All Kinds of Blurry

In my very first post I wrote a little about myopia, which is near-sightedness. Here we'll discuss all the other "-opias" and "-isms" that can make your vision blurry. They are generally referred to as "refractive errors".

A quick review of Myopia. It is due the eye being longer than average. So, rather than an image being focused right on the retina, it falls a little short. Of course, this gives us blurry vision for distant objects which can be corrected with "minus" prescription glasses and contacts, or laser surgery. Example of near-sighted prescription is: -3.25.

Hyperopia. This is what we call far-sightedness. As you would expect, a hyperopic person would have more trouble with near and less trouble with distance. This is a result of the eye being a little bit shorter, thus images fall behind the retina. This is corrected with "plus" prescriptions. Also can be corrected with laser.

Astigmatism. Is not affected by the length of the eye. Astigmatism is a result of the shape of the front of the eye (the cornea). With astigmatism, the cornea is not perfectly round, it is a little steeper in one direction than the other. The common analogy is a basketball compared to a football. So, light cannot be focused to one point on the retina. It is split by the different curves of the cornea. To correct this, the prescription needs two powers (one for each curve of the cornea). An example of this would be -1.50 -0.75 x180. The "-0.75" is the astigmatism part of the prescription and "x180" shows that this prescription needs to be placed at 180 degrees. Astigmatism can be corrected with glasses, contacts, and laser.

  

Presbyopia. The first three refractive errors are mostly hereditary. The last one, however, is purely age-related and happens to everyone. As we age, the accomodative system (system inside our eyes that helps us focus at near) slowly stops working. Eventually, as we make it through our 30s into our 40s, we notice that things up close are not as clear as they used to be. Often, patients will say that they need to hold reading material further away. And eventually no matter how far away you hold it, its just not clear enough! Correction usually involves reading glasses, bifocals, or multi-focal contact lenses. Laser surgery is not a very useful option because it does nothing to improve the accomodative system.

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Doc, My Vision Is Blurry But Glasses Don't Help!

Last week, I had a patient (let's call her Mary) come to see me because she noticed that she was having difficulty seeing the board at the front of the class clearly. Mary was in her early 30s and mentioned she had worn glasses for a little while as a teen but never thought they helped very much.

Turns out that our friend Mary has a prescription with high astigmatism in both eyes. While many of my near-sighted friends and patients can attest that their vision progressively gets worse throughout their teenage years and into their twenties, astigmatism is generally present from childhood and remains relatively constant throughout our lives. (Learn more about astigmatism in the "All Kinds of Blurry" post)

Why is this important? This means that since Mary was a child, her brain has been receiving blurry images. And our mushy, emotion-filled noodle is a very picky person. If it sees blurry images (or double images, for that matter), it will stop forming connections with the eye that it dislikes (in Mary's case, that was both of her eyes!).

This process is called Amblyopia. If we catch these types of high prescriptions before the age of 7, its usually simple enough to reverse the process and convince our gray and white-mattered friend to start liking the patient's eyes again. Unfortunately, in a case like Mary's there is not too much to be done. At this point, not glasses or contacts, not even lasers will be able to significantly improve her vision.

But this doesn't mean we don't try! A lower prescription was given that did mildly improve vision and we hope that Mary's eyes (and brain) will adapt with time.

What is the moral of the story? Kids should get their eyes examined early and often to catch high prescriptions or changes in prescriptions and to avoid amblyopia!

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Night Vision

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Night Vision:

As was mentioned in an earlier blog, there are two types of cells in the eye that detect light: Rods and Cones.

• Cones are for bright light and colour vision. Rods are for night vision and detecting motion in our peripheral vision.

• Rods are very sensitive to small amounts of light because they have a high amount of pigment to absorb light and because there are many more rods than cones.

Night Vision Goggles (NVG)

There are multiple steps to NVG function:

• First, light is gathered
• Sensors detect small amounts of light that are reflected off objects (this includes low levels of infra-red light which is not visible to the human eye)
• Then, light is amplified
• Just like turning the volume up on a stereo, the small amounts of light are made brighter
• Finally, an image is projected
• The new amplified image is shown on a small LCD screen

Since night vision goggles are sensitive to infra-red light, objects that give off a lot of heat will appear very bright (ex. light bulbs and headlights)


Humans vs. Animals:

Human night vision is very poor compared to most animals. This is because a lot of animals have an extra layer in the retina called tapetum lucidum

• This extra layer reflects light within the eye, basically making it more intense (kind of like NVGs)
• It is also the reason why we see different coloured reflections through the pupil of most animals

FAQ:
Q: What if a person had only rods, and no cones?
A: This person would be completely colour blind because rods cannot detect colour. They would also have very poor vision since cones are needed for central vision.

Q: How many rods are there in the retina?
A: There are approximately 120 million rods and about 7 million cones. Cones are packed tightly in a tiny central area called the macula. Rods are spread out over the rest of the retina.

Q: Do night vision goggles always show a green image?
A: Yes. This is done deliberately because human vision works best with greens and yellows.

Q: Can I get night vision goggles?
A: Yes, but don't expect them to be as cool as what you see in movies. Goggles that are available to consumers are older technology and lower quality. The newer, better stuff is reserved for military use only!

Q: Can I get tapetum lucidum?
A: Not unless you plan on stealing a raccoon's eyes. Good luck.

As always, thank you for reading. Please feel free to pass this information on to anyone who may find it useful. Questions, comments, and suggestions are welcome.

Whats Your Eye-Q?

The American Optometric Association published the results from their 5th annual Eye-Q Survey. The survey asks men and women all sorts of questions about their eye health including allergies, UV protection, nutrition, and aging. Interestingly, men and women didn't always see eye to eye (yes, pun intended).

Check out this year's Eye-Q Survey Results here.

Take a simple Eye-Q Test for yourself!

Grade yourself as follows: 19-20, I understand my eyes very well; 17-18, my view of my eyes is pretty clear; 15-16, my concept of my eyes is a little fuzzy; 13-14, the way I see my eyes could use a little correcting; and 12 or under, my eyes need much more understanding.

True	False	Questions
		1. At a distance of ten inches, my eyes can detect an object as small as four thousandths of an inch in size.
		2. My eyes can distinguish only four colors.
		3. My eyes can see a candle 14 miles away.
		4. Ten percent of what I know comes through my eyes.
		5. Reading in dim light can put a strain on my eyes.
		6. When viewing the TV, I should sit a distance equal to twice the width of the screen.
		7. A lack of vitamin A in my diet can cause reduced night vision.
		8. Dilation of the pupils allows my doctor to see a better view of the inside of my eyes.
		9. The best color for sunglasses is blue.
		10. Tears contain substances that slow down bacterial growth.
		11. My eyelids work much like a car's windshield wipers.
		12. Sunglasses will allow me to look directly at the sun.
		13. Many prescriptions for eyeglasses are identical.
		14. Smoking can effect my vision.
		15. If I have 20/20 vision, I don't have any eye problems.
		16. Air pollution affects only my lungs and breathing.
		17. If I am nearsighted, I see near objects more clearly than distant ones.
		18. If I am farsighted, I see distant object more clearly than near ones.
		19. Glaucoma is a serious eye disease that can cause blindness.
		20. Regular eye examinations can help protect my eyes and general health.

ANSWERS: 1.T. 2.F. 3.T. 4.F. 5.F. 6.F. 7.T. 8.T. 9.F. 10.T. 11.T. 12.F. 13.F. 14.T. 15.F. 16.F. 17.T. 18.T. 19.T. 20.T.

Why Aren't My Eyes Blue?

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What determines a person's eye colour?

Genetics play a important role. However, determining the combination of genes and chromosomes is very complicated and random mutations happen quite often.

The main factors that determines the colour of a person's eyes are:

• The amount of melanin (a dark pigment), which is determined by the number of melanocytes (cells that make the pigment) in the iris (coloured part of the eye)
• Presence of some other less common pigments in the iris
  
• Deposits of proteins in the iris
• All of these come together and affect the way light is scattered and absorbed at the front of the eye

For this reason darker-skinned people generally have darker coloured eyes and lighter-skinned people have lighter eyes.

FAQ:
Q: Is it possible for eyes to change colour?
A: Yes. But it would most likely happen early in life. Babies can be born with a low amount of melanocytes which slowly increases with age.

Q: Can I change my eye colour?
A: Yes, with contact lenses :-)

Q: Is it possible to have two different coloured eyes?
A: Yes. It's called heterochromia. Its also possible to have different parts of the same iris be different colours. This is partially genetic and partially the way the pigment is dispersed.

Q: Are there any medical implications to eye colour?
A: Yes. Lighter eyes tend to be at higher risk for Age-Related Macular Degeneration and ocular cancers. Likely due to some protective effects of pigment.

Q: Why do you keep spelling colour with the letter "U" in it?
A: Because I am a British Canadian.

Thanks for reading. Your questions, comments, and suggestions are always very welcome. Please feel free to pass this info on to anyone who may be interested.

The Eye Exam - Why Is It So Important?

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Everyone knows that your Optometrist is the person to see for your glasses and contact lens prescriptions. But, the health portion of the exam is often overlooked by patients.

There are many, many ocular and systemic conditions that can be detected and followed by your Optometrist with regular eye exams. Here is a short list of some of the more important/common conditions:

• Glaucoma
• Cataracts
• Macular degeneration
• Retinal detachments
• Retinal holes and tears (common in highly near-sighted patients)
• Bacterial and viral infections
• Eye turns and lazy eyes
• Colour deficiencies
• Stereopsis (our ability to see 3D)

• Diabetes
• High blood pressure
• High cholesterol
• Thyroid problems
• Inflammatory conditions such as: colitis, Crohn's disease, rheumatoid arthritis, psoriasis
• Vitamin deficiencies
• Brain tumors
• Nerve problems in the eye and brain
• Stroke
• Blocked arteries in the neck and head
• HIV/AIDS
• And many more...

Thanks for reading. Any and all feedback, questions and comments are always welcome. Please feel free to pass this information on to anyone who may be interested.

Diabetes and the Eye

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Diabetes is a disease that has grown and spread exponentially in the last 20 years, reaching epidemic proportions. Yet, many people do not know how devastating it can be and the effects it can have on the eye.

Background:

There are 2 main types of diabetes:

• Type 1 (Insulin dependent):
• Early onset (usually by teenage years)
• Autoimmune disease - the body attacks itself and causes destruction of the cells that make insulin
• Insulin is the chemical which promotes uptake of sugars from the blood into muscle and other tissues
• Treated with insulin replacement
• Can lead to death if not treated

• Type 2 (Non-insulin dependent):
• Later onset (usually over the age of 40)
• Body tissues develop resistance to insulin
• Very commonly associated with sedentary lifestyle, high fat diets, and obesity (No surprise its huge in North America!)
• Treatment:
• Early/mild: weight loss, diet changes, and exercise
• Moderate: All of the above plus oral meds that encourage glucose uptake
• Severe: All of the above plus insulin
• Significantly increases risk of heart attack, stroke, and kidney failure

The end result for both, if not well controlled, is high sugar (glucose) levels in the blood stream.

Normal blood sugar levels:

• Healthy patients should have glucose levels of approx 4 mM
• Diabetic patients are instructed to try to maintain them below 6 mM
• Uncontrolled diabetics often have glucose levels of 15-20 mM (if not higher)
  

The Eye:
While high sugar levels in the blood can affect the structure and function of cells and chemicals, the main concern in the eye is loss of integrity of the blood vessel walls.

The tiny retinal blood vessels can become leaky, thus allowing fluid, blood, and proteins to seep into the retina. If left uncontrolled, this can result in any combination of the following:

• Diabetic retinopathy:
• bleeding in the back of the eye, including leakage into the vitreous gel thus causing loss of vision
• lack of blood and oxygen delivery to areas of the retina
• death of retinal tissue - permanent loss of vision
• development of new, weaker blood vessels (neovascularization) which can cause further leaking and fibrosis of the retina
• Macular edema
  
• swelling of the macula (central part of retina) causing decrease of vision
• Retinal detachment:
• Fluid leakage behind the retina or fibrosis due to new blood vessels causing it to be pulled away
• Neovascular glaucoma:
• Due to the lack of oxygen delivery, new blood vessels begin to grow at the front of the eye and block the drainage of fluid causing increased pressure in the eye which can result in damage to the optic nerve - yet another way to cause vision loss
  

If the diabetes is adequately treated, some of the milder problems can be reversed and vision may be restored.

If you have diabetes, or know someone who does, it is very important to keep in mind the effect it can have on your eyes. Regular, annual eye exams are imperative and are no less than the standard of care of diabetic patients.

If there are any questions please feel free to ask. And as usual, please forward this information on to anyone who may find it useful.

Thanks for reading.