Causes of Eye Conditions

Blepharitis

An inflammation of the eyelids, often caused by bacteria living on the skin or clogged oil glands at the base of the eyelashes. It’s like having dandruff on your eyelids that causes irritation.

Pterygium

A non-cancerous growth of pink, fleshy tissue on the white part of the eye. It is usually caused by long-term exposure to UV light, wind, and dust leading the eye to protect itself by growing an extra protective layer of tissue.

Pinguecula

A small yellowish deposit on the white part of the eye. It usually results from sun damage, wind or dust exposure. It can sometimes grow into a fleshy tissue but it is non-cancerous.

Cataract

A clouding of the eye’s natural lens. Over time like a tree trunk, our lens adds layers to itself as it ages. The innermost layers are the oldest, and after many years, they begin to rub against each other and they become less efficient at getting rid of debris and regenerating new cells. This begins to accumulate making the once transparent clear lens to become clouded and yellow.

Corneal Ulcer

An open sore on the eye that is caused by an infection that has broken through all layers of the first structure of the eye called the cornea.

Anterior Uveitis

Inflammation of the front part of the eye. It is often an immune system response where the body’s defense system has become overactive and causes swelling inside of the eye. This can be linked to systemic autoimmune conditions, but a lot of the time it is idiopathic which means we don’t actually know why it’s happened.

Diabetic Retinopathy

High blood sugar levels over time weaken the blood vessels throughout our entire body. We have lot’s of blood vessels at the back our eye. The damaged blood vessels are more prone to leaking and becoming blocked which causes small haemorrhages at the back of the eye making things appear blurry, or tiny black spots might appear in the vision.

Glaucoma

A condition where the optic nerve which is the data cable connecting the eye and the brain, becomes damaged. This is often caused by fluid not draining from the eye properly which leads to high pressure that slowly puts pressure on the back of the eye, harming the fibres inside of the optic nerve.

Posterior Vitreous Detachment

As we age, the gel-like substance inside the eye naturally shrinks and pulls away from the back wall of the eye. It’s normal aging process but it can cause new flashes of light or black floaters as the gel detaches. Sometimes there can be a residual floater that moves with your vision, which is caused by a tiny bit of that tissue remaining on the jelly, rather than staying with the rest of the back layer of the eye.

Age-Related Macular Degeneration

As we get older, the cells at the back of our eye get less efficient at removing waste products. This means they can begin to accumulate making the centre of your vision become blurry while your side vision stays normal. There is a large genetic component to it, but things like smoking, poor diet, and poor cardiovascular health can also be associated with it.

AAION

A serious condition where the blood vessels supplying the optic nerve (PCA) have become inflamed. This inflammation, usually caused by an underlying condition called giant cell arteritis, restricts blood flow to the nerve. Because the nerve is suddenly deprived of oxygen and nutrients, it stops functioning properly, which leads to a sudden and significant loss of vision. 15% of the time, the vision can get worse, 25% of the time there can be some improvement, but most of the time, the vision you have now, is the vision you will maintain even with treatment.

NAION

This occurs when the blood flow to the optic nerve is reduced or blocked, essentially a stroke of the optic nerve. In most cases the cause of this is unknown but sometimes it can be associated with high blood pressure, diabetes, and other systemic vascular problems that happen with age. These systemic issues prevent the oxygen from reaching the nerve. People with small nerves and small cups can also be at a greater risk because it’s the same number of nerve fibres as someone with a big nerve, just less space so it’s very crowded which means if the fibres become slightly blocked, they swell, and they are more likely to cause blockages to other nerves because of the very compact area.

Optic Neuritis

Is a condition where the optic nerve is inflamed. The optic nerve is the main cable connecting the eye to the brain. In many cases, it happens when the body’s immune system attacks the protective coating around the nerve fibres. This causes the fibres to swell, which then interferes with the electrical signals travelling from the eye to the brain, causing vision to become blurry or colours to appear washed out. It is sometimes one of the first signs of an immune-related condition in the body. A common condition that occurs with this is Multiple Sclerosis.

CRVO

This is a condition where the main drainage vein of the retina is blocked. The main vein that carries blood away from the back of your eye has become blocked which is often by a blood chlot or a cholesterol plaque. This causes blood and fluid to back up, leading to swelling and bleeding throughout the entire retina, which makes your vision blurry or distorted. Similar to if you kink a hose, the water has no where to go but back which can cause the tap to come off (causing a large haemorrhage) or if there’s already damage along the tap from systemic diseases, then small dot/blot haemorrhages occur along the tap at the weak points.

BRVO

A smaller branch of the main drainage vein for the eye has become blocked. The swelling and bleeding is limited to parts of the back of your eye, which is why only part of your vision seems affected, or it might even be completely unnoticeable.

CRAO

The main artery supplying blood to the back of your eye is blocked. This means that fresh oxygen cannot get to your eye due to blockage from a blood clot or bit of cholesterol. This is an emergency because the retina is currently not receiving any oxygen which can cause permanent, vision loss as you’re currently experiencing. Depending on what’s caused the blockage there are different techniques to help dislodge the blockage. They may perform a massage to try and physically dislodge it, or may give you medication to open up the blood vessels. The doctor’s will also check over your overrall general health to try and prevent something similar happening throughout the body, and as a result your general medications might change.

BRAO

A small branch of the main artery supplying your eye is blocked. This area is cut off from it’s oxygen supply which is why you might have noticed some change in your vision in this specific area of your field of view.

Myopia/Nearisghtedness

To see an object clearly, we need light from the object to go through our eyes focusing system which bends light to focus it directly on our retina, which is the back surface of our eye. If the light is focused in front or behind that thin structure, that is when objects will appear blurry. In your case, there’s a mis match between your eyes focusing ability and the length of your eyeball which is causing light to be focused in front of your retina rather than directly on it, which makes things especially in the distance look blurry. This is usually because your eye is too long for the focusing system, or the focusing system is too strong compared to the length of the eye.

Hyperopia/Farsightedness

To see an object clearly, we need light from the object to go through our eyes focusing system which bends light to focus it directly on our retina, which is the back surface of our eye. If the light is focused in front or behind that thin structure, that is when objects will appear blurry. In your case, there’s a mis match between your eyes focusing ability and the length of your eyeball which is causing light to be focused behind your retina rather than directly on it, which is making things especially up close more difficult to make clear. This is usually because the eye is shorter than normal, or the focusing system is not powerful enough.

Presbyopia

To see an object clearly we have a clear structure in our eye called a lens which can change it’s shape to be thicker or thinner depending on how far away an object is that we want to see clearly. So when we look at an object up close, our lens gets thicker, to increase our focusing power. As we get older, the lens inside of our eye loses its flexibility and becomes stiff, similar to a tree trunk, where when it is a young sapling its very flexible and easy to move, but as the tree ages and more layers are added, we can no longer easily move that trunk. This means the muscles in our eye struggle to move the lens and it gradually gets stuck in its most relaxed position. Because we cannot change its shape as easily, the eye struggles to focus on things up close, so you’ll notice it’s hard to read a book or look at your phone, but if you pull it further away, it gets clearer, because you don’t need as much focusing power when something is 60cm away rather than 40cm away. Over time though, your arms will no longer be long enough, and only things in the distance will be clear because the muscles can’t change the shape of the lens. The process usually begins in the early to mid 40s and by your early 60s it will have reached that point where it is immovable. The good thing is, we have glasses to help replace that focusing power that you no longer have. There’s special calculations that we can do to know the exact amount of extra help you need for each distance. There are many different ways we can go about incorporating this extra bit of focusing power either through single vision lenses where the whole area of the glasses have been set to that specific distance, so no matter which part of the lens you look through anything 30cm away will be clear. But things 60cm away will be blurry. We also have multifocal lenses which is where the focusing help in the lens gradually gets stronger the lower you look in the glasses. For example when you look out into the distance at eye level, it will be just your distance prescription, but if you move your eyes slightly slower, say at computer screen height, which is usually about 75cm away from you, the power of the lenses change to allow anything at 75cm to be clear. Then if you look even further down in the lenses, the power of the glasses gets even stronger, to allow anything at 30cm to be clear. This is the best option to mimic the natural lens in our eye, however its not the perfect replacement, because it relies on eye positioning as well as object positioning for things to be clear, whereas with our natural lens, if we looked up, but at something close, our eye could change the focusing power on the spot, whereas with multifocal glasses, you would have to move your head to find the portion of the lens with right focusing power.

Strabismus - Accommodative

This is a condition where the two eyes do not align together correctly, meaning they are not pointing at the same object at the same time. In order to see an object clearly we need our eyes too look directly at an object. In order to know where that object is in space, and know how far away from the object we are, in other words have depth perception, we rely cues.

When we look in the distance, our eye together know to turn out to be straight, and as we look at objects that are closer, our eyes turn inwards more and more the closer something gets. That is the first cue we rely on for 3D vision.

The second cue that our brain uses for 3D vision is blur. We need different amounts of focusing power based on how far away an object is. If an object is close it requires more focusing power than if we look at an object in the distance. If an object appears blurry, our brain will strengthen or relax our focusing system to help make that image come into focus, and depending on how much power we need, is also a cue for how far away something is. So if I look at that pencil, the objects behind it are blurry, but then if I choose to focus on the objects behind it, my focusing system relaxes slightly, and that tells my brain that the objects are further away.

A third cue for depth perception is actually based on the knowledge that our eyes are separated. Because our eyes are slightly spread apart, what we perceive in the world is slightly different. Our brain uses that to our advantage and it combines all of that information to create one single 3d image of the world.

Strabismus disrupts these cues because A. the eyes are not pointing in the same direction in the same amount, this means that if we look at the pencil with the RE, but the LE is turning out slightly, the RE image of pencil is also very clear, but the LE image of the pencil is blurry but the object behind it is clear. This means that when the brain receives the two different images from the eyes, the images are TOO different to be able to combine them and create that 3D vision.

The biggest problem with this is that the brain only likes producing one single image, it hates double. So rather than trying hard to combine those two images to create one image, it just ignores one of them. It's sort of like rather than hearing one song, you're listening to two different songs and the only way to actually hear the words if you block one song out. Unfortunately if the brain ignores one eye, this can mean that the muscles, and the nerves don’t fully develop because they’re missing out on that consistent practice on what it actually needs to do.

The good news is, the cause of your daughters eye turn can be fixed with glasses because the focusing systems are mis matched. Her RE is slightly weaker than the LE. If we correct this mis match, it means then objects will appear equally clear between the two eyes and therefore the images that the brain receives will be easier to combine, and the distance she needs to look to make things clear will be equal between the two eyes so her eyes will be aligned. Unfortunately as soon as she takes the glasses off, one of her eyes will turn out again.

Amblyopia

Is a condition where the vision in one eye has not developed as well as it should have, even when the structures of the eye itself are physically very healthy.

To understand this, it helps to think of our brain as the processing centre, whereas our eyes are just two screens. We think we see with our eyes, but we actually see with our brain. As soon as we’re born, our eyes begin sending messages to the brain about what is happening in the world, but at this point it’s two separate pieces of information from our two separate eyes. The brain learns how to combine the information from the two images and turn it into one clear sharp 3D picture after about 6 months. This process requires constant, clear signal from both eyes.

Amblyopia happens the brain stops receiving a clear signal from the eye. This usually happens for one of three reasons. The first is if one eye has a much stronger prescription than the other, causing the image from one eye to be blurry all the time. The second is if the eyes are misaligned due to an eye turning in or out, causing the brain to receive two different images that are so different that it can’t combine them. The third is if there’s been something blocking one eye such as if there’s a cataract, or a growth in the eye, or the eye has been covered for some other reason. In any of the cases, the brain faces a challenge, it’s receiving one clear image and one blurry image, so to avoid the confusion and double vision, the brain turns down the signal volume from the blurry eye so it can use the input from the stronger eye with more reliable information.

Over time, because the brain is not using the signal from that weaker eye, the nerve pathways don’t develop properly. it is as if connection between that eye and the brain is under practiced, so no matter what glasses we give, the nerve pathway just isn’t as good on that eye.