Elevations in your pet’s blood pressure can have serious consequences, but this condition is possibly one of the most underdiagnosed systemic illnesses in pets because of the disease’s silent nature. Our team at Veterinary Vision Center shares information about hypertensive retinopathy, and explains how high blood pressure can affect your pet’s vision.
What is hypertension in pets?
Blood pressure measures the pressure blood exerts against the artery walls during and between heart beats, and depends on cardiac output, as well as systemic peripheral resistance. The renin-angiotensin system, a hormone system that plays a role in balancing fluid and electrolytes, is a critical component to regulating blood pressure. Patients with high blood pressure are classified as having primary or secondary hypertension.
- Primary hypertension — This occurs when no known cause can be determined for an imbalance between cardiac output and systemic vascular resistance. More than 90% of human cases are caused by primary hypertension.
- Secondary hypertension — This occurs as a result of systemic disease or medication. Almost all cases of elevated blood pressure in pets are caused by secondary hypertension.
Conditions associated with hypertension in pets include:
- Hyperadrenocorticism — This condition causes prolonged, elevated cortisol levels, causing the liver to produce a hormone that causes overstimulation of the renin-angiotensin system.
- Hyperthyroidism — Increased thyroid hormones act on cardiac muscle tissue, causing increased cardiac output.
- Kidney disease — The exact mechanism leading to hypertension is unknown, but likely involves the kidney’s inability to process electrolytes and fluids properly, leading to increased blood return to the heart, and an increase in cardiac output.
- Diabetes mellitus — Type 1 diabetes affects kidney function, leading to hypertension. Type 2 diabetes causes increased insulin in the blood, leading to abnormalities in sodium and calcium levels, which cause increased blood volume and peripheral resistance.
- Liver disease — The mechanism leading to elevated blood pressure is undetermined.
How does hypertension affect vision in pets?
Capillaries are the most pressure-sensitive structures in the vascular system, and three layers of capillary networks run throughout the retina. This structure lines the back of the eye, and consists of photoreceptors that capture incoming light rays, and transmit them as electrical and chemical signals along neuronal pathways to the brain, to form a visual picture. When a pet’s blood pressure is elevated, blood vessels throughout their body are damaged, including the sensitive retina capillaries. This damage results in leakage from the vessels, causing fluid accumulation under the retina that leads to retinal detachment. When a pet’s retina detaches, they suddenly lose vision in the affected eye. In addition to blindness, other signs can include one pupil appearing larger than the other, blood in the eye, and in some cases, neurological issues, such as disorientation, incoordination, and seizures.
How is hypertensive retinopathy diagnosed?
Any pet who is diagnosed with a condition that puts them at higher risk for developing hypertension should have their blood pressure monitored, and a thorough ophthalmic examination, since subtle signs can be appreciated before retinal detachment occurs. A pet’s blood pressure measurement should always be performed in a quiet setting, after the pet has calmly acclimated to their surroundings. Several readings should be taken, to ensure accuracy. Methods to measure a pet’s blood pressure include:
- Doppler flow — This method uses a Doppler ultrasound to estimate the blood flow through blood vessels by bouncing high-frequency sound waves off circulating red blood cells. A cuff is placed on the pet’s limb, and a sphygmomanometer is used to inflate the cuff. The point at which flow sounds return when the pressure in the cuff is released is the systolic blood pressure. A more subtle second sound can be appreciated as more pressure is released. This is the diastolic pressure.
- Oscillometry — This automated device works by inflating a cuff around an extremity until arterial blood flow stops, and then slowly reducing the inflation while monitoring the pulse waves generated by arterial pulsations. This method is reasonably accurate for medium- and large-breed dogs, but should not be used in cats or small dogs, because readings in these pets are consistently underestimated.
How is hypertensive retinopathy treated in pets?
The main concern in treating hypertensive retinopathy is controlling the pet’s elevated blood pressure. Since hypertension is typically a secondary condition in pets, controlling their elevated blood pressure usually involves treating the primary disease, which must first be identified. This involves diagnostics, such as a complete health history, physical examination, blood work, and urinalysis. If a pet experiences vision loss as a result of a retinal detachment caused by hypertension, the retina can sometimes be reattached, if the condition is addressed immediately. In addition to ocular damage, hypertension can severely injure other organs, such as the heart, brain, and kidneys. If diagnosed with hypertensive retinopathy, your pet will require regular eye examinations and blood pressure monitoring, to ensure their condition remains controlled.
Hypertensive retinopathy is a concerning condition in pets, but regular wellness examinations to screen for conditions that put your pet at risk for hypertension can protect their vision. If your pet is diagnosed with hypertension, contact our team at Veterinary Vision Center, so we can take the necessary steps to protect their eyes.