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Flashcards in intro and history Deck (48):
1

horizontal radii is 43.5
vertical radii is 45.5

What type of astigmatism is that?

with the rule

horizontal has weaker power

2

Your patient's flat corneal radius (Flat K) is 40.50 D. What is the equivalent?

8.33 mm

337.5/r (will convert Diopter to mm)

3

patient corneal radius (Flat-K) is 51.00 D. What is correct?

cornea with keratoconus
*high focal power, unusually steep

also, possible for refractive surgery, but not likely

4

What is the relationship between radius and diopter?

inversely related

5

What is an average cornea HVID and VVID?

HVID 11.70
VVID 10.60

6

What slitlamp illumination technique is used to observe CORNEAL LAYERS (therefore also tearfilm thickness and lens thickness in CL)?

optic section

7

What is the appropriate thickness of the corneal epithelium?

50 microns

8

What is the thickness of the total cornea?

520 microns

9

What is the appropriate water content of the cornea?

78%

10

How dose the cornea react under oxygen deprivation? (fast reaction)

edema

11

• One of the most important properties of a contact lens material
• Inherent material property
• Not a function of lens thickness, shape or back
vertex power
• D = diffusion coefficient of the material
• k = solubility of the gas in the material

oxygen permeability Dk

12

What specifies contact lens material?

Dk/t

13

What is the SI unit of Dk?

1 Barrer (10-11 (cm3 O2 cm)/(cm3 sec mmHg)

14

What is an acceptable minimum Dk/t value to avoid corneal edema?

• Daily wear: Dk/t = 24
• Extended wear: Dk/t = 87

15

What is an acceptable minimum Dk/t value to avoid anoxia for open and closed eye?

• Daily wear: Dk/t = 35
• Extended wear: Dk/t = 125

16

What type of measurements are Dk and Dk/t?

indirect in vivo measurements which infer oxygen transmissibility

17

What goes along with cornea edema?

swelling and change in k readings

18

Oxygen concentration of a gas mixture which produces an equivalent corneal response

equivalent oxygen percentage (EOP)

19

Wettability is crucial for what?

comfort and vision

20

How is wettability detected?

• Can be detected in vitro and in vivo

21

In vitro = ?

wetting angle

22

3 ways to measure wetting angle

A. Sessile drop
B. Captive bubble
C. Wilhelmy plate

23

What type of angle is a good wetting angle?

low angle

24

What are in vivo measurements for wettability?

• Tear coverage
• Break-up time
• Drying time

25

What type of treatment can improve wettability?

plasma treatment (super cleaning)

26

plasma treatment

• Plasma cleaning
• Ionized gas (oxygen)
• Around room temperature
• Plasma interacts with any surface
• Plasma’s UV energy is very effective in the breaking
organic bonds
• Super cleaning—lasts a few days to months

27

What does the human tearfilm contain?

Mucin, lipids, lactoferrin, lysozyme

28

Class I devices

• Are deemed to be low to moderate risk
• Subject to the least regulatory controls
• Example: dental floss

29

• Class II devices

• Are moderate to high risk
• Require greater regulatory controls to provide
reasonable assurance of the device’s safety and
effectiveness
• General controls and special controls
• Examples
• Contact lenses worn during daytime (soft, GP, care
products)
ex: condoms

30

• Class III devices

• Are high risk
• Most stringent regulatory controls
• General controls and pre-market approval (PMA)
• Examples
• Extended wear contact lenses
• Overnight orthokeratology lenses

31

• National requirements (Federal State Law)

• All prescriptions for corrective lenses must be released to patients, whether requested or not

32

• Eyeglass rule (Federal State Law)

• Eyeglass prescriptions must be given to the patient
immediately following the eye exam

33

• Contact lens rule (FCLCA)

• Contact lens prescriptions must be given to the patient
immediately upon completion of the eye exam or the
contact lens fitting (if a fitting is necessary)
• Contact lens fitting means the process that begins after an initial eye examination for contact lenses and ends when a successful fit has been achieved
• In cases of renewal prescriptions, the fitting ends when the prescriber determines that no change in the existing prescription is required

34

California State Law regarding valid CL Rx

• Requires a valid contact lens prescription include
• Power, material or manufacturer or both, base curve or
appropriate designation, diameter (when appropriate), and an appropriate expiration date
• The prescription should also include
• Patients name
• Optometrists name, address, telephone number, license
number, and signature

35

California State Law regarding internet sites

should ask for information about your doctor so they may verify the prescription with the doctor
• California law requires them to do this if they don’t have a copy of the written prescription
• If the company does not ask for this information, they are not complying with state law

36

California State law regarding copy of CLs

• In exchange for a copy of the contact lens
prescription, prescribers CANNOT require patients to
• Buy contact lenses
• Pay additional fees
• Sign a waiver or release

37

CSL regarding third party

• If a patient elects to purchase contact lenses from a third party, the seller must verify the prescription before filling it
• When requested, optometrists are required to respond to sellers’ requests for prescription verification within eight business hours
• ‘passive verification’

38

CSL regarding detailed Rx

• More detailed prescriptions will include directions
for safe use such as
• Wearing schedule
• Whether the lenses are for daily or extended wear
• Number of refills
• Whether lens material substitutions are allowed

39

CSL regarding verification

• More detailed prescriptions will include directions
for safe use such as
• Wearing schedule
• Whether the lenses are for daily or extended wear
• Number of refills
• Whether lens material substitutions are allowed

40

Pt: +2.00 DS soft CL
VA decreased
over the lens keratometry, the mires are irregular.

What is the most likely reason?

lenses are inside out

theoretically: we can find this in:
keratoconus (associated in myopia, not +2.00 lens) or
irregular astigmatism (should be fit with GP CLs)

41

pt: -2.00 DS GP CL
over the lens keratometry: -0.75 x 180

Why is that?

Lens flexure

42

Why is n=1.3375 for the cornea?

cornea is considered a single surface

43

pt spectacle lenses (12 mm from cornea): -10.00 D

What is his CLs power?

-9.00 D

44

power rule for glasses/contacts changing

If Rx is 10.00 D, then the power change will be 1 D change either more or less depending

45

Daily wear CL should have at least what Dk/t value?

24

46

Extended wear CL should have at least what Dk/t value?

87

47

What is a true description for plasma treatment of lenses?

intense surface cleaning

48

What is an example of an in-vivo test of CL wettability?

TBUT