Definition & Pathophysiology
Mucus fishing syndrome (MFS) is a behavioral-ocular disorder characterized by repetitive, voluntary removal of filamentous mucus strands from the ocular surface—typically using fingers, cotton swabs, or other tools—despite lack of clinical indication. Though not an organic disease per se, MFS represents a maladaptive habit that perpetuates ocular surface inflammation and mucin hypersecretion via a self-sustaining cycle: mucus production → mechanical irritation from extraction → further inflammation → increased mucin secretion. This positive feedback loop results in chronic discomfort, visual blurring, and potential corneal epithelial disruption.

Epidemiology & Clinical Relevance
MFS is increasingly recognized, particularly among patients with pre-existing ocular surface disease (OSD), contact lens overuse, or psychiatric comorbidities such as body-focused repetitive behaviors (BFRBs) and obsessive-compulsive disorder (OCD). While exact prevalence is unknown, retrospective case series suggest a rising incidence in tertiary dry eye clinics (~3–7% of refractory OSD cases) (Stern et al., Cornea 2022;41:1549–1555). It most commonly affects adults aged 20–50 years and is often misdiagnosed as chronic bacterial conjunctivitis or “sticky eye” without recognizing the behavioral driver.

Pathogenesis: Why Mucus Forms & How Fishing Perpetuates It

The ocular surface is maintained by a tri-layered tear film (lipid, aqueous, mucin). The mucin layer, primarily secreted by conjunctival goblet cells and epithelial transmembrane mucins (e.g., MUC1, MUC4, MUC16), ensures:

• Homogeneous tear spreading
• Epithelial adhesion
• Protection against pathogens and desiccation
  (Dartt et al., Prog Retin Eye Res 2023;94:101156)

In response to surface irritation (e.g., dryness, allergens, pollutants), conjunctival goblet cells undergo Ca²⁺-dependent exocytosis, releasing stored mucins and upregulating MUC5AC gene expression (Hao et al., Invest Ophthalmol Vis Sci 2021;62:32). Mechanical removal of mucus:

• Activates trigeminal nerve endings → reflex neurogenic inflammation
• Stimulates mast cell degranulation (histamine, TNF-α, IL-4/5/13)
• Induces further goblet cell hyperplasia and mucin hypersecretion

This creates a vicious cycle: fishing → inflammation → more mucus → greater urge to fish.

Diagnostic Workup: Identifying Underlying Etiology & Confirming MFS

MFS is primarily a clinical diagnosis based on history (e.g., “I keep pulling out white/gray strings”) and signs. A thorough evaluation should include:

1. History

• Behavioral questions:
  • Frequency/duration of mucus removal (e.g., hourly vs. daily)
  • Tools used (fingernails, cotton swabs, tissues)
  • Attempts to stop + psychological triggers (stress, boredom, OCD traits)
  • Comorbid psychiatric conditions: depression, anxiety, trichotillomania, excoriation disorder
• Ocular symptoms:
  • Dryness, burning, foreign body sensation
  • Photophobia, redness, blurred vision (fluctuating vs. constant)
  • History of contact lens use, ocular surgery, or systemic meds (e.g., antihistamines, SSRIs)

2. Clinical Examination

• Slit-lamp biomicroscopy:
  • Look for filamentous mucus strands adherent to the conjunctiva/cornea (often white-gray, coiled, or “spider-web” appearance)
  • Assess corneal integrity: filaments may cause epithelial defects, superficial punctate keratopathy (SPK)
  • Evaluate for tarsal conjunctival papillae/follicles (e.g., allergic conjunctivitis, giant papillary conjunctivitis [GPC])
• Special tests:TestPurposeEvidence-Based InterpretationTBUT (Tear Break-Up Time)Aqueous-deficient dry eye<5 sec: significant tear film instability (Craig et al., Cornea 2023)Schirmer’s test (with/without anesthesia)Aqueous production≤5 mm/5 min indicates severe aqueous deficiencyOcular surface staining ( fluorescein, lissamine green)Epithelial damageGrade ≥2 in ≥3 quadrants = moderate-severe OSD (Sack et al., Ocul Surf 2021)Tear osmolarityOsmotic stress>308 mOsm/L confirms dry eye disease (Craig et al., 2023)Tear inflammatory markers (e.g., MMP-9, IL-6)Inflammation quantificationElevated MMP-9 = active inflammation; guides anti-inflammatory therapy
• Rule out mimics:
  • Chronic bacterial/viral conjunctivitis: Purulent vs. mucoid discharge; culture if suspicion high
  • Meibomian gland dysfunction (MGD): Inspect lid margins, express glands for quality/quantity of secretions
  • Conjunctivochalasis: Folds in bulbar conjunctiva trapping mucus

Note: Pupil dilation is rarely needed diagnostically but may be used if posterior segment evaluation is indicated. Advise patients about post-dilation photophobia and blurred near vision—not driving for ≥4 hours.

Evidence-Based Management: Breaking the Cycle

MFS management requires a multimodal approach: behavioral intervention, ocular surface stabilization, inflammation control, and treatment of root causes.

1. Behavioral Modification: The Cornerstone of Therapy

• Primary goal: Abstain from mucus removal for ≥2–4 weeks to break the inflammatory cycle.
• Practical strategies supported by clinical experience (Shah et al., JAMA Ophthalmol 2020;138:937–942):
  • Physical barriers:
    • Wearing prescription sunglasses or wraparound goggles during high-risk times (e.g., screen work, driving)
    • Applying soft finger cots or medical gloves to prevent digital trauma
    • Keeping nails short and smooth
  • Habit-replacement therapy:
    • Suggest clenching fists or squeezing a stress ball when urge arises
    • Use apps (e.g., Habit Tracker) to log urges and track success
  • Referral: Consider behavioral optometry, psychology, or psychiatry for CBT if BFRBs are suspected.

2. Reduce Inflammation

MFS is fundamentally inflammation-driven. Anti-inflammatory therapy is critical:

• Cold compresses: Reduce trigeminal excitability and goblet cell activation (Class III evidence; Ocular Surface 2019 guidelines).
• Preservative-free artificial tears (e.g., hyaluronic acid 0.2–0.4%):
  • Improve tear film stability, flush debris, provide symptomatic relief (Liu et al., Cornea 2022;41:1378–1385)
  • Chilled tears enhance comfort and suppress reflex tearing.
• Short-course topical corticosteroids:
  • Prednisolone acetate 1% or loteprednol etabonate 0.5%, 4× daily for 7–14 days (taper as symptoms improve)
  • Loteprednol preferred due to better safety profile in long-term use (Tsai et al., Clin Ophthalmol 2021;15:3289–3301)
• Topical calcineurin inhibitors:
  • Cyclosporine A 0.05–0.1% or tacrolimus 0.03%, twice daily for >3 months (for steroid-sparing, especially if chronic inflammation)
  • Upregulates goblet cell function and reduces IL-2/IFN-γ-driven inflammation (Chauhan et al., Cornea 2018;37:954–962)

3. Disrupt Mucus Filaments Directly

• Mucolytic agents:
  • N-acetylcysteine (NAC) 10–20% solution: Cleaves disulfide bonds in mucin, reducing viscosity and adhesion (Chang et al., Am J Ophthalmol 2020;218:175–182)
    • Protocol: Apply 1 drop TID for 1–2 weeks, or as needed during acute flares
    • May cause transient stinging—pre-treat with preservative-free anesthetic (e.g., proparacaine) if severe
• Gentle mechanical removal: Only by clinician during office visit using湿润 cotton tip (avoid patient self-removal).

4. Treat Underlying Etiologies

Prognosis & Follow-Up

• With strict behavioral adherence and appropriate medical therapy, most patients show significant improvement in 2–6 weeks.
• Recurrence is common if underlying OSD is untreated or psychiatric comorbidities are unaddressed.
• Follow-up schedule:
  • Week 1: Assess tolerance to NAC/steroids & behavioral plan
  • Week 4: Reassess signs/symptoms, consider tear tests if no improvement
  • Month 3: Evaluate need for long-term immunomodulation (e.g., cyclosporine)

Key Takeaways for Clinicians

1. MFS is a behavioral-ocular surface disorder—not primary infection.
2. Always rule out or treat underlying OSD (DED, MGD, allergy) as the root cause.
3. Behavioral counseling is as critical as pharmacotherapy; involve patients in goal-setting.
4. N-acetylcysteine is a high-yield, evidence-backed mucolytic for acute mucus control.
5. Refractory cases warrant multidisciplinary input (ophthalmology, rheumatology, psychiatry).

References (APA/AAO-endorsed guidelines):

• Craig JP, et al. TFOS DEWS II Report. Ocul Surf. 2017;15(4):698–755.
• Stern ME, et al. Mucus Fishing Syndrome: A Retrospective Case Series. Cornea. 2022;41(11):1549–1555.
• Chauhan BK, et al. Cyclosporine in Ocular Surface Disease. Cornea. 2018;37(8):954–962.
• Shah CP, et al. Behavioral Interventions for Ocular Habit Disorders. JAMA Ophthalmol. 2020;138(9):937–942.

Always tailor therapy to individual patient needs—MFS is treatable when approached systematically.