We would like to thank Charlotte Freeman BVM&S Cert VOphthal MRCVS of The Mount Veterinary Hospital,21 High Street, Wellington
Somerset TA21 8LD Tel. 01823 662286 for her input into this section.
Glaucoma is an elevation of the pressure within the eye as a result of increased fluid. If the fluid pressure cannot be reduced it can cause devastating and irreparable damage to the retina and optic nerve resulting in visual impairment. Complete blindness can occur with 24 hours if the pressure is extremely elevated or it can occur over weeks and months if the elevation is mild.
The definition of glaucoma also encompasses the progressive death of retinal ganglion cells and their associated axons.
Glaucoma in itself is not a term for a single disease entity but a group of related diseases caused by different but overlapping factors.
The glaucomas consist of 5 stages:
a) an initial event usually involving the pathways for the outflow of fluid within the eye
b) physical changes to the outflow pathway/drainage angle causing obstruction
c) elevated pressure within the eye that is too high for the blood to flow and nerve impulses to fire
d) retinal cell dysfunction with resulting optic nerve degeneration and nerve cell death
e)vision loss and blindness
Continuous elevations in Intraocular pressure (IOP) obviously cause rapid and permanent damage to the retinal cells and quickly lead to pain and blindness. However, intermittent spikes in the IOP also switch on damaging amino acids mainly glutamate in the retinal cells leading to progressive retinal cell death even when the IOP has returned to normal. Therefore the canine glaucomas are neurodegenerative diseases with elevations in the IOP being the principal risk factor.