Measurements that help the optometrist properly fit contact lenses.
- Keratometry – This is a measure of the curvature of the eye using a keratometer.
- Iris Diameter – The diameter of the iris measured in millimeters.
- Refractive error – This is obtained by using the phoropter.
- Vertex Distance – This is the distance between the back surface of the glasses and the front of the cornea.
Instructions for patients using soft contact lenses include:
- Wash hands before handling contact lenses.
- Preform the taco test to make sure the lens is not inside out.
- Lens should be wet and the finger dry.
- Lens should be placed directly on cornea.
- Remove remove the lens by pinching the lens.
- Long fingernails are the nemesis of contact lenses.
- Do not “top off”. Topping off refers to adding a little extra solution to what was left in the case from the last cleaning. This is dangerous because it dilutes the solution and no longer guarantees a disinfected solution.
Instructions for patients using hard contact lenses include:
- Always locate the CL before using the plunger. Damage can be done to the cornea if the plunger attaches to it.
- Wet the plunger before using. This will give the plunger better suction.
Pathology from Contact Lens Misuse
Note: This is not an official section, but this material is important to cover
Lack of oxygen due to improper wearing of contact lenses results in vascularization and corneal edema.
Vascularization- is the growth of new blood vessels. This is an effort made by the body to get more oxygen. When a patient has been wearing contact lenses
Corneal Edema- is swelling that occurs from lack of oxygen. Three symptoms are blurred vision, rainbows around lights, and burning
Giant papillary conjunctivitis is an allergic response. Proteins from the eye attach to the contact lens. When these proteins break down into smaller subunits the body thinks that it is being invaded. The result is an allergic response. The main symptom is big bumps on the inner upper lid.
For someone to be a candidate for contact lenses they need to have a sufficient tear film. Some people like to be fitted for monovision contacts. This means that one eye is good for seeing at a distance and one eye is good for reading.
Soft contacts are hydrophilc, “water loving”. Because of this characteristic they can retain a lot of water and with the water comes oxygen “H2O” which the eye needs to stay healthy. The higher the water content of a soft contact lens the more oxygen will get to the cornea. To fit someone for soft contact lenses you will have to determine the spherical equivalent. Toric contact lenses are a type of soft CL
- They are more comfortable than hard contacts.
- Less lens displacement. Soft contacts are larger they don’t move around as much
- Less lens loss. Soft contact lenses are larger which means that they are harder to lose than hard contacts
- Not as durable has hard contact
Hard contacts are smaller than soft contacts. RGP(Ridged Gas Permeable) is a word you might see on the test. RGP contacts are hard contacts. RGP are smaller in diameter than soft contacts.
- Hard contacts give crisper vision.
- Hard contacts last longer and are durable.
- Not as comfortable as soft contact lenses.
- Hard contact lenses are smaller in diameter which makes them easier to get lost.
PMMA Lenses (Polymethylmethacrylate)
Theses lenses are not used as mush as they were in the past. This is due mainly to their poor oxygen permeability many patients that use these lenses experience some amount of anoxia (without oxygen). Practitioners usually prefer to give patients a RGP CL over PMMA CL.
Bandage Contact Lenses
Bandage contact lenses are used to help the eye heal. The practitioner will add a medication to a CL then place it in the eye. The lens that is chosen is usually a Plano lens. This is because plano lenses are thin and thin lenses increased oxygen permeability.
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