AUTO REFRACTOME- basic review formulaes and recent advances

AUto refractome
Basic overview

1. AUTO
REFRACTOMETRY
-
-Dr.Ajay Rawte
(pg opthalmology )

2. REFRACTION
The process of determining and correcting
refractive error is termed as clinical refraction.
2 method
1.objective refraction
2.subjective refraction

3. OBJECTIVE REFRACTION
The type and degree of refractive error without
the active participation of patient is determined.
Involve following methods
1. retinoscopy
2.auto refractometry
3. photo refraction
4.electro physiological method of objective
refraction.

4. Retinoscopy
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It is a objective method of finding out the error
of refraction by utilising the technique of
neutralization
when light ray is reflected from the mirror into
the eye, the direction in which the light will
travel across the pupils will depend upon the
refractive state of the eye.
It is a time consuming procedure and not every
practictioner manage to do accurately.

5. AUTO REFRACTOMETRY
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It is alternative method of finding out the error
of refraction by use of optical equipment called
refractometer or optometer.
It is based on two principle
A.Scheinerprinciple and
B.optometer principle

7. SCHEINER
PRINCIPAL
-1619
Here theRefractive error of eye can be
determined by using double pinhole
aperture i before the pupils
A.parallel rays of light entering the eye
from distant object are focus on a
retina in emmetropic pt limited to
small bundle when double pinhole
aperture are place in front of pupils.
B. In myopic eye two Ray bundles
cross each other before reaching the
retina and two small spot of the light
seen
C. In hypermetropic eye bundle are
intercepted by retina before they meet
and again to small spot of the light
seen.
-this two points of light can be
coaleased to a single point by moving
the double pinhole to the far point of
eye
Thus from the far point of the eye
refractive error of eye can be
determine.

8. Optometer
principle 1759
Here porterfield coin the term
optometer to describe instrument
for measuring limit of distinct
vision this principle permit
continuous variation of power in
refractive instrument.
A. Auto refractometer based on
this principle you just single
converging lens place at its focal
length from I instead of
interchangeable trial lenses
B. Light from the target on the fore
side of less enter the eye with
versions of different amount (zero
A, minus B. Plus C.)depending on
position of target
Versions of light in the focal plane
of optometer is linearly related to
displacement of target.
This major versions of light at
spectacle plane and convert it into
diapter of correction.

9. Development of auto
refractometer
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Can be group as
1.early refractometer
2. and modern AR

EARLY REFRACTOMETER
A.-subjective- 1.badal optometer
2.Youngs optometer
B. and objective

LIMITATIONS of early Optometer
Alignment problems
irregular astigmatism and
accommodation

10. Modern refractometer
Objective refractometer and
Subjective refractometers

11. OBJECTIVE REFRACTOMETER SUBJECTIVE
REFRACTOMETERS
Use low level of invisible
infrared light
Use visible light
Takes 2 to 3 minute Takes 4-8 minute
Not provide more information
and corrected visual equity
Provide better visual equity and
corrected information
Require less patient cooperation More patient cooperation
Give better result in macular
disease with clear media also
Poor result
In presence of hazy media
causing drop in visual a more
than 6 /18 it do not function
properly
It function properly
Over refraction in patient with
spectacle, contact lens and iol is
comparatively difficult
No such problem in subjective
refractors
It provide only preliminary
refractive findingu
Provides binocular refraction
capability

12. Objective auto refractometer
(AR)
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Present day objective auto refractometer use
near infrared radiation(NIR) of wavelength 780-
950 mm as a primary source of
electromagnetic radiation
because it efficiently reflected back from
fundus and essentially invisible to patient.

13. Nulling versus open loop
measurement principle
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Present day AR finds the refractive error using
other nulling or open loop measurement
principle
1 Nulling principal refractometer change their
optical system until refractive error of eye is
neutralize or until null point is reached.
2. open loop principle refractometer or non-
nulling instrument are generally able to more
quickly arrive ,because they do not require to
alter the optical system to move the null point.

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Scheiners principle
the optometric principle(retinoscopic principl)
best focus principle
knife edge principle
Ray deflection principle
image size principle
Commercially available objective
auto refractometers based on

15. AR base on scheiner principal
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They are nulling refractor
use the concept of badal Optometer to
accomplish projection of NIR
It has a specialised photodetection device to
analyse the position of fundus images created
by source optical train
it remove Corneal reflexes
Meridien refractive error are neutralize.
Example ,
Acuity system6600, topcon Nidek

16. Subjective auto refractors
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Vision analyzer(based on over refraction
system)
SR4 program subjective refractor ( base on
optometer principle)
subjective auto refractor 7(using spherical
optics)

17. THANK YOU