Week 4 Quiz Revision Flashcards
How many curves are in a RGP lens? And what are they
3 Curves
Periphery curve
secondary curve
base curve
The edge of an RGP lens is divided into 3 zones. What are they?
Posterior zone
Anterior zone
Apex zone
The radiuscope is used to determine the power of an RGP lens. T/F
False - the radiuscope measures the BC. the lensmeter measures the power
The image in a radiuscope comes into focus but the images are not 090 degress aprt. This means the lens is warped. T/F
TRUE
What 3 methods are used to inspect the RGP lens edge?
Slit lamp/ Biomicroscope
Measuring Magnifier
Projection Magnifier
Identify the style of the RGP.
In the lensmeter you measure -3.00/-4.00. In the radiuscope you measure 7.83mm
Front Toric
Identify the style of the RGP.
In the lensmeter you measure -3.00/-4.00. In the radiuscope you measure 7.50/7.03. 45.00/48.00
Bi Toric as the residual astigmatism is above 0.75D
If the tear lens under the RGP, sitting against the cornea is a plus power how has the lens been fit?
Steeper than K
What does FAP indicate? 2
Add plus to the CL RX
The tear lens forms a minus power against the cornea.
What does SAM indicate? 2
Add minus to the CL RX
The tear lens forms a plus power against the cornea
What does the keratometer measure?
The corneal cap
What does BC stand for?
Base Curve
A plus powered lens moved towards the eye is effectively………..
More minus (weaker)
What is the purpose of the radiuscope?
Measure the base curve of a lens
What is the design of the RGP if it has 2 base curves and a spherocylinder reading in the lensmeter and 2 powers on the lab order?
Bi-Toric lens
If the RGP lens has 2 back curves and 2 spherical powers reading in the lensmeter? There is only one power on the lab order. What design is this lens?
Back Toric lens
If the lens is too thin and bends on the blink this is known as what?
Flexure
What does DK stand for?
Oxygen Permeability
An eyeglass wearer just got fitted for contact lenses. He wears +12.00D OU eyeglasses. The power in his contact lens (compensated power) should be a higher plus or lower plus than his eyeglasses?
Higher Plus
A radisucope reading of an RGP shows the lens only has one curve and when the power is checked it is determined that it is sphero-cylinder. What type of lens design is this?
Front Toric Lens
When a person is wearing spectacles and a refraction is conducted over the spectacles. It is found that both the eyeglasses and the over refraction have two spherocylinder prescriptions with different axis. What is this known as?
Obliquely crossed cylinders
Which equipment is used to determine if a fit of an RGP is steep or flat?
Slit Lamp, fluorescein and colbalt blue filter
What does DK/t stand for?
Oxygen Transmissibility
What is used to measure corneal thickness?
Pachymeter
A patient comes in complaining of not being able to wear their lens due to comfort and blurred vision while wearing the lenses. What is the probable cause?1 What is it NOT and why?2
Scratches and/or dirty lens
(not corneal edema as blurry only with CL on)
(not fit as they ‘come back’ complaining and we would have fit well)
What does HVID stand for?
Horizontal visible Iris diameter
If the K’readings is: 43.00 sphere but fit at 42.00. CL RX is: -3.00D What is the new lens power?
-2.00D (FAP. it was fit 1.00 flatter than K so -3.00+1.00=-2.00)
If the RGP lens shows no movement/adhesion on the lens. Would this indicate a flat fit or steep fit?
Steep fit
What does BOZD stand for?
Back Optic Zone diameter
What does the v-gauge measure?
Diameter of a RGP lens
If the radiuscope shows 1 curve and the lensmeter shows one power. What type of RGP lens is this?
Spherical
What is the corneal cyl of 41.00/41.75 @090?
-0.75D (MUST BE MINUS)
The px K’reading: 44.00/45.00 @090 The fitter fits 43,75 flattest K. Is it fit flatter/ on K or steeper?
flatter
What is the main advantage of switching from a PMMA to RGP lens?
Oxygen Permeability (DK)
If the spokes on a radiuscope all come into focus the same time this tell you what about the lens?
There is only one curve (spherical)
If you are making an Bi Toric or Back Toric lens once you have found DIA/BC what do you do? next 3 steps
-Find ∆k 2.75D
-Find induced cyl = ∆K X 0.4 1.1D
-Find Calculated over correction (Coc)= induced cyl - Residual cyl
a. If Coc <0.75 use back toric
b. If Coc > 0.75 use bi-toric
Once the COC has been found and the design has been confirmed, you use the orginal two vertexed meridians with the residual cyl to find the final power and apply FAP/SAM to. T/F
true
