unit 1 Flashcards
Refracting Equipment
Phoropter
Trial lenses
Retinoscope
Visual acuitu charts
Automated refraction equpiment
Referrals from OPTICIANS
An optician must use their professional judgment to assess any indication or complication that arises during a refraction for referral to another regulated health professional
For a rx to be valid it must be a duplication of a pxs existing glasses or contain…
The name/identifier of the prescriber
The patients name
The patients rx
The date of examination
When duplication existing glasses..
It is to be noted on the patents record that it is a duplication and the optician should confirm the suitability of the prescriptions to a patient
What does an Optician have the duty to do?
Inform their patients of the importance of a regular eye exam and recommend regular testing as appropriate
When should a child have their first EE
Between 6-9 months
How many EE should be done between the ages 2-5
At least 1
When should healthy 19-40 have an EE
At least every 10 years
When should healthy 41-55 have an EE
At least every 5 years
When should healthy 56-65 have an EE
At least every 3 years
When should pxs over 65 have EE
At least every 2 years
Pxs at high risk over age 40 should have an EE
At least every 3 years
pxs at high risk over age 50 should have an EE
At least every 2 years
pxs at high risk over age 60 should have an EE
At lleast once a year
Canadians at higher risk
-People w diabetes, thyroid disease, rheumatological diseases including lupus
-People of african or hispanic descent
-Anyone prone to high IOP
-Anyone with a family history of glaucoma, cataract, macular degeneration or retinal detachement
-Anyone w a previous eye injury
-Ppl taking certain medications (plaquenil, prednisonse, ethambutol)
Fundamental concepts
Index of refraction
Fundamental paraxial equation I=n/L
Prentices rule
Index of refraction formula
n= Speed of light in air / speed of light in substance
Substances with higher index will have/do
More dense
Slows down the light
Glass index..
1.52
Air index
1.00
Aqueous and vitreous index
1.34
Cornea index
1.376
Water index
1.33
Snells law / refraction of light
n sin I = n’ sin I’
I= angle of incidence
n’ refractive index of second medium
I’ angle of refraction in second medium
Fundamental paraxial equation
L’ = L + F
L= object vergence
F= lens power
L’= image vergence
What does the fundamental paraxial equation do
Determine the position of an image formed by an optical device
Applied to thin lenses/single refracting service
What does paraxial stand for
Rays near the axis
Vergence power of a lens formual
U + P = V
U= vergence power of object rays
P= power of lens in diopters
V= vergence power of image rays
What does vergence power of a lens equation mean
Amount that a lens or optical system converges or diverges the light
Distance of the object from the lens formula
U= 1/u
U= vergence of the object rays
u= distance of the object from the lens (m)
Distance of the image from the lens formula
V=1/v
V= vergence of the image rays
v= distance of the image from the lens
Focal length formula
P= 1/f
P= power of the lens
f= focal length
prentices rule
p=cF
USed when a rx is not centered properly. Meaning oc is not in the requested area
Prentices formula
Prism= F x decentration (mm) / 10
Emmetropia
An eye that does not need any correction / no refraction error
Ametropia
A deviation from emmetropia
Myopia
-The second focal point F’e lies in front of the centre of the macula “short sight”
-The far point lies at a finite distance in front of the eye - the position at which an object has to be placed for an eye to see it clearly
-Corrected using negative lenses
Hypermetropia
-The second focal point F’ lies behind the centre of the macula “long sight”
-The far point lies at a finite distance behind the eye
-Corrected using positive lenses
Astigmatism
-Needs a corrective lens with a power that differs along the principal meridians of the lens
Astigmatic ametropia
Can originate at the cornea (corneal astigmatism), crystaline lens (lenticular astigmatism) or combination
When astigmatism is measured through an EE what does it mean
It measures the total astigmatism - does not differentiate between corneal and lenticular
Can a keratometer measure corneal astigmatism?
yes
With the rule astigmatism
Occurs when the flattest corneal meridian is near the horizontal
-Axis of the correcting cly closest to 180
Against the rule astigmatism
Occurs when the flattest corneal meridian is closer to the vertical
-axis is closest to 90
Regular astigmatism
Refractive error is constant over the refracting surface
Irregular astigmatism
Refractice error varies over the refracting surface
Possible causes of irregulr astigmatism
-Corneal scars
-Pterygium
-Dislocation of the crystalline lens
-Kerataconus
-Lenticonus
-Eyelid lesions that press on the cornea
-cataract
when should a healthy 36 year old asian px get an EE
at least every 10 years
when should a 55 year old diabetic get an EE
at least every 2 years
when should a healthy 70 year old caucasion px get an ee
At least every 2 years
when should a healthy 45 year old hispanic get an ee
at least every 3 years
when should a 55 year old px on plaquenil get an ee
at least every 2 years
