Retinoscopy for undergraduates and post-graduates. salient points covering examinations and PGMEE. Detailed discussion of the technique of retinoscopy and its utility in deducing refractive errors. Use of cycloplegic refraction and subjective refraction has been discussed.

1. Refraction and Retinoscopy
Dr. Abhishek Onkar

2. • Refraction is vergence (bending) of light ray
when it passes from one medium to another
medium of different optical density (refractive
index ).
• Normal refraction (optical state) of the eye is
essential for normal vision.
• Eye with normal optical state is Emmetropic
and that with abnormality is Ametropic (with
Refractive Error).

3. Object at
infinity
Parallel
light rays
Emmetropia:
focussed on retina:
no corrective lens required
Myopia:
focussed in front of retina:
requires –ve lens for correction
Hypermetropia:
focussed behind retina:
requires +ve lens for correction
Summary of spherical refractive errors

4. • In emmetropia parallel rays from infinity are
focused on the retina (with accommodation at
rest). This will give a clear image of object at
infinity (which has sufficient size).
• In ametropia parallel rays from infinity are not
focused on retina. So no clear image of object
at infinity is formed on the retina of that eye.

5. Far point
• Far Point (FP) is the furthest point at which
objects can be seen clearly by the eye with
accommodation at rest.
• Position of FP depends on the optical state
(static refraction) of the eye.
• The Far Point and the Point of Focus on the
retina are Conjugate Foci.
• In Optics Direction of Light Ray is Reversible.

6. • In emmetropia the FP is at infinity. So the rays coming from FP,
and entering the eye are parallel. They are focused upon the
retina to give a clear image of object at FP.
• In emmetropia light rays coming out from a point on the
retina through the optical system of the eye will be parallel.
These rays can meet only at infinity ( ie. where the Far Point is
located in emmetropia).

7. • In myopia the FP is at a finite distance. So the rays coming
from object at the far point, and entering the eye are
divergent. These rays are focused upon the retina to give a
clear image.
• In myopia light rays coming out from a point on the retina
through the optical system of the eye will be convergent.
These rays meet at the FP of the eye (at a finite distance).

8. • In hypermetropia object can't be placed at the FP ( It is a
virtual point behind the retina).Here the converging rays
directed towards the FP behind the retina can be focused
upon the retina to give a clear image by the dioptric (optical)
system of the eye.
• In hypermetropia light rays coming out are divergent. They
will only meet "beyond infinity". They can meet only at the FP
of the eye, which is a virtual point behind the retina (by
extrapolating the divergent rays in the reverse direction to
meet behind the retina).

9. • Optical state (refraction) of the eye decides
the position of the FP of the eye.
• If the position of the FP is known the
refraction can be calculated.

10. Calculating the focal point distance
• The method used for calculation is keeping the subject
and the observer at fixed places, and bringing (shifting)
the FP of the subject to the position of the nodal point
of observer's eye.
• This is done by using converging or diverging lenses.
• Now we know the exact distance of the FP from
patient's eye (ie. exact distance at which we are sitting)
and also the power of lens used to bring the FP to this
position.( From the measurement of distance we can
calculate the power required to bring the FP to this
position).

11. • Distance between subject and patient’s eye while
performing refraction is called “ working
distance.”
• Ideally, refraction is performed at a working
distance of 1 metres.
• Practically, it is done at 2/3 meters (67 cm
approx.).
• In final correction of refractive error, power
equivalent to this working distance is to be
subtracted from the power of lens used to bring
the FP at observer’s eye.

12. For refraction at 1metre distance
• In emmetropia the parallel rays coming out of the subject's
eye can be brought to a focus at 1 metre by using converging
(convex) lens of 1 Dioptre kept close to subject's eye.
• In other words, if the power of the lens used to bring the FP
to 1 metre is +1 D then we know that the rays coming out are
parallel (which normally meet at infinity) and the eye we are
examining is emmetropic.

13. • In hypermetropia the diverging rays coming
out of the eye are brought to a focus at 1
metre by using converging lenses of power
more than +1 D.

14. • In myopia of less than 1 Dioptre the
converging rays coming out are focused at 1
metre by using converging lens of power less
than +1 D.

15. • In myopia of 1 Dioptre the rays coming out of
the eye are convergent and meet at 1 metre
with out using any lenses.

16. • In myopia of more than 1 Dioptre the converging rays coming
out of the eye will focus at the FP which is less than 1 metre
from the eye. (between the patient and the observer).
• So this focus (FP) can be brought to 1 metre by using diverging
(concave) lens.

17. • When you are sitting at 1 metre from the
patient, how do you know that you have
brought the FP of the patient's eye (by using
lenses) to the nodal point of your eye at 1
metre ?
• The technique of Objective method of
Refraction (Retinoscopy) will answer these
questions.

18. Retinoscopy

19. Retinoscopy
• Examiner determines the refractive state of the
eye on the basis of the Optical Principles of
refraction.
• Objective measurement of refractive error
– Starting point for subjective refraction
– Used to prescribe where subjective refraction
can’t be performed
• Screening for ocular disease
– Keratoconus, media opacities

20. • It is an objective test - it does not need any input
from the patient
• May be the only way of determining refractive error
for non-communicative or non-cooperative patients
– Infants/Children
– Non-English/Hindi speaking
– Learning difficulties
– Malingerers
– Low vision
– Laboratory animals

21. The self-illuminating Streak
retinoscope
• Eyepiece
• Light source
– Spot or streak bulb
• Collar
– Moves up and down to change
the vergence of the light
– Rotates to change the angle of
the beam
• On/off/brightness control

22. • Static retinoscopy
– To determine refractive state by patient fixating at distance
so that accommodation is at rest
• Dynamic retinoscopy
– To determine refractive state by patient fixating at near,
accommodation is active.
• Principle:
– Estimate the patients refractive state by bringing patient’s
far point at the entrance pupil of examiner with the help of
appropriate lens.
– The state of refraction at this particular point is called as
neutralization.

23. • Principle : Behaviour of the luminous reflex in
the pupil of the patient is studied by moving
the illumination across the fundus.
• This behaviour depends on the vergence of
the light rays coming out of the pupil.
• It also depends on the position of the
observer.

24. “WITH” Movement
• The luminous reflex in the pupil will move in the
same direction of movement of the illumination
across the retina ('With Movement'):
o When the observer is at 1 metre from the patient
and the rays coming out from the patient's eye
form a focus (FP of the patient):
1. behind the observer at a finite distance
(myopia< 1D) or
2. at infinity (emmetropia)
3. or 'beyond infinity' (virtual point behind
patient's retina): hypermetropia

26. “AGAINST” Movement
• When the observer is at 1 metre from the patient and if the
rays coming out from the patient's eye form a focus (FP) in
front of the observer (between patient and observer- in
myopia> 1D) the
• luminous reflex in the pupil will move in the opposite
direction of movement of the illumination across the retina
('Against Movement').

27. • When the observer is at 1 metre from the patient
and if the rays coming out from the patient's eye
form a focus (FP) at the nodal point of the
observer then the pupil of the patient will appear
uniformly illuminated.
• By slight tilt of illumination across retina the pupil
will appear uniformly dark.
• This finding we get in myopia of 1D and also as
the end point of retinoscopy with the observer at
1 metre from the patient.)

29. Optics 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.

30. Reflex & Projection Stages
• Rays coming out of Subject's Eye
• If the illuminated patch on Patient's retina is away from the
principal axis, the rays coming out will not enter Observer's
eye.
• When the illumination is moved across the fundus towards
the principal axis the rays coming out enters observer's eye.

31. • The first ray of light entering observer's eye is from the same
edge of the pupil as the first position of retinal illumination.
• As the illumination on the retina moves towards the principal
axis the light reflex in the pupil also moves in the same
direction.
• The last ray of light entering the observer's eye is from the
other edge of the pupil.
• This gives a with movement reflex in the pupil.

32. • The first ray of light entering observer's eye is from the
opposite edge of the pupil when the position of the retinal
illumination is considered. (Light rays cross at FP and the
diverging rays are entering observer's eye).
• As the retinal illumination moves towards the principal axis
the light reflex in the pupil moves in the opposite direction.
• The last ray of light entering the observer's eye is from the
other edge of the pupil.
• This gives an against movement reflex in the pupil. (seen in
myopia more than 1D)

33. • As the retinal illumination moves towards the principal axis,
the rays coming out will focus on the nodal point of
observer's eye.
• This makes the pupil of the patient uniformly illuminated.
(The rays coming out through all the parts of the pupil are
focused at the nodal point of observer's eye).
• By a slight shift of retinal illumination this focal point is
displaced away from observer's eye making patient's pupil
uniformly dark.
• This finding is observed as end point of retinoscopy and in
eyes with 1 D myopia(retinoscopy done at 1 metres).

35. Illumination Stage
• Light rays entering subject's eye.
• Consider only the immediate source of illumination in front of
the subject's eye .
• This may be a virtual image or real image of an original source
of illumination behind the subject.
• When the immediate source is towards one side, the other
side of the retina will be illuminated.
• When the source is shifted to the other side, illumination will
be shifted to the opposite side of the retina.
• This will be the situation in all states of refraction of the eye.

36. • If we are using a Plane mirror, the virtual image of the original
source of illumination is formed as far behind the mirror as
the original source is in front of it.
• So, the tilt of the mirror to one side will shift the image
(immediate source of illumination) to the other side.
• Tilt of the plane mirror and the shift of illuminated patch on
the retina are in the same direction.

37. • If we are using a Concave mirror, the real image of the original
source of illumination is formed in front of the mirror (
position depends on the focal length of the mirror).
• So, the tilt of the mirror to one side will shift the image
(immediate source of illumination) to the same side itself.
• Tilt of the concave mirror and the shift of illuminated patch on
the retina are in opposite directions.

38. • In Practice we are considering the movement of the mirror.
• When we use plane mirror we get movement of the mirror
and movement of the retinal illumination in the same
direction.( because of the movement of immediate source
of illumination – ie virtual image formed behind the mirror
–is in the opposite direction of movement of the mirror).
• When we use concave mirror we get movement of the
mirror and movement of retinal illumination in opposite
directions (because of the movement of immediate source
of illumination - ie real image formed in front of the mirror
– in the same direction of movement of the mirror).
• Movement of reflex is decided by the movement of
immediate source of illumination and the refractive state of
the eye.
• Movement of immediate source of illumination is decided
by the type of mirror used.

39. Identifying end point
1. Intensity
• In high refractive errors we get a faint reflex and in low
refractive errors we get a brighter reflex.
2. Speed
• In high refractive error we get a slow movement, and in low
refractive error a rapid movement of the reflex. As the
neutral point is reached the movement of the reflex is fast.
3. Size
• In high refractive error we get a narrow reflex. Reflex will fill
the pupil when the neutral point is reached.

40. To refine result –
• If your assessment is correct you will get
• the following results--
• After reaching the neutral point (end point) in
Retinoscopy (with plane mirror) moving slightly
towards the subject will give a ‘with movement’
(because the Far Point is now behind the
Observer).
• Moving slightly away from the subject will get an
‘against movement’ (because now the Far Point is
between the observer and the subject).

42. Recording of retinoscopy results- the
Cross diagram

43. Determining axes of astigmatism

44. Principle of cycloplegic refraction
• Determination of total
refractive error during
temporary paralysis of
cilliary muscles as an
instillation of
cycloplegic drugs which
otherwise doesn’t
manifest on subjective
non-cycloplegic
refraction
Total Hyperopia
Latent
hyperopia
Manifest
hyperopia
facultative
hyperopia
Absolute
hyperopia

45. Indication for cycloplegic refraction
• Accommodative esotropia
• All children younger than 3 yrs
• Suspected latent hyperopia
• Suspected pseudomyopia
• Uncooperative/noncommunicative patients
• Variable and inconsistent end point of
refraction

46. Indication for cycloplegic refraction
• Visual acuity not corrected to a predicted level
• Strabismic children
• Amblyopic children
• Suspected malingering and hysterical patients

47. Gauri S Shrestha, M.Optom,
FIACLE
Selection and use of specific cycloplegic
agents
• Variable degree of pupil dilatation and cycloplegia
• Instill cycloplegic alone or with mydriatrics
Agent [C%] Dosage Max
cyclople
Duration
of effect
Residual
accom
Atropine
sulfate
1, 2 1D TID
3 days
3-6 hrs 10-18
days
Ngble
Sco-mine
HBR
0.25% 1D TID 60 mins 5-7 days ngble
Cyclo-
late HCL
0.5, 1, 2 1D TID 30-45
mins
24 hrs minimal
Tro-mide
HCL
0.5, 1 1D TID 20-30
mins
4-8 hrs moderate

48. Indication of Cycloplegic refraction
• All hyperopes.
• One who complains of Asthenopic symptoms.
• Who come for glass for first time
• Accommodation is abnormally active.

49. • When cycloplegics are used, a correction must
be made to compensate for the normal tone
of ciliary muscles.
• When atropine is used, 1 D is deducted in
final correction.
• When other cycloplegics are used, 0.5 D is
deducted in final correction.

50. Examples
+4.0DS +4.0DS
+4.0DS +4.0DS
For retinoscopy done at 1m ( without any cycloplegic), final
correction would be = +3.0 DS Both eyes
For retinoscopy done at 2/3m ( without any cycloplegic), final
correction would be = +2.5 DS Both eyes
If atropine had been used for cycloplegia (D=1m), final correction
would be= 2.0DS BE

51. +5.0DS +5.0DS
+4.0DS +4.0DS
For retinoscopy done at 1m ( without any cycloplegic), final
correction would be = +3.0 DS, +1.0 DC @ 180° Both eyes

52. Principle of subjective refraction
• Subjective determination of the combination of
sphere and cylindrical lenses that artificially
places the far point of Each Eye of patient at
infinity
• This is the combination of lenses that provides
best VA with accommodation relaxed
• To find the strongest plus lens or the weakest
minus lens which allows the patient to obtain the
best possible visual acuity

53. When to start subjective refraction?
• After objective retinoscopy/Auto refraction
• Accurate refining when objective retinoscopy
is inaccurate
– Media opacities, keratoconus, oblique and
irregular astigmatism
• Post mydriatic cycloplegic refraction
• When retinoscope or auto-refractor is absent

54. Subjective refraction techniques
• Fogging
• Stenopaic slit
• Jackson’s cross-
cylinder

55. Subjective refraction techniques
• Astigmatic fan/
Clock dial/ Sunburst
dial
• Phoropter