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Contacts Test 2

Keratometer; Astigmatism; CL Parameters...

What is another name for the keratometer? ophthalmometer
What is the keratometer used to measure? The radius of curvature of the cornea.
What is the corneal cap? The 3-5 mm in the center of the cornea that we measure with the keratometer; if measured off-center K's will be too flat.
What N is the keratometer calibrated for? The N of tears = 1.3375
What are the measurements from the keratometer called, and how are recorded? K's or K-readings; recorded horizontal reading/vertical reading X axis
The axis always goes with the ________ meridian. flattest (weakest)
What does the difference between the horizontal and vertical K-readings represent? The amount of corneal astigmatism.
When using the keratometer, always start with the _____ eye? right
Measure right eye, then left eye how many times? Three
After you take all the measurements in both eyes, you then take an....? average
If the mires are blurry and do not clear up after having the patient blink, what could be the causes? keratoconus, corneal warpage; injury; surgery; over-wear of contact lenses
What is transient mire distortion? When the mires are blurry, but clear up after the patient blinks a few times.
What is the average range of the power drum? 36 to 52 D
What is the extended range of the power drum? 30 to 61 D
Which lenses are used to extend the range of the power drum? -1.00 and +1.25
What are other uses for the keratometer? check contact fit; check flexing of GP lens; follow up K's to see if contact changed shape of cornea; use conta-check to check the BC of a GP lens
What is a topogometer? An attachment to the keratometer used to measure corneal curvature values across mutliple points on the cornea.
Who invented the topogometer? What else did he invent? Joseph Soper; also invented lenses for keratoconus
What are other names for a corneal topographer? Video Keratoscope; Photokeratoscope
What does a corneal topographer do? Produces a color-coded map of the whole cornea to show where it is steepest and flattest.
What do the blue or cool colors represent on a topographer map? Flat curves
What do the red or hot colors represent on a topographer map? Steep curves
Corneal astigmatism is always represented with a plus or minus? Minus
What is with-the-rule astigmatism? (WRA) when the cornea has the flattest meridian horizontal and the steepest meridian vertical; has an axis between 0-30 or 150-180 degrees.
What is against-the-rule astigmatism? (ARA) when the cornea has the flattest meridian vertically and the steepest meridian horizontally; has an axis between 60 and 120 degrees
What is oblique astigmatism? the two principal meridians are located diagonally; Axis is between 31-59 and 121-149 degrees
What is irregular astigmatism? the two principal meridians are not 90 degrees away from each other
Most patients have which type of astigmatism? With the rule (WRA)
What is the sagittal depth? The distance between the posterior surface of the central portion of the lens and a flat surface.
What are two other names for the Base Curve? Posterior Central Curve (PCC); Central Posterior Curve (CPC)
Base curve is also known as the _______ curve. fitting
What is base curve? radius of curvature of the central posterior portion of the lens expressed in mm or diopter power
Steeper K's have a _______ radius? shorter
Flatter K's have a _______ radius? longer
What is the optical zone (OZ or POZ)? The diameter over which the BC extends on the posterior surface of the lens; described in mm; contains the refractive power
Where is the Posterior Secondary Curve (Intermediate Curve) located? between the base curve and the peripheral curve
Why is the Posterior Secondary Curve flatter than the base curve? To align the flatter portion of the cornea.
What is the outermost curve? Posterior Peripheral Curve
What is the function of the posterior peripheral curve? to clear the flatter periphery of the cornea and to prevent impingement in the limbal area as the lens moves.
What is the average diameter of a GP lens? 7.0 to 10.5 mm
What is the average diameter of a soft contact lens. 12.5 to 16.0
What is a juncture? Where the posterior radii meet, between the BC, PIC, and PPC.
What are blends? contour modification to the posterior side to smooth out the junctures between the radii.
What is center thickness? measured in mm at the GC from posterior to anterior; varies depending on the lens power
What is the anterior optical zone also known as? Refractive Power; Power Curve; Lenticular Curve
What is the difference between the radii of the anterior and posterior lens surface. Lens power
What is the lenticular flange? The increase or decrease in anterior edge thickness to change the lens mass and aid in lens positioning.
What type of flange decreases edge thickness? hyperflange
What type of flange increases edge thickness? myoflange
What is the portion of the CL in contact with the upper lid when blinking? anterior zone
What is the function of the anterior zone? minimize lid irritation during the blink
What is the posterior zone? The small reverse curve on the posterior lens surface to flare the edge away from the cornea.
What is the function of the posterior zone? To allow free movement of the lens across the cornea.
What is the junction between the anterior and posterior zones? Edge Apex
Why does the edge apex have to be smooth? to mininmize lid awareness during the blink
What is the SAG a combination of? The base curve and diameter
Magic number for converting diopter power to radius of curvature.... 337.5
All PMMA lenses have what type of replacement schedule? Conventional
What type of contact lenses can never be slept in and are only daily wear (DW)? PMMA
Who invented the PMMA lens? Kevin Touhy
What are advantages of PMMA lenses? durable and good optical quality
What are disadvantages of PMMA lenses? hypoxia which leads to edema
Which type of lens is not offered with a disposable replacement schedule. GP
What was the first GP lens? CAB - cellulose acetate butyrate; was not successful and is no longer used
What are GP lenses made of today? SA - silicone acrylate; FSA - fluoro-silicone acrylate
Why was silicone added to GP lenses? Allow more oxygen to the cornea
Why was fluoro added to GP lenses? to improve wetability
What are advantages of GP lenses? oxygen permeability; less chance of edema; excellent optical quality; corrects regular and irregular astigmatism; easier to care for than soft conventional; parameters verifiable; polish and modify; use fluorescein to evaluate lens; last longer
What are disadvantages of GP lenses? initial comfort; harder to fit; more chair-time; more follow-ups; cost more initially; can pop-out easier
What is the lacrimal lens? Tears formed by the back of a GP lens and the front of the cornea that is used to help correct astigmatism.
Who created soft hydrogel lenses? Otto Wichterle
Who gained FDA approval to distribute soft hydrogel and when? Bausch and Lomb in 1971
What are other names for soft hydrogel lenses? hydrogel; HEMA; gel lens; hydrophilic
When was the first silicone hydrogel lens available? late 90s
What was the first silicone hydrogel lens? Ciba Focus Night and Day
What type of disposable lenses are available in silicone hydrogel? 1 day; 1 week; and 30 days
What type of planned replacement lenses are available in silicone hydrogel? 2 weeks and 1 month
Are there conventional lenses available in silicone hydrogel? No
What was the second silcone hydrogel lens available? Bausch and Lomb Purevision
What are advantages of soft lenses (hydrogel and silicone hydrogel)? initial comfort; best for occasional wear; good for sports (stay on better); less sensitivity to light; less edge reflections; available in single use; available in 2 week and 2 month planned replacement
What are soft hydrogel advantages? available in color enhancement and opaque; higher water content (more oxygen); and thinner lens
What are silicone hydrogel advantages? allows more oxygen due to the silicone
What are problems with silicone? makes the lens stiffer, so while it may be easier to handle it is less comfortable
What are soft lens disadvantages? spherical lenses do not correct astigmatism; cannot use fluorescein; cannot easily verify parameters; conventional need more lens care; cannot polish or modify
Created by: griffiskr