Contact lens eye examinations
The examination required for contact lenses is different to that done in a standard eye test.
Because contact lenses sit right on the surface of your eye, the power of the lens is different to that required for spectacles. Also because different lens designs, material, shapes and sizes affect the prescription, special calculations need to be done to ensure you have the best possible vision with the contact lenses.
What testing is required for contact lenses?
If you have never worn contact lenses before, your optometrist will generally do the following:
- Firstly they will need to gather information about your eye history as to any eye infections you have suffered, previous eye injuries, surgery or dry eyes. They will also need to know any medications you are taking in case they will affect your ability to wear contact lenses comfortably.
- Your optometrist will also ask about how often you want to wear contact lenses and what activities (sports, hobbies, computer work) that you will need to use them for.
- It is also important to find out if you work in a dry or dusty environment as some contact lenses are better than others for this.
- If you are over 40 and need help for reading, we will discuss the various options for correcting your close vision, such as monovision or multifocal contact lenses.
Types of eye examinations:
Before your optometrist takes any measurements for contact lenses, they need to make sure that your eyes are healthy and you do not have dry eyes.
Your tear film is assessed first using the slit lamp biomicroscope where we can see any dry patches. Often we will use fluorescein dye (a yellow dye that glows green under blue light) to look at the time it takes for your tears to dry on your eye and any patches where the corneal epithelial cells have dried out. We can also use a non-invasive instrument call the tearscope developed by our very own Dr Jean-Pierre Guillon, to look at the oily layer on the surface of your tears. It is this layer that stops the tears from evaporating and whilst it is only thin it is very important.
We also need to look for signs of allergy such as papillae under your eyelids or red eyes. Contact lenses can make allergies worse as the allergens such as pollen and dust can stick to the contact lenses. You can also become sensitised to contact lens solutions or the protein build up on the surface of the contact lens.
The first step is to measure the shape of your cornea. Because contact lenses come in many different sizes and shapes we need to know the exact shape of your eyes.
This is first measured using a Keratometer which gives us a simple measure of the curvature and power of the front of your eyes.
For a more accurate measurement we use a corneal topographer. It is a device that uses a series of concentric rings imaged onto the cornea to measure the exact height and shape of your eye. This is like a topographic map of the earth showing the hills and valleys. Using this data, it is possible to fit a contact lenses precisely to match the shape of your eye. This makes the lens as comfortable as possible and gives you the best vision.
It is also important to measure the size of your cornea and pupil size to make sure the lens is going to correct your vision right out to the edge of your pupil.
We can also use a wavefront aberrometer to measure any distortions to your optical system (entire eye) that can then potentially be corrected by a contact lens.
Sometimes we find that people have irregular astigmatism. This is where the shape of your eye is not round like a soccer ball or oval like an AFL football but more distorted. We then need to fit a type of lens that is designed to correct irregular astigmatism such as a hybid contact lens or RGP contact lens.
If you already wear contact lenses, your optometrists will need to check the following:
- What your vision is like with the lenses (each eye by itself then both together).
- If your vision can be improved with a new prescription.
- How well the lenses are fitting and if they move well on the eye.
- Your eye health. Is there any sign of contact lens overwear or lack of oxygen?
How to choose the right contact lenses for you?
To make a decision on which contact lenses are best for you then we need to gather all the information possible about:
- How often you want to wear the lenses.
- What you want to wear them for?
- Do you work in dry/dusty environments or do a lot of computer work?
- Do you take medications or suffer from allergies?
- Do you want to be able to sleep in the lenses?
- Do you need to wear multifocal contact lenses or consider monovision where you have one eye for distance and one for reading?
- How much are you prepared to pay?
After checking the health of your eyes and measuring your prescription, we will go through the above to work out which is the best lens for you. So make a time to see Andrew or Jean-Pierre today to discuss contact lenses.
Contact lens shapes
Contact lenses are designed to correct different types of refractive error (short/long sightedness or astigmatism)
Spherical – If you only have short or long sightedness your vision can be corrected with a spherical lens.
Toric – If you also have astigmatism then a toric lens will be needed to correct your vision.
Multifocal – Some lenses are designed to correct your reading vision especially as you get older. These lenses have alternating near and distance zones that allow both distance and near objects to be in focus.
OrthoKeratoloy (OrthoK) – These lenses are worn overnight and change the shape of your eyes so the next morning you are able to see without glasses. The effect is transient and the lenses must be worn most nights to temporarily reshape your cornea.
Advanced contact lens fittings – specialised skills and equipment required
Why choose Eye5 Optometrists?
Fitting a contact lenses to someone who has had refractive or corneal surgery is a very special skill that few practices offer. You need to invest a huge amount of money into special equipment, training and contact lens designs before you can even start. If your optometrist needs to wait for a loan contact lens fitting set to be sent to them, that is a sign that they don’t do this often. Both Andrew Godfrey and Jean-Pierre Guillon have many years experience in complex contact lens fitting and take the time to get things right.
We have fitted thousands of people in Perth with contact lenses after eye surgery and we have all the technology to do the best job possible. Every fitting is different and it does take time to do.
Do your eyes need an advanced contact lens fitting?
The following conditions make contact lens fitting more interesting:
- Post Corneal Grafting surgery
- Post Radial Keratotomy
- Pellucid Marginal Degeneration
- Dry eyes
- High Astigmatism
- Irregular Astigmatism
If you have one of the above conditions, then wearing contact lenses to improve your vision is definitely possible. It may just take more specialised skills and time than the average optometrist can offer. At Eye5 Optometrists we have invested in equipment and training to provide these services.
Specialty contact lenses
Contacts for challenging situations
There are several situations where special skills and equipment are required to successfully fit someone with contact lenses. If you have any of the following, it can sometimes be hard to find an optometrist to spend the time required to obtain a successful fitting of lenses which is both comfortable and clear.
- Astigmatism both regular and irregular
- Pellucid marginal degeneration
- Post corneal graft
- Dry eyes
- After laser vision correction
- Presbyopia – when you need vision at both near and far