Neuse River Golden Retiever Rescue
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Neuse River Golden Retiever Rescue

Maxamillion and his special eyes

by User Not Found | Jan 20, 2014

This is Maxamillion.  He is my foster dog.  He has special eyes. 

Ok well not really much different than any other 9 year old golden retriever, but he’s my foster dog, so I say that makes him special.  Max has cataracts and although they are normal with aging eyes, some cataracts are more harmful than others.  Let’s back up a bit.  In order to talk about eye problems, like cataracts, we need to know how normal eyes work.

Eyes are really cool, they just get a bad rap because most eye stuff grosses people out.  When they are where they should be, doing what they are supposed to be doing, no problem, but anything outside of the norm can be pretty creepy looking and downright scary.  I may not change your mind about the look of eye problems, but I think you’ll admit this is pretty fascinating stuff. 

Canine eyes have three major parts, outer (fibrous), middle (vascular) and inner (nervous).  The outermost layer has two major sections.  The back of this layer, called the sclera, which is tough, stretchy is much like a jello-filled water balloon.  And the cornea which is and extremely thin layer of cells, so thin in fact, that it’s transparent.  The cornea lets light in to the eye.  Remember, not gross, cool.

 The middle vascular section is just as it sounds, a network of blood vessels that supplies oxygen and nutrients to the tissues of the eye.  Hey, eyes gotta eat too.  Within this section are teeny tiny little ligaments and muscles that hold the lens in place and change its shape depending on how far away something is.  Think of them as tiny zoom ligaments.  The vascular section is also home to the iris, or colored portion of the eye.  Side note:  Did you know that puppies are all born with dark eyes?  They don’t open their little peepers until they are about 8 days old and it isn’t until they are 12 weeks old that their actual eye color finally starts to emerge.  Ok, vascular section, home to the iris and to the pupil, or the opening in the middle of the iris.  The iris dilates or constricts to regulate the amount of light coming in so in bright light, the pupil should be small, but in dim light large to let as much light in as possible.

Last but not least, the nervous section.  This is home to the retina, one we all know.  The retina is a layer of photoreceptor cells that are able to change light to electrochemical signals which are transmitted to the nervous system.  There are two kinds of photoreceptor cells, rods and cones…..its all coming back from high school biology now right guys?  Cones need bright light for sharpness and rods are very light sensitive.  Rods are found mostly in nocturnal animals and our dogs have mainly cones.  Here is where the color-blind debate comes in….ah, science. 

The lens is most responsible for clear vision.  Its shape changes allow our dogs to either see far away or objects close to them, that’s why it’s soft and transparent.  The liquids all around the eye help to focus light and their pressure keeps the eyeball shape, but they also keep the lens and the tissues around it happily fed and remove wastes.  This focused light that comes in to the eye is projected on the retina but the two projectors in the eye cross making the image upside-down!  Our brains actually flip the image the right way.  If the pressure is wrong or the lens isn't changing shape like it should, the light is projected behind or in front of the retina and that results in blurry vision.  All animals have binocular vision which means the brain uses images from both eyes and forms them in to one image.  So, if only one eye is functional, it’s difficult to judge distances between objects.

Eyes also love to accessorize.  Eyelids, eyelashes, tear glands, conjunctiva and nictitating membranes (third eyelids) are all additional structures that help to protect, lubricate and nourish the eyeball.  The conjunctiva is a delicate membrane that lines the inside of the upper and lower lid.  Large eyelashes keep dust and other particles from getting in.  Eyelids also keep stuff from getting in but they are responsible for “blinking” which helps spread tears and other oils over the cornea to keep it lubricated and clean the microscopic dust bunnies.  Tears are produced by lacrimal glands and actually contain an antibacterial enzyme!  The tear duct or lacrimal duct is a small opening at the corner of the eye that tears can drain into. 

Most animals have a reflective layer in the eye called tapetum lucidum.  This is what causes their eyes to shine in the dark or when you’re trying to take a picture!  The layer allows more light to be reflected back in to the eye for better night vision.

Perhaps that’s all the eye talk you can handle for one sitting.  Now that we all know how eyes work normally, next time we’ll talk about cataracts and other eye problems you may encounter with your canine companion.  I didn’t trick you, I’m just keeping you coming back for more =)  

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