Up Time (TBUT) - Primary Dynamic Test

1. Instill fluorescein (strip or drop)
2. Ask patient to blink 2-3 times, then hold gaze
3. With cobalt blue illumination and wide slit beam, observe for first black spot / dry area
4. Measure time in seconds (repeat 3x, take average)

• 10 sec: Normal

• 5-10 sec: Borderline / mild instability
• <5 sec: Significant instability

"Less than 10 seconds indicates tear film instability." - Wills Eye Manual

B. Schirmer Tests

Wills Eye Manual: Anesthetized method preferred (less irritating); <10 mm may be borderline; ≤5 mm is abnormal.

C. Phenol Red Thread (PRT) Test

• Thread impregnated with pH-sensitive dye
• Placed over lower lid for 15 seconds
• Dye changes from yellow to red in tears
• Abnormal: ≤6 mm
• Comparable to Schirmer but faster; less reflex stimulation

D. Tear Osmolarity

• Emerging as accurate diagnostic measure
• Normal threshold: 308 mOsm/L (widely accepted)
• 316 mOsm/L distinguishes mild from moderate/severe dry eye
• Range of abnormality: 305-316 mOsm/L depending on degree of tear film instability
• Correlates with treatment response long-term

E. Vital Dye Staining (Rose Bengal / Lissamine Green / Fluorescein)

• van Bijsterveld score for rose Bengal staining (0-9 scale)
• Score >3.5: significant staining

F. Tear Constituent Measurement

• MMP-9 (matrix metalloproteinase-9): elevated in dry eye - tested with InflammaDry point-of-care device (positive if ≥40 ng/mL)
• Lactoferrin: decreased in aqueous-deficient dry eye
• Provides objective biomarker evidence

G. Other Tests (Rarely Clinical)

• Fluorescein clearance test / Tear function index: assesses delayed clearance in all dry eye states
• Tear meniscometry: quantifies volume of lower lid meniscus
• Impression cytology: determines goblet cell numbers
• Meibography: infrared imaging of meibomian glands - shows gland atrophy in MGD

7.2 DEWS II Diagnostic Algorithm (2017 Update)

STEP 1: Triaging questionnaire (OSDI/SPEED) + risk factors
         ↓
STEP 2: Homeostasis markers:
    - TBUT
    - Ocular surface staining (fluorescein/lissamine green)
    - Symptom questionnaire
         ↓
STEP 3 (if positive): Etiologic subclassification
    - Aqueous deficient? → Schirmer test
    - Evaporative? → Meibomian gland assessment, LIPCOF, lipid layer thickness
         ↓
STEP 4: Contributing factors assessment
    (lid margin, meibomian glands, conjunctival chalasis, nasolacrimal obstruction)

---

8. SEVERITY GRADING (DEWS)

---

9. MANAGEMENT

9.1 DEWS Treatment Levels (Step-Up Approach)

LEVEL 1 (Mild Dry Eye)

• Education and environmental/dietary modifications:
  • Realistic expectations; compliance emphasis
  • Blink exercises during screen use
  • Screen below eye level (minimizes palpebral aperture)
  • Increase humidity; avoid fans/drafts
  • Omega-3 fatty acid supplementation (flaxseed oil, fish oil)
• Artificial tear substitutes (preserved, QID):
  • Cellulose derivatives (hypromellose, methylcellulose): mild cases
  • Carbomer gels: longer-lasting
  • PVA (polyvinyl alcohol): mucin deficiency
  • Sodium hyaluronate, povidone, glycerine, propylene glycol, polysorbate
  • Diquafosol: topical secretagogue (newer agent)
• Eyelid therapy: warm compresses + lid hygiene for blepharitis/MGD
• Contact lens modification / discontinuation if symptomatic

LEVEL 2 (Moderate Dry Eye)

• Non-preserved tear substitutes (frequency >QID)
• Anti-inflammatory therapy (key for this level):
  • Cyclosporine 0.05% or 0.09% b.i.d. (e.g., Restasis, Cequa): effective for chronic dry eye with decreased tears secondary to ocular inflammation; takes 1-3 months for significant improvement; burns on instillation initially; consider concurrent mild topical steroid for first month
  • Lifitegrast 5% b.i.d. (Xiidra): LFA-1 antagonist; symptomatic improvement may occur within 2 weeks; causes burning, transient blurred vision, metallic taste
  • Topical corticosteroids (short course): loteprednol 0.5%, fluorometholone 0.1% - used as bridge therapy
  • Oral omega-3 fatty acids
• Tetracyclines (doxycycline 100 mg OD): for meibomianitis, rosacea (anti-inflammatory + antimicrobial)
• Punctal plugs (temporary collagen or permanent silicone):
  • Lower puncta first; add upper puncta if needed
  • Contraindicated in active lid/conjunctival inflammation
• Secretagogues: pilocarpine, cevimeline, rebamipide
• Moisture chamber spectacles / sidearm shields

LEVEL 3 (Severe Dry Eye)

• Autologous serum eye drops (20-100%): contains growth factors, vitamins, anti-inflammatory mediators; lacks preservatives; refrigerated storage
• Umbilical cord serum drops: similar to autologous, more available
• Bandage soft contact lens or scleral lens (fluid reservoir over cornea)
• Permanent punctal occlusion (thermal cautery)
• Filament removal with forceps + 10% N-acetylcysteine QID for filamentary keratitis
• Vitamin A topical drops

LEVEL 4 (Very Severe / Refractory)

• Systemic anti-inflammatory agents: hydroxychloroquine, immunosuppressants (for Sjögren syndrome)
• Surgery:
  • Tarsorrhaphy (lateral, partial/complete): reduces palpebral aperture, decreases evaporation - permanent or temporary adhesive tape
  • Salivary gland auto-transplantation
  • Mucous membrane transplantation for severe conjunctival disease
  • Amniotic membrane transplantation for corneal complications (perforation/melting)
  • Moisture chamber goggles with humidification

9.2 Artificial Tear Formulations

Important: Use preservative-free formulations if dosing >QID to prevent preservative toxicity (benzalkonium chloride toxicity)

---

10. SPECIAL SITUATIONS

Post-LASIK / Post-Refractive Surgery Dry Eye

• Dry eye and tear film instability: commonest side effects of LASIK, occurring in up to 70% of patients
• Usually improve spontaneously with time
• Mechanism: disruption of corneal subbasal nerve plexus → reflex hyposecretion
• SMILE (small incision lenticule extraction) has lower incidence than LASIK due to smaller corneal nerve disruption

Sjögren Syndrome

• Increased incidence of lymphoma (50x baseline) - monitor
• Requires multidisciplinary follow-up: internal medicine, rheumatology, dental, gynecology
• Systemic immunomodulatory therapy (hydroxychloroquine) may help
• Increased risk with connective tissue diseases: RA (30%), SLE, primary biliary cirrhosis

Drug-Induced Dry Eye (Causes to Know for Examination)

---

11. RECENT UPDATES (2023-2026)

11.1 Gut-Eye Axis in Dry Eye Disease

11.2 Botulinum Toxin A in Dry Eye

11.3 NLRP3 Inflammasome as Therapeutic Target

11.4 Punctal Plugs - Updated Evidence

11.5 Exosome-Based Therapy (Emerging)

11.6 DEWS II (2017) Key Updates (Still Current Standard)

• New definition emphasizes tear film homeostasis as central concept
• Added neurosensory abnormalities as a recognized component
• Introduced TFOS DEWS II Diagnostic Methodology Report with stepwise approach
• Validated OSDI and SPEED questionnaires as standard patient-reported outcome measures
• Recognized noninvasive TBUT (NITBUT) using Keratograph/topographers as gold standard to avoid fluorescein interference

---

12. HIGH-YIELD EXAMINATION POINTS

---

13. DIFFERENTIAL DIAGNOSIS

---

• Kanski's Clinical Ophthalmology: A Systematic Approach, 10th Edition (Chapter 5, pp. 173-182)
• Wills Eye Manual, 7th Edition (Section 4.3, pp. 171-176)
• Goodman & Gilman's Pharmacological Basis of Therapeutics, 14th Edition (Chapter on Treatment of Dry Eye)
• TFOS DEWS II Report 2017 (The Ocular Surface)
• PubMed: Recent meta-analyses and systematic reviews (2024-2026) as cited aboveThese are your complete, exam-ready MS Ophthalmology notes on tear film instability. Here is a brief summary of what's covered:

---

1. Definitions - DED, KCS, xerophthalmia, xerosis, Sjögren syndrome
2. Physiology - Three-layer tear film structure with textbook diagram (Kanski Fig 5.1), lipid/aqueous/mucous layer composition, spread mechanisms, hormonal regulation
3. Pathophysiology - The four-core-mechanism cycle (tear instability → hyperosmolarity ↔ inflammation ↔ ocular surface damage)
4. Classification - DEWS 2007 aqueous-deficient vs evaporative with full sub-classification tree
5. Symptoms - Pattern differences between aqueous-deficient and evaporative subtypes
6. Dynamic Clinical Features - Tear meniscus assessment, TBUT with technique and interpretation, vital dye staining patterns (fluorescein/rose Bengal/lissamine green), filamentary keratitis, severe complications - all with clinical photographs from Kanski
7. Diagnosis - Complete technique for TBUT, Schirmer I/II, phenol red thread test, tear osmolarity, MMP-9 (InflammaDry), DEWS II diagnostic algorithm
8. Severity Grading - DEWS grade 1-4 table with all parameters
9. Management - DEWS four-level step-up approach with specific drugs, doses, and mechanisms
10. Recent Updates (2024-2026) - Gut-eye axis, NLRP3 inflammasome, botulinum toxin, punctal plug meta-analyses, exosome therapy
11. High-yield table for rapid examination revision