Millions of people around the world wear eyeglasses to help them see. Short-sightedness is the most common visual issue that requires glasses to correct. We know that dogs get many of the same eye diseases as humans, like cataracts, glaucoma and conjunctivitis. So can dogs become short-sighted too? How can you tell? Does being short-sighted affect their lives?

Table of contents

How Does Vision Work?

Let’s briefly outline how dogs and humans see the world, as this will help with understanding short-sightedness later.

We see the world when light bounces off objects and is reflected into our eyes. The light passes into the eye via the cornea and through the pupil; the pupil will dilate or constrict to vary how much light passes into the eye. The light then travels through the lens, a clear structure that focuses the light into a single point. The lens will also adjust to help focus the light, similar to a camera focussing on different distances. The light travels through the back of the eye to the retina, an area of light sensitive tissue that converts the light to an electrical signal. The electrical signal is passed up the optic nerve to the brain. The brain then processes this image so we can understand the world around us. All of this happens almost instantaneously.  

What is Short-Sightedness?

Short-sightedness, also called myopia, is a condition that causes distant objects to appear blurry. The opposite is long-sightedness, or hyperopia, where nearby objects appear blurry. A person can have one or the other of these conditions, or even one in either eye. The degree of myopia is measured in dioptres, with -0.50 to -3.00 being mild, -3.00 to -6.00 moderate, and below -6.00 severe myopia.

Myopia is generally caused by the eyeball being too long, or the refractive parts of the eye (cornea, lens or fluids) being abnormal. In both cases, rather than light being directed at the retina, the light is directed just before it; an image is still transmitted to the brain, but the distant objects appear blurry while close objects are normal (assuming there is no long-sightedness too). 

As well as blurry vision, myopia can lead to headaches and eye strain, as well as damage to the retina, glaucoma (high eye pressure) and cataracts. 

There are likely genetic and environmental factors that cause myopia, as it is commonly associated with people who spend time working on objects up close, and spending a lot of time indoors. It tends to first present in early childhood, but can develop at any age. It is diagnosed via a number of tests performed by an ophthalmologist or optometrist.

The most common way to correct myopia is by wearing prescription glasses or contact lenses. Laser surgery or artificial lens implants offer more permanent solutions. 

Do Dogs Get Short-Sightedness?

As you might imagine, it is quite difficult to assess whether dogs are short-sighted, given they cannot read a series of increasingly small letters from a distance! However, there have been some studies into canine myopia. 

Study 1

A study in 1992 analysed myopia in 240 dogs using streak retinoscopy; a technique that measures the degree of myopia by looking at the movement of reflected light in the pupil. Some of the dogs, all German Shepherds, also had tests that measured the shape of the eye. 

They found that 160 eyes were considered hyperoptic (far-sighted), and most breeds had either normal or mildly hyperoptic eyes. However, the mean dioptre of Rottweilers was -1.77, with 64% considered myopic.  In miniature schnauzers, the average was -0.67 with 50% myopic (notably four from one family), and non-guide dog German Shepherds was -0.86 (53% myopic). Interestingly, German Shepherds that were guide dogs had an average dioptre of +0.22, and only 19% were myopic.  There was an association between age and abnormal dioptre, with older animals more likely to have a condition called nuclear sclerosis as well as myopia.  

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The study also looked into the shape of the eyes of the German Shepherd guide dogs, and found no difference in the shape of the eyeball or the corneal surface between normal and myopic-eye dogs. 

When taken together, these findings indicate that the vast majority of dogs have normal vision or are considered long-sighted. Previous studies also matched these results. However, certain breeds may be more predisposed to myopia. There is likely a genetic component, as one family of schnauzers had myopia, while others did not. It was unclear why guide dogs were less likely to have myopia, but it may be due to selection for training that filters out dogs with myopia. The actual cause of myopia may be related to lens abnormalities, as the cornea and eyeball-size were considered normal in myopic dogs.  It is important to note, however, that the numbers in each breed was small.

Study 2

A more recent 2016 study looked in detail about the effects of age on canine myopia. They measured the dioptre, using an autorefractor, of 9 beagles and compared this with their age. None of the dogs had cataracts affecting their vision. But three did have nuclear sclerosis, the aforementioned condition where the lens becomes denser over time. Generally, the condition is thought not to affect vision.

The study found that the older dogs had a lower dioptre, indicating they were more short-sighted. Conversely, younger dogs were able to adjust their lenses slightly to different light conditions, indicating more flexibility than older dogs. They concluded that older dogs are more likely to be myopic, which the previous study alluded to. This may be due to nuclear sclerosis (which can lead to myopia in humans) or other degenerative factors – however, a recent 2023 study found that nuclear sclerosis was only weakly associated with myopia. 

Studies 3 and 4

Although the first study didn’t identify Labrador retrievers as a breed with a high incidence of myopia, subsequent studies have investigated the condition more in Labs. Initially, in 1999, the dioptre of 75 Labradors was measured via streak retinoscopy, as well as the dimensions of the eyes of 57 of them. They found that 11 (14.7%) were myopic in one eye, and 6 (8.0%) were myopic in both eyes. Subsequent testing found that an increased horizontal length of the vitreous chamber of the eye was associated with an increased myopia, something not identified in the earlier 1992 study.

A later 2008 study built upon this work and tried to determine how far genetics played a role in myopia. They measured the dioptre of 116 Labrador retrievers that all originated from a single male known to be myopic (-2.00 dioptre). They didn’t want to test the effects of age, so excluded dogs older than 8. The authors found that the number of myopic dogs was higher than the previous study, with 31% considered myopic (and 9% hyperopic). They believe that this is due to the fact these dogs were all closely related, indicating that myopia can be an inherited genetic predisposition. It was noted that smaller litters were likely to be more myopic than large litters, though it was unclear whether this was due to genetic or environmental factors. 

Other Studies

Some other findings from different studies are also worth briefly mentioning. A study of Springer spaniels, toy poodles and Collies identified 63.9% of toy poodles, and around 35-36% of the other breeds as being myopic. In these dogs, the lens had some abnormalities. 

A large study that collected results from previous papers identified a number of breeds as having either short- or long-sighted vision on average. Within these breeds, there were small groups, often entire litters, that were myopic. These breeds included German Shepherds, Rottweilers, Collies, Miniature schnauzers and toy poodles. Age was also related to the degree of myopia, curiously more so in female dogs, which previous studies did not note. They did also note that most dogs are considered emmetropic, with normal vision, contrasting with the earliest studies. 

Summary of Findings

When taken together, we can conclude that while most dogs on average have emmetropic (normal) vision, certain breeds are predisposed to short- or long-sightedness. The anatomical reason for this seems to vary but can be associated with the length of the eyeball, shape of the cornea or abnormalities within the lens. Older dogs are more likely to become myopic, but it is not proven if having nuclear sclerosis increases this risk. There is likely a high hereditary factor in myopia, as related dogs are more likely to all be myopic. Guide and other working dogs are less likely to be myopic, likely due to selection for these roles filtering out imperfect vision. 

The Effects of Myopia on Vision

Throughout this article, we’ve been assuming that the effects of a low dioptre (myopia) in dogs is the same as humans, negatively affecting their long-distance vision. But how can we know this? One study did investigate this. In the study, 8 retriever dogs were fitted with different contact lenses to effectively give them myopia in one eye. The dogs were then given 3 tests to retrieve an object at distance. With increasing myopia, 3 dogs needed assistance to find the object, and all dogs took longer finding it. This indicated that myopia does negatively affect a dog’s visual abilities… Although this was also a very small-scale study.

However, the large collaborative study noted that mild myopia is unlikely to be noticed by owners as routine activities do not require high visual acuity at distance. Even some performance dogs with myopia are less likely to be affected depending on their work – they noted two Springer spaniels that both had low myopia (-1.00 and -0.75) were both field trial champions, likely because their sport involved them finding a larger object at a medium distance (27-46m away) that their degree of myopia may not hinder.  

We can thus conclude that for the majority of dogs with normal to mild-myopia, the dog and owner are unlikely to notice any deficiencies in their vision during day-to-day activities. There may be some noticeable decline in older age. High-performance dogs, especially those that need to see objects at distance, likely will have noticeable problems if they develop myopia, though selection for these sports may filter those dogs with reduced vision in the first place. Visual defects in dogs, particularly if sudden, are far more likely to be caused by more common ocular diseases, such as ulcers, glaucoma or cataracts. 

Sources:

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