...Doctor, my eyes... Tell me what you see... ...Just say if it's too late for me.
...Doctor, my eyes... I cannot see the sky.
A couple of weeks ago, we presented a short teaser comparing dog and cat vision in order to get you ready for this issue on eye problems in pets. There is one more article I want to offer that will explain the relationship of the size of the mammalian eye to the maximum running speed of the mammal:
Eye Size Determined by Maximum Running Speed in Mammals
ScienceDaily (May 2, 2012) — Maximum running speed is the most important variable influencing mammalian eye size other than body size, according to new research from The University of Texas at Austin.
Species with larger eyes usually have higher visual acuity, says Chris Kirk, associate professor in the Department of Anthropology. But what are the ecological factors that cause some mammals to develop larger eyes than others?
"If you can think of mammals that are fast like a cheetah or horse, you can almost guarantee they've got really big eyes," says Kirk. "This gives them better vision to avoid colliding with obstacles in their environment when they're moving very quickly."
Kirk and physical anthropology doctoral student Amber Heard-Booth are the first to apply Leuckart's Law -- a hypothesis that was developed specifically for birds and speed of flight -- to 50 species of mammals. The paper is forthcoming in the journal Anatomical Record. Heard-Booth presented the findings at the 2011 American Association of Physical Anthropology Meeting, where she was awarded the Mildred Trotter Prize for exceptional graduate research in evolutionary morphology.
Previously it was thought that the time of day that an animal is active (nocturnal or diurnal) would be the main factor driving the evolution of mammalian eye size. However, comparative research on the anatomy of the eye has shown that although nocturnal and diurnal species differ in eye shape, they often have similar eye sizes. Although nocturnal species may appear to have bigger eyes because more of the cornea is exposed to let in more light, activity pattern only has a modest effect on eye size.
By comparison, body mass plus maximum running speed together can explain 89 percent of the variation in eye size among mammals.
The researchers controlled for body size and evolutionary relationships, and found that the relationship between eye diameter and maximum running speed is stronger than the relationship between body mass and running speed.
"You start looking at comparative data and one thing that is always going to influence eye size is body size. An elephant is always going to have bigger eyes than a mouse," Kirk says. "Elephants are the biggest animals we measured, but they are not that fast compared to a cheetah or zebra. At the same time, porcupines -- the biggest of the rodents in our sample -- are slow while some smaller rodents are much faster.
"There is going to be the effect of body mass, but when you look at maximum running speed in isolation or when you hold body mass constant, it's still significantly related to eye size," Kirk says. "And when you combine maximum running speed and body mass as your two variables influencing how big an eye is, they can explain almost all of the differences observed between species. This is a highly significant result."
Adapted from: http://www.sciencedaily.com/releases/2012/05/120502112606.htm
OK, that gets the pure science out of the way and we can continue with the medical part of eye problems.
Do dogs get eye problems?
You bet. Dogs can get many eye diseases including glaucoma, inflammation in the eye, and corneal ulcers. Eye injuries are common - many of which can be prevented. They are commonly caused by dogs getting shampoo in their eyes during bathing. Frequently either the shampoo irritates sensitive eye tissue or they rub their eyes and create an ulcer. The most frequently damaged portion of the eye is the cornea. This transparent structure covers the outside of front of the eye and protects its sensitive contents. At only a half-millimeter to a millimeter thick, it doesn't take much to injure this crucial part of your dog's anatomy.
Exposure to foreign materials such as dust or wood chips can further damage eyes. In particular, household spray cleaners must be used with caution and NEVER while a pet is in the room. We frequently see ulcers in the eyes of dogs who were scratched by another pet or ran into something in the yard. Shampoo and cleaners are by far the biggest culprits.
Signs of an eye injury include squinting, rubbing at the eye, or redness in the surrounding tissues. Some dogs might experience watery eyes. If you see any of these signs, please call your vet. Care of an injured eye must begin as quickly as possible to prevent further damage.
Adapted from: http://view.petplace.com/?j=fe6c15747460057c7711&m=feff1273766004&ls=fded10797066007876137876&jb=ffcf14
Dr. Jon just mentioned a watery discharge from the eyes. That is just one type of discharge you might see.
Dog Eye Discharge: Common Causes
Dog eye discharge -- we've all dealt with it. In fact, it's a rare morning when our pups wake up without a bit of icky goop in the corners of their eyes. Yes, we know: eeeewwww.
However, there's a difference between the harmless daily discharge that occurs in all dogs and dog eye discharge caused by an infection or disease. According to PetPlace.com, abnormal dog eye discharge can appear suddenly or gradually and can come in many forms, including somewhat clear and watery, mucoid (or gray and rope-like), mucopurulent (meaning it's a thick yellow-green color) or bloody. Watch the tissue around the eye for irritation and puffiness, and remember that, generally speaking, more discharge means a more serious problem.
These different types of dog eye discharge have a few possible causes. A problem with the tear duct can prevent normal tear drainage, or there could be excess tear production caused by eye pain. Inflammation of the eyelid, cornea, iris or blood vessels in the eye can cause this, or it could be due to another problem, such as corneal ulcers, lens displacement, or another defect within the eyelid.
If your pet seems otherwise perfectly normal, try cleaning the area with a warm, damp cloth and flushing the eye with saline solution, says Natural Dog Health Remedies. However, you should never use human eye drops or other human eye medications on your dog.
If the problem isn't resolved in a couple of days, or if your dog seems at all bothered by the eye (acting differently or rubbing the area), get to your vet right away for an accurate diagnosis.
Adapted from: http://www.pawnation.com/2009/11/11/dog-eye-discharge-common-causes/
From a veterinary eye specialist, here are the biggest eye problems for an older dog
Eye problems in aging dogs?
Posted by Neena Pellegrini
Dr. Tom Sullivan, a veterinary ophthalmologist at Animal Eye Clinic in Seattle, answers this week's questions about eye problems in aging dogs. It is part of our continuing series about the health issues facing senior dogs.
Question: Eye issues can be prevalent in senior pets and something owners often ignore or underestimate. Why are seniors particularly vulnerable to eye problems, and what are the most common eye issues you see in your older patients?
Answer: Seniors are more likely to have eye problems for a few reasons. First, some disorders are a result of aging and wear and tear. Cataracts and retinal degeneration, for example, are often age-related degenerative conditions.
Second, older animals have had more opportunity to sustain injury to the eyes, which can lead to long-term complications like glaucoma.
Lastly, some eye diseases are a result of systemic conditions -- such as diabetes, high blood pressure, cancers -- all of which are more common in the elderly.
Nuclear Sclerosis: This is a normal change seen in aging lenses. The lens sits behind the iris -- the colored part of the eye. The pupil is simply a hole in the iris through which we see. The lens is transparent, so we normally don't see it when we look at our dog.
The lens continues to grow throughout life and forms rings similar to the growth of a tree. Instead of increasing in diameter, each new ring compresses the central part of the lens more and more. As more and more rings compress that nucleus into a smaller and smaller ball, the compressed lens proteins lose some transparency and begin to reflect light approaching from certain angles.
This reflected light makes the pupil appear cloudy when viewed from the exterior but interferes very little with vision.
This is the cloudy appearance seen in older dogs, and it is a normal change. It generally begins at about 7 years of age, but it doesn't tend to become noticeable until 10 or 11. If you have a dog 10 or older with cloudy looking eyes but no signs of poor vision, it is very likely this.
Nuclear sclerosis gets more pronounced over time and will eventually become truly opaque -- a cataract -- usually in the 15-18 year range.
Giant breeds tend to age faster and have a shorter life span than smaller breeds. Even so, their lenses age the same as all dogs -- they'll start to develop nuclear sclerosis at about age 7 and not have that progress to true opacity until 15 to 18.
Cataract: A cataract is when some or all of the lens becomes opaque, or white. The lens is made mostly of protein, and ideally it is transparent.
It is similar in this way to an egg white. When heat is applied to the clear part of a raw egg, it turns white. The loss of transparency is from permanent changes in the arrangement of the proteins caused by the heat.
A cataract is likewise a result of damage to the protein arrangement of the lens material.
Cataracts can occur for many reasons, but the most common reasons in dogs are either genetic (inherited abnormalities in lens function); diabetes (too much sugar, or glucose, gets into the lens and damages the lens; or advanced age. If a dog's pupil appears cloudy/white and vision appears compromised some or all of the time, then that could very well be a cataract.
The only treatment for cataracts is surgery to remove the cloudy lens material and replace it with an artificial-lens implant.
Just as egg white can't go back to transparency after it's been cooked, lens protein opacity is a permanent change, and despite claims to the contrary, no medications will treat cataracts.
Glaucoma: This occurs when pressure inside the eye increases and damages the optic nerve and retina, leading to vision loss.
Fluid is continually produced inside the eye, behind the pupil. This fluid flows forward through the pupil into the front of the eye, where it fills the space between the cornea and iris. This then flows continually out of the eye through a drain into the bloodstream.
Glaucoma occurs when this drain gets plugged, making outflow slower.
Fluid buildup causes increased pressure. This damages the optic nerve, which connects the eye to brain, leading to vision loss. If it reaches above a certain level, it is painful -- causes a headache sensation.
The most common type of glaucoma in people -- slowly increasing pressure in the elderly -- is very uncommon in dogs.
Anything that plugs up the drain can lead to glaucoma though, including tumors in the eye, previous trauma to an eye, long-standing cataracts (causes inflammation and scarring in the drain). So senior dogs have a higher incidence of glaucoma than younger dogs.
Signs of glaucoma include increased cloudiness (of the cornea, so it would look like the whole eye is cloudy, not just the pupil), bulging appearance to the eye or bloodshot appearance to the white of the eye.
Treatment depends on the cause. Sometimes it can be controlled with drops or surgery, but sometimes the eye needs to be removed to restore comfort.
Dry-eye disorders: As the name implies, this refers to problems with the tear film leading to drying and increased exposure of the ocular surface. You can have a decrease in the amount of tears produced (KCS-keratoconjunctivitis sicca) or problems with the quality of the tear film.
Normal tears spread across the surface of the eye and maintain a stable film. Problems occur when the tears basically bead like water on a freshly waxed surface. This results in drying of the surface of the eye.
Dry-eye disorders are important for a few reasons. First, dry eyes are uncomfortable. Second, tears are very important to the health of the cornea.
The cornea is the "windshield" portion of the eye. One of the reasons it is transparent is because there are no blood vessels within the cornea.
Tears provide a large part of the oxygen and nutrients to the cornea. Decreases in tear volume or quality leads to corneal starvation. This, in turn, results in the surface of the cornea becoming more skinlike as a protective response (similar to a callous), which can appear hazy or cloudy. These changes can lead to vision loss over time.
The cornea can develop open sores (corneal ulcers), and these are much more susceptible to infection in dry-eye disorders and can be disastrous to the eye.
Many times the first sign of a dry-eye condition is increased mucous -- the eye attempting to lubricate in response to the drying.
Blindness from retinal disease: There are several different types of retinal diseases in dogs. The one most associated with age would be senile retinal degeneration.
The retina lies against the inner surface of the back wall of the eye. The cornea and lens focus light such that images outside are projected onto the retina like a movie projector and it's screen.
Cells in the retina (rods and cones) are stimulated by light, turning the image into electrical signals that are transformed into "vision" by the brain. Rods are stimulated by dim light. Cones are stimulated by bright light and color (yes, dogs see color, but they only have cones for blue and yellow light, they don't see red).
It is normal to lose retinal cells with age, but some individuals lose more than others.
Many dogs will start having difficulty in dim light or darkness by 11 or 12 years of age. They will stop at the top of stairs or the edge of the bed and wait until lights are switched on before proceeding. This suggests that rods are more affected than cones.
Most dogs (and people) will experience these changes with age, but some seem to start earlier than others and progress more with time.
Factors that can affect this would include genetic influences, possibly nutrition and excessive sunlight exposure, and some systemic diseases (diabetes and high blood pressure, to name a couple).
Asteroid hyalosis: This is an accumulation of cholesterol deposits within the vitreous cavity.
The vitreous is a gel that fills the part of the eye behind the lens. It is transparent to allow vision and acts to keep structures inside the globe stable when the eye is in motion. It basically is like Styrofoam peanuts in a box of fine glassware.
With age, some dogs will develop white cholesterol deposits in the vitreous -- they look like a shaken snowglobe suspended in time. With a few such deposits vision is not affected, but many can result in poor vision, especially in bright conditions, as they scatter light like highbeams in a fog.
This is fairly common, but rarely results in severe loss of vision.
Calcific corneal degeneration: This one is more important. Some older dogs will start to mineralize the surface of the cornea in one or both eyes.
These deposits are gritty and uncomfortable in the beginning, then portions of calcified cornea can slough leading to deep ulcers. These are very slow to heal, in some cases they do not heal at all.
The areas of sloughing are thinner than normal, and in extreme cases the thin spot can rupture, leading to loss of fluid from inside the eye.
Calcific corneal degeneration can be seen with certain diseases (Cushing's disease, kidney failure), but can happen as a consequence of aging alone.
It typically develops in dogs 14 or older. It looks like white spots on the surface of the cornea, and often it isn't noticed until an ulcer develops and persists beyond normal healing time (at which point the patient makes their way to an ophthalmologist).
If caught early this can often be treated and maintained with drops to remove minerals from the corneal tissues.
Question: What can owners do to maintain eye health?
Answer: Basically be aware that eye problems can worsen very rapidly in pets, so if a change is noted seek attention quickly.
Signs of a problem include increasing cloudiness, squinting, discharge (a new onset of tearing, mucous or especially yellow/green, infected-looking discharge), bulging or sinking in of the eye in the orbit, or a decrease in vision.
You want to feed a balanced diet and keep the hair around the eyes trimmed short enough to be able to keep it from irritating the eyes, as well as letting you, the owner, see the eyes clearly enough to notice a problem early. (Groomers often are the first to notice an eye problem in longer-haired breeds.)
Some age-related conditions -- senile retinal degeneration and age-related cataract development in particular -- can result from oxidative stress, a fancy name for the wear and tear of everyday life, such as sunlight, UV exposure and time.
Antioxidant supplementation can help prevent this type of damage if the diet does not contain enough to do the job. Check with your vet about specific supplements and dosages.
These will not help with conditions that are a result of other types of damage, such as diabetic cataracts, inherited retinal diseases or glaucoma.
If these articles on eye problems prompt any questions for you, please send an e-mail to: firstname.lastname@example.org or leave a comment at the end of this issue.
SPORTS NEWS Even with the LA Dodgers being the victim of a no-hitter (thrown by 6 pitchers!) on Friday night in Seattle, we still have the best record in baseball. The no-hitter will no doubt lead to a movie titled Hitless in Seattle? We swept a 4-game series in Philadelphia, the first time we've done that in 66 years!
The youth and vigor of the Oklahoma City Thunder eventually wore down the experience and maturity of the San Antonio Spurs to send the Thunder to the NBA Finals against the Miami Heat. Helpful Buckeye will be pulling for the Thunder to win the championship.
PERSONAL STUFF According to the latest issue of Outside magazine, Flagstaff has been ranked #8 in the USA on the list of most bikeable towns. That means it's a friendly place for bicyclists, with good bike lanes, good visibility, and general awareness of the public of bicycling activity. Tucson, where Helpful Buckeye will be riding in the 30th Annual Tour de Tucson this November, is ranked #1. I feel very fortunate to be able to ride in such good locations!
This past week, Desperado and Helpful Buckeye went with some friends to the US Naval Observatory here in Flagstaff to observe the transit of Venus across the face of the sun. This was quite an affair at the observatory, with numerous telescopes set up for viewing. In particular, a copper-tubed telescope that was used 112 years ago to witness the same phenomenon was available to use. The image of the transit on this scope was really impressive!
I was able to purchase and plant most of my flowers and herbs for this season...it's still a few days short of the last possible frost here in Flagstaff but the nights have been fairly warm. While I was planting them, the song, Laredo Rose, came on the CD of cowboy songs that I had playing...followed shortly by Happy Trails To You. What appropriate timing....
A trip to the Grand Canyon and lunch at the El Tovar awaits us this week in celebration of #43....
Helpful Buckeye is putting the finishing touches on several biking/hiking trips and short quick-hitting trips around Arizona...I enjoy the planning almost as much as the actual experience. In the words of Gloria Steinem: "Without leaps of imagination, or dreaming, we lose the excitement of possibilities. Dreaming, after all, is a form of planning."
~~The goal of this blog is to provide general information and advice to help you be a better pet owner and to have a more rewarding relationship with your pet. This blog does not intend to replace the professional one-on-one care your pet receives from a practicing veterinarian. When in doubt about your pet's health, always visit a veterinarian.~~