Interesting Fact About Dog Eye:-

Dog Eye Anatomy is very similar to that of a human eye, but dogs' eyesight differs from humans. They see mainly in red and green hues and have better night sight and a wider field of vision. They also have an upper and lower eyelid and a third eyelid on the outside of the eye for protection. Rods and cones are how images and light are processed and important for vision. Puppies are born with their eyelids closed because their eyes are not fully developed. It's quite endearing. Because their eyes are still developing for the first two weeks, their eyelids remain closed to protect them. Puppy eyes open around 14 days and usually one at a time. Puppies do quite alright without their eyes being open at the start, actually, they don't need their vision as much as newborns. All they need is to find their mother for milk, and they mainly rely on their sense of smell for this. When they first open their eyes, their vision will be poor, and their eyes will look grey or blueish and a little milky. As the weeks go by, their eyesight develops more, and they'll start seeing more clearly and recognizing shapes better. Puppy eyes reach full development at around 8 weeks of age.

Structure Of Dog Eyes:-

There are many similarities between dogs and the human eye, including:

Sclera: This is the white part of the eye fibrous layer that surrounds the iris. Cornea: The transparent dome-like structure that covers the front of the eye. It bends light as it enters the eye.

Eyelids: Dogs have three eyelids: an upper, a lower, and then a third eyelid. They mainly serve to protect the eye, the third eyelid sweeping back and forth to spread tear film and keep the eye moisturized., an upper, a lower, and then a third eyelid. They mainly serve to protect the eye, the third eyelid sweeping back and forth to spread tear film and keep the eye moisturized. That can be injured easily.

Conjunctiva: Lining of the eyelids that can become inflamed and pink in color when dogs get excited, have allergies, or have an eye infection.

Eyelids: Dogs have three eyelids, an upper, a lower, and then a third eyelid. They mainly serve to protect the eye, the third eyelid sweeping back and forth to spread tear film and keep the eye moisturized.

Iris: This is the colored part of a dog's eye, that contains smooth muscle and controls the size of the pupil, making them beautiful, essentially. It can be yellow, brown, blue, or even white, which expands and contracts in low light or bright light.

Pupil: Black area in the center of the iris; It contracts (gets smaller) in bright light or dilates (gets bigger) in dim light, according to light intensity, the pupil opens and closes.

Lens: Located behind the iris; it changes shape to focus light on the retina

Retina: Located in the back of the eye; it contains photoreceptors called rods, which sense light and movement, and other photoreceptors called cones, which sense colors

Rods and Cones: There are photoreceptors found in the retina, which process light signals. Cones allow dogs to see colors, while rods allow them to see shapes. Dogs also have some eye features in structures that are different from people.

Tapetum lucidum:  Located behind the retina, the tapetum lucidum reflects light through the retina, increasing the light available to the photoreceptors. This is why animals see better at night, and it makes an animal's eyes appear to glow at night when lights reflect from the animal's eye. Progressive retinal atrophy (PRA), is a group of degenerative diseases that affect photoreceptor cells in the eyes. With this disease, the cells deteriorate over time, eventually leading to blindness. There are two main forms of PRA recognized in dogs: an early-onset, inherited form called retinal dysplasia, and a late-onset form. PRA is an inherited disease that occurs in many breeds of dogs.

Third eyelid:

The gland of the third eyelid contributes a significant portion of the tear film that bathes the eye, in addition to that which is produced by the lacrimal gland. It is known as the nictitating membrane, the third eyelid is whitish and is located at the corner of the eye, near the nose, and also contains tissue that secretes immunologic agents to help fight infection. If the gland suddenly “pops” forward, this condition is called “cherry eye” because it looks as if there is a small red cherry on the inside corner of the eye. The correct term is “prolapsed gland of the third eyelid”. When this happens, the supporting cartilage of the membrane folds over and the third eyelid loses its windshield wiper function. It also protects the cornea from injury and helps to protect the eye from scratches and also moves across the eye when a dog blinks to help produce tears.

Eye conditions and Symptoms:-

Just like humans, dogs can suffer bacterial or viral infections. The surface of the eye can also be damaged by foreign objects, particularly if they enjoy rolling around and running through the undergrowth while out walking. Dogs can also suffer a general deterioration of their eyesight as they age. There are many conditions which can affect your dog's eyesight:

Conjunctivitis:

Conjunctivitis, also called pink eye, is a common condition in dogs (just like it is in humans). The term conjunctivitis means inflammation (swelling) of the conjunctiva, which is the tissue covering the eyeball and eyelids. Dogs have a third eyelid, or nictitating membrane, in the inner corner of the eye, which is also covered by conjunctiva. In healthy dogs, the conjunctiva of the eyelids is not readily visible and has a pale pink color. When conjunctivitis occurs, the conjunctival membranes become red and swollen. Symptoms include red or pink eyes, discharge, swelling, and excessive blinking. If left untreated, it can lead to corneal ulcers or scarring.

 Cataracts:

A dog cataract is an imperfection or a “clouding” of the lens of the eye. A dog's eye lens should be crystal clear, but diseases of the lens—like cataracts—can change its transparency or clarity. When a dog develops a cataract, the normally clear lens develops a cloudy or opaque appearance that interferes with the light reaching the retina. Symptoms include cloudy or hazy eyes, difficulty seeing, and increased sensitivity to light. If left untreated, it can lead to glaucoma or blindness.

Glaucoma:

 Dogs, like people, can develop glaucoma. Glaucoma occurs when an imbalance in the production and drainage of fluid in the eye (aqueous humor) causes a buildup of fluid that increases eye pressure to unhealthy levels. The increased pressure can destroy the retina and optic disk (the spot where the optic nerve enters the eye). Open-angle glaucoma is a painless and gradual development of blind spots or loss of vision over a long period. Closed-angle glaucoma is a sudden increase in eye pressure with severe pain, redness, and loss of vision.. symptoms include excessive pressure in and around the eye, which can lead to pain and blindness.

Cherry Eye:

The third eyelid gland is normally anchored to the lower inner rim of the eye by a fibrous attachment. This attachment is thought to be weak in certain dog breeds, allowing the gland to prolapse easily. When the gland in the third eyelid swells, it creates a small pink bulge that covers part of the eye. It protrudes from the corner of the eye nearest the nose.  The cherry eye in dogs usually includes the classic “cherry pit” appearance. Cherry eye is located in the corner of your dog's eye nearest the nose, and it's fairly unmistakable. This swelling may come and go, but often permanently prolapses, which can lead to complications if left untreated. Symptoms include a swollen and protruding third eyelid gland. It can be present at birth or acquired.

Corneal Ulcers:

The outermost layer of the cornea is called epithelium. The epithelium could be considered the “skin of the eye”. When this epithelium is missing, a corneal ulcer appears. Corneal ulcers commonly occur in animals. Most ulcers in dogs and cats are the result of trauma like scratches during walks, thorns, playing, or scratches from other animals. Other causes of ulceration are dry eye, eyelid anomalies (entropion, ectopic cilia) or primary abnormalities of the cornea A corneal ulcer is deeper erosion through the entire epithelium and into the stroma. With a corneal ulcer, fluid accumulates in the stroma, giving a cloudy appearance to the eye. Symptoms include pain, chronic mucus drainage, and corneal ulcers.

Progressive Retinal Atrophy:

Progressive retinal atrophy (PRA) is an inherited eye disease that leads to blindness in dogs. PRA's progression is usually slow, with complete loss of vision taking place throughout one to two years. But that can occur faster depending on the dog's breed and the form of the disease. The condition can also strike dogs of almost any age PRA is a non-painful condition that tends to progress slowly over time, often starting with a decreased ability to see well at night, symptoms of Loss of night vision, and Dilated pupils., Complete blindness, Depression, and Reluctance to go into darker rooms.

Insufficient Tears:

Keratoconjunctivitis sicca, otherwise known as ‘KCS' or ‘dry eye' is a common condition of dogs (very occasionally cats) caused by an insufficient amount of tears, or change in tear film quality. Dogs with this condition typically have red eyes from irritation as well as some thick mucoid discharge. They will squint frequently and may blink excessively or keep their eyes closed. Dry eye usually shows up in dogs that are between 4 and 6 years old, but can happen at any age, symptoms include Redness and swelling of the conjunctiva, or the tissues around the eye.

Diabetes:

Diabetes is an insulin deficiency that makes it difficult for the body to regulate energy metabolism. There are two types of diabetes, commonly referred to as type I and type II. Diabetes is a chronic disease that can affect dogs, diabetes mellitus, or “sugar diabetes,” is the type of diabetes seen most often in dogs. It is a metabolism disorder, In contrast, hypoglycemia can become very dangerous very quickly, even in diabetics who are receiving appropriate insulin therapy regularly. Symptoms include dogs peeking more Frequently and they're hungry all the time, Eyes Look Cloudy, and losing weight.

Entropion:

Entropion is an abnormality of the eyelids in which the eyelid rolls inward. This inward rolling often causes the hair on the surface of the eyelid to rub against the cornea, resulting in pain, corneal ulcers, perforations, or pigment developing on the cornea, which can interfere with vision. Entropion is usually a developmental or anatomic problem, and is generally seen in young, rapidly growing dogs. Entropion (inversion of an eyelid) is caused by age-related tissue relaxation. Eyelashes rub against the globe and may lead to corneal ulceration and scarring, Symptoms can include foreign body sensation, tearing, and red eye.

Ectropion:

Ectropion, or outward rolling of the eyelid, can cause problems such as recurring conjunctivitis and drying out of the cornea. The clinical signs are a "sagging" or outward-rolling lower eyelid, although ectropion can affect any of the eyelids. Entropion, or rolling in of the eyelids, is seen in many breeds and is considered a hereditary disorder. Most dogs will squint, hold the eye shut, and tear excessively (epiphora), though some patients will develop a mucoid discharge. Ectropion (eversion of the lower eyelid) is caused by age-related tissue relaxation, Symptoms are tearing (due to poor drainage of tears through the nasolacrimal system, which may no longer contact the globe) and dry eyes.

Inherited Conditions:

There are multiple methods of inheritance that determine which characteristics (or phenotypes) are displayed by the offspring, including autosomal dominant, autosomal recessive, and sex-linked inheritance. There are also many polygenic traits ( associated with multiple genes) as well as environmental factors that make it much more complicated to predict disease or the likelihood of passing disease onto offspring. Genetic eye conditions in dogs can occur at birth or appear later in life. They can range from mild to severe. Some can be treated. Others will eventually lead to blindness or consistent monitoring and management, symptoms are Behavioral changes or disturbances., Breathing problems, inability to process nutrients, Poor growth and movement disorders due to muscle stiffness or weakness.