Primary congenital glaucoma is an inherited ocular disease described in the Siamese cat in which abnormal development of the drainage angle prevents the normal outflow of aqueous humour. The result is an increase in intraocular pressure from the first weeks or months of life. It progressively and painfully affects the eyeball: corneal oedema, mydriasis, disproportionate growth of the eye (buphthalmos) and blindness. Treatment, medical or surgical, is palliative and does not restore lost vision.

Associated with the Siamese. It is an uncommon disease within the breed and no reliable carrier frequencies are available: limited data.

- Epiphora and blepharospasm in kittens or young cats\n- Mydriasis that does not respond to light\n- Corneal oedema (bluish eye) and increased corneal diameter\n- Buphthalmos (enlargement of the eyeball) as it grows\n- Ocular pain, rubbing, lethargy\n- Progressive blindness, unilateral or bilateral

Primary congenital glaucoma has been known in the Siamese cat for decades as a very early-onset increase in intraocular pressure with altered development of the drainage angle. Kuehn et al. (2016) established a breeding colony with fully penetrant autosomal recessive segregation and, by linkage on chromosome B3 and a candidate gene approach, identified a 4-bp insertion in exon 8 of LTBP2 as the cause of the disease. The DNA test makes it possible to identify carriers before breeding.

- Test Siamese breeding animals before breeding: it distinguishes clear, carrier and at-risk animals.\n- Avoid mating two carriers: 25% of the offspring could be affected.\n- A carrier can be mated to a clear animal without risk; test the offspring that remain in the programme.\n- Complement with early ophthalmological examination of the kittens at any sign of ocular pain or mydriasis.

Differential diagnosis with secondary glaucomas (uveitis, lens luxation, tumours) and with other causes of juvenile buphthalmos. Tonometry and gonioscopy confirm the clinical diagnosis; the genetic test supports management of the line. Congenital glaucoma is an emergency: elevated pressure damages the optic nerve within days or weeks and the visual prognosis is guarded.

1. Kuehn MH et al. 2016. A Mutation in LTBP2 Causes Congenital Glaucoma in Domestic Cats (Felis catus). PLoS One. PMID: 27149523
OMIA002017-9685.