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clinical skills > Contact lens 1 > Flashcards

Contact lens 1 Flashcards

1
Q

what are the types of contact lenses?

A

rigid gas permeable (RGB)
soft contact lenses (SCL)
speciality

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2
Q

describe the properties of RGB?

A

. approx 9mm diameter
. re-usable 1-3 years
. clean after each week
.more fitted in eye

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3
Q

describe the properties of SCL?

A

. approx 14mm diameter
. disposable or re-usable
. covers the whole eye

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4
Q

why do we use speciality contact lenses?

A

they are used for specific purpose
e.g. complex corneal shape
they are re-usable

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5
Q

give examples of speciality contact lenses?

A

. hybrids ( 14mm ) RGB + SCL
. mini-sclerals (14mm) RGB
.ortho-keratology ( correct during sleep)

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6
Q

what does modalities mean?

A

. how someone wears contact lenses

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7
Q

what are the two types of modalities?

A

. replacement

. wear modality

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8
Q

what are the two types of replacement lenses?

A

. soft lenses

.RGB

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9
Q

what are the types of soft replacement lenses?

A

. daily disposables
. 2- weekly
. monthly disposables
. annual

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10
Q

what are the types of RGB replacement lenses

A

. replacement every 1-3 years

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11
Q

what are the types of soft wear modality lenses?

A

. daily (DW)
. 7 days and 6 nights (EW) extended wear
sleep with lenses
for people with long shifts
.30 days and 29 nights (CW) continuous wear

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12
Q

what are the types of RGB wear modality lenses?

A

. DW
. overnight
only with (ortho keratology ) used to correct short sight over night

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13
Q

what are types of prescription?

A

. spherical ( myopia , hypermetropia)
. toric (astigmatism)
.multifocal (reading , near)

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14
Q

what are the types of materials used for rigid contact lenses?

A

.PMMA ( polymethyl methacrylate)

. Gas permeable

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15
Q

what is PMMA?

A

. first material
. no oxygen permeability
. excellent vision

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16
Q

what is gas permeable material ?

A

. much better oxygen permeability

. healthier

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17
Q

what are the types of material used for soft contact lenses?

A

. hydrogel

. silicone hydrogel

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18
Q

what is hydrogel?

A

. contains water
. very comfortable
. don’t allow much oxygen around

19
Q

what is silicone hydrogel?

A

. allows more oxygen than hydrogel
. allowed to use for EW/CW
. more expensive

20
Q

which material is most popular in order?

A
  1. silicone hydrogel
  2. hydrogel
  3. GP
  4. hybrid
  5. PMMA
21
Q

what baseline measurements are used for CL fitting?

A
  1. spectacle conversion
    - convert to ocular prescription
  2. measure curvature of cornea
    - use keratometry
  3. measure diameter of cornea
    - measure horizontal visible iris diameter (HIVD)(IN essence its the diameter od cornea)
22
Q

what is back vertex distance (BVD) ?

A

. how far away your glasses sit from your eyes

23
Q

why do we convert spectacle prescription into ocular prescription ?

A

. this is because average BVD is usually 12mm
while contact lenses and eye distance is 0 so the power of contact lens must be different to spectacle to get some correction .
. same optical prescription
. conversion only applies to high prescription above 4

24
Q

how do we convert spectacle prescription into ocular prescription ?

A

. using BVD table

25
Q

what is astigmatism?

A

. two focal points at back eye

points are on two different meridians causing blurr

26
Q

what are the two types of astigmatism due to?

A

. corneal astigmatism

. reticular astigmatism (lens)

27
Q

how to correct astigmatism?

A

use two different prescriptions simultaneously in principle meridians

28
Q

what is regular astigmatism?

A

. Rx in one meridian is 90 deg to Rx in second meridian

29
Q

what is irregular astigmatism?

A

. meridian not 90 deg apart , due to trauma , disease

30
Q

how to prescribe astigmatic spectacle prescription?

A

. different powers in two principle meridians

31
Q

why do we have to prescribe different powers in two principle meridians for astigmatism?

A 
to correct
.blurry vision
. headache
. fatigue or eyestrain
. distorted vision 
. light sensitivity
32
Q

what are the two types of corneal astigmatism?

A

. with the rule

. against the rule

33
Q

what is with the rule corneal astigmatism?

A

. vertical meridian is steeper ( more curved)

34
Q

what is against the rule corneal astigmatism?

A

. horizontal meridian is steeper ( more curved )

35
Q

how to write spectacle Rx for astigmatic prescription?

A

. most positive meridian is spherical power
. difference between two powers is cylinder power
. the axis is more positive reading

36
Q

1st meridian = -7.50 along 25

2nd meridian= -5.50 along 115

A

-5.50/+2.00x115

37
Q

convert -6.50/-1.00x10 spectacle Rx to ocular prescription?

11mm BVD

A 
. first meridian = -6.50
. second meridian = -7.50
use BVD at 11mm
. first meridian = -6.12
. second meridian = -6.87
difference is 0.75
38
Q

what is a keratometry?

A

measurement of radii of anterior surface of cornea

. cornea acts as mirror since light is reflected from it

39
Q

pros and cons of automated keratometry?

A 
pros
. quick
.easy
con
. can't cope with irregular astigmatism
. if someone focuses too much can have affect on result
40
Q

why do we use keratometry?

A

determination of
. central corneal radius (mm) and power (D) in both principle meridian of cornea
.differentiate between regular and irregular astigmatism
. measurement of radius of contact lenses
. observe quality of tears

41
Q

why do we measure (HVID) ?

A

. for total diameter CL
e.g . soft lenses = lens beyond size of HVID
RGP = we want lens to stay within
allows us to know what diameter of contact lenses we want to use

42
Q

what do we measure (HVID) ?

A

. measure with PD ruler

or comparator scale

43
Q

what is expected HVID ?

A

. expected 11.6 mm

. between 10.2 - 13.0 mm

44
Q

How to write an astigamtic prescription?

A

difference between 2 meridians is 90 (between the axis)

  • Use more positive power for sph
  • Subtract sph to get negative cyl
  • The axis is from the more positive reading.

clinical skills (13 decks)

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