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contact lens > intro and history > Flashcards

intro and history Flashcards

1
Q

horizontal radii is 43.5
vertical radii is 45.5

What type of astigmatism is that?

A

with the rule

horizontal has weaker power

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2
Q

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

A
  1. 33 mm

337. 5/r (will convert Diopter to mm)

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3
Q

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

A

cornea with keratoconus
*high focal power, unusually steep

also, possible for refractive surgery, but not likely

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4
Q

What is the relationship between radius and diopter?

A

inversely related

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5
Q

What is an average cornea HVID and VVID?

A

HVID 11.70

VVID 10.60

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6
Q

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

A

optic section

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7
Q

What is the appropriate thickness of the corneal epithelium?

A

50 microns

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8
Q

What is the thickness of the total cornea?

A

520 microns

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9
Q

What is the appropriate water content of the cornea?

A

78%

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10
Q

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

A

edema

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11
Q

• 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

A

oxygen permeability Dk

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12
Q

What specifies contact lens material?

A

Dk/t

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13
Q

What is the SI unit of Dk?

A

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

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14
Q

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

A
  • Daily wear: Dk/t = 24

* Extended wear: Dk/t = 87

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15
Q

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

A
  • Daily wear: Dk/t = 35

* Extended wear: Dk/t = 125

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16
Q

What type of measurements are Dk and Dk/t?

A

indirect in vivo measurements which infer oxygen transmissibility

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17
Q

What goes along with cornea edema?

A

swelling and change in k readings

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18
Q

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

A

equivalent oxygen percentage (EOP)

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19
Q

Wettability is crucial for what?

A

comfort and vision

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20
Q

How is wettability detected?

A

• Can be detected in vitro and in vivo

21
Q

In vitro = ?

A

wetting angle

22
Q

3 ways to measure wetting angle

A

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

23
Q

What type of angle is a good wetting angle?

A

low angle

24
Q

What are in vivo measurements for wettability?

A
  • Tear coverage
  • Break-up time
  • Drying time
25
Q

What type of treatment can improve wettability?

A

plasma treatment (super cleaning)

26
Q

plasma treatment

A

• 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
Q

What does the human tearfilm contain?

A

Mucin, lipids, lactoferrin, lysozyme

28
Q

Class I devices

A
  • Are deemed to be low to moderate risk
  • Subject to the least regulatory controls
  • Example: dental floss
29
Q

• Class II devices

A

• 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
Q

• Class III devices

A
  • Are high risk
  • Most stringent regulatory controls
  • General controls and pre-market approval (PMA)
  • Examples
  • Extended wear contact lenses
  • Overnight orthokeratology lenses
31
Q

• National requirements (Federal State Law)

A

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

32
Q

• Eyeglass rule (Federal State Law)

A

• Eyeglass prescriptions must be given to the patient

immediately following the eye exam

33
Q

• Contact lens rule (FCLCA)

A

• 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
Q

California State Law regarding valid CL Rx

A

• 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
Q

California State Law regarding internet sites

A

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
Q

California State law regarding copy of CLs

A

• 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
Q

CSL regarding third party

A
  • 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
Q

CSL regarding detailed Rx

A

• 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
Q

CSL regarding verification

A

• 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
Q

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

What is the most likely reason?

A

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
Q

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

Why is that?

A

Lens flexure

42
Q

Why is n=1.3375 for the cornea?

A

cornea is considered a single surface

43
Q

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

What is his CLs power?

A

-9.00 D

44
Q

power rule for glasses/contacts changing

A

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

45
Q

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

A

24

46
Q

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

A

87

47
Q

What is a true description for plasma treatment of lenses?

A

intense surface cleaning

48
Q

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

A

TBUT

contact lens (4 decks)

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