Prevalence and risk factors of caterpillar hair-induced ophthalmitis: A retrospective analysis

INTRODUCTION

Caterpillar hair-induced ophthalmia (CHIO), also known as ophthalmia nodosa, is an ocular inflammatory condition resulting from the penetration of caterpillar setae (hairs) into the eye [Figure 1].^[1-4] These hairs can incite both a mechanical and toxic reaction characterised by tissue inflammation, granuloma formation composed of epithelioid cells, giant cells and lymphocytes.^[2,3,5] Vigorous eye rubbing can further drive hairs deeper, leading to complications such as corneal abrasions, subconjunctival abscesses, scleral inflammation and, in severe cases, exudative retinal detachment.^[4,6-8] The pathology is thus a combination of direct mechanical trauma and chemical toxicity from urticating substances associated with the hairs.^[9] A classification is devised by Cadera et al.:^[4]

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Figure 1:

(a) Caterpillar image credits: Robert Webster, xpda. com (licensed under CC BY-SA 4.0) (accessed through wikipedia/wikimedia commons). (b) caterpillar hair as seen under low power (10x magnification) on light microscopy.

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• Type 1. An acute toxic reaction to hair (chemosis and inflammation)

• Type 2. Chronic mechanical keratoconjunctivitis caused by hair found in the bulbar or palpebral conjunctiva with foreign body sensation and corneal abrasions

• Type 3. Formation of conjunctival granulomas due to subconjunctival or intracorneal setae

• Type 4. Iritis secondary to hair penetration of the anterior segment

• Type 5. Early or late vitreoretinal involvement due to penetration of the hair through the cornea, iris and lens or through the transscleral route; vitritis, cystoid macular edema, papillitis or endophthalmitis may occur.

Clinically, patients present with a range of signs and symptoms based on the depth and location of the setae. Early signs include conjunctival hyperemia, chemosis, eyelid edema, intense foreign-body sensation, tearing, photophobia and pain.^[4,6] Visible embedded hairs may be noted on slit-lamp examination with multiple foci of conjunctival or corneal inflammation. Granulomatous nodules often form on the conjunctiva or iris. More severe presentations include anterior chamber inflammation (iritis), vitreoretinal involvement with vitritis,^[9] retinal scars or retinal detachment.^[10] Symptoms can persist or worsen if hairs penetrate intraocularly, requiring repeated examinations.

Treatment necessitates early and aggressive removal of setae through forceps or surgical intervention as needed.^[5,11,12] Adjunctive therapies include topical or systemic corticosteroids to quell inflammation, broad-spectrum antibiotics to forestall secondary infections and possibly surgical procedures (e.g. vitrectomy) for intraocular involvement.^[10,13] Delayed or incomplete treatment may result in persistent inflammation, granuloma formation or vision-threatening complications. Regular follow-up is important to monitor for intraocular migration and late sequelae. Protective measures such as eye protection in high-risk environments are essential to prevention.^[14]

This condition illustrates a complex interplay of mechanical penetration and immunologic response to an otherwise environmental exposure, highlighting the importance of awareness among clinicians regarding the potential severity of caterpillar hair ocular injuries.

Seasonal trends in CHIO have been reported, with peak incidence during the monsoon and winter seasons.^[15] Ophthalmia nodosa is recognised as an occupational hazard in endemic regions, largely due to limited awareness and inadequate use of protective measures among at-risk workers.^[14,15] Delayed or missed diagnosis has been reported in several studies, often resulting in prolonged inflammation or preventable complications, underscoring the need for heightened clinical suspicion in areas where caterpillar exposure is common.^[16] Existing literature consistently describes ophthalmia nodosa as a distinctly seasonal and occupation-linked condition, typically occurring in regions where specific caterpillar species proliferate, highlighting the importance of both community education and clinician vigilance.^[5,14,15] This study aims to determine the epidemiology and risk factors of CHIO in rural Gujarat.

MATERIALS AND METHODS

Medical records of all patients diagnosed with CHIO from August 2021 to March 2024 were retrieved from the hospital’s electronic medical record system. Patient history, including mode of exposure, symptom onset, prior ocular disease and environmental background, was reviewed from medical records. The demographic details, occupational exposure, clinical features and seasonal distribution were reviewed. All patients underwent slit-lamp examination and indirect ophthalmoscopy to determine the presence, number and anatomical location of caterpillar hairs. Paediatric patients and those with poor cooperation were examined under general anesthesia using an operating microscope whenever necessary.

Clinical characteristics recorded included the site of hair lodgement (upper tarsal conjunctiva, fornix, cornea or deeper tissues), laterality, symptom duration and presence of intraocular penetration. As part of routine care, visible superficial hairs were removed during the first examination. Medical treatment consisted of lubricants, antibiotic ointments and topical corticosteroids when granulomatous inflammation was noted. Systemic corticosteroids were used in cases with anterior or posterior segment involvement.

Demographic variables (age, gender and residence), occupational category, clinical findings and seasonal trends were extracted for analysis. Data entry and statistical analysis were performed using STATA 14. Frequencies and percentages were calculated, and univariate analysis was used to assess associations between background characteristics and the occurrence of CHIO.

RESULTS

Of the 112 CHIO patients, 57 (50.9%) were male and 55 (49.1%) were female. Only 5.4% of cases exhibited intraocular penetration [Figure 2]. The upper tarsal conjunctiva was the most commonly affected site (54.5%)[Figure 3]. Rural residents accounted for 88.4% of cases, while only 11.6% were from urban areas. 20-39 years age group was most affected followed by 40-59 year age group [Figure 4]. About 70% patients belonged to agricultural sector [Figure 5]. The left eye (52.7%) was slightly more frequently involved than the right eye (47.3%). The highest prevalence was observed in winter (66.1%), followed by monsoon (31.3%) and summer (2.7%). 54.5% patients presented within 1-3 days of onset of symptoms, but 20.5% presented after 3 days and 25% could not exactly recall the onset of symptoms.

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Figure 2:

Intraocular penetration of caterpillar hair.

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Figure 3:

Anatomical location of lodgement of hair.

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Figure 4:

Occupational status of patients with caterpillar hair-induced ophthalmitis.

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Figure 5:

Prevalence of caterpillar hair-induced ophthalmitis by age.

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DISCUSSION

Our study demonstrates that CHIO predominantly affects individuals living in rural areas, particularly those working in the agricultural sector. Rural areas typically have more abundant natural habitats conducive to the proliferation of caterpillars, thereby increasing the risk of exposure. This is in contrast to a study by Das et al.,^[16] in which a higher prevalence was seen in the urban population. The possible explanation can be the difference in the population sample, with their primary sample being the urban population.

The highest involved age group of 20–39 years suggests that working-age adults are at greater risk due to their increased exposure to outdoor environments where caterpillar hairs are prevalent. A nearly equal distribution between male and female patients indicates that both genders are equally susceptible to CHIO, likely due to shared occupational and environmental exposures, aligning with the findings of a previous study.^[16]

The peak incidence was observed in winter, consistent with previous studies. Bishop and Morton (1967) reported a higher occurrence in December and January among 103 cases in their study.^[17] Similarly, Sethi and Dwivedi (1982) found ophthalmia nodosa to be more prevalent during the winter season in India.^[3] This seasonal pattern may be attributed to increased caterpillar activity during months, leading to a higher likelihood of exposure.

The low rate of intraocular penetration (5.4%) is reassuring, indicating that while CHIO can be symptomatic and cause significant ocular irritation, it rarely results in severe vision-threatening complications. However, patients with prolonged symptoms should be monitored for secondary complications such as chronic conjunctivitis or corneal involvement.

The upper tarsal conjunctiva is the most frequently affected site (52.7%). The upper fornix is the most common location for caterpillar hairs due to its recessed anatomical structure beneath the upper eyelid, which facilitates the entrapment and accumulation of these hairs, making it a prime site for irritation and inflammation.

Given the predominance of CHIO among individuals engaged in agricultural work and the clear winter seasonality observed in our study, targeted preventive strategies are well justified. Exposure to caterpillar hairs commonly occurs during farm activities and while handling vegetation, placing agricultural workers at particular risk. Therefore, public health initiatives should emphasise the use of protective eyewear during high-risk seasons and increase community awareness about environmental and seasonal risk factors. Furthermore, because early recognition and prompt removal of setae significantly reduce complications, improved training of ophthalmologists and peripheral health workers in identifying CHIO manifestations is supported by both our findings and existing literature.

CONCLUSION

CHIO emerges as a preventable, exposure-related ocular condition predominantly affecting young, working-age adults in rural agricultural settings. The clear seasonal clustering – with a significant winter peak – highlights predictable periods of heightened risk. Although most cases are limited to the ocular surface, delayed presentation can lead to persistent inflammation or deeper penetration. Strengthening community awareness, promoting timely care-seeking and encouraging protective measures for high-risk groups can substantially reduce disease burden. These findings emphasise the need for region-specific preventive strategies and further prospective studies to better characterise exposure patterns and long-term outcomes.