objective refraction
-determining refractive status without input by the patient
What are the three types of objective refraction?
- retinoscopy
- autorefraction
- photorefraction
Autorefraction
- no evaluations of patient of clinician
- no judgement from operator
Photreception
-photo or video graph of pupils interpreted by trained clinician or instrument
what does retinoscopy rely on?
- the eye is a closed optical system
- image detection during subjective refraction effectively occurs at outer limiting membrane
- reflection of light from inside the eye produces a fundus reflex
- effective occular reflecting surface for visible light is also at the out limiting membrane
what does all this limiting membrane stuff mean?
- where the patient interprets the light is where we see the light reflected
- we dont have to ask, we can see it
why do we do retinoscopy?
- starting point for subjective refraction
- independent objective confirmation of subjective results
- may be heavily relied on to determine prescription for patients that cant talk to us
how do you determine if spherical of astigmatic?
- is reflex the same in all meridians?(spherical)
- if different reflex, astigmatic. determine the two principal meridians
what meridian do you netrualize if spherical?
-any
if you see with motion, what lens should you neutralize with?
-add plus lenses
if you see against motion, what lens should you neutralize with?
-add minus lenses
how do you determine working distance?
- measure length from scope to eye
- 1/meters
once you stop seeing motion, are you done?
- nope
- add a minus working distance
endpoint of retinoscopy
-when patient’s farpoint coincides with aperture of retinoscope
will the same lenses be used and get the same endpoint with different doctors?*****
-MUST CORRECT FOR SPECIFIC WORKING DISTANCE
static retinoscopy
- moving farpoint to the retinoscope
- use lenses
direct retinoscopy
- move retinoscope to far point of patients eye
- usually special circumstance/kids
why is fundus reflex red/orange
–reflected from retina
bracket
- neutrality is a range of uncertainty between perceptible “with” and “against” motion
- between absolute yes and absolute no
six aspects of reflex
- brightness
- direction of motion
- speed of motion
- width
- definition
- alignment
six aspects of reflex as you get closer to neutrality
- brighter
- motion decreases
- speed increases
- width narrows
- difinition increases
- becomes more aligned with streak
speed increases when you get closer to neutrality???
- yea.
- it moves so fast it looks like there is no motion
in general fundus reflex…
-gets easier to read as you get closer to neutrality
abnormal fundus reflex
- some portions may behave different than others
- due to higher order aberrations
- scissors motion
