details about autorefractometer and other objective methods of assessing visual acuity

1. Company
LOGO Dr Sneha Thapliyal
OBJECTIVE REFRACTION

2. CLINICAL REFRACTION
Determines and corrects refractive errors
Objective refraction Subjective refraction
Essential in:
Young children
Mental disability
Language difficulty
Deaf or mute

3. OBJECTIVE METHODS OF
REFRACTION
1. Retinoscopy
2. Autorefractometry
3. Photorefraction
4. Electrophysiological method of objective
refraction

4. RETINOSCOPY/SKIASCOPY
/SHADOW TEST
 Objective method of finding out the error of
refraction by means of retinoscope
utilizing the technique of NEUTRALIZATION

5. Far point concept
 The far point of eye is defined as the point in space that is
conjugate with the fovea when accomodation is relaxed.
 Emmetropia: Parallel rays focus on fovea.
 Retina conjugate with infinity.
 Far point is at infinity.
 Ammetropias: Parallel rays do not focus on retina.
 Ammetropic eyes require a correcting lens to make retina
conjugate with infinity, i.e., to move far point to infinity
 Hyperopia: Deficient refractive power.
 Parallel rays focus behind retina.
 Far point is beyond infinity.
 Plus lens converges rays on to retina and conjugate
fovea with infinity.

6. Far point concept
 Myopia: Excessive refractive power.
 Parallel rays focus in front of retina.
 Far point is between infinity and eye.
 Minus lens diverges rays on to the retina and conjugate
fovea with infinity.
 Aspherical ammetropias:
 This indicates different types of astigmatism.
 This type of errors have two far points.
 As a set of rays converge at one place and other at different
place due to cornea not having same radius of curvature in all
the meridians.

7. Principle of retinoscopy:
 To bring the far point of patient at the
nodal point of the observer at the
working distance

8. NEUTRALIZATION
1. No movement of red
reflex = NEUTRAL POINT
2. Reversal with
overcorrection by 0.25 D
3. On alternating the
working distance, slight
forward, ‘with’ movement
and an ‘against’
movement by slight
backward movement.

9. PREREQUISITES FOR
RETINOSCOPY

10. PREREQUISITES FOR
RETINOSCOPY
1. Dark room: 6 m long
2. A trial set:
 64 pairs of Spherical lenses(plus and minus)
0.12D
0.25-4.0D
4.0-6.0D
6.0-14D
14-20D
0.25
0.51D2D

11. 20 pairs of Cylindrical lenses (plus and
minus)
0.25-2.00D
2.0-6.0D
10 Prisms:
½ to 6
8,10,12
0.250.5

12.  Accessories:
Plano lenses
Opaque discs
Pinhole
Stenopaeic discs
Maddox rods
Red and Green glasses

13. 3. A trail frame
 Light weight
 Aluminium alloy- 30 g
 Adjustable- horizontally and vertically
 3 compartments: spherical, cylindrical, prisms
 Cylindrical compartment : smooth and accurate rotation
 Side pieces should be joint- tilted while testing for near vision
 Back lens in trial frames should occupy as nearly as possible the
position of spectacle lens i.e. around 12 mm in front of the cornea.
4. Phoropter or refractor
 Turn the dial – change the lens before
the aperture of the viewing system

14. 5. Distance-vision chart
6. Near vision charts
7. Retinoscope:
Invented by Dr Jack Copeland
REFLECTING (MIRROR)
RETINOSCOPES
Priestley-Smith’s mirror
Plane mirror
SELF-ILLUMINATED
RETINOSCOPES
Spot self-illuminous
Streak retinoscope

15. HEAD
NECK
HANDLE
SLEEVE UP
PEEPHOLE
SLEEVE DOWN
STREAK RETINOSCOPE

16. HEAD
HANDLE
NECK
MIRROR
LENS
SLEEVE
PARASTOP
BULB
BATTERIES

17. bulb

18. Dark mirror
Reflecting
mirror
Sleeve

19.  Observing the optics of retinoscope we find two main
systems
- Projection system:
Light source
Condensing lens
Focusing sleeve
Current source
- Obsevation system:
Peep hole
RETINOSCOPE AND IT’S
PARTS:

20. The retinoscope:
how it works?
 PROJECTION SYSTEM:
illuminates the retina
 Light source: a bulb with
linear filament that projects
a line or streak of light
 Condensing lens: focuses
rays from bulb onto the
mirror
 Mirror : placed in the head
of instrument at 45 degree
angle, it bends the path of
light at right angles to the
axis of the handle

21.  Focusing sleeve controls
 Meridian:Turning the sleeve rotates the streak of light.
 Vergence:By varying the distance between the lens and
the bulb
 Bulb: Moved up-Plane mirror effect(Parallel rays)
Moved down-Concave mirror effect(converging
rays)
 Lens: Moved up-Concave mirror effect
Moved down-Plane mirror effect

22.  In Copelands instrument,
 moving the sleeve up or down moves the bulb.
 Sleeve up creates plane mirror effect & sleeve down
creates concave mirror effect
Copeland type- fixed lens with moving bulb

23.  In other Retinoscopes,
 the lens rather than the bulb moves on moving the
sleeve
 Sleeve up creates a concave mirror effect & sleeve
down creates plane mirror effect
Fixed bulb type, the lens moves

24.  OBSERVATON SYTEM:
 Allows to see the retinal reflex
 Light reflected by the illuminated retina enters the
retinoscope, passes through an aperture in the
mirror & out of the peephole at the rear end of the
head.

25. Optics in Retinoscopy
 Illumination stage: light is directed into the
subject’s eye to illuminate the retina
 Reflex stage: image of the illuminated retina
is formed at subject’s far point
 Observation stage: image of the far point is
located by moving the illumination across the
fundus and noting the behavior of the luminous
reflex seen by the observer in the subject’s pupil

26. Clinician
So
S1
S2
Patient
The light in the pupil is called the
“ret reflex”

27. The final goal

28. Observer Subject
Reflex disappears
Reflex moves down,
i.e. with direction
of movement of light
Mirror tilts further forwards
Mirror tilts forwards
S2
S2
Far point behind
observers pupil
Within pupil
Outside pupil
No S2
S1
Far point behind observers
pupil.
With movement of reflex,
gradual change from red reflex
to no reflex

29. With movement

30. Observer Subject
Far point in front of
observers pupil
Reflex disappears
Reflex moves up,
i.e. against direction
of movement of light
Mirror tilts forwards
Mirror tilts further forwards
S2
S2
Within pupil
Outside pupil
No S2
S1
Far point in front of observers pupil.
Against movement of reflex,
gradual change from red reflex to no
reflex

31. Against movement

32. Reflecting mirror:
 Perforated mirror
 Central hole: 2.5mm anteriorly
4 mm posteriorly
 By a plane mirror, rays are slightly divergent causing
less illumination
 Small hole corresponding to the central hole reduces
illumination in pupillary area by causing central dark
patch
 Sides of the small hole are blackened to prevent
annoying reflexes from entering the eye
 Slightly concave mirror with central opening of 4mm
and focal length greater than the distance between
observer and patient; 150 cm

33. LUMINOUS
RETINOSCOPE
 Streak retinoscope is the most popular
 Both light source and mirror are incorporated
 Intensity and type of beam can be controlled.

34.  Two main techniques of retinoscopy
are
Static Retinoscopy:
 It is the refractive state
determined when patient fixates an
object at a distance of 6 m with
accomodation relaxed.
Dynamic Retinoscopy:
 The refractive state is
determined while the subject fixates
an object at some closer distance,
usually at or near the plane of
retinoscope itself with
accommodation under action.
RETINOSCOPY
TECHNIQUES:

35. PROCEDURE OF
RETINOSCOPY
 Patient is made to sit at a
distance of 2/3rd of a meter
 Accomodation should be
relaxed
 Use right eye for patient’s right
eye and left eye for left
 Trial frame is fitted
 Direct the light from retinoscope
into patient’s pupil
 Move the retinoscope in
horizontally and observe the red
reflex.

36.  Suitable lens is placed
before the eyes to
neutralize the band when
the pupil will be filled with
uniform light
 Now move vertically, if still
pupil is filled with uniform
light, no astigmatism.
Examiner sits just enough to the side
to avoid blocking patient’s fixation

37. Characteristics of the moving
retinal reflex
Speed and brilliance
Low refractive High refractive
Bright Faint
Moves rapidly Moves slowly

38. 2.Width of reflex
Narrow Wide
High degree of ametropia Low degree of ametropia
3. Presence of astigmatism
When the axis does not correspond with the movement of the mirror,
the shadow appears to swirl around.

39. Examiner should scope both vertical and
horizontal meridian.
We correct the astigmatism with cylindrical
lens.
Cylindrical lens may be plus or minus, but
have power in only one meridian, that
which is perpendicular to the axis of the
cylinder.
The axis meridian is flat and has no
power.
ASTIGMATISM

40. CYLINDRICAL AXIS
 Break in the alignment
between the reflex in the
pupil and the band
outside it when the streak
is off the axis
 Rotate the streak until the
break disappears
 Width of the streak
appears narrowest when
the streak aligns with the
true axis.

41. STRADDLING
 Confirmation of axis
 Retinoscope streak- 45
degree off axis in both
directions
 Correct axis- width of
streak equal in both
positions
 Axis not correct- width is
unequal
 Narrow reflex is guide
towards which cylinder’s
axis should be turned

42. PROBLEMS IN
RETINOSCOPY:
1. Red reflex may not be visible or maybe poor
 Small pupil
 Hazy media
 High degree of refractive error
 Overcome by causing mydriasis and/or use of
converging light with concave mirror retinoscope
2. Changing retinoscopic findings
 Abnormally active accomodation
 Overcome by fogging retinoscopy and cycloplegic
3. Spherical aberrations
 Dilated pupils

43. 4. Conflicting shadows
 Irregular astigmatism
5. Triangular shadows
 Conical cornea

44. www.phacotube.com
Scissoring shadows
Astigmatism
Overcome by: undilated
pupil

45. Cycloplegics in retinoscopy
 When retinoscopy is performed after instilling
cycloplegic drugs it is termed as Wet Retinoscopy
1. Atropine 1% ointment
 Used in children < 7yrs age
 Dose:1% eye ointment 3times daily for 3days
 Effect lasts for 10-20days
 Deduction for cycloplegia with atropine is 1D

46. 2. Homatropine 2% drops
 Used in hypermetropes between 7 to 35yrs
 Dose:1drop instilled every 10mins for 6times &
retinoscopy is performed after 1-2hrs
 Effect lasts for 48-72hrs
 Deduction for cycloplegia with homatropine is
0.5D
3. Cyclopentolate I% drops
 Used in persons between 7 to 35yrs
 Dose:1drop instilled every 10mins for 3 times &
retinoscopy is performed after 1- 1 1/2hrs
 Effect lasts for 6 to 18hrs
 Deduction for cycloplegia with Cyclopentolate is
0.75D

47.  Only mydriatic [ 10% phenylephrine] may is used in
elderly patients to enhance the pupillary reflex when the
pupil is narrow or media is slightly hazy
 Later it should be counteracted by use of miotic drug[ 2%
pilocarpine]

48. Clinician
S2
Patient
We now have neutral
We have also introduced
negative vergence due to
our working distance
(WD)
= 1/d (m)
Where d = distance in m,
measured between your
ret and patient’s eye
We have added lenses
To get the right prescription
we need to compensate
Rx = lens power – 1/d
So to get neutral, we needed:
lens power = Rx + 1/d

49. Working distance
compensation
Calculation
 For example, if neutrality
is achieved with a
+3.00DS lens and your
working distance is 50cm
 Rx = +3.00DS – (1/0.50)
 = +3.00 – 2.00
 =+1.00DS
Working distance lens
 Before you begin, add a
“working distance lens”
 A +ve lens to cancel out
the negative vergence
 As in eg., WD = 50cm
 WD lens = 1/0.50 =
+2.00DS
 Neutrality for the same
patient is still +3.00DS
 WD lens = +2.00DS
 Lens power = +1.00DS
Rx = lens power - 1/d

50. AUTOREFRACTOMETRY
Alternative method of assessing error of
refraction by use of an optical equipment
called refractometer or optometer
OBJECTIVE SUBJECTIVE

51. History
 Collins(1937) developed the first semi automated electronic
refractionometer.
 Safir (1964) automated the retinoscope and this work led to
the first commercial autorefractor-the Ophthalmometron.
 6600 Autorefractor was the second commercial autorefractor
(1969).
 Munnerlyn (1978) design using a best contrast principle with
moving gratings led to the Dioptron, an automated objective
refractor.

52. OBJECTIVE SUBJECTIVE
SOURCE OF LIGHT
TIME REQUIRED
Infra-red light
2-4 min
Visible light
4-8 min
INFORMATION PROVIDED Less informative More informative (corrected
visual acuity)
PATIENT CO-OPERATION Required less (only
has to look straight at
target)
More co-operation (patient
has to turn knob, focus
target, answer questions
about appearance of target)
OCULAR FACTORS Better in macular
diseases with clear
ocular media
Can be done in hazy ocular
media
OVER REFRACTION
CAPABILITY WITH
SPECTACLES, CL, IOL
Difficult No problem
EXPECTED RESULTS Preliminary refractive
findings
Gives refined subjective
result.

53. TOPCON
RM 8900/8800
Monitor
Control lever
with
measurement
switch
Forehead
rest
Chin rest
Examination
window
Power
switch
1.Print switch
2.Menu switch
3.IOL switch

54. SPECIFICATIONS AND
PERFORMANCE

55. OPTICAL PRINCIPLES
1. The Scheiner principle
2. The optometer principle
3. Retinoscopic principle
4. Knife edge principle
5. Ray- deflection princile
6. Image size principle

56. Basic design
 Infrared source (IR-LED)
 Fixation target
 Badal lens system
 Polarized beam splitter
 Light sensor

57. Autorefractors:
Primary and secondary source of electromagnetic
radiation:
 Primary- NIR (Near Infrared Radiation): 780-
950nm
 Efficiently reflected back from the fundus
 Essentially invisible to the patient
 Secondary- back scatter from the fundus
 Determine sphere power, cylinder power, and
cylinder axis

58.  Fixation target
Accomodation is most relaxed when target is-
 Of low spatial frequency
 Same as typically seen at distance

59. Nulling vs open-loop
measurement principle
 NULLING PRINCIPLE REFRACTOMETERS:
 Change their optical system until the refractive error
of the eye is neutralized.
 OPEN-LOOP PRINCIPLE REFRACTOMETERS:
 Makes measurements by analysing the
characteristics of the radiation exiting the eye
 Do not alter their optical system

60. ALLOWANCE
•NIR = 800-900nm
•The reflectance of the
fundus increases
towards the red end of
the spectrum
•Into the infra red,
there will be multiple
reflections of
scattered radiation
within the eye which
will degrade the image
•A 800-900nm will
create hypermetropia
of 0.75-1.00 DS
relative to 550nm

61. Basic Principle
Infrared light
Rotating
chopper
Badal
lens
To PC
Polarised
filter
Slit
imagemore minus 0 more plus
Slit
mask
Light
sensor

62. BADAL OPTOMETER:
Infrared light is collimated
passes through rectangular masks
housed in a
rotating drum
beam splitter
Optometer system
Moves laterally to find the optimal
focus of the slit on the retina

63. Optimal Focus:
Optimal focus is achieved when a peak
signal is received from the light sensor.

64. SCHEINER DOUBLE PIN-
HOLE
 The original Scheiner double pin-hole was invented in
the 16th century.
 In a clinical setting, the double pin-hole identifies the
level of ametropia in a subject by placing it directly in
front of the patient’s pupil

65.  In a myopic eye, the patient
sees crossed diplopic
images, whereas in
hyperopia, the patient sees
uncrossed images.
 Crossed and uncrossed
doubling can easily be
differentiated by asking the
patient which image has
disappeared, when either top
or bottom pin-hole is
occluded.

66. OPTOMETER PRINCIPLE
 Aim: to study the number of dioptres of correction on a
scale with fixed spacing when the light from the target on
the far side of the lens enter the eye with vergence of
different amounts-
 0
 -
 +
 The vergence of the light
in the focal plane of the
optometer lens is linearly
related to the displacement
of the target.

67. Modern optometers
 Limitations of early optometers:
1. Alignment problem: both pin-hole apertures
must fit within the pupil.
2. Irregular astigmatism: the best refraction over
the whole pupil may be different in contrast to
the two small pin hole areas of the pupil.
3. Accommodation: the instrument myopia alters
the actual refractive status of the patient.

68. Scheiner’s Principle:
 Two LEDs (light emitting diodes) are imaged
to the pupillary plane.
 These effectively act as a modified Scheiner pin-
hole by virtue of the narrow pencils of light
produced by the small aperture pinhole located
at the focal point of the objective lens.

69. 2 LEDs imaged to the
pupillary plane
Ocular refraction
l/t doubling of LED if
refractive error is
present
Reflection of LEDs
from retina back out of the
eye
Reflection by a semi-
silvered mirror
Dual photodetectors

70. RETINOSCOPIC
PRINCIPLE
 Autoretinoscopes
 Source of optical train corresponds to streak
retinoscope.
 Source of light is drum rotating about a source of
NIR which produces incident rectangular beam.
 Neutralization is by badal optometer
 Unwanted reflexes filtered by polarization of
incoming NIR
 Meridional refractors

71. 1. Autoretinoscope based on direction of fundus
streak motion are nulling refractors.
2. Autoretinoscope based on speed of fundus
streak motion are non nulling refractors.

72. BEST FOCUS
PRINCIPLE:
 Aim: to find the best focus of an image on retina
through the analysis of maximum contrast that
can be captured by autorefractor.
 Both meridional and nulling
 Neutralization is by badal optometer
 Filters unwanted reflexes by polarization

73. Knife-edge principle
 Aim: to evaluate the refractive uniformity of the lens.
 These are nulling autorefracors that are not meridional
 Based on principle of reciprocity
 All light returning through the system passes completely
back into the source.
 Theoretically, no light should escape past the knife-edge.

74. Knife edge principle
Foucault Knife edge test for an
emmetropic eye.
The reflex on the detector
moves over most of the surface
Knife edge test for myopic eye.
The motion of the reflex across the
detector provides information on the
nature of the refractive error.
The speed of the reflex describes
the magnitude of refraction

75. Ray deflection principle
 Aim: to measure
 Linear deflection of the fundus image in 3 or more
meridia at a fixed distance from the eye
 Angular deflection of rays
 Position of far point in those meridia trignometrically
 Open loop (non-nulling) meridional refractors
 Corneal reflexes removed by central aperture in the
plane
 Coaxial reflexes removed by polarization

76. Image size principle
 Aim: to measure the size of fundus image in 3 or more
different meridia and calculate the full refractive error on
the basis of ocular magnification or minification of the
image relative to emmetropia.
 Non nulling
 Detection system : fundus camera- CCD camera, video
imaging of the fundus reflex, analysis by sophisticated
computer programme

77. Conclusion
 Autorefraction is a valuable tool in
determining a starting point for refraction.
 Modern technology has resulted in
improvements in design, size, speed and
accuracy.
 There are primarily two principles utilised in
current autorefractors
 the Scheiner principle
 Retinoscopic principle.
 Improvements in target design (auto-fogging
distance targets and open view
autorefractors) attempt to relax
accommodation in patients.
 Autorefractor should not be used as the final
refractive correction without further
confirmation.