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Year : 2020  |  Volume : 68  |  Issue : 8  |  Page : 1672-1675

Comparing in-vivo confocal microscopy and ex-vivo light and scanning electron microscopy images of the hairs of the pine processionary caterpillar embedded in the cornea: Report of three cases

1 Department of Ophthalmology, Hospital Universitario Ramón y Cajal, Universidad Alcalá de Henares, Spain
2 Department of Ophthalmology, Hospital Clínic, Barcelona, Spain
3 Department of Ophthalmology, Hospital Clínico San Carlos, Universidad Complutense de Madrid, Madrid, Spain
4 Department of Ophthalmology, Hospital del Henares, Coslada, Universidad Francisco de Vitoria, Madrid, Spain

Date of Submission25-Sep-2019
Date of Acceptance20-Feb-2020
Date of Web Publication24-Jul-2020

Correspondence Address:
Dr. Francisco Pérez-Bartolomé
Department of Ophthalmology, Hospital Universitario Ramon y Cajal, Ctra. Colmenar Viejo, Km. 9, 100, 28034 Madrid
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijo.IJO_1735_19

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This report describes three cases of pine processionary caterpillar hairs (setae) embedded in the cornea: one in a 69-year-old man with acute keratouveitis, a second case in a 65-year-old man with an epithelial defect and a stromal infiltrate, and the third case affecting a 54-year-old woman with mild keratitis. The two first patients had one hair embedded in the anterior corneal layers while the last one had several hairs deeply embedded in the stroma. By comparing in-vivo confocal microscopy (IVCM) with ex-vivo light microscopy (LM) and scanning electron microscopy (SEM) images, the morphology of the setae was identified and confirmed.

Keywords: In-vivo confocal microscopy, keratitis, light microscopy, processionary caterpillar, scanning electron microscopy

How to cite this article:
Pérez-Bartolomé F, Peraza-Nieves J, Fernández-Vigo J I, Méndez-Fernández R, Gonzalez Martín-Moro J, Arriola-Villalobos P. Comparing in-vivo confocal microscopy and ex-vivo light and scanning electron microscopy images of the hairs of the pine processionary caterpillar embedded in the cornea: Report of three cases. Indian J Ophthalmol 2020;68:1672-5

How to cite this URL:
Pérez-Bartolomé F, Peraza-Nieves J, Fernández-Vigo J I, Méndez-Fernández R, Gonzalez Martín-Moro J, Arriola-Villalobos P. Comparing in-vivo confocal microscopy and ex-vivo light and scanning electron microscopy images of the hairs of the pine processionary caterpillar embedded in the cornea: Report of three cases. Indian J Ophthalmol [serial online] 2020 [cited 2020 Aug 12];68:1672-5. Available from: http://www.ijo.in/text.asp?2020/68/8/1672/290396

Accidental contact with the hairs of the pine processionary caterpillar Thaumetopoea pityocampa can induce from mild keratitis to severe systemic reactions.[1],[2],[3],[4],[5] The morphology of these hairs, or setae, on in-vivo confocal microscopy (IVCM) seems to be pathognomonic.[6] We here describe three cases in which processionary caterpillar hairs were found embedded in the cornea. The diagnosis was confirmed by IVCM, scanning electron microscopy (SEM), and light microscopy (LM).

  Case Reports Top

Case 1

A 69-year-old man presented at the emergency room with intense pain in his left eye [oculus sinister (OS)]. Symptoms had started 3 days after visiting a pine forest. On slit-lamp examination (SLE), the OS showed a small central epithelial defect, a diffuse infiltrate in the adjacent stroma, mild stromal edema and folds in Descemet's membrane [Figure 1]a. We observed a small elongated brown foreign body in the middle of the stroma that resembled a caterpillar hair. In an anterior segment optical coherence tomography (AS-OCT) (Heidelberg Engineering GmbH, Heidelberg, Germany), a hyperreflective point could be seen in the anterior stroma [Figure 1]b. IVCM (Heidelberg IVCM HRTIII-Rostock Cornea Module) revealed a harpoon-shaped foreign body compatible with a processionary caterpillar seta [Figure 1]c.
Figure 1: Patient 1: (a) Slit lamp: elongated brown foreign body compatible with the hair of a processionary caterpillar. (b) Anterior segment optical coherence tomography (AS.OCT): hyperreflective point in the anterior stroma with adjacent indirect hyporeflectivity. (c) In vivo confocal microscopy (IVCM): harpoon-shaped foreign body consisting of a stalk with spicules orientated towards its sharp tip

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Treatment was topical dexamethasone 1 mg/ml tapered, ofloxacin 3 mg/ml, and cyclopentolate 1mg/ml. Within two weeks, the pain and inflammation subsided although the hair was still visible in the corneal stroma.

Case 2

A 65-year-old man presented at the emergency room because of pain in his OS starting a few hours previously. He reported having been walking near a pinewood and felt something enter his eye, realizing later it was a caterpillar which he brought to our center. On SLE, the OS showed a paracentral infiltrate in the middle and deep stroma without epitheliopathy. Adjacent to the infiltrate, several long, thin brown foreign bodies were observed [Figure 2]a. In an AS-OCT, hyperreflective lines could be seen, one of which had penetrated the corneal endothelium [Figure 2]b. On IVCM, we detected multiple spiculated hairs, similar to those observed in Case 1 [Figure 2]c. In LM and SEM images of the caterpillar brought by the patient, we could distinguish spicules on the hairs [Figure 2]d, [Figure 2]e, [Figure 2]f and [Figure 3]. In response to the same treatment as in Case 1, inflammation resolved within three weeks.
Figure 2: Patient 2: (a) Slit lamp: elongated thin brown foreign bodies. (b) AS.OCT: numerous hyperreflective lines compatible with caterpillar hairs, one of which can be seen to cross into the corneal endothelium. (c) IVCM: multiple spiculated foreign bodies similar to those of the previous case. (d) Bright field microscopy (BFM) of the hairs obtained from the caterpillar brought by the patient showing numerous spicules orientated towards the hair tip. (e and f) Scanning electron microscopy (SEM) of the caterpillar revealed the similar morphology of the hairs observed by LM and IVCM

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Figure 3: Stereomicroscopy and SEM of the caterpillar. (a-c). Stereomicroscopy image showing at increasing magnification the size ratio between the body and hairs of the caterpillar. (d-f). SEM micrograph showing the characteristic spicules at increasing magnification

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Case 3

A 54-year-old woman presented at the emergency room complaining of mild pain in her OS after having spent the previous day in her garden. On biomicroscopy, a long brown foreign body was detected on the epithelium in the OS [Figure 4]a. AS-OCT revealed no apparent injury. On IVCM, we detected a long foreign body with spicules on its margins compatible again with the hairs of the processionary caterpillar [Figure 4]b. After removing the hair with a cotton swab, LM and SEM observations confirmed the similar seta morphology as in the previous case [Figure 4]c and [Figure 4]d. In response to the same treatment as described for Cases 1 and 2, inflammation resolved in two weeks.
Figure 4: Patient 3: (a) A single elongated brown foreign body on the surface of the epithelium penetrating into the mid stroma without evident corneal inflammation. (b) IVCM revealed a hyperreflective foreign body on the surface of the epithelium with the same serrated edges as in patients 1 and 2. (c) BFM of the hair extracted from the cornea of the patient. The same serrated edges with spicules facing the hair tip were observed as in the BFM image obtained in patient 2. (d) SEM of the hair removed

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  Discussion Top

The hairs of the pine processionary caterpillar are lethal airborne weapons able to penetrate the skin or ocular surface producing a broad spectrum of disorders. The pathogenic mechanism could be mechanical irritation through contact with the spiculated sharp-tipped hairs or a massive immune reaction resulting in overlapping of allergic and non-allergic responses. The protein thaumetopoein found in the caterpillar's hairs is capable of inducing immunoglobulin E (IgE)-dependent basophil degranulation.[7] Despite an antigen stimulus of similar magnitude (one hair) in two of our patients, Case 1 showed a likely allergic keratouveitis with intense inflammation, while in Case 3 there was only mildly irritating keratitis. The deeper position of the embedded hair in Case 1 could explain this allergic reaction. Similarly, a high antigen load in the second case triggered an inflammatory response that was not as intense as in Case 1 and only in the deep corneal stroma. Thus, it seems that not only the antigen load is responsible for variation in symptom intensity.

Epithelial debridement and removal of embedded hairs are controversial because of iatrogenic risks. When pulled, hairs may break into smaller fragments, which may exacerbate the inflammatory reaction by releasing new toxins.[6] Corneal perforation is rare but has been described.[4],[8]

Imaging the cornea with non-invasive techniques such as IVCM is useful to confirm a suspected diagnosis made after SLE, and also to locate, and assess the size and shape of the foreign body.[6] The hairs found here showed a pathognomonic morphology: hyper-reflective, non-branched, tiny linear foreign bodies with sharp tips and serrated edges consisting of spicules pointing towards the tips. These are the main features that distinguish them from corneal nerves.[5] Some authors report that AS-OCT offers images of sufficiently high resolution to assess the location, size, and depth of hairs and to monitor their possible migration, which is useful for planning surgical removal.[5],[9] However, in Case 3, we were unable to locate the embedded hair by AS-OCT while IVCM was successful as it offers information at the cellular level. As limitations of IVCM, we should mention that it requires specific training and image interpretation is subjective. Furthermore, because it is a contact technique, it may exacerbate symptoms.[6]

  Conclusion Top

To the best of our knowledge, this is the first study to compare the use of IVCM, SEM, and LM to examine the morphology of pine processionary caterpillar setae inducing keratitis. IVCM emerged as a useful diagnostic tool recommended when the etiology of corneal inflammation is uncertain.


The authors acknowledge the help provided by María de la Concepción Magaña Loarte at the Forensic Anatomy Department of the Complutense University Medical School of Madrid and Department of Non-destructive Techniques of the Natural Science Museum of Madrid.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Portero A, Carreño E, Galarreta D, Herreras JM. Corneal inflammation from pine processionary caterpillar hairs. Cornea 2013;32:161-4.  Back to cited text no. 1
Ramesh Bhat Y, Vinayaka G, Sushma S. Systemic allergic reaction to a caterpillar in a 3-month-old infant. Ann Trop Paediatr 2010;30:83-6.  Back to cited text no. 2
Cadera W, Pachtman MA, Fountain JA, Ellis FD, Wilson FM. Ocular lesions caused by caterpillar hairs (ophthalmia nodosa). Can J Ophthalmol 1984;19:40-4.  Back to cited text no. 3
Sengupta S, Reddy PR, Gyatsho J, Ravindran RD, Thiruvengadakrishnan K, Vaidee V. Risk factors for intraocular penetration of caterpillar hair in Ophthalmia Nodosa: A retrospective analysis. Indian J Ophthalmol 2010;58:540-3.  Back to cited text no. 4
[PUBMED]  [Full text]  
Shibui H, Kawashima H, Kamata K, Sasaki H, Inoda S, Shimizu H. Vitrectomy for caterpillar seta-induced endophthalmitis. Arch Ophthalmol 1997;115:555-6.  Back to cited text no. 5
Jullienne R, He Z, Manoli P, Grivet D, Cinotti E, Perrot JL, et al. In vivo confocal microscopy of pine processionary caterpillar hair-induced keratitis. Cornea 2015;34:350-2.  Back to cited text no. 6
Vega JM, Moneo I, García-Ortiz JC, González-Muñoz M, Ruiz C, Rodríguez-Mahillo AI, et al. IgE sensitization to thaumetopoea pityocampa: Diagnostic utility of a setae extract, clinical picture and associated risk factors. Int Arch Allergy Immunol 2014;165:283-90.  Back to cited text no. 7
González-Martín-Moro J, Contreras-Martín I, Castro-Rebollo M, Fuentes-Vega I, Zarallo-Gallardo J. Focal cortical cataract due to caterpillar hair migration. Clin Exp Optom 2019;102:89-90.  Back to cited text no. 8
Mantopoulos D, Cruzat A, Hamrah P. In vivo imaging of corneal inflammation: New tools for clinical practice and research. Semin Ophthalmol 2010;25:178-85.  Back to cited text no. 9


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]


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