Daniel Ng, OD

• Why can't I focus underwater without swimming goggles?

  First, there is the refraction of light rays as they pass through the water surface. Second, when you are underwater, the water will press against your eyeball, so the index of refraction changes and you can't focus on the things underwater. Third, the brownian motion of the water will also make your eyes out of focus.

• What does BC stand for on contact lenses prescription?

  BC on contact lenses stands for ""base curve."" The base curve of a contact lens is related to the shape of the patient's eye. It is one of the items in your eyes examination. In most cases, the base curve is the same for both eyes.

• Can your contact lenses be melted by the heat from barbeque ?

  I've ever heard someone's contact lenses were melt while having a barbeque because he was too close to the grill for a long time. So to avoid the same tragegy, you'd better keep your contact lenses away from the grill or reduce the time that they are exposed to the grill for.

• How can I know my contact lens is inside out?

  If your contact lenses are turned inside out, this will cause some discomfort when blinking your eyes and won't fit close to your eye, as well as cause some slight vision problems. While it's on your finger, an inside-out lens will look like a U with flared edges. A lens in the proper bowl shape, with smooth edges, is in the correct position.

• How to prevent my contact lens from wind?

  Sunglasses/goggles may work. If you want to proect your eyes better, the oversized sunglasses may be your first choice cause they can wrap your eyes around.

• Where can I buy one pair of contact lenses?

  Contact lenses are sold in many different types of packaging. Some of the contact lenses are packaged in one case but some of the lenses are available as a package of 6 or 12 lenses, it is depends on your prescription and the types of lenses you prescribed.

• Is it necessary to wear sunglasses over the contact lenses?

  It is OK to do so. Wearing sunglasses over the contact lenses add double protection to your eyes, they are much safer from the UV rays, and less likely to be injured.

• What is the difference between a contact lens prescription and glasses prescription?

  This depends on how strong your power is. A contact lens prescription can be the same as a prescription for glasses when: - the prescription is a lower power, ie: -4.00 to +4.00 and - there is absolutely no astigmatism present. If you have any astigmatism or require a lens power greater than +/-4.00, the parameters of the contact lens can change. - if you have astigmatism under 0.50, a spherical lens should be prescribed. - astigmatism of 0.50 to 0.75 can be effectively corrected with an aspheric lens. - astigmatism greater than 1.00 should be managed with a toric lens. If your prescription power for glasses is greater than +/-4.00, you should see a difference in the power of your contact lens prescription. Generally, every time your glasses prescription increases or decreases by a power of 2, your contact lens prescription will increase by an additional power of +0.25. For every power change of 2 in a glasses prescription, the difference of +0.25 power is needed to compensate for the location of the contact lens. Your glasses are much further from the front surface of the cornea than contact lenses. Sources: http://www.contactlenses.co.uk/education/public/spectacle_vs_contact_lens_rx.htm

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