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3 Retinoscopy
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Fig. 3.6 Reex and
intercept
33
Intercept
Reflex
ab c
Fig. 3.7 Images captured from a retinoscopy video demonstrate the intercept and reex moving in the same direction when the streak is moved from the patient’s right to
their left side. (a) The intercept and reex are both seen on
the right side of the Purkinje image. (b, c) Show the
change in position of reex as intercept moves toward
Purkinje
image
patient’s left. Both intercept and reex are in the same
direction, left of the Purkinje image. A “with” reex is
neutralized with a plus spherical lens. It indicates hypermetropia, or myopia of power less than the working distance equivalent
abc
Fig. 3.8 The above images illustrate the “against” movement of the reex, this time with a horizontal streak moving downwards. In the rst image (a), the reex can be
seen at the lower edge of the pupil. The reex moves up as
the light beam (intercept) moves down in the third image
(c). The reex has moved in the opposite direction—this
is known as “against reex.” Panel (b) shows the reex in
the center of the pupil when the intercept is in the midposition vertically. The “against” reex indicates myopia,
and the endpoint of retinoscopy is achieved by placing the
appropriate concave lenses
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D. K. Bagga and J. M. Woodhouse
minus meridian is neutralized rst. If the examiner prefers to work with a minus cylinder, the
most plus/least minus meridian is rst
neutralized.
3.5.4 Alignment
The best alignment would be refracting along the
patient’s visual axis. Therefore, the examiner
checks for the rst Purkinje image while the
patient is asked to look toward the distance target. If this image is in the center of the pupil, it
indicates good alignment (Fig.3.9).
Note that the Purkinje image cannot be considered for reference in patients with eccentric
viewing, such as patients with Stargardt’s disease
or macular degeneration. In these cases, the
examiner should refract in the patient’s adapted
viewing position.
The patient usually has both eyes open during
retinoscopy, but in the case of strabismus, it may
be necessary to cover the xing eye to ensure the
deviated eye takes up xation and is aligned.
Otherwise, refracting patients with both eyes
open may assist the examiner in maintaining
good alignment. The patient’s right eye should be
refracted using the examiner’s right eye and vice
versa to avoid parallax errors.
3.5.5 Controlling Accommodation
In conventional or “static” retinoscopy, the
patient xates on a target at a distance (6m or
20ft), thus encouraging relaxed accommodation.
To minimize accommodation, the xation target
should be large (e.g., a 6/60 letter or picture for
children). Relaxed accommodation can be further encouraged by “fogging” (blurring with
plus/+ve lenses) the eye not under the test. For
young hypermetropes with active accommodation, it may be useful to fog with a plus lens that
is 2.00 D greater than their previous
prescription.
Other forms of retinoscopy, including cycloplegic and Mohindra, will be discussed later
(Sect. 3.8.1). These techniques control accommodation by different means, but the underlying
principles of retinoscopy remain the same.
3.5.6 Ambient Light
Retinoscopy is a darkroom procedure. Reducing
the ambient light helps by increasing the patient’s
pupil size and relaxing the accommodation. In
addition, the dark room improves the examiner’s
ability to perceive the reex by enhancing the
contrast.
Good
alignment Ö
Fig. 3.9 Images reecting (a) good and (b) poor align-
ment based on the location of the Purkinje image observed
during retinoscopy. The examiner can change their posi-
Poor
alignment X
Purkinje
image
Purkinje
image
tion vertically and horizontally to ensure appropriate
alignment during the retinoscopy
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Table 3.2 Centimeters to D conversion scale
Working lens power in diopter (D) 33.33 20 10 5 2.5 2 1.25 1
Test distance in cm 3 5 10 20 40 60 80 100
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3.5.7 Use ofBrightness Controls
The rheostat of a streak retinoscope helps control
the brightness of the light beam. An appropriate
brightness level provides adequate visibility of
reex for the examiner without causing glare for
the patient. There are a few ocular conditions
where patients may experience signicant intolerance to light, such as achromatopsia, congenital glaucoma, or aniridia. In these cases, if the
media (cornea, lens, and vitreous) are clear and
the examiner can observe at a low brightness
level, the brightness can be adjusted to a level the
patient can tolerate. In contrast, in some cases
with media opacication, using the maximum
brightness may help visualize the characteristics
of the reex.
3.5.8 Working Distance
andSpherical Errors
inRetinoscopy
Table 3.2 shows the centimeters (cm) to diopter
(D) conversion scale and represents the test distance and corresponding working lens correction.
It shows that the examiner must be precise about
their working distance correction for shorter test
distances. This is because even a small change at
a shorter working distance accounts for a large
dioptric change. For a working distance of 50cm
or longer, a minor incorrect estimation of the
working distance may not make a clinically signicant error (over 0.25 D). The other advantage
of using a longer working distance is to encourage the patient to relax their accommodation, as
some patients might intermittently look at the
retinoscope’s light or the examiner’s face. A
shorter working distance will stimulate proximal
accommodation, adding inaccuracies in measuring the refractive errors.
While there are advantages to using longer
working distances (≥50 cm), there are special
situations, such as a miotic pupil or media opacity, where the examiner may need to use a shorter
test distance.
3.6 Estimation ofRefractive
Errors
At the outset of retinoscopy, estimating the
approximate refractive error is very useful so that
the rst lens inserted brings the reex close to the
endpoint.
3.6.1 When theObservation Is
an“Against” Movement
oftheReex
As the far point in a myopic eye is within a nite
distance, it is easy to estimate the magnitude of
myopia. Simply reduce the test distance to
observe the rst noticeable “with” and then move
back to the rst noticeable “against”; between
these two points lies the far point. Estimate the
distance between the point of reversal and the
patient’s eye and convert it to D.For example, if
the point of reversal was observed at 20cm, the
person would have 5.00 D myopia.
3.6.2 When theObservation Is
a“with” Movement
oftheReex
The “enhancement” technique helps estimate the
strength of the “with” reex up to about 5 D [1].
The examiner slowly moves the sleeve position
to vary positive vergence and achieve an enhanced
reex (thinnest, sharpest, and brightest) while
remaining in the plane mirror effect of retinoscopy (i.e., not reversing the movement). If the
examiner needs to apply the maximum positive
vergence (moving the sleeve upwards to its fur-
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D. K. Bagga and J. M. Woodhouse
thest) possible in the plane mirror effect to
enhance the reex, it represents +5.00 D or more.
3.6.3 Estimating andConrming
theAxis ofAstigmatic Error
If the sleeve at the bottom-most position itself
provides the enhanced reex, then it means about
+0.5 D.For estimating the magnitude of hypermetropia for the complete range between +0.5 D
and +5.0 D, the examiner needs to consider the
beam width that produces the enhanced reex
and interpret it in relation to the difference
between the two extreme sleeve positions.
Figure 3.10 demonstrates how the width of the
beam (intercept) guides the estimate of the magnitude of hypermetropia.
Three commonly used techniques for estimating
the axis of astigmatic error are (1) thickness, (2)
break, and (3) skew phenomena [1].
Thickness phenomena: The examiner must
observe the change in the thickness of the reex
when observing the reex across different meridians. The direction providing the thinnest, brightest, and sharpest reex is the axis for the plus
cylinder (Fig.3.11). The thickness phenomenon
is best observed when refracting the eye using
ab cde
Fig. 3.10 The above gures illustrate the change in
thickness, brightness, and sharpness of the reex as the
sleeve is moved up {Panel (a) (sleeve at the bottom most
position) to panel (e) (sleeve position upwards with maximum convergence, in plane mirror)}. This change in
sleeve position causes a change in the vergence of the rays
entering the eye. In the enhancement technique, hypermetropia is estimated by the width of the intercept that produces enhanced reex (thinnest, brightest, and sharpest).
Panel (d) is an enhanced reex, and the estimate for this
case will be +3.50 D
Fig. 3.11 Thickness phenomenon: Panel (a) illustrates a thicker reex than panel (b), as the streak is not aligned to the
correct axis in panel (a)
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plus cylinders, as it would be most readily visualized using the enhancement technique described
above (Sect. 3.6.2). If the examiner wishes to use
minus cylinders, the method can be used with the
sleeve at its highest, thus reversing the reex to
“with” and moving it downwards to enhance the
reex.
Break phenomena: The examiner observes
the direction of the reex in relation to the direction of the intercept. In astigmatic errors, a break
will be observed as an angle between the intercept (the light beam of streak) and reex when
the intercept is not aligned with one of the principal meridians of astigmatism (Fig.3.12).
Skew phenomenon: A skew phenomenon is
observed in the dynamic movement of the reex
in relation to the direction of the light beam of a
streak (the intercept). When the intercept is offaxis/not aligned to the principal meridians of
astigmatic error, the intercept and reex move in
different directions, called the skewing phenomena. Therefore, the axis of the cylindrical lens
will be in a direction in which the reex and
intercept move in the same direction.
The straddling technique allows the exam-
iner to conrm the cylindrical axis once a cylindrical lens is placed in the trial frame. First, a
correcting cylindrical lens is placed in the trial
frame based on the estimations obtained using
the thickness, break, and skewing phenomena.
If the estimated axis is incorrect, an orientation
difference (break and skew) between the three
components: the retinoscope streak (intercept),
cylindrical lens markings, and reex will be
observed. This difference can be best visualized
at 45° away from the axis of the cylindrical lens
placed in the trial frame (Fig.3.13). The orientation of the axis must be adjusted until all three
align [1]. When the orientation of the axis is
correct, straddling will show similar characteristics (thickness, brightness, and movement) of
reex at 45° to either side. If not, these characteristics will differ, as shown in Fig. 3.13.
Particularly for the movement of the reex, one
side of the straddle could show a “with” reex
while on the other side, an “against” movement
can be observed.
ab c
Fig. 3.12 Demonstration of the break phenomenon.
There is a distinct angle, called the “break” between the
intercept and the direction of reex, in all three examples
(Fig.3.12a–c). The break will disappear if the streak in
panel (c) is moved slightly to 85°, the true axis
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D. K. Bagga and J. M. Woodhouse
Fig. 3.13 Straddling technique: In Fig. (a), the axis of a
convex cylindrical lens is placed at 95°. The observations
at 140° (a) and 50° (b) reveal the difference in thickness,
3.6.4 Finalizing theMagnitude
ofAstigmatism
When the reex movement has been neutralized
with a cylindrical lens at the correct orientation, it
is important to check the opposite (sphere) meridian again. It is all too easy for the examiner to
inadvertently change the working distance
brightness, and movement of reex (not appreciated in a
static picture), indicating the inaccurate placement of the
astigmatic lens
slightly between neutralizing the sphere and
moving on to correct astigmatism. When comparing the movement of reex across all meridians, it should move (or remain neutral) in the
same way.
3.7 Tips forPerforming
Retinoscopy (Table3.3)
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Table 3.3 Tips for performing retinoscopy in complex conditions
Conditions posing
challenges Recommendations
Nystagmus Keep the retinoscope still and allow the patient’s eye movements to replace the
retinoscope movements. Concentrate on observing the movement of reex to
determine “with” or “against,” when the patient’s eye is directed in the appropriate
direction
Media opacity Reduce the test distance, try dimming room lights further, and use the maximum
brightness of the retinoscope
Accommodation Contralateral (fellow eye) fogging. In the testing eye, begin with over plus lens to get
an “against” reex and reduce to neutral
Multiple reexes—
different zones in the
pupillary area showing
different refractive errors
Central shadow Refract the immediate next zone to the shadow
Miotic pupil Reduce working distance and room illumination
Subluxated lens
(example: Marfan’s
syndrome)
Reection from trial
lenses
High refractive errors When the reex is close to neutral, it appears bright and has crisp movement. In
Focus on the central 2–3mm zone, close to the Purkinje image, and ignore the reexes
seen in the periphery
Refract the zone closer to the Purkinje image; it may be possible to refract both
aphakic and phakic zones. Later, improvement in the visual acuity should be assessed
monocularly and binocularly to decide the spectacle prescription
Use of trial lenses with anti-reection coatings; in the case of planoconcave lenses, ip
the lens with a concave surface facing the patient; this will reduce the size of the
annoying reections
contrast, a reex far from the neutral is dim, wide, and slow. In high refractive errors, it
can be challenging to determine the movement, and inexperienced examiner can
sometimes assume neutrality because there is no apparent movement. Moving the
retinoscope further and closer does not produce the “against” and “with” movements
that conrm neutrality. If the reex is difcult to interpret, simply holding up a
high-power plus and minus lens will quickly help since one will reveal a brighter
reex, and the other will worsen matters
39
3.8 Special Techniques
3.8.1 Cycloplegic andMohindra
Retinoscopy
Static retinoscopy, as described above, controls
accommodation by asking the patient to xate on
a distant target, fogging the fellow eye, etc. The
static technique may be inappropriate for some
patients, particularly young children or people
with learning disabilities, who cannot reliably
maintain xation at a distance.
Cycloplegic retinoscopy eliminates accommodation by using cycloplegic eye drops that
temporarily paralyze the ciliary muscles. Once
the cycloplegic eye drops have taken effect, the
patient can directly xate the retinoscope light,
with the advantage that the refraction is now con-
ducted on the visual axis, and the examiner can
use her/his preferred eye. The disadvantage (apart
from patient discomfort and time for instillation
and drug action) is that cycloplegic drugs also
dilate the pupils, giving rise to aberrations and
making the retinoscopy reex more challenging
to interpret [4].
Mohindra retinoscopy uses the phenomenon
known as “tonic accommodation” or “empty
eld myopia” [4, 5]. It is conducted in total darkness apart from the retinoscopy light, which is
dimmed as much as possible. Eyes in darkness
adopt a stable, small amount of accommodation.
The patient xates on the retinoscope light, and
refraction is carried out as normal. However,
occluding one eye is a recommended exception
to cut out convergence cues that might trigger
accommodation. The working distance allow-
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ance is modied to allow for the small amount of
accommodation the patient adopts in the dark [5].
According to research studies, [6] to obtain the
same refraction as under cycloplegia and for a
working distance of 50cm, the examiner should
deduct 0.75 D for an infant under 2years, 1.00 D
for a child aged 2 and over, and 1.25 D for a
young adult. Unfortunately, there are no guidelines for the age at which the examiner changes
from child-appropriate to adult-appropriate
deductions. Since the difference between the two
is only 0.25 D, this is probably trivial. Mohindra
has the advantages of being non-invasive and
allowing other visual functions, such as accommodation, to be assessed after refraction.
D. K. Bagga and J. M. Woodhouse
Fig. 3.14 A central shadow seen in the retinoscopy reex
due to posterior subcapsular opacity in the lens
3.9 Additional Observations
The retinoscopy reex can provide additional
information and indicate eye disorders causing a
change in the pupil size, shape, color of reex,
scissors/irregular reex, a shadow in reex, or
invisible reex. Media opacities/disturbances
(such as early keratoconus) can be much easier to
spot with a retinoscope than with other means so
that appropriate examinations can be carried out
(Fig.3.14). Retinal disturbances, such as detachment and coloboma, can be seen in the different
colorations of the retinoscopy reex, especially
as the patient looks around. In patients with
severe disabilities, the ability to xate can be
assessed with a retinoscope.
3.10 Comparison Between
Autorefraction
andRetinoscopy
Both retinoscopy and autorefraction have their
own merits and belong in a state-of-the-art eye
examination room. Table 3.4 provides a quick
comparison of the key parameters of both techniques to enable clinicians to determine when to
use retinoscopy, autorefraction, or both.
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Table 3.4 Comparing retinoscopy and autorefraction
Parameter Autorefraction Retinoscopy
Cost of
equipment
Cost of
refraction
Accuracy Reasonably accurate ndings in most
Suitability In most cases, with normal pupil size and
Expensive Less expensive
Less expensive Expensive (considering the time taken to perform the
test)
Completely depends on the skills of the examiner
cases, irrespective of the skills of the
examiner
Suitable for all patients irrespective of age and abilities/
simple refractive errors. However,
autorefraction may show an error in
measuring complex refractions, such as
high refractive errors, eyes with
nystagmus, large eccentric xation, or
miotic pupils
Suitable for able-bodied, condent, and
compliant patients
disabilities. Can be used in most of the complex cases of
high refractive errors, such as 20D of astigmatism or
50D of myopia, and a large variety of challenges;
application of estimation techniques, such as direct
retinoscopy or enhancement, and can provide a useful
starting point for subjective refraction
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3.11 Conclusion
Retinoscopy is essential for all eye care professionals involved in refractive correction. In cases
where subjective refraction is not possible (for
example, children and people with special needs),
inconsistent or non-availability of autorefraction
values (cases with uveal coloboma, aniridia, or
irregular cornea), and high refractive errors
where large variability may be observed in different methods, retinoscopy by an experienced eye
care service provider can be the only way of
determining the refractive correction. In addition
to providing information about the refractive status, examiners can identify other ocular ndings,
such as posterior subcapsular cataracts, vitreous
opacities, and spherical aberrations. Retinoscopy
has two major limitations: one, it is dependent on
the skills of the professional; two, it could take a
longer time to perform than an autorefractorbased examination. Despite these limitations, this
is one of the important objective methods to measure refractive errors in all, including the vulnerable and challenging cases.
Finally, reading about retinoscopy might
motivate the reader, but unless the reader prac-
tices the various techniques step by step and multiple times, it may not help the reader and those
waiting to get an appropriate refractive correction. Therefore, practice is essential to improve
refractive corrections to make the patient see
clearly.
Funding Hyderabad Eye Research Foundation.
Disclosure None.
References
1. Corboy JM. The retinoscopy book: an introductory
manual for eye care professionals. Slack Incorporated;
2003.
2. Bennett AG. An historical review of optometric
principles and techniques. Ophthalmic Physiol Opt.
1986;6(1):3–21.
3. Bennett A, Rabbetts R.Clinical visual optics, vol. 62.
London: Butterworths; 1984. p.924.
4. Benjamin WJ. Borish’s clinical refraction-E-book.
Elsevier Health Sciences; 2006.
5. Mohindra I. A technique for infant vision examination. Optom Vis Sci. 1975;52(12):867–70.
6. Saunders KJ, Westall CA. Comparison between
near retinoscopy and cycloplegic retinoscopy in the
refraction of infants and children. Optom Vis Sci.
1992;69(8):615–22.
Prescribing Spectacles
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4
PremNandhiniSatgunam
4.1 Introduction
Vision is a collective process of optics, physiology, and visual perception at the higher centers of
the brain. To achieve clear vision, all these processes must be intact. Imperfect optics, resulting
in refractive error, can be alleviated through a
pair of spectacles. However, all the processes that
contribute collectively toward vision also determine the nal spectacle prescription for a patient.
As a result of this complex interplay and physiological variabilities, the same patient examined
by the same examiner may end up with different
spectacle prescriptions on two separate occasions. This variability must be kept in mind, especially while changing earlier spectacles.
Determining a spectacle prescription is a collaborative effort, involving both the examiner and
the patient. Truly, prescribing a pair of spectacles
is both an art and a science. Science is learned,
and art comes with practice. This chapter aims to
give tips on both science and craft.
P. Satgunam (*)
Brien Holden Institute of Optometry and Vision
Sciences, Prof. Brien Holden Eye Research Centre,
L V Prasad Eye Institute, Hyderabad, Telangana, India
e-mail: premnandhini@lvpei.org
4.2 Background
The procedure for prescribing spectacles is called
subjective refraction. The “subjectivity” in this
involves factors related to the patient (e.g., their
tolerance of blur) and the examiner (e.g., their
technique). Because of this subjectivity, spectacles cannot be prescribed directly to a patient
based solely on the autorefractor or the retinoscopic value. In a study that evaluated the
patient’s tolerance to spectacles prescribed based
on autorefraction and subjective refraction done
by an optometrist, the latter was more tolerable
[1]. Patient–clinician communication is important to dispense the appropriate spectacles. A systematic review and meta-analysis found that
about 16% of spectacles non-tolerance resulted
from poor communication [2].
The rst step toward giving a spectacle pre-
scription, before subjective refraction, is good
objective refraction. Readers can refer to Chap. 3
in this book for objective refraction. A list of
good references [3–7] for prescribing spectacles
is also put together at the end of this chapter. In
addition, guidelines for spectacle prescription,
especially for children (considering the risk of
amblyopia), are also available from the websites
of different professional organizations (including
Ophthalmology and Optometry) [8, 9]. There are
several tools and techniques that can be used for
subjective refraction. Not all of these are
described in this chapter. Only those techniques
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024
T. Das, P. Satgunam (eds.), Ophthalmic Diagnostics, https://doi.org/10.1007/978-981-97-0138-4_4
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