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57 Cards in this Set
- Front
- Back
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Contact rests on the |
Tearfilm layer of the cornea |
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What produces the power of a contact len? |
The difference between the front surface curvature and the back surface curvature. |
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Two ways to list k readings? |
1.list the flat k first followed by the steep k and its axis 2. List horizontal meridians first regardless if its the steep k or not. |
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If the back surface of a lens is to be the same radius as the k's then that is called? |
Fitting on the k |
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Rgp lens can be fitted? |
Flatter, steeper , or on the k |
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Soft contacts are fitted how? |
3-5 diopters flatter than k |
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How is the total lens diameter measured? |
One edge of the lens to the opposite side. |
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The higher the the minus the ___ the center of the lens. The higher the plus the _____the center of the lens. |
Thin, thick |
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Why are lenses truncated? |
It adds stabilty, and prevents rotation. |
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When a base curve lens says it needs to be steeper what happens to posterior radius of the curvature? |
Its decreased it is opposite if the curvature lens needs to be flatter. |
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How is the wetabililty of a surface measured? |
Its measured in terms of contact or wetting angle. |
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The lower the wetting angle the greater the? |
Spreading of tears |
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The oxygen abbreviation in contacts is? |
Dk |
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What is the minimal safe level of equivalent oxygen percentage (EOP) in dailies, extended wear? Whats ideal for extended wear? |
9% 12% 18% |
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When the corneas astigmatism is different than the cylinder in the prescription this is known as? |
Residual astigmatism |
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How is the optic zone determined? |
The difference bt the diameter and width of the peripheral curves. |
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What are the causes of a 3:00-9:00 staining from contacts? |
Lid gap, poor blinking , poor tear film. |
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What instrument measures the base curve of a lens? |
Contacto gauge (radiusscope) |
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How can the power of a lens me measured? |
Lensometer |
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Describe giant papillary conjunctivitis. |
Its more common with gas perm, has a cobblestone appearance under the lid. |
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What is a 'tight ' lens |
A lens that causes hypoxia aka low oxygen causing corneal edema. |
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What causes one to change their blink rate? |
Awareness of the lens. |
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What are multiple causes of a contact lens causing corneal edema? |
Flat lens compressing cornea Steep lens lacking tear flow Poorly centered lens Incorrect blinking Incorrect cleaning of lens |
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Edema can do what to previous k readings |
Increase |
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How are soft lenses classified ? |
How their made, water content. Dk permeability, and by their function |
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Advantage a of hydrophilic soft contacts? |
Comfort, rapid adaptation, lack of spectacle blur, dispisability, minimal lens loss, minimal overwear reaction, protects entire cornea, no corneal abraisions on insert, lack of glare. |
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Advantages of silicone hydrogel? |
Rapid adaptation, low rate of deposits, easy to handle, high DK value, suitable for extended wear. |
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What are disadvantages of a soft contact? |
Doesn't corrext high astigmatism, variable vision, lack of durability, faulty duplication, deposit forms, modifications are impossible, disinfect problems |
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How can one disinfect soft lenses? |
Boiling , chemical, and uv methods. |
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Thing to consider in a patient interested in contacts? |
Age Hygiene Reoccurent infections, susyemic disease, dryness of eyes Patients motivation Corneal sensitivity test Occupation Lid tension |
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How are soft lenses manufactured and which is the most common? |
Spin casting, lathecut, and molding methods. Lathe cut and molded are most common. |
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A soft lens should rest on how many points? |
Three, apex and at the periphery of the cornea |
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When fitting a soft contact lens the goal is to have |
The flattest lens possible with clear vision and comfort. |
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Symptoms of a tight lens |
Fluctuating vision Comfort at first that gets worse throughout the day Coneal injection around the cornea Corneal indentation No movement after blinking K's that are clear than are distorted after a blink Retinoscopic reflex is fuzzy than clear . |
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Signs of a loose lens |
Fluctuating vision Awareness of lens Poor centering Lens falls out Bubble under lens Ks that blur after blinking Retinoscopic reflex that is clear than is fuzzy. |
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The lens is cleaned by rubbing both sides of a lens with a finger for 20 seconds, this is known as? |
Digital cleaning. |
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What is the minimal time needed to disinfect lenses with peroxide? |
20 minutes |
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What is bullous keratopathy |
Described as a corneal blister. |
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Symptoms like flare or streaming lights with contacts could mean? |
Optic zone is too small |
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Blurring vision in daytime could be a result of |
The contact lens riding too high or too low |
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Signs that indicate a contact lens needs to be changed or wear time needs to be reduced? |
Change in k's over 1 diopter and distortion in the mires. |
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What does a contact wetting solution do? |
Turns surface into a water loving surface making the tear film spread easier. |
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What do soaking solutions do? |
Cleans lens of oil and sebaceous secretions. |
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What does a cleaning solution do? |
Cleans lens of oil, mucus, crystalline deposits. |
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What kind of diameter does a tricurve lens have? |
Large diameter |
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Tinted lenses use what type of scale to note tint intensity? |
1-3 1 being the lightest. |
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What does it mean when the base curve of the lens is made steeper? |
Posterior radius curvature is decreased |
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What is a frequent cause of patients rejection of contacts? |
Edge design |
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What are the peripheral curves designed for? |
Allows tear flow under the lens |
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Lid gap is more prone in what script and why? |
High myopes from thickness of periphery of lens |
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Is it helpful to wet the finger befor putting a gp lens in? |
Yes but don't have to wet a finger for soft lenses |
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How often and how is a contact lens case cleaned? |
Scrub with a toothbrush and soap atleast once a week |
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How often should a soft contact be cleaned with an enzyme and what needs to be done after its cleaned? |
Twice per month, rinse with saline and disinfectant before insertion |
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Should contacts be removed for air tonometer? |
Yes |
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Should contacts be removed during a vf? |
No |
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True or false? The zone of flare is always opposite of the displacement of lens? |
True |
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If a keratometer can't read a steep cornea what can be attached? |
INNS extension disc |
