Transcript Retinoscopy

Theory of
Retinoscopy
DEFINITION
 Retinoscopy is the name given to the
objective method of determining the
refractive errors by using retinoscope.
Retinoscopy
procedure
 The fundus is illuminated by means of a
mirror or by a self illuminated streak
retinoscope situated classically 1 or 2/3
meter away from the subject.
Principle
 The illuminated area of fundus is not
seen by the observer but only acts as a
source. The rays emanating from the
source from an illuminated area in the
plane of the pupil of the subject which is
called retinoscope shadow or reflex.
Objective method
 Examiner sits at 67 cms away from the
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patient ( Point of reversal is at 1.50D)
The Patient is normally seated and looking
towards the far end of the room.
Source of light is from behind the patient.
The Examiner looks through a plane mirror
with central perforation, and light is
reflected into the patient’s eye.
The Examiner is slowly moved from side to
side in different meridians, and movement of
the shadow is noted.
Stages of retinoscopy
 Illumination stage :
Light is directed into the patient’s
eye to illuminate the retina .
 Reflex stage :
A image of the illuminated retina is
formed at the patient’s far point.
 Projection stage :
The image at 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
patient’s pupil.
Illumination Stage Plane mirror
Illumination by Streak
Retinoscopy
Reflex Stages
Reflex Stages
Reflex Stages
Projection Stage
Hypermetropia
Emmetropia
Myopia less than 1.50D
Myopia of 1.50D
Myopia > 1.50D
Retinoscopy Movement
 Speed
 Brilliance
 Width
Methods
 In Hypermetropia, emmetropia and myopia <1.50D =
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the reflex moves in the same direction.( with
movement)
In Myopia of 1.50D= there is no shadow
In Myopia of > 1.5D= the shadow moves in the
opposite direction.
( against movement)
The procedure is done for each meridians separately
In astigmatism, they are different. If the axes are
oblique, the shadow themselves will seem to move
obliquely and the mirror is then tilted accordingly.
Calculation
 Refraction of Patients eye = lens
required to reach end point =
-1.50D(Myopia)
 Since the Examiner is sitting at 1mt
distance and if he is at 2/3rd mt, it will be
-1.5D(myopic)
 So the refraction of the eye= -1.50D
+lens
Example
 If the end point is with +4.0D lens:
Refraction = -1.50D +4.0D lens= +2.50D
 Similarly with -3.50D lens:
Refraction = -1.50D -3.50D = -5.0D
 If the end point is with +1.50D lens
Refraction = -1.50 +1.50D = 0
the patient is emmetropic
 In case of astigmatism, each meridian is
to be calculated separately
Subjective Verification
of Refraction
Subjective Verification
After objective test, it
should always be verified
subjectively by testing the
visual acuity
Procedures
 Each eye is to be tested separately, the
other eye being blocked, and then finally
tested together.
 Appropriate lenses, as found by objective
test, are inserted in the trial frame.
 Slight modification of the inserted lens gives
a maximum visual acuity.
 Verification may be needed with a cross
cylinder, or astigmatic fan in case of
astigmatism
Duochrome Test
 To test if the eye
has been under
corrected or over
corrected or is
properly
corrected
Astigmatic fan
To know the axis and power in Astigmatism.
Jackson's Cross Cylinder
 To refine the axis and power of Cylinder.
Fogging Method
 Sometimes fogging method is
necessary to induce a relaxation
of accommodation especially in
hypermetropia.
Example
 Here, the eyes are made artificially
myopic by addition of convex lenses
(Ex+4.0D). This is then gradually
lessened by a small fraction (0.50D)
until the maximum acuity is just
reached. The first lens is not removed
until the next is in position, to prevent
from accommodation becoming
active.
Procedures
 As a rule, the patient is given the strongest
hypermetropic, or weakest myopic
correction with normal visual acuity.
 The addition of the correction for near work
(if necessary), and testing of the acuity with
near- types, uniocularly and then binocularly
 Then the spectacles have been ordered with
necessary comments (Ex) Constant wear,
Near works only