Flashing Lights: It's A Camera... It's Lightning... No, It's Your Retina!

It's not uncommon for patients to come in to the clinic and mention they have recently seen something that looked like a streak of lightning or a flash bulb going off in some part of their vision.


How does this happen?The retina is a thin film that covers the inside of our eyes. It is the part of the eye responsible for receiving light signals and sending them to the brain. As you can expect, it needs to be very sensitive.

Due to this high sensitivity, any small movement of the retina can cause signals to be fired back to the brain, making us think that eye is sensing light.


3 most common situations in which flashes are noticed:
1) Patients with near-sighted prescriptions. Near-sightedness is mostly due to the eye ball being larger than average. As the eye grows, the retina becomes stretched. This can lead to areas of thinning and tension.

2) The vitreous gel inside the eye is attached to the retina in multiple areas. Movement of the vitreous can pull on the retina leading to the sensation of flashes.

3) Pressing on the eye. Mechanically releases the chemicals (Phosphenes) that start the signal to the brain.


FAQ:
Q: Are flashes a sign of something bad?
A: Potentially. Flashes could be the first signs of the retina is being pulled, torn, or detached.

If you notice flashes in your vision, especially if combined with new floaters, it is very important to see your eye doctor right away to make sure there are no signs of any tears or detachments.
Q: Do people who have had laser eye surgery still need to worry about their retinas?
A: YES YES YES!!! It is vital for patient's who have had any kind of surgery to have regular eye exams.


Thanks for reading. Please feel free to send me questions and comments about this or any other topic.

Contact Lenses

They come in a variety of shapes, sizes, and colours...

Soft contact lenses (SCL):These are the most common and they are disposable.

• This means that after wearing the lenses for a period of time, they are disposed of and a new, fresh pair is used
• Lenses can be monthly (ex. Air Optix, Frequency 55, Proclear, Biofinity, etc), two week (Acuvue Oasys), and daily disposable (CIBA Dailies, Acuvue 1-day, etc)
• Also available for astigmatism and patients over 40 who need reading glasses (more information in my post All Kinds of Blurry)

Daily disposable lenses are the healthier option for your eyes for the simple reason that a fresh, sterile lens is being used every single time. Most infections are a result of poor storage or lens care. A lot of these problems can be avoided with daily lenses.

Rigid Gas Permeable (RGP):AKA Hard lenses. Considered older technology but actually provide better optics, better oxygen flow, and less infections. Less popular simply because they are uncomfortable to begin with. But patients who get used to them, stick to them.

Hybrid Lenses:Combination of a hard lens with a soft "skirt". Supposed to provide superior vision of RGPs without being as uncomfortable. But, they haven't been as successful as expected.

Orthokeratology (Ortho-K):Contact lenses that are worn while you sleep. Over night, they flatten the cornea and temporarily correct near-sightedness. Also mentioned in my post Laser Eye Surgery.

Important things to REMEMBER:No matter how good a contact lens claims to be at allowing oxygen pass, or keeping your eyes hydrated, or preventing bacteria from sticking to it, at the end of the day it is still a piece of plastic in your eye.

Contact lenses are considered to be medical devices and, as such, should be looked at by a doctor before they are dispensed and any time the patient experiences any problems.

Three big NOs:

• No sleeping
• No swimming
• No tap water

These are the quickest ways to cause infections which can be potentially vision threatening (see picture below).

Other uses:Contact lenses are not only used to improve vision. Here are a couple of other interesting uses:

• Diabetic patients
• Lens changes colour when sugar levels in tears increase
• Bandage
• Used to cover scratched corneas or after LASIK surgery
• Administer drugs over long periods of time
• Tracking eye movements in ocular studies

FAQ:

Q: Can I get coloured contact lenses even if I have no prescription?

A: Yes. But FYI, these lenses tend to be the least healthy for your eyes.

Q: How often should I replace my contact lens case?
A: Usually every 3 months or when your solution runs out. Whichever comes first.

Q: If I wear contact lenses, do I still need a pair of glasses?
A: Yes, you should always have a good pair of glasses to give your eyes a break and just in case something happens to the contacts.

Q: What if I'm on vacation and I forgot my contact lens solution and my contacts are bothering me and there isn't a pharmacy close by and my cousin says its no big deal, can I just store my contacts in tap water?
A: No. No tap water. Ever. I hope that is clear enough :)

Healthy Cornea

Acanthamoeba infection (from tap water)

Corneal Ulcer due to overwear

Lazy Eye

"Contrary to what some believe, a lazy eye is not one that doesn't like to wake up and go to work in the morning."
- Anonymous Eye Doctor with a sense of humour

The medical term for Lazy Eye is Amblyopia

So why do eyes become lazy?

• The brain is very picky! When it is not receiving a clear image or if it is receiving double images, it begins to shut off connections to the eye that is causing it the most grief
• This process usually happens during childhood and if it is caught before the age of 7, it can be reversed depending on how bad the situation is and how cooperative the patient is

There are two main situations in which this happens:

• Eye turn
• In this case, the patient probably has double vision so the brain will stop communicating with the eye that is turned in/out, which will stop the double vision
• Sometimes surgery is needed to straighten the turned eye, other times simple wearing a patch over the good eye will help force the turned eye back
• Difference in prescription
• If there is a large difference and one eye is very blurry, the brain will again shut it off because it doesn't like dealing with two eyes producing different images
• Glasses are the obvious answer. Sometimes a patch over the good eye will help force the blurry eye to work harder

As you can see a Lazy Eye problem actually becomes more of a Picky Brain problem.

And as the saying goes, "you can't teach an old dog new tricks".

So, once the brain has made all the connections it wants to make, it is very difficult to make it go back. This is why it is important to catch it early! (Before age 7 or 8)

After this cutoff, even providing a patient their full prescription may not improve their vision because no matter how clear the image is, it is not being sent to the brain.


FAQ:
Q: Can a person have 2 lazy eyes?
A: That is a fantastic question! And, yes. I recently blogged about a patient I had seen who had high astigmatism in both eyes. So the connections for both eyes were not fully formed during childhood due to blurry vision and at this point in her life, glasses did not help very much.

Q: What is astigmatism?
A: The answer to this can be found in am earlier post called "All Kinds of Blurry" along with info on other causes of blurry vision

Q: How early should kids have their eyes checked?
A: Both the Canadian and American Association of Optometrists recommend that children have their first eye exam at 6-12 months and again at age 3.

Thanks for reading. I hope this information was helpful. Please feel free to send me any questions or comments. And also pass this on to anyone who may find it useful.

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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What does 20/20 mean?

This week's topic is something I get asked almost everyday. Unfortunately, the answer is never as simple as it may seem. I will do my best to explain it here.

Simple definition: 20/20 is the size of letter that the average person should be able to see when fully corrected (assuming that there are no visual opacities or retinal problems). It is what we aim to achieve when correcting patients with contact lenses, glasses, and laser surgery.

More specifically: A 20/20 letter is exactly 8.726mm in height at a distance of 20 feet.

FAQ:
Q: Does 20/20 mean "perfect vision"?
A: No, this is a common misconception. There really isn't such a thing as perfect vision. The sharpest estimated human visual acuity is about 20/8. Which, with a little math, equates to a minuscule 3.49mm letter at 20 feet!

Q: How is the size of the letter determined?
A: The letter size for 20/20 is based on the average spacing of the light-sensing cells in the retina, thus the average eye's ability to discern spaces between letters

Q: Why 20 feet?
A: That is the approximate distance at which the internal focusing system of the eye (used for near vision) is relaxed thus allowing your eyes to effectively see into the distance.

Q: What if I can't see any of the letters without my glasses? Does that mean I'm Legally Blind?
A: Vision without correction does not really provide any significant information about your eyes (other than the fact that correction may be needed).
The definition of Legal Blindness in Canada and USA is 20/200 in the better eye with correction. Thats 10 times the size of a 20/20 letter.

Q: Do I need to see 20/20 to drive?
A: No. This may come as a surprise. But, the legal requirement for driving is 20/40 in one eye. That's double the size of a 20/20.


Thanks for reading. Please feel free to pass this info on to anyone who may find it useful and don't hesitate to send me your questions and comments.

Laser Eye Surgery

Laser procedures are commonly used to treat refractive errors (ie. near- or far-sightedness and astigmatism), with the end goal of providing the patient with clear vision without glasses or contact lenses.

There are 2 major types of Laser Refractive Surgery. While the process is a little different, they both essentially flatten the cornea (for near-sighted) or steepen it (for far-sighted):

LASIK - Laser-ASsisted In-situ Keratomileusis

• The more recent of the 2 procedures
• Most common due to shorter recovery period after surgery (not necessarily better results)
• Requires the surgeon to make a thin "flap" of the surface of the cornea before using the laser
• The flap is replaced after the the surgery - effectively producing a natural bandage for the eye

PRK - PhotoRefractive Keratecomy

• The older of the two procedures
• Less common of the two due to longer healing period
• Still produces accurate results
• Usually used for patients with thinner corneas (not enough thickness to form flap before using laser)

FAQ:
Q: Do I still need to have regular eye exams if I can see perfectly after my surgery?
A: YES YES YES!!! Patients who have had laser surgery need regular eye exams more than the average population! Firstly, they have had surgery. Next, the majority of patients that have these procedures are near-sighted and the primary cause of near-sightedness is an increased length of the eye. This causes stretching of internal structures (such as the retina) and leaves these patients with a higher risk for retinal detachments. This does not change just because they no longer have to wear glasses!

Q: Is it safe?
A: Yes. The surgeons that do these procedures, do hundreds to thousands per year. Technology is improving daily to provide more accurate results. Complications occur in less than 0.5% of patients.

Q: Is my prescription too high?
A: Most likely not. Refractive errors as high as -12.00 can be successfully treated. Tiger Woods and Roberto Luongo were about -10.00 and -11.00 respectively before having their surgeries.

Q: What are the common side effects or complications?
A: The number one post-operative complaint is dry eyes. Halos around lights, decreased night vision, sensitivity to light, and recurrence of prescription are also well documented. Most surgeries are guaranteed for 5-10 years. After which, it is possible the patient will require glasses again or a "touch up" surgery.

Q: What are the alternatives?
A: Intacs and Ortho-K are 2 possible options. Intacs are very small corneal implants that create the same effect as laser surgery of flattening the cornea. Ortho-K are contacts that you wear while you sleep. Again, these have the effect of flattening the cornea. In the morning, you take them out and don't need to wear any glasses or contacts during the day. The benefits of these 2 alternatives is that they are both fully reversible. These are limited to lower prescriptions of approximately -1.00 to -4.00.

Thank you for reading. I hope you found this information useful. Please feel free to contact me with questions and comments.

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Near-sightedness

• The medical term for being near-sighted is Myopia
• The term near-sighted is used simply because myopes are able to see close objects more clearly than distant objects
• The most common cause for myopia is an increase in axial length (front to back) of the eye during childhood and teenage years
• This results in images being focused in front of the retina
• Near-sightedness is easily correctable using "minus" lenses, thus a myopic person's prescription will always have a negative sign in front
  

Ex. If you consider a movie projector and screen. A myopic eye would be analogous to someone pulling the screen back so the image is out of focus.