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Dry eye disease (DED) is one of the most prevalent ocular conditions encountered in clinical practice, affecting an estimated 16 million Americans with diagnosed disease and many millions more with undiagnosed symptoms. For the COA, dry eye management is a daily encounter -- patients present with burning, grittiness, redness, blurred vision, and tearing (paradoxically, reflex tearing can occur with dry eye). Mastery of DED diagnostics is high-yield for both the COA exam and real-world practice.
The 2017 TFOS DEWS II (Tear Film and Ocular Surface Society Dry Eye Workshop II) report is the current evidence-based framework for understanding, diagnosing, and managing DED. Its definition: "Dry eye is a multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film, accompanied by ocular symptoms, in which tear film instability and hyperosmolarity, ocular surface inflammation, and neurosensory abnormalities play etiological roles."
This guide covers the TFOS DEWS II classification (aqueous deficient vs. evaporative), all major diagnostic tests (TBUT, Schirmer, vital staining), questionnaire scoring (SPEED, OSDI), slit-lamp findings, meibomian gland dysfunction (MGD) and meibography, and the stepwise treatment pyramid the COA should know to support patient education.
Insufficient tear production from the lacrimal gland. Low tear volume and low tear meniscus height.
Normal aqueous production but excessive evaporation from inadequate lipid layer. Most common form (~65-80% of DED cases).
Symptoms vs. Signs Discordance
A hallmark finding in dry eye disease is that symptoms and clinical signs often do not correlate well. A patient with severely symptomatic dry eye (high OSDI score) may have minimally abnormal tests, while a patient with significant corneal staining may report few symptoms. This discordance is recognized in TFOS DEWS II -- diagnosis requires either symptoms OR signs (or both). The COA should document both independently without assuming one will parallel the other.
Procedure
Interpretation
Most sensitive test for evaporative DED. Avoid excess fluorescein (dilutes tear film, artifactually lengthens TBUT).
Procedure (Schirmer I)
Interpretation
Perform TBUT BEFORE Schirmer (Schirmer strips disrupt the tear film). Both eyes tested simultaneously.
Fluorescein
Rose Bengal
Lissamine Green
Standard Patient Evaluation of Eye Dryness -- 8 questions on symptom frequency and severity.
Quick, practical for routine screening at check-in. Tracks changes over time with treatment.
Ocular Surface Disease Index -- 12 questions on ocular symptoms, visual function, and triggers.
Widely used in clinical trials; more comprehensive but takes ~5 minutes. Gold standard PRO measure.
MGD is the most common cause of dry eye disease worldwide and a primary reason why TBUT is low even in patients with normal Schirmer values. Understanding MGD is essential for the COA because assessment of the meibomian glands is now a routine part of the dry eye workup.
Opterio's COA practice questions cover TFOS DEWS II classification, diagnostic testing values, MGD, and questionnaire scoring with AI explanations.
Meibomian glands (tarsal glands) are elongated sebaceous glands running vertically within the tarsal plate. Upper lid: approximately 25-30 glands. Lower lid: approximately 20-25 glands. Each gland secretes meibum (a complex lipid mixture) through an orifice at the posterior lid margin. Meibum forms the outermost lipid layer of the tear film, retarding evaporation and stabilizing the tear film. Meibomian gland orifices are visible on slit-lamp examination along the posterior lid margin (the grey line = mucocutaneous junction marks the anterior border of the gland orifices).
Slit-Lamp Lid Margin Findings
Gland Expression
Meibography is infrared imaging of the meibomian gland structure within the everted eyelid. Modern instruments (Oculus Keratograph, LipiView, Topcon Maestro) allow non-contact meibography with automated gland area analysis. Images show the gland acini and ducts as bright structures against a dark background. Gland loss (dropout) appears as dark areas where gland tissue should be. The meibography grade is typically a 0-3 scale: 0 = no gland loss; 1 = <1/3 gland area lost; 2 = 1/3 to 2/3 lost; 3 = >2/3 gland area lost. Progressive gland loss correlates with more severe MGD and evaporative DED. Meibography is increasingly standard-of-care in comprehensive dry eye evaluations.
| Finding | Significance | Assessment Method |
|---|---|---|
| Tear meniscus height (TMH) | Low (<0.20mm) suggests reduced aqueous production (ADDE) | Slit-beam 0.1mm height comparison; keratograph quantification |
| Corneal fluorescein staining | Inferior 1/3 pattern = classic DED; superior = exposure / lagophthalmos | Cobalt blue illumination; Oxford staining scale 0-5 |
| Conjunctival staining (fluorescein/lissamine) | Nasal/temporal interpalpebral = DED; superior = superior limbic keratoconjunctivitis (SLK) | Broad beam illumination; Van Bijsterveld scale |
| 3,9 o'clock staining | Fluorescein staining at 3 and 9 o'clock positions = soft contact lens-related DED | Cobalt blue filter; look at lens-bearing area |
| Bulbar conjunctival redness | Graded 0-4 (Efron scale); increased redness correlates with inflammation | Slit-lamp direct illumination; standardized grading scale |
| Mucous filaments/strands | Filamentary keratitis -- mucus anchored to corneal epithelium, severe DED | Direct illumination; fluorescein staining highlights filaments |
The TFOS DEWS II treatment pyramid organizes management stepwise from first-line conservative therapy to advanced interventions. The COA should understand this framework to support patient education and recognize which stage a patient is at in their management journey.
Step 1: Education and Lifestyle Modifications
Environmental modifications (humidifier, reduced screen time, blink exercises), dietary omega-3 supplementation (fish oil), elimination of offending systemic medications where possible, eyelid hygiene and warm compresses for MGD, over-the-counter lubricant eye drops (preservative-free preferred for frequent use).
Step 2: Prescription Treatments
Topical anti-inflammatory agents: cyclosporine A 0.05% (Restasis, Cequa) and lifitegrast 5% (Xiidra) -- both target T-cell-mediated ocular surface inflammation. Short-term topical corticosteroids (loteprednol, fluorometholone) for inflammatory flares. Punctal plugs (temporary collagen or permanent silicone) to reduce tear drainage and increase tear volume. Oral doxycycline for meibomian gland dysfunction (anti-inflammatory, not antibiotic effect).
Step 3: In-Office Procedures
Intense pulsed light (IPL) therapy for MGD -- light energy applied to periocular skin triggers meibomian gland function improvement and reduces inflammation. LipiFlow thermal pulsation -- applies vectored thermal pulse to the inner eyelid surface to liquefy and express meibomian gland content. Both are effective for evaporative DED secondary to MGD.
Step 4: Advanced Options
Autologous serum eye drops (patient's own blood serum processed as drops -- contains growth factors, vitamins) for severe, refractory DED. Scleral contact lenses (large-diameter GP lenses that vault over the cornea and rest on the conjunctiva -- maintain a fluid reservoir, protecting the ocular surface) for severe DED with or without ocular surface disease. Surgical lid procedures (tarsorrhaphy, amniotic membrane transplant) for the most severe cases.
Illumination techniques and anterior segment examination skills for the COA exam.
Corneal diseases, conjunctivitis types, and anterior chamber findings for COA candidates.
Five-layer corneal anatomy and the relevance of each layer to clinical examination.
Full domain breakdown, study timeline, and practice strategies for the COA exam.
The TFOS DEWS II (2017) classification divides dry eye disease (DED) into two etiologic categories. Aqueous-deficient dry eye (ADDE): insufficient tear production from the lacrimal gland. The most common cause is Sjogren's syndrome (primary: autoimmune disease affecting lacrimal and salivary glands; secondary: associated with rheumatoid arthritis or lupus). Other causes: lacrimal gland ablation, radiation, systemic medications (antihistamines, antidepressants, isotretinoin). Characterized by low Schirmer values and low tear meniscus. Evaporative dry eye (EDE): normal lacrimal gland production but excessive evaporation from the tear film. The most common cause by far is meibomian gland dysfunction (MGD), where the meibomian glands produce inadequate or poor-quality lipid layer, allowing rapid tear evaporation. EDE accounts for the majority (~65-80%) of all dry eye. These categories can coexist (mixed mechanism DED).
Tear break-up time (TBUT or BUT) measures the stability of the tear film by recording the time between a complete blink and the first appearance of a dry spot or dark area in the fluorescein-stained tear film. Normal TBUT is greater than 10 seconds. TBUT under 10 seconds is abnormal; under 5 seconds is significantly abnormal. Procedure: instill a small amount of preservative-free fluorescein (or a wetted fluorescein strip -- avoid excess liquid to minimize dilution artifact). Ask the patient to blink once, then keep the eye open. Use the cobalt blue filter on the slit lamp (broad illumination). Time from last blink to first break in the fluorescein-stained tear film. Record the first break time. Repeat 3 times and average. Non-invasive TBUT (NIBUT) using instruments like the Oculus Keratograph avoids fluorescein and is increasingly used in research.
The Schirmer test measures aqueous tear production using calibrated filter paper strips placed in the inferior fornix. Two versions: Schirmer I (without anesthesia) tests basal and reflex secretion -- strip placed at the junction of the medial and middle thirds of the lower eyelid; patient closes eyes gently for 5 minutes; measure the length of wetting. Normal: ≥10mm of wetting in 5 minutes. Schirmer I with anesthesia (Schirmer II or "basic secretion test") uses topical anesthetic before placing the strip, suppressing reflex secretion to measure only basal secretion. Normal ≥6mm/5 min with anesthesia. A value of ≤5mm in 5 minutes is significantly abnormal and suggests aqueous deficiency. Schirmer values correlate better with severe dry eye than mild-moderate disease. Both eyes are usually tested simultaneously for comparison.
Meibomian gland dysfunction (MGD) is the most common cause of evaporative dry eye and the most common cause of dry eye disease overall. Meibomian glands are sebaceous glands in the tarsal plates of the upper and lower eyelids (approximately 25-30 in the upper lid, 20-25 in the lower lid) that secrete meibum -- the lipid component of the tear film. Meibum prevents evaporation and maintains tear film stability. In MGD, the gland orifices become obstructed, the meibum quality degrades (becomes more solid and waxy), and the lipid layer is insufficient. The TBUT is shortened because the lipid layer does not prevent evaporation. MGD can be diagnosed clinically by gland expression (firm, thickened, or absent secretion on pressure), by slit-lamp examination of the lid margins (capping, notching, vascularity, meibomian gland orifice plugging), and by meibography (imaging of the gland structure). Treatment includes warm compresses, lid hygiene, omega-3 fatty acids, intense pulsed light (IPL), and LipiFlow thermal pulsation.
SPEED (Standard Patient Evaluation of Eye Dryness) and OSDI (Ocular Surface Disease Index) are validated patient-reported outcome measures used to assess DED symptom severity. SPEED questionnaire: 8 questions assessing dryness, grittiness, scratchiness, and burning at different times of day. Score range: 0-28. Score ≥6 suggests symptomatic dry eye; ≥10 is significant. Quick to administer (2-3 minutes). OSDI questionnaire: 12 questions covering ocular symptoms, vision-related function, and environmental triggers. Score range: 0-100 (0=no disability, 100=complete disability). Interpretation: 0-12 = normal; 13-22 = mild DED; 23-32 = moderate DED; 33-100 = severe DED. The OSDI is one of the most widely used and validated DED questionnaires in clinical trials. Important COA note: there is a well-documented discordance in dry eye between symptoms (high SPEED/OSDI) and signs (normal or near-normal TBUT, Schirmer) -- the TFOS DEWS II framework explicitly acknowledges this mismatch and defines DED based on the presence of either symptoms OR signs.