If you usually wear glasses and are considering switching to contact lenses, whether you are planning on using them full time or just when it’s not convenient to wear your glasses, you’ll need to have a contact lens exam. Let’s find out why.
Quite simply, you can’t use a regular glasses prescription on a pair of contact lenses. The reason for this is because of where each lens sits in relation to the surface of the eye. Lenses for glasses are placed in frames that sit on your nose, so they are usually a centimeter or more in front of your eyes. In contrast, contact lenses are directly placed onto the eye. This means that the power of the lenses needed to correct your vision at each distance is different. If you were to use your glasses lens prescription for contact lenses, you wouldn’t be able to see clearly.
You also need a contact lens exam to ensure that you get the right type of contact lens for you. There is a huge range of different varieties available, from daily disposable soft lenses to monthly or even longer-wear specialty contacts that are designed for people with specific corneal abnormalities which means that regular contact lenses may not be suitable. This includes people with astigmatism, dry eyes, and keratoconus. Your eye doctor will be able to recommend the most suitable contact lenses for you based on your individual needs.
A contact lens exam involves several different elements. These include:
Visual acuity testing. This test involves looking at a chart of letters but will be used to determine what prescription you need for contact lenses rather than glasses.
Corneal surface evaluation. To check the type of contact lenses that will suit you best, your eye doctor will want to evaluate the surface of your cornea to check for any abnormalities that could indicate that you would benefit from specialty contacts. This may be done manually, using a tool called a keratometer, or using laser technology. The latter is called corneal topography and produces a 3D image of the surface of your eyes.
Pupil measurement. Your eye doctor will need to measure the distance between your pupils, and from the pupil to the edge of the iris of each eye. This can be done using a handheld ruler or a piece of equipment called a slit lamp.
Tear film assessment. Your contact lenses will sit on a layer of the tear film which will keep them comfortable on the surface of your eyes and enable them to move around with your eyes when you look around. To check that you have enough tear film, tiny strips of paper will be placed into the lower eyelids to see how quickly they take on moisture.
Once these evaluations have been carried out, your eye doctor will be able to recommend several types of contact lenses for you to try, to determine which fit best and are the most comfortable. You’ll be given generic versions of these to try on before your eye doctor orders your contact lenses.
Got further questions about contact lens exams? Please speak to our friendly and knowledgeable eye care specialists today.