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Contact Lenses 1 > Lecture 1 - Theory and Practice > Flashcards

Lecture 1 - Theory and Practice Flashcards

1
Q

what index of refraction does the keratometer use when making measurements?

A

1.3375 (not 1.376 to account for the small contribution from posterior cornea and corneal thickness)

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2
Q

what portion of the cornea does the keratometer measure?

A

the central 3-4mm (assumes axes are separated by 90 degrees)

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3
Q

what can you use if the dioptric measurment ralls outside of the keratometer range?

A

+1.25 or -1.00 sphere lens = extends range to 36-52D to 31-60D

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4
Q

what do you multiply the results by if you use a +1.25D lens? what about for a -1.00D lens?

A 
\+1.25 = 1.166
-1.00 = 0.8576
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5
Q

how do you calculate diopters from mm (radius)?

A

surface power equation (337.5/r mm)

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6
Q

how do you record the keratometry results?

A

flat radius (weak power) and meridian comes first and then the steeper power and meridian

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7
Q

what shape is the cornea? what are the HVID and VVID averages?

A

elliptical
HVID = 11.7mm
VVID = 10.6mm
(both are 0.1mm less in females)

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8
Q

what is the average corneal thickness? central radius? sagittal depth?

A

thickness = 0.52mm (center) and 0.67mm (limbus)
radius = 7.80mm
sagittal depth = 2.6mm

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9
Q

what happens to the corneal curvature in the periphery?

A

the curvature flattens towards the periphery

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10
Q

what is the corneal front apical radius? back apical radius?

A 
front = 7.8mm (43.27D)
back = 6.5mm (-6.15D)
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11
Q

what is the average corneal refractive index?

A

1.376 (not optically homogenous)

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12
Q

what is the cornea made of?

A

78% water
15% collagen
5% other parts
1% GAGs

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13
Q

how much of the corneal thickness are the corneal epithelium and stroma?

A 
epithelium = 50 microns (10% of cornea's wet weight)
stroma = 90%
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14
Q

what nerves are present in the cornea?

A

(about 30 nerves)
ophthalmic division of CN5
appear as axon bundles near limbus and lose myelin sheath before 1st division

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15
Q

what will a keratometry over a soft CL show?

A

the front surface’s eye radius (not the front surface manufactured radius)

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16
Q

what does it mean if the mires appear irregular over a soft CL?

A

the front surface is irregular - keratoconus or the CL is inside out

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17
Q

what will the keratometer show over a GP lens?

A

gives the manufactured radius and will reveal unwanted lens flexure (induced astigmatism)

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18
Q

what is Dk?

A

oxygen permeability - one of most important properties of a CL material (inherent material property)

19
Q

what is Dk/t?

A

oxygen transmissibility - Dk of the material divided by the lens thickness (10^-9)

20
Q

what is the unit for Dk?

A

Barrer (10^-11 and CT is in cm)

21
Q

what is an acceptable minimum Dk/t value for avoidance of corneal edema?

A

daily wear = 24

extended wear = 87

22
Q

what is an acceptable minimum Dk/t value for avoidance of anoxia for open and closed conditions?

A

daily wear = 35

extended wear = 125

23
Q

what 3 things occur with lack of oxygen to the cornea?

A

edema, swelling and change in K readings

24
Q

what is wettability?

A

crucial for comfort and vision - can be detected in vitro and in vivo (determine wetting angle)

25
Q

is a large angle good for wettability?

A

no - the lesser the angle = better wettability

26
Q

what are the in vivo methods for determining wettability (visual analysis)?

A

tear coverage (look for dry spots), break-up time and drying time

27
Q

what are plasma treatments, what does it do to wettability?

A

improves - uses a good cleaning of the lens (UV energy breaks organic bonds - lasts a few days to months)

28
Q

what are some natural wetting agents in the human tearfilm?

A

mucin, lipids, lactoferrin and lysozyme

29
Q

what is the stem filcon for?

A

hydrogel lenses

30
Q

which groups in the filcon lenses are ionic and have high water content?

A 
1 = low content, non-ionic
2 = high content, non-ionic
3 = low content, ionic
4 = high content, ionic
31
Q

what is group 5 filcon?

A

silicone hydrogel lenses

32
Q

what is the stem focon?

A

non-hydrogel lenses

33
Q

what is group 1 focon description and material?

A

no silicone or fluroine

material = cellulose acetate butyrate

34
Q

what is group 2 focon description and material?

A

silicone and no fluorine

material = silicone acrylate

35
Q

what is group 3 focon description and material?

A

silicone and flurorine

material = flurosilicone acrylate

36
Q

what is group 4 focon description and material?

A

fluorine and no silicone

material = fluorocarbon

37
Q

what are class 1 FDA devices?

A

low to moderate risk

Ex: dental floss

38
Q

what are class 2 FDA devices?

A

moderate to high risk

contact lenses worn during daytime (soft, GP, and care products)

39
Q

what are class 3 FDA devices?

A

high risk

extended wear CL (overnight) and orthokeratology lenses

40
Q

what is the national requirement for prescriptions? Eyeglass rule?

A

all Rx for corrective lenses must be released to the patient (requested or not)
immediately following exam

41
Q

what is the contact lens rule (FCLCA)?

A

Rx must be given to patient upon completion of exam or the CL fitting

42
Q

what things does a valid CL Rx need?

A

power, material, base curve, diameter, expiration date (patient name, optometrist name license number, signature)

43
Q

can you ask the patient for money, additional fees or to sign a wavier if they want a copy of the Rx?

A

no

44
Q

what is passive verification of a CL Rx?

A

an optometrist has 8 business hours to verify an Rx from a third part before it is verified automatically

Contact Lenses 1 (6 decks)

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