Systemic Hypertension (SH) in dogs and cats is an affection more and more taken into consideration due to the longer life span and to the increasing number of geriatric patients in daily clinic.
Either in its primary or secondary form, SH causes multisystemic damages, among which Ocular Lesions stand out as they appear and are detected first.
Like in humans, SH is frequently detected in the course of the ophthalmologic clinical examination, either routine or non-routine, except for those cases where the first sign is an acute vascular accident (cerebral hemorrhage, thrombosis...).
Ocular manifestations in SH in dogs and cats are quite similar, although there are notorious differences therebetween, as the vast majority of SH cases in dogs seem to be secondary to other (renal, thyroid, diabetic ...) pathologies, while, in cats, the evidence shows that primary HS would be much more frequent.
Manifestations within the posterior segment prevail over those within the anterior segment, usually preceding them. Vascular lesions initially appear on the delicate choroid, retina and anterior uvea precapillary arteriole networks.
Although choroid choriocapillaris vessels would be most sensitive to sudden variations in pressure (secondary SH), those changes occurring as a consequence of a sustained and progressive SH (primary SH) would affect predominantly the retinal vessel network, as it happens in humans. This would account for the observations in cats, where very severe affections of the eye are not ordinarily accompanied by renal lesions with equal intensity. On the contrary, response to treatment is usually better with respect to renal function than to ocular fundus lesions.
The presence of hyphema is always preceded by lesion in the fundus of the eye, choroidal exudates, hemorrhages, retinal detachments, optical neuropathy... Choriocapillaris passive exudates with retinal detachment in the peripapillary area are the earliest alterations to be detected in secondary SH. Contrarily, changes in the retinal arterial bed, with arteriolar sacculation, precapillary arteriolar leackage and thrombosis in the papilla-central area bundle with intraretinal edema, are fequent findings in primary SH in cats, previous to complete retinal detachment. Thus, we should talk of HYPERTENSIVE RETINOPATHY in this species.
References
1. Crispin S.M. and Mould J.R.B. Systemic hypertensive disease and the feline fundus. Veterinary Ophthalmology 2001, 4, 2, 131-140.
2. Villagrasa M. and Cascales M.J. Hipertensión arterial: Aspectos angiográficos del fondo ocular en el perro. Estudio de 24 casos. Clínica Veterinaria de Pequeños Animales. 1999, 19, (1), p. 30-40.