Ahmed Ellabban

Introduction

Conjunctival foreign bodies are a common ophthalmic presentation frequently encountered in routine clinical practice. However, the appearance of a worm-like conjunctival lesion can pose a diagnostic challenge, particularly in patients with a history of travel to regions endemic for parasitic infections. This report outlines the investigation, diagnostic work-up, and management of conjunctival foreign bodies, reflecting on a case of suspected Axenfeld nerve loops masquerading as a conjunctival foreign body. In such cases, careful clinical assessment and appropriate diagnostic evaluation are essential to establish an accurate diagnosis and guide optimal management.

This condition review was inspired by a case that presented itself in one of the clinics. It was a middle-aged from West Africa who was referred to our cornea and external disease service with a several-month history of redness and irritation of his left eye. The referring clinician was concerned by a raised, worm-like structure visible on the inferior conjunctiva, particularly given the patient’s history of frequent travel to West Africa. On slit-lamp examination, a small, slightly pigmented, linear lesion was seen beneath the inferior conjunctiva, giving the appearance of a subconjunctival foreign body or possible parasitic structure.

Given the clinical appearance and travel history, systemic investigations were arranged to exclude filarial infection, although these returned negative. The lesion was subsequently excised for diagnostic and therapeutic purposes. Histopathological correlation and clinical features were ultimately consistent with Axenfeld nerve loops masquerading as a conjunctival foreign body.

This experience prompted a broader interest in the differential diagnosis and management of atypical conjunctival lesions, particularly those that mimic foreign bodies or parasitic infections.

Axenfeld Nerve Loops Theory

First described in 1902 by T. Axenfeld, the intrascleral Axenfeld nerve arises from the long posterior ciliary nerves (1). It travels through the sclera, first piercing it near the optic nerve and ending by looping back in the region of the ciliary body. Sometimes it may loop out through the sclera in the region of the anterior ciliary arteries or between the rectus muscles insertions, forming a clinically visible nodular elevation 4-7 mm posterior to the limbus (2).

One of the possible embryological explanations for these loops, is given by Ernst Fuchs, who believed the development of these nerve loops rest on abnormal growth tendencies; some ciliary nerves grow more rapidly than the sclera and their greater length is compensated by their duplication or loops in the sclera (3).

Although Axenfeld nerve loops are common, large loops are rarely seen. These loops are virtually all associated with blood vessels, and all are pigmented. This is clinically significant, because even though they are a natural anatomical landmark, Axenfeld nerve loops may appear cystic and/or pigmented, producing an elevated pigmented nodule on the sclera, which may lead to surgical misadventures or be mistaken by a scleral foreign body. Axenfeld nerve loops have also been confused with nevi, cysts, and malignant melanomas (4, 5, 6).  

Workup learning points

As with any suspected conjunctival or corneal foreign body, the initial evaluation should be systematic yet focused: a careful history of the mechanism of injury and symptoms (pain, foreign body sensation, photophobia and tearing) is crucial, alongside measurement of visual acuity and slit-lamp examination with fluorescein staining to localise epithelial defects and identify any embedded material (7). Fluorescein assists in detecting epithelial disruption consistent with retained foreign bodies, while white-light inspection with lid eversion allows detection of subtarsal particles that may otherwise be overlooked. Where there is concern for deeper penetration or globe compromise—such as an irregular pupil, significantly reduced vision or suspected full-thickness injury—the Seidel test under cobalt blue illumination can be used to identify aqueous leakage and prompt urgent escalation for imaging and specialist review (8). In most cases, these steps permit safe identification and removal of superficial conjunctival and corneal foreign bodies with appropriate post-procedural care.

However, not all raised or linear subconjunctival lesions represent retained material. A critical differential—particularly when a lesion appears fixed, well-demarcated and associated with surrounding pigmentation—is the Axenfeld nerve loop. These structures may be seen on slit-lamp examination as grey or white nodules beneath the bulbar conjunctiva, typically located a few millimetres posterior to the limbus and often surrounded by pigment (9,10). They are a normal anatomical finding and may be mistaken for foreign bodies, particularly in the absence of a clear traumatic history. Pain elicited on manipulation of the overlying conjunctiva provides a useful clinical clue to their neural origin (11). Unlike true foreign bodies, Axenfeld nerve loops do not move with irrigation or probing, and attempted removal risks unnecessary tissue trauma.

Diagnosis is usually made clinically on the basis of appearance, localisation and immobility. Where uncertainty remains—such as in atypical presentations or when differentiating from pigmented lesions, cysts or episcleral pathology—ultrasound biomicroscopy may be used to demonstrate the characteristic intrascleral course of the nerve and its relationship to adjacent structures (12).

Conclusion

This encounter illustrated the diagnostic uncertainty that can arise when conjunctival lesions present with a worm-like appearance, particularly in patients with travel histories that suggest parasitic disease. Although a filarial infection was a reasonable initial consideration, it also highlighted the importance of including anatomical variants such as Axenfeld nerve loops in the differential diagnosis. Three key learning points emerged: the value of meticulous slit-lamp examination in identifying defining features of conjunctival lesions; the role of a structured investigative approach, including targeted blood tests and histopathological analysis; and the need to recognise that benign anatomical variants may closely resemble pathological entities. Together, these reinforce the importance of maintaining diagnostic breadth and avoiding premature conclusions, helping to ensure appropriate management and prevent unnecessary intervention.

References

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