Contact lens 1

Question 1

what are the types of contact lenses?

Answer 1

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

Question 2

describe the properties of RGB?

Answer 2

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

Question 3

describe the properties of SCL?

Answer 3

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

Question 4

why do we use speciality contact lenses?

Answer 4

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

Question 5

give examples of speciality contact lenses?

Answer 5

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

Question 6

what does modalities mean?

Answer 6

. how someone wears contact lenses

Question 7

what are the two types of modalities?

Answer 7

. replacement

. wear modality

Question 8

what are the two types of replacement lenses?

Answer 8

. soft lenses

.RGB

Question 9

what are the types of soft replacement lenses?

Answer 9

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

Question 10

what are the types of RGB replacement lenses

Answer 10

. replacement every 1-3 years

Question 11

what are the types of soft wear modality lenses?

Answer 11

. 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

Question 12

what are the types of RGB wear modality lenses?

Answer 12

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

Question 13

what are types of prescription?

Answer 13

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

Question 14

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

Answer 14

.PMMA ( polymethyl methacrylate)

. Gas permeable

Question 15

what is PMMA?

Answer 15

. first material
. no oxygen permeability
. excellent vision

Question 16

what is gas permeable material ?

Answer 16

. much better oxygen permeability

. healthier

Question 17

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

Answer 17

. hydrogel

. silicone hydrogel

Question 18

what is hydrogel?

Answer 18

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

Question 19

what is silicone hydrogel?

Answer 19

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

Question 20

which material is most popular in order?

Answer 20

1. silicone hydrogel
2. hydrogel
3. GP
4. hybrid
5. PMMA

Question 21

what baseline measurements are used for CL fitting?

Answer 21

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)

Question 22

what is back vertex distance (BVD) ?

Answer 22

. how far away your glasses sit from your eyes

Question 23

why do we convert spectacle prescription into ocular prescription ?

Answer 23

. 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

Question 24

how do we convert spectacle prescription into ocular prescription ?

Answer 24

. using BVD table

Question 25

what is astigmatism?

Answer 25

. two focal points at back eye | points are on two different meridians causing blurr

Question 26

what are the two types of astigmatism due to?

Answer 26

. corneal astigmatism | . reticular astigmatism (lens)

Question 27

how to correct astigmatism?

Answer 27

use two different prescriptions simultaneously in principle meridians

Question 28

what is regular astigmatism?

Answer 28

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

Question 29

what is irregular astigmatism?

Answer 29

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

Question 30

how to prescribe astigmatic spectacle prescription?

Answer 30

. different powers in two principle meridians

Question 31

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

Answer 31

``` to correct .blurry vision . headache . fatigue or eyestrain . distorted vision . light sensitivity ```

Question 32

what are the two types of corneal astigmatism?

Answer 32

. with the rule | . against the rule

Question 33

what is with the rule corneal astigmatism?

Answer 33

. vertical meridian is steeper ( more curved)

Question 34

what is against the rule corneal astigmatism?

Answer 34

. horizontal meridian is steeper ( more curved )

Question 35

how to write spectacle Rx for astigmatic prescription?

Answer 35

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

Question 36

1st meridian = -7.50 along 25 | 2nd meridian= -5.50 along 115

Answer 36

-5.50/+2.00x115

Question 37

convert -6.50/-1.00x10 spectacle Rx to ocular prescription? | 11mm BVD

Answer 37

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

Question 38

what is a keratometry?

Answer 38

measurement of radii of anterior surface of cornea | . cornea acts as mirror since light is reflected from it

Question 39

pros and cons of automated keratometry?

Answer 39

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

Question 40

why do we use keratometry?

Answer 40

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

Question 41

why do we measure (HVID) ?

Answer 41

. 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

Question 42

what do we measure (HVID) ?

Answer 42

. measure with PD ruler | or comparator scale

Question 43

what is expected HVID ?

Answer 43

. expected 11.6 mm | . between 10.2 - 13.0 mm

Question 44

How to write an astigamtic prescription?

Answer 44

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.