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Posted on by Dr. Sherman Tung

20/20 Vision

When having an eye exam done you might have been told that you have 20/20 vision, but what exactly does that mean? To put it simply, having 20/20 vision indicates that at a distance of 20 feet, you are able to see the smallest letters that should be seen at 20 feet. If you have 20/40 vision, it indicates that you need to be at 20 feet to see what a person with 20/20 vision can see at 40 feet. On the other hand, if you have 20/15 vision, you can see at 20 feet what a person with 20/20 vision can see at 15 feet.

How do we measure our visual acuity?

There are many ways to measure a patient’s visual acuity, but the most common way is through using a Snellen chart that presents with numerous lines of letters above one another. Letters found at the top of the chart are larger and easier to see but become smaller and difficult to read as you move down the chart. Patients are tested by covering one eye and reading the letters from top to bottom at which point they repeat these steps while covering the other eye. Afterwards, patients will use both eyes together to determine the lowest line they are able to read clearly.

Posted on by Dr. Sherman Tung

How do my eyes adjust to different lighting?

Photo by Agence Olloweb on Unsplash

Our eyes are incredible at adapting to different lighting conditions. This is done through the iris and pupil of the eye. Our pupils are the dark hole at the front of the eye which allows light to enter and form an image on the back portion of our eye. This pupil size is controlled by muscles found on the iris, which is the coloured portion surrounding the pupil. In bright sunlight, our pupils will begin to constrict, allowing less light to enter into the eye. On the other hand, when we are in a dark room our pupils will become bigger and increase the amount of light getting into the eye.

credit: https://www.sciencelearn.org.nz/resources/50-how-the-eye-focuses-light

Once the light enters through our pupil, it hits the back of our eye called the retina. The retina has two types of photoreceptors called rods and cones. Rods are responsible for night time vision and cones are responsible for day time vision. When we are in a dark room, rods are the ones that let us see.

Dark adaptation

The reason you are momentarily blind in the dark when going from a well-lit room is because it takes some time for our eyes to adjust. This is referred to as dark adaptation. During this period, the rod receptors are the key players to fully adapt and return vision to normal.

Posted on by Dr. Elisa Xiao

How can I have Dry Eye if my eyes feel watery?

Photo by Pascal Chanel on Unsplash

Tearing

Tears are needed to keep the eye’s front surface healthy and to maintain clear vision. It is
common to temporarily produce excess tears when you are emotional, laughing, coughing,
vomiting, experiencing strong taste sensations, or yawning.

Types of Tears

photo credit: allaboutvision.com

Different types of tearing consist of basal tears, emotional tears, and reflex tears. Basal tears are your basic functional tears. They are released in tiny amounts to lubricate your ocular surface and keep it clear of any dust. These are vital for good vision and comfort. Emotional tears are triggered by strong feelings such as joy or sadness. Reflex tears result from irritation in the eye by foreign bodies, or from the presence of irritant substances in the environment. They can also occur with bright lights hot or peppery stimuli to the tongue and mouth, when we yawn, cough or even vomit. These types of tears are released in larger amounts than basal tears. Their goal is to protect one’s eye.

How can I have Dry Eyes if my eyes are so watery?

The two common causes of watery eyes are blocked tears ducts and excessive production of tears. The common cause of excessive production of tears is dry eye syndrome. This occurs due to the glands around our lid margins not producing enough oil resulting the tears drying up very quick. This lack of lubrication results in our eyes producing an abundance of tears to compensate.

Posted on by Dr. Melody Tong

Is it true that eating carrots can improve my vision?

Photo by Nick Fewings on Unsplash

It is often said that eating carrots will help you see better due to the high amounts of vitamin A. Although vitamin A plays an important role in our vision, it is unable to improve the quality of our vision. Vitamin A is able to prevent diseases such as macular degeneration which can result in severe vision loss if left untreated.

What is Vitamin A?

Vitamin A is derived from beta-carotene which acts as an antioxidant. This is essential in protecting our cells against heart disease, cancer, and many other diseases. Deficiency in vitamin A is the leading cause of preventable blindness in children across the world. Due to this, it is important to have some type of source for vitamin A such as carrots, eggs, spinach, or broccoli.

What does Vitamin A do for our eyes?

Vitamin A allows us to produce pigments needed in-order for the retina to function properly. Without these pigments, it would become much more difficult to see in the dark leading to eventual night blindness. Lack of vitamin A can also lead to a lack of nourishment to the cornea resulting in the eyes not producing enough moisture to keep the cornea lubricated. This can lead to our eyes becoming dry which can result in severe complications such as ulceration of the cornea and eventual blindness if not appropriately treated.

Posted on by Dr. Sherman Tung

Is it okay to buy glasses online? Do I really need an optometrist/ optician?

Photo by wu yi on Unsplash

When considering whether to buy your glasses online, at first it may seem more convenient and likely less costly. But the prescription given to you by your optometrist is only one piece of information that will determine how effective your glasses will be in improving your vision. Let’s consider the pros and cons:

Pros of buying online:

  • Wider selection of styles and colors
  • Many choices between different websites
  • Often can save on cost (but more on that later)

Cons of buying online:

  • You miss out on having a trained professional aid you in ensuring your glasses are the right fit in
    terms of comfort and effectiveness
  • Quality control of frames may often be sacrificed to maintain that low price you see online
  • Specific measurements such as PD, finding the best optical center, and measurements for
    progressives will either often be wrong or not available for online retailers
  • Prescription issues in general occur much more commonly when ordered online as opposed to
    in person

What could initially be seen as a way to save time and money in the first place may end up more costly for both in the long run if any of the above issues occur. In addition, common complaints with improperly selected glasses may include: headaches, fatigue, nausea/dizziness, eyestrain, glasses slipping off the nose, and pain/pressure marks on your nose/around the ears. Those with high prescriptions, children, complicated prescriptions, and multifocal prescriptions should especially consider in person options as opposed to online.

Posted on by Dr. Sherman Tung

What reading under the covers does to your eyes

Image by Freepik

While it is untrue that reading in the dark will permanently damage your eyes it can cause shorter term issues. You may have to strain harder which can lead to headaches, irritated eyes, general eye fatigue. If this is coupled with other existing issues you may also experience blurry vision or even double vision temporarily. The extra strain and need to focus may also prevent you from blinking as often, leading to dry eye symptoms.

Posted on by Dr. Elisa Xiao

Will I Develop Presbyopia?

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Presbyopia is the gradual loss of your eyes’ ability to focus up close. This tends to start around your early 40s and progresses until around the age of 65. You may notice starting to hold reading material further away to keep it clear, blurry vision at previously normal reading distance, eyestrain or headaches after extended periods of reading.

Managing presbyopia

Depending on your health, lifestyle and preferences, your eye care specialist may suggest any of the following methods to correct presbyopia:

  • Eyeglasses in the form of readers, bifocals, progressives, etc.
  • Contact lenses, typically multifocal or monovision
  • Surgeries
  • Eye drops such as Vuity

Can I prevent presbyopia?

You can’t prevent presbyopia since it’s a part of the natural aging process. You can, however, take steps to protect your eye health. This includes:

  • Wearing sunglasses to shield your eyes from harmful ultraviolet (UV) rays.
  • Eat foods rich in nutrients that promote eye health, including vitamin A, vitamin C, vitamin E and lutein, and Omega-3s
  • Improve lighting in work areas
  • Increase font and change contrast in smart phones or computer devices etc.
Posted on by Dr. Sherman Tung

Can I Wear my Contact Lenses for Longer than I’m Suppose to?

Photo by Lensabl on Unsplash

If I’m careful with cleaning, can I wear my dailies for more than 1 day?

Daily disposables are thinner and are made of a material that is not made to resist bacteria and buildup. So, if you try to clean or disinfect these thin lenses you may actually create breaks instead, further increasing infection risk. Using a compatible brand of soft contact lens rewetting drops to hydrate your daily disposables for comfort is acceptable.

What happens if I wear dailies for more than 1 day?

Wearing daily disposable contact lenses more than once puts you at risk for discomfort, dryness, corneal ulceration/scarring, and eye infections.

Differences between Dailies, Bi-weeklies, and Monthlies

Dailies are worn only for one day and discarded when you remove them, these are typically very thin and have a high water content. Natural deposits from your eyes build up easily on their surface, and they cannot be reused. This could mean more convenience but also, depending on how often you replace them, more costly.

Monthly or bi-weekly contact lenses are thicker than daily disposables. The thicker composition makes them more durable and long-lasting, and they are usually more resistant to drying out. However, they must be disinfected regularly in order to ensure healthy wearing.

Posted on by Dr. Melody Tong

What does my eye prescription mean?

Photo by Josh Calabrese on Unsplash

Eyeglass and contact lenses prescriptions can contain components and abbreviations that may be harder to decipher. Here are some of the common abbreviations and what they mean:

  • OD: or oculus dexter refers to your right eye
  • OS: or oculus sinister refers to your left eye
  • SPH: is the sphere and refers to the lens power required to help correct your vision. A (-) negative
    indicates nearsightedness and (+) positive indicates farsightedness
  • CYL: is the cylinder and refers to how much astigmatism you have if any. Astigmatism is caused
    by a cornea or lens that has a different shape than normal and multiple focal points.
    Astigmatism is very common.
  • AXIS: a number between 1 and 180, indicates exactly where the astigmatism appears on your
    eye
  • ADD: stands for the additional lens power needed to make it easier for you to read. This is seen
    on prescriptions for reading glasses or the lower portion of bifocal/progressive lenses
  • BO, BI, BU, BD stand for base out, base in, base up, and base down. These refer to the position
    of the prism on eyeglasses that correct double vision

For contact lenses you may see additional information such as the brand, mode of wear, and BC +
DIA.

  • BC: The base curve is the measurement that indicates the curvature and shape of your contact
    lenses. This is taken when the steepness or flatness of your cornea is measured.
  • DIA: The diameter is the measurement of the length that your contacts need to be to
    completely cover your cornea.
Posted on by Dr. Elisa Xiao

Are optometrists, opticians, and ophthalmologists the same?

Image by macrovector on Freepik

As a patient, understanding the role and the services offered by each of these three eye care
professionals will help you get the specific eye care you need, know what questions to ask, and work
with your health care provider to determine appropriate solutions that work for you.

Optometrists

Optometrists perform eye exams to check the overall health of your eyes and issue prescriptions for contact lenses or glasses, or low vision devices. The optometrist will perform a number of tests including visual acuity (how well you can see letters/symbols from a distance and near), your ability to see colour, your depth perception, retinal health, the pressure inside your eyes etc. The optometrist may use eye drops to dilate your pupils to help them detect conditions such as glaucoma, cataracts and macular degeneration and more.

Ophthalmologists

An ophthalmologist is a medical doctor who specializes in eye health and related diseases. Ophthalmologists undergo post-graduate training that qualifies them to treat eye diseases both medically and surgically. Ophthalmologists provide surgical solutions to common eye problems such as cataracts, and monitor eye conditions like glaucoma as well as perform laser corrective surgery.

Opticians

Opticians fit, adjust and dispense prescription and non-prescription eyewear. They do not perform eye exams nor prescribe but can assist with filling your prescription, adjusting glasses, and ordering new/replacement contact lenses.