Mucus fishing syndrome (MFS) is a chronic inflammatory ocular surface disease caused by repeatedly manually removing strands of mucus from the conjunctival fornix. It was first reported by McCulley et al. in 1985 1). The term “fishing” derives from the characteristic behavior of patients who “fish” mucus from the eye with their fingers 1).
MFS is a rare condition, with a frequency of less than 1 in 2000 individuals 2). It often occurs secondary to underlying conditions that cause ocular irritation or increased mucus production, such as allergic conjunctivitis, bacterial conjunctivitis, blepharitis, and keratoconjunctivitis sicca (dry eye) 2).
Mechanical trauma from manually removing mucus from the conjunctival surface stimulates goblet cells, further increasing mucus production. The increased mucus then triggers further removal, creating a vicious cycle that is the essence of this syndrome 1)2). This cycle superimposed on the underlying disease leads to persistent inflammation despite appropriate treatment 1).
QWhy is mucus fishing syndrome easily overlooked?
A
The main symptoms of MFS (redness, tearing, foreign body sensation, mucus discharge) are nonspecific and resemble dry eye or bacterial conjunctivitis. Patients themselves are often unaware of their mucus removal habit, and diagnosis is not made unless the physician actively inquires about the history of mucus removal. In fact, in the initial case series, all 25 cases were diagnosed only after confirming a history of mucus removal 1).
Redness: Awareness of redness in the bulbar and palpebral conjunctiva
Foreign body sensation: Complaints of feeling something in the eye
Burning sensation: May complain of persistent burning pain in the eye2)
Tearing: Excessive tearing
Blurred vision: May complain of blurred vision
Mucus hypersecretion: The sensation of mucus strands accumulating in the eye is the most characteristic complaint1)
Photophobia: Severe cases may cause light sensitivity2)
A history of underlying disease that initially caused a foreign body sensation is often noted. Symptoms are nonspecific, so misdiagnosis or oversight is common1).
Clinical Findings (Findings Confirmed by Physician Examination)
Conjunctival injection: Mild to severe injection of the bulbar and palpebral conjunctiva1)
Mucus strands: Fluorescein-positive mucus strands in the conjunctival fornix (especially lower eyelid)1)
Conjunctival epithelial defect: Fluorescein or rose bengal staining reveals a well-demarcated palpebral conjunctival epithelial defect near the lower punctum1). Findings are often asymmetric.
Palpebral conjunctival edema: Edema of the palpebral conjunctiva may be present2)
Decreased tear function: Shortened tear breakup time (TBUT) and reduced tear meniscus height are observed2)
MFS develops from a combination of increased mucus production due to an underlying disease and manual removal behavior. The following conditions are considered risk factors.
Dry eye (keratoconjunctivitis sicca): One of the most common comorbidities2)
Conjunctival squamous cell carcinoma: Reported as a rare cause
Exposure keratoconjunctivitis: Causes ocular surface dryness and irritation
QHow are dry eye and mucus fishing syndrome related?
A
Dry eye causes ocular surface irritation due to quantitative and qualitative abnormalities of tears. This irritation often triggers mucus removal behavior. Additionally, in dry eye, reactive mucus secretion from goblet cells increases, making mucus strands more likely to form. It has been reported that many MFS patients have dry eye as a comorbid underlying condition 2).
Detailed medical history taking is most important in diagnosing MFS. Confirming that the patient repeatedly manually removes mucus from the conjunctiva is key to diagnosis 1).
The diagnostic accuracy based solely on medical history has been reported to reach 88% 1). In McCulley et al.’s initial case series, all 25 cases were diagnosed only after confirming a history of mucus removal 1).
If the patient is unaware of the behavior, information from family members is useful.
Fluorescein staining: Visualizes epithelial defects of the palpebral conjunctiva and mucus strands. Characteristically, well-demarcated epithelial defects near the lower punctum are observed 1)
Rose Bengal staining: Stains damaged conjunctival epithelium and evaluates the extent of injury
Non-invasive tear evaluation using devices such as Keratograph 5M is useful 2). Tear meniscus height (TMH), non-invasive tear break-up time (NIKBUT), and OSDI (Ocular Surface Disease Index) score objectively assess the ocular surface condition.
Treatment of MFS requires three main pillars: behavioral modification, pharmacotherapy, and treatment of underlying diseases2).
Behavioral Modification (Most Important)
Patient education: Cessation of mucus removal behavior is the cornerstone of treatment1)2). Explain the mechanism of the vicious cycle to the patient and instruct them to completely avoid touching the ocular surface.
Family involvement: If the patient performs the behavior unconsciously, having family members point it out can be effective.
Psychological evaluation: If obsessive-compulsive disorder (OCD) or anxiety disorder is involved, consider psychiatric evaluation 2)
Medication therapy
Mucolytic agents: Acetylcysteine 5% eye drops administered 4 times daily 2). They break up mucus aggregates and improve tear film clarity.
Topical steroids: Used to suppress ocular surface inflammation. Loteprednol 0.5% 1), fluorometholone 0.1% 2), and hydrocortisone 2) are commonly used.
Antibiotics: Levofloxacin 1.5% eye drops, etc., are used concomitantly to prevent secondary bacterial infection 1).
Autologous serum eye drops: In severe or refractory cases, autologous serum 20% eye drops promote epithelial repair 2).
Treatment of underlying conditions such as dry eye, blepharitis, and MGD is essential. Depending on the underlying disease, tear supplementation with artificial tears, warm compresses and eyelid hygiene, and use of anti-allergic medications are performed 2).
QWhat should I do if I cannot stop the habit of removing mucus?
A
Mucus removal behavior can be compulsive in nature, and simply saying “stop” may not be sufficient. Using mucolytic agents such as acetylcysteine 5% eye drops to reduce mucus aggregation can help stop the behavior. If anxiety disorder or OCD is underlying, psychiatric evaluation or cognitive behavioral therapy may be effective 2). Temporary discomfort may occur during recovery, but developing psychological tolerance leads to long-term improvement.
The core of MFS pathophysiology is a vicious cycle of “mechanical trauma → goblet cell stimulation → mucus overproduction → further removal behavior” 1)2).
When underlying conditions (dry eye, conjunctivitis, etc.) cause foreign body sensation or mucus accumulation on the ocular surface, patients attempt to remove the mucus with their fingers. This mechanical trauma directly stimulates goblet cells in the conjunctiva, increasing secretion of mucin (mucus glycoprotein) 2).
Furthermore, manipulation with fingers introduces external irritants to the ocular surface. This triggers the following immune responses.
Complement activation: Innate immune response to foreign substances is induced
Mast cell degranulation: Mast cells in the conjunctival substantia propria are activated
Histamine secretion: Causes increased vascular permeability and conjunctival hyperemia
Mancini et al. reported that conjunctival epithelial damage triggers inflammation and promotes goblet cell hyperactivity, worsening mucus hypersecretion. This process, combined with disruption of tear film homeostasis, further exacerbates ocular surface instability 2).
Mechanical trauma-induced conjunctival epithelial defects commonly occur near the lower lacrimal punctum. This corresponds to the patient’s action of pinching mucus from the inner canthus with fingers 1).
In 2025, Mancini et al. reported two cases of MFS patients who received adjunctive low-level light therapy (LLLT). An infrared-emitting mask using red light (wavelength 633±10 nm, irradiance approximately 15 mW/cm²) was applied once a week for 15 minutes. Combined with conventional treatment (steroid eye drops, acetylcysteine 5%, eyelid hygiene), both cases showed improvement in OSDI score and TBUT 2).
Assessment Parameter
Case 1 (Before → After Treatment)
Case 2 (Before → After Treatment)
TBUT (seconds)
5 → 8
2 → 6
OSDI
45→35
58→38
LLLT may improve meibomian gland function and promote lipid layer secretion, thereby reducing evaporative tear loss 2). However, it is difficult to isolate its contribution from combination therapy, and comparative studies with control groups are needed to establish efficacy 2).
Elucidation of goblet cell regulatory mechanisms and development of drugs targeting mucus hypersecretion are cited as future research topics 2). Since MFS is a rare disease, large-scale studies are difficult, and accumulation of case reports and increased disease awareness among clinicians are important.
Chiew RLJ, Au Eong DTM, Au Eong KG. Mucus fishing syndrome. BMJ Case Rep. 2022;15(4):e249188.
Mancini A, Carnovale-Scalzo G, Mancini M, et al. Low-Level Light Therapy as a Potential Adjunctive Approach in Mucus Fishing Syndrome: Report of Two Clinical Cases. Int Med Case Rep J. 2025;18:1679-1684.
Cooper CM, Sitto MM, Azar NS, Hoopes PC, Moshirfar M. Mucus Fishing Syndrome: Case Series and a Narrative Review of Literature. Ophthalmol Ther. 2026. PMID: 41870843.
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