glaukom-en

Glaucoma in Shibas

Hereditary eye diseases can be found in almost all dog breeds. The most common is cataract which is a partial or total opacity of the lens leading in the majority of cases to blindness. Less frequent but also diagnosed in several breeds is glaucoma. Glaucoma is an abnormal state of the eye caused by an increase of intraocular pressure over a longer period of time. Glaucoma also leads to blindness. Both eye diseases are recessively inherited.

How does glaucoma develop?

A healthy eye has a constant pressure which is achieved due to the permanent generation of eye fluid (chamber fluid) and its outflow. The chamber fluid

– is generated by means of the ciliary muscle in the posterior chamber,

– flows through the pupil into the anterior chamber

– towards the so-called iridocorneal angle (ICA) which is formed by the cornea and the iris,

– and finally flows off outwards via a permeable tissue called pectinate ligament (PL) and via a drainage canal (see figure).

In some dog breeds the ICA is irregular (too large or too small) and the PL malformed (dysplasia) which may cause outflow dysfunctions of the chamber fluid. In such cases the intraocular pressure increases abnormally – having fatal effects.

Predisposition in Shibas?

The Shiba Inu so far was not numbered among the breeds being especially susceptible to glaucoma. Apparently this opinion has to be revised now. In the latest issue of the journal Veterinary Ophthalmology [1] researchers from the University of Tokyo have published the results of a study concerning this disease. From 1998 to 2003 the scientists investigated a total of 114 Shibas. 46 dogs were affected unilaterally or bilaterally, the remaining 68 dogs served as control group. In this control group a more or less strong narrowing of the iridocorneal angle (ICA) was detected in the majority of the dogs. On the basis of their results the researchers assume "that ICA narrowing and PL (pectinate ligament) thickening is a common abnormality in Shiba Inu dogs in Japan and may predispose those dogs to glaucoma". In a further Japanese investigation of 1244 dogs of 29 breeds by the same group of researchers the Shiba again showed the by far highest incidence of glaucoma. [2]

Diagnosis and therapy

Glaucoma is so dangerous because symptoms appear very slowly and irregularly. For this reason a special sensibility is required from the owner and the veterinarian in endangered breeds. If glaucoma exists the following three symptoms are always present:

– a reddened eye

– a widened pupil

– an increased intraocular pressure

Attempts can be made to normalise the eye pressure by means of medication and various types of surgery, but the long-range prognosis is not favourable. Dogs with glaucoma should be categorically excluded from breeding.

The researchers in Tokyo write cautiously and talk of a probable predisposition to glaucoma in Shibas in Japan. It is necessary to wait and watch if this suspicion also proves to be true with Shibas in Europe and America.

Notes

[1] Kumiko Kato, Nobuo Sasaki, Satoru Matsunaga, Manabu Mochizuki, Ryohei Nishimura, Hiroyuki Ogawa: Possible association of glaucoma with pectinate ligament dysplasia and narrowing of the iridocorneal angle in Shiba Inu dogs in Japan, Veterinary Ophthalmology 9/2 (2006), pp. 71-75.

[2] Kumiko Kato, Nobuo Sasaki, Satoru Matsunaga, Ryohei Nishimura, Hiroyuki Ogawa: Incidence of canine glaucoma with goniodysplasia in Japan: a retrospective study, The Journal of Veterinary Medical Science 68 (2006), pp. 853-858.

–	is generated by means of the ciliary muscle in the posterior chamber,
–	flows through the pupil into the anterior chamber
–	towards the so-called iridocorneal angle (ICA) which is formed by the cornea and the iris,
–	and finally flows off outwards via a permeable tissue called pectinate ligament (PL) and via a drainage canal (see figure).

–	a reddened eye
–	a widened pupil
–	an increased intraocular pressure

[1]	Kumiko Kato, Nobuo Sasaki, Satoru Matsunaga, Manabu Mochizuki, Ryohei Nishimura, Hiroyuki Ogawa: Possible association of glaucoma with pectinate ligament dysplasia and narrowing of the iridocorneal angle in Shiba Inu dogs in Japan, Veterinary Ophthalmology 9/2 (2006), pp. 71-75.
[2]	Kumiko Kato, Nobuo Sasaki, Satoru Matsunaga, Ryohei Nishimura, Hiroyuki Ogawa: Incidence of canine glaucoma with goniodysplasia in Japan: a retrospective study, The Journal of Veterinary Medical Science 68 (2006), pp. 853-858.