Contact Lenses 6% Flashcards
The contact lens rests on the _____of the peripheral K
tear film
_____helps to smooth out irregularities on the K and makes the K more _____
Tear film
spherical
CL can correct astigmatism with a spherical lens if…..
why?
it is a small amount of astig
because the tear film can create a cylindrical lens and correct small amounts of astig
The CL changes the refractive power of the eye by providing a _____that’s different than that of the K.
radius of curvature
The back surface of a CL is contoured to fit_____
the cornea
The front surface of CL contains____
the refractive power
What are the 3 different ways the K is oxygenated?
Tear film, aqueous humor, ambient room air
____ and _____can be disrupted by an ill fitted CL.
ambient room air and tear film
What is the primary goal when fitting a CL?
to keep the K well oxygenated
What happens if tissue is starved of oxygen?
It will be much more susceptible to infection
What are the 3 main types of CL lenses?
Regular Old Soft lenses, Silicone Hydrogel, and Rigid Gas Permeable
Regular old soft lenses were made of ___
plastic
What are the disadvantages of the old regular soft lenses?
They were problematic for dry eyes, lenses dehydrated during wear, and decreased oxygen to the K
Why are silicone hydrogel lenses better than regular soft lenses?
They are hydrophilic
They are 6x more oxygen than regular soft lenses
They have less bacterial build up
They are best for dry eye pts
What does hydrophilic mean?
Wetted by water
Rigid gas permeable lenses also allow _________
excellent transmissability
Rigid gas permeable lenses are hard lenses and are smaller in ____ than in the _____
diameter
cornea
The central corneal ____ is much steeper than the pericentral part of the K.
cap
The CL rests on the tear film of the _____K not the ____K
peripheral
central
The steepness of the curve of the CL that fits against the K
Base curve
The entire width of the CL in mm
Diameter
If you leave the diameter the same on a CL but make the radius of curvature (or base curve) larger the lens becomes_____
flatter
It you leave the diameter the same on a CL but make the radius of curvature (BC) smaller the lens becomes _____
steeper
In CL (leaving the base curve the same) the larger the diameter the _____ the lens, in contrast the smaller the diameter the ____the lens.
steeper
flatter
CL: Curvature of the central portion of the BACK surface of the lens in mm (aka Central Posterior Curve or CPC)
Base curve
CL: Edge to edge measurement in mm
Diameter
CL: distance between flat surface and back surface of center(apex) of lens
Sagittal height
The smaller the BC the higher the _____
Sagittal height
Smaller the number on BC the _____the CL
steeper
The larger the number on the BC the flatter the CL
CL: Back surface of tlens is same radius as K is referred to as
Fitting on K
Cornea is about ____mm on average in diameter
11.5
CL: Lens diameter is larger than the cornea is referred to
steeper than K
CL: Lens diameter is smaller than cornea is referred to as
flatter than K
____lenses are smaller in diameter than the K
Rigid lens design
____lenses are larger than the K
Soft lenses
____lenses are fit flatter than the flattest K
soft
What is the best method for measuring a contact lens
an optical method because there’s no physical distortion of the contact lens
What can be used to measure the diameter of the CL in mm?
PD stick
A Radiuscope uses the ______principle
Drysdale
The Radiuscope uses the back of the CL as a ____mirror.
concave
What does the Radiuscope measure?
The base curve of RGP lenses.
Radiuscope is also known as
Microspherometer
What does an ultrasonic transducer measure?
contact lens BC, Lens Height, and thickness
Explain how ultrasonic transducer works.
Has a CL holding tank, you fill with saline solution with CL concave side down on a pedistool with an accurately known diameter. Then introduce ultrasonic transducer beam into the BSS and aim sound waves at the contact lens.
______measures the spherical abberation of CL.
Wavefront Aberrometry
_____is an optical imperfection in any optical system(an eye, a pair of glasses, CL, telescope, microscope, IOL)
Spherical aberration
Spherical aberration creates a little bit of _____
blurring
The blurring where the light doesn’t come to a perfect focal point is called
sperical aberration
Lenses use to correct spherical aberrations(makes the light rays come to a perfect focal point)
aspherical lenses
A measurement of the the amount of oxygen that is transmitted through the K to the eye
DK value
The higher he DK value the more _____ transmitted to the eye
oxygen
Another way to measure the amount of total oxygen that passes through lens and reaches K
EOP (Equivalent Oxygen Performance)
What are the 3 things EOP(Equivalent Oxygen Performance) are based on?
Lens Material
Design of lens
Thickness at center and periphery
How do you evaluate the fit of CL?
Instill a drop flurouscein, ask pt to look up , down, left and right while viewing they eye through the slit lamp.
When assessing the fit of CL when pt looks up there should be slightly ______than when looking in other positions of gaze.
more movement
Explain the finger push up method when checking CL fit?
with pt at slit lamp and CL on eye use finger and their lower eye lid to push CL up. Then let go to see if CL floats back down to rest along the lower lid margin.
What is the KCN pt optimal staining Pattern called?
Three point touch
Explain 3 point touch
This means that CL is touching at the apex and the periphery in KCN CL pts.
If you get an air bubble centrally when looking at the CL fit this means…
CL too steep
If you get an uneven distribution of fluorescein across K of CL this means…
CL too flat
When CL touches periphery of K this means…
CL fits just right
CL; If the fluorescein staining pattern shows that he lens is too steep or tight we need a ___BC
flatter
If CL is too flat or loose then we need a ___BC
steeper
If the CL doesn’t move well the CL can become ___
distressed
If you have excessive movement of the CL the pt will be _____
uncomfortable and have lens awareness
What are the signs of CL being too steep?
Centers well but fits tight, doesn’t move well, VA can fluctuate with blink, comfort at first but then becomes uncomfortable.
What is he solution to CL that is too steep/tight
Flatter BC
What are signs of CL too flat/loose?
Doesn’t center well, moves excessively, VA fluctuates with blink, Uncomforatble
What is the solution to CL being too flat/loose?
Steeper BC
When counseling pt about CL care let them know that it is not a ___device but a____device
cosmetic
medical
What should you instruct CL pts about when talking about CL care?
Goal: Keep lenses, clean, hydrated, and free from microbes as possible
Pt can get ___form using tap water to place CL in their eye.
Acanthomeiba
Pt should not insert CL with anything except…
Sterile contact lens solution
What are the factors to consider with CL
convenience, comfort, anti-microbial efficiency
What must we do before we can disinfect our CL?
Clean them
Why is it important to clean CL before we disinfect them?
Tor remove deposits (cellular, lipid, protein, makeup)
What is the the first and most important step in disinfecting CL?
Cleaning it with digital rubbing
How do you perform digital rubbing?
Place lens in palm of hand, place a few drops of cleaning solution on lens, rub with finger from other hand,
What is the purpose digital rubbing important when cleaning CL?
to decrease microbial load before disinfection(important step)
What does MPS(multi purpose solution) lens care systems do?
Cleans, disinfects, stores
What are the advantages of MPS?
convenient, easy to use, readily available
What are things we need to consider with MPS?
Alleriges, lens solution incompatibility
How does hydrogen peroxide lens care systems work differently from MPS(red top)?
It requires a special type of CL case that has a platinum coated disc in it, you must neutralized the hydrogen peroxide before you insert it into the eye(is PF after neutralized)
What are the advantages of hydrogen peroxide lens care system?
Preservative free (after neutralization), easy to use, excellent cleaner and disinfectant, better comfort and VA
What are things to consider with Hydrogen peroxide lens care system?
never rinse lens with hydrogen peroxide then insert (must neutralize first), Never put hydrogen peroxide in they eye, never put in regular case (can’t neutralize), Be sure neutralization is done before inserting lens
Why should a pt not sleep in CL
It substantially increases the risk of infection
What are some common pathogens associated with CL wear?
Pseudomonas aeruginosa and acanthomoeba
what is CL overwear syndrome called
Corneal hypoxia
When K is starved of oxygen it causes…
corneal neovascularization
___is a bacterial infection in corneal ulcers caused by CL use
Pseudomonas aeruginosa
____microorganism foundin soil and water caused K infections, and is associated with salt tablets and tap water and improperly sterilized distilled water in homemade CL solutions.
Acanthoamoeba
What are some conditions that increase the risk of infection with CL wear?
-Reduced oxygen transmission with CL wear
-Atmospheric pollution during day
-Closed lids further decreases oxygen transmission
-Lack of eye movement
-Lack of lid movement
What are the possible causes of central K edema in a CL wearer and how to fix it?
Insufficient O2:
Blend junctions of CL curve better, flatten peripheral curve, reduce diameter, reduce diameter of OZ, fenestrating lens.
Cause and cure of K abrasion with CL use..
Insufficient oxygen:
Increase CL diameter, OZ, reduce edge thickness, steepen OZ or peripheral curve, increase BC.
Cause and cure with CL pt:
3 & 9 o’clock staining.
Dryness: (inadequate blink/use smaller, thinner CL, tears, blinking exercises.
Improper removal: reinstruct pt
Cause and cure CL pt:
Zig zag/irregular staining
FB under lens: remove CL and FB
Cause and cure CL pt:
Arc staining
Poor insertion techniques: reinstruct
Sharp juncture lines between central posterior curve and intermediate or peripheral curve: better blended lenses.
Cause and cure CL pt:
Bubbles
CL too steep: flatter lens
Cause and cure CL pt:
Flare/streaming lights at night
Optical sone too small: larger CL or optical zone (OZ)
Cause and cure for CL pt:
Blurring if VA in daylight
Lens rides too high:
High minus
Small lens/tight lids
Cause and cure CL pt:
Gravitating too low after blinking
Too heavy/high plus or too thin at edge: redesign lens
Cause and cure CL:
Lens displaces nasally or temporally
Abnormally centered K: larger CL or OZ
