Aetiology

Phthiriasis (pediculosis ciliaris) is an infestation of lid margins by the crab louse (Phthirus pubis), a blood-feeding obligate ectoparasite affecting only humans

• crab lice infest coarsely spaced hair, predominantly pubic hair
• eyelashes also provide ideal spacing
• genital-to-eye transmission, either through direct contact or possibly on contaminated bedding, clothes and towels
• crab lice survive no more than 48 hours if separated from human host
• this insect is not a vector for other diseases
• in severe cases, lice faeces can cause keratoconjunctivitis
• NB in Pediculosis capitis, i.e. infestation by head lice [Pediculus humanus capitis], the lashes are rarely involved. The same is true in Pediculosis corporis, i.e. infestation by body lice (Pediculus humanus corporis)

Predisposing factors

Sexual contact with a louse-infested individual
Can be contracted within families through poor hygiene and close contact

Symptoms of phthiriasis

Intense itching of lid margins
Red watery eye
Unilateral or bilateral

Signs of phthiriasis

• madarosis (loss of lashes)
• blepharoconjunctival hyperaemia and oedema
• superficial punctate keratopathy (SPK)
• bites leave red inflamed areas on lid margins (petechial macules)
• possible pre-auricular lymphadenopathy
• adult lice (1.0–1.5mm long) attached to lash; almost completely transparent (high magnification [x40] required at slit lamp)
• eggs (termed nits) in greyish white cigar-shaped shells (0.5mm long) attached near base of lashes. Empty shells remain after hatching
• reddish-brown deposits at the base of the lashes are a mixture of louse faeces and host blood following louse bites

Differential diagnosis

Blepharitis (anterior)

• nits may be confused with lash debris
• Demodex mites are much smaller than crab lice (0.1–0.4mm long) and are not usually seen outside the lash follicle

Allergic or infective conjunctivitis

Eczema affecting lid skin

Management by optometrist

Practitioners should recognise their limitations and where necessary seek further advice or refer the patient elsewhere

Sensitive counselling (i.e. by GP) required as this is a sexually transmitted disease

• advice on personal hygiene: wash hands after touching pubic region
• NB possibility of sexual abuse of children

Remove lice, nits and shells (casts) at slit lamp

• use forceps (lice have a tenacious grip on the lashes)

Advise on any symptoms of pubic infestation

• effective treatments (e.g. malathion, permathrin) available without prescription from pharmacies

Sexual partners or family members at risk should have their eyes examined and treated if necessary
Bed linen, towels and clothes should be washed at 60°C for at least 5 min
(GRADE*: Level of evidence=low, Strength of recommendation=strong)

Application of unmedicated paraffin-based ointment (e.g. Simple Eye Ointment) to the lid margins will suffocate lice (unmedicated ointment, applied twice daily for at least 2 weeks)
(GRADE*: Level of evidence=low, Strength of recommendation=strong)

Permethrin 1% lotion applied to lashes for 10 minutes with eyes closed and then rinsed to remove 
NB: insecticides can be toxic to the cornea

• should only be undertaken by experienced practitioners as such preparations are toxic to the ocular surface. Great care is needed so that only lid tissue is treated, and afterwards the lid margins should be carefully wiped with dry cotton buds in order to remove residual permethrin

(GRADE*: Level of evidence=low, Strength of recommendation=weak)

Management category

Referral via GP for management of non-ocular aspects, including tracing and screening close contacts; also screening for other sexually-transmitted diseases

B1 (modified): possible prescription of drugs: telephone GP to discuss referral to STD clinic and for advice on local safeguarding arrangements in the case of a child

Possible management by ophthalmologist

Normally no referral.

Evidence base

*GRADE: Grading of Recommendations Assessment, Development and Evaluation (www.gradeworkinggroup.org)

Sources of evidence

Centers for Disease Control and Prevention: Lice – Pubic ‘Crab’ Resources for Health Professionals

Clinical Effectiveness Group (British Association of Sexual Health and HIV) United Kingdom National Guideline on the Management of Phthirus pubis infestation (2007)

Karabela Y, Yardimci G, Yildirim I, Atalay E, Karabela SN. Treatment of Phthiriasis Palpebrarum and Crab Louse: Petrolatum Jelly and 1% Permethrin Shampoo. Case Rep Med. 2015;2015:287906

Ma D-L, Vano-Galvan S. Infestation of the eyelashes with Phthirus pubis. CMAJ. 2010;182(4):E187.

Panos GD, Petropoulos IK, Dardabounis D, Gatzioufas Z. Phthiriasis palpebrarum. BMJ Case Rep. 2013; bcr-2013-009272

Ryan MF. Phthiriasis palpebrarum infection: a concern for child abuse. J Emerg Med. 2014;46(6):e159-62

Wang DH, Liu XQ. Case report: A case of corneal epithelial injury associated with Pthiriasis palpebrarum. Front Med (Lausanne). 2022;9:955052.

Wu N, Zhang H, Sun FY. Phthiriasis palpebrarum: A case of eyelash infestation with Pthirus pubis. Exp Ther Med. 2017;13(5):2000-2002

Phthiriasis
Version 11
Date of search 04.05.23
Date of revision 29.06.23
Date of publication 01.09.23
Date for review 03.05.25
© College of Optometrists