Clinical Optometric Procedures: Pupillary Testing

Clinical Optometric Procedures: Pupillary Testing

CHAPTER 7 – PUPILLARY TESTING

• This chapter includes a review of the:
• Anatomy of the pupil and iris
• Pupillary pathways
• Evaluation of pupil size and symmetry
• Evaluation of pupil reflexes

Background information

Pupillary testing provides the practitioner information regarding the integrity and function of the iris, the optic nerve, anterior visual pathways, parasympathetic and sympathetic nervous systems and general systemic health.

In order to fully understand pupillary testing, one must be familiar with the iris anatomy and neural pathways which regulate pupil size.

• Terminology
• Miosis = pupil constriction
• Mydriasis = pupil dilation

Anisocoria = unequal pupil size

ANATOMY OF THE PUPIL AND IRIS

The pupil is bounded by the iris, which determines its shape and size. The iris is made up of 2 groups of muscle, viz.

the circular muscle fibres at the pupil margin = sphincter pupillae. The other group consists of the radial fibres that extend from the iris root to the border of the iris = dilator pupillae.

PUPILLARY PATHWAYS

There are several parts that make up the pupil reflex pathways. It involves transmission of signals from the outside world to the brain via the afferent papillary pathway. The control of the pupil size is controlled by the Parasympathetic Nervous System (PNS) and Sympathetic Nervous System (SNS) which makes up the efferent pathways involved in transmission of signals from the brain to the effector organs.

• A simple way to remember this is:
• Afferent = At brain
• Efferent = Exit or Effector International Centre for Eyecare Education

Afferent pupil pathway

The afferent pupil pathway begins with the primary sensor for light, i.e. the photopic system which comprises primarily the cones of the retina. The light reaching the retina is the primary determinant of the pupillary light reflex. Once the fovea is stimulated by light entering the eye, it sets ups signals that are transmitted by retinal nerve fibers. This then relays information for pupil control through the optic nerve to the optic chiasm, at which point half the fibers decussate to the contralateral (opposite) optic tract which the remaining fibers continue on the ipsilateral (same) optic tract to the pupil light control centers in the midbrain. This entire section of the light reflex pathway is the afferent system. The system returning from the midbrain is the parasympathetic pathway (discussed below).

Parasympathetic pathway

This is a 3 neuron pathway (Fig. 6.1). The pathway begins at the Pretectal nucleus of the midbrain and ends at the iris.

The fibres from the pretectal nucleus semidecussate to the Edinger Westphal nuclei (i.e. one fibre from each pretectal nucleus to both Edinger Westphal nuclei) at which point they exit the midbrain as the 3rd nerve and synapse in the ciliary ganglion, and finally reach the sphincter pupillae of the iris via the short ciliary nerves. The majority of the fibres of the 3rd nerve, innervate the ciliary muscle which controls accommodation while only about 3% of fibers innervate the iris sphincter muscle (Benjamin: Borish’s Clincial refraction).

Flow chart of the parasympathetic pathway Figure 6.1 The parasympathetic pathway International Centre for Eyecare Education Sympathetic pathway

This is a 3 neuron pathway that begins in the posterior hypothalamus (Fig. 6.2). The efferent fibers travel to the brain stem and synapse in ciliospinal center of Budge (intermediolateral gray matter of the spinal cord) at the level of T2 along the spinal cord. The fibers from this point on, are the preganglionic fibers (second order neurons). They exit the spine at the level of the thorax (T1) and travel to the synapse in the superior cervical ganglion which is located at the level of the angle of the jaw. From here the post ganglionic fibers (third order neurons) follow the internal carotid artery, through the cavernous sinus and reach the orbit through the superior orbital fissures. These nerves join the ophthalmic division of the 5th cranial nerve to reach the iris dilator pupillae via the long ciliary nerves. The nerves split at the carotid bifurcation, to supply various organs including the sweat glands, iris dilator fibers and Muller’s muscle in the upper lid.

Flow chart of the sympathetic pathway Figure 6.2 The sympathetic pathway

Ocular Voluntary Nervous System

The ocular voluntary nervous system provides the output for the Near Synkinesis (also called Near Triad). The Near Synkinesis is a combination of 3 functions (accommodation + convergence + pupil constriction) that normally function in a connected way. Under normal conditions, they occur simultaneously and are inseparable from one another. When one accommodates, both convergence and pupil constriction automatically occur. This function is technically not controllable but is categorized as a voluntary function because it requires conscious voluntary effort. It can occur even in the blind.

The pathway for the Near Synkinesis is not fully known but it appears to begin in the frontal visual association areas (# 19):

• Anterior visual
• association areas
• CN III nuclei
• (more ventral than pre-tectal input) Follows p
• route
• Accommodation
• Convergence

Pupillary ConstrictionInternational Centre for Eyecare Education

EVALUATION OF PUPILS

• When evaluating a pupil we have to consider several criteria, viz.
• Size and symmetry/shape of the pupil
• Pupil reaction to light and accommodation (briskness)
• Speed of the reflex
• Analysis of pupil size

Ruler or HAAB scale method

The assessment of pupil size requires that the patient be adapted to the level of light within the environment. This is typically done under normal room illumination. The patient fixates a distance target. The diameter of the pupil is measured using a millimeter rule (PD rule) or a HAAB scale which comprises series of coloured circles of known diameters. The ruler is held against the patient’s cheekbones while covering the lower half of the patient’s pupil. When measuring the pupil diameter using the millimeter rule, the size should be recorded. In cases when the iris color is very dark, additional overhead lighting to be able to observe the pupil diameter will be needed. If the practitioner notices a significant difference in pupil diameter (anisocoria), the pupil diameter can be estimated under bright and dim illumination conditions in order to determine if the anisocoria is physiological or pathological. Physiological anisocoria is observed when the difference in pupil size in bright light is comparable to that under reduced lighting conditions. Physiological anisocoria of ≥ 0.4mm difference is observed in 20% of the normal population. This ratio increases with age thereby resulting in 33% of individuals above 60 years old having physiological anisocoria. In 25% of cases, anisocoria is not constantly present.

An exact measurement value of the pupil diameter is not absolutely critical for clinical purposes since the pupils are constantly changing in size due to variable light conditions and the inherent tonic pupil reflex (hippus). An estimation of pupil size is therefore sufficient. The measurement of pupil size becomes more critical when there are specific clinical needs, e.g. contact lens fitting or research studies where ambient conditions are controlled. However, clinically, the most relevant aspect is to assess whether the pupil is abnormally large (mydriatic pupil) or abnormally small (miotic pupil) or whether there is a difference between the two (anisocoria).

• Procedure:
• Patient fixates at distance target to minimize accommodation
• Room illumination is dim to produce large pupils & maximize observable reaction
• The stimulus should be a cool and bright light. The transilluminator or binocular indirect ophthalmoscopes are

ideal, as they are both cool & bright but also adjustable.

• The light (in relatively dim state) is directly from below the line of sight to illuminate both eyes equally
• The pupils are observed simultaneously to compare their relative size
• Estimate the pupil sizes. You can measure the pupils if need be. However for clinical purposes, since pupils are

constantly changing, estimating the pupil size is sufficient.

• If anisocoria is present however, the difference should be evaluated with a pupil ruler or qualitatively assessed for

a varying difference in dim & bright illumination.

• If relative difference() in dim equals difference in bright illumination, it must be noted in the chart:

 Dim =  Bright

• Figure 6.3 HAAB scale
• along the side of an
• occluderInternational Centre for Eyecare Education

Direct ophthalmoscope method

An alternative method of assessing the pupil diameter is with the use of a direct ophthalmoscope. This is done with a +1.00DS lens in place, a testing distance of 1 meter and illumination set to maximum. The intensity of the ophthalmoscope is reduced for assessment of the pupil under reduced illumination conditions and the pupil size differences are compared under dim and bright light settings. Infants and uncooperative patients can be assessed more easily with this method.

• Expected findings
• In bright light: pupil diameter normally ranges between 2 to 4 mm in size

In dim light: pupil diameter normally ranges between 4 to 8 mm in size (Benjamin, 2006).

Physiological anisocoria: is when the difference in pupil diameter remains the same in dim and bright light settings.

Pathological anisocoria can reflect a problem either with the PNS or SNS systems.

When considering the difference in pupil size under bright light: the pupil with the larger diameter is considered to be the pathological pupil. Under dim light settings, the pupil with the smaller diameter is considered to be the pathological pupil. Conditions that result in anisocoria that is greater in bright conditions include Adie’s tonic pupil or a third nerve palsy, while conditions that result in anisocoria that is greater in dim light include Horner’s syndrome.

Recording

The pupil size must be recorded separately for dim and bright light settings ( = change).

 Dim =  BrightInternational Centre for Eyecare Education

EVALUATION OF PUPIL REFLEXES

The evaluation of pupil reflexes involves a series of assessments that collectively will be able to indicate the integrity of the neural pathways involved in the maintenance of pupil size, symmetry and response to light and accommodation.

The direct light reflex

The direct light reflex involves the assessment of the pupil’s response when a light source is introduced before the eye being tested to observe the expected constriction. This constriction is followed by slight dilation, followed by constriction again, until the pupil size has stabilised. This is referred to as the tonic pupil reflex or hippus, which occurs because the iris is constantly trying to allow an adequate amount of light onto the retina. A successful direct response indicates that the efferent systems are working appropriately and helps us rule out mechanical restriction that may impair the pupil’s reaction. An afferent defect may still be present if the direct reflex appears intact.

• Instrumentation
• Penlight / transilluminator
• Distance target
• Near target

Procedure

1. The test is conducted under conditions of normal or dim room illumination with the patient’s fixation is directed to a distance target to avoid accommodation.

2. A handheld source of light (penlight, transilluminator) is directed toward the patient’s right eye from slightly below the line of sight (to avoid the patient fixating the light source and inducing accommodation) for 2 to 4 seconds and is then removed.

3. The magnitude (quantity) of change of the pupil size and its rapidity (quality) is assessed in the pupil that is illuminated. When conducting the procedure, it is important to avoid illuminating the fellow eye simultaneously. It is normal for the constriction of the pupil to be faster than that of the dilation.

• 4. The procedure is repeat about 2 or 3 times to confirm the patient’s response.

5. The procedure is repeated for the left eye.

6. One should ensure that they do not “bleach” the eye by presenting the light source for too long on the eye. In addition, the light should always be kept below eye level to avoid accommodation and illumination of the fellow eye must be avoided.

Expected findings:

• The expected response is a brisk constriction followed by a pupillary escape – a slow dilation to an intermediate

pupillary size. A physiological pupil unrest called Hippus should also be seen: this is a bilaterally symmetrical variation in size variation when the light is kept on the eye. The size change is usually less than 1 mm and has a frequency (~ 3 Hz) that decreases with age. International Centre for Eyecare Education

 Evaluate & Note:

• Quantity: amplitude of constriction graded from 0 (no reaction) to 3 (big reaction)
• &
• Quality: briskness or speed of reaction graded fast (+) or slow (-)

Consensual light response

The consensual response is produced by the neuro-anatomical decussations of the pupillary neuro-pathways at the chiasm and at the posterior commissure. The efferent response triggered by a light stimulus in one eye is normally distributed to both eyes equally and simultaneously. The resulting constriction observed in one eye that is directly stimulated with light should be observed in the fellow eye.

•  The Key clinical observation for normals is that the:

Procedure:

With the same setup as above, one can note the consensual response of 1 eye by directly stimulating the fellow eye (i.e. looking at the non-illuminated eye) & comparing the response obtained. Clinically, this method is not practical & the consensual response is not tested this way. Instead the Swinging or Alternating Light Test is used.

The Swinging Light Test allows us to directly compare the direct response with the consensual response of an eye.

As stated above, when a direct response is triggered in one eye, a similar response should be observed in the other eye through the consensual pupil pathways. Under normal conditions, if the light stimulus is moved from one eye to the other, therefore, no change should be observed in the fellow eye. If the light is the swung back to the first eye, again, no change should be observed, and so on.

A slight constriction followed by a slight dilation may be observable given the pupillary escape. The intermediary pupil size reached however should be the same in both eyes. In other words, direct stimulation in one eye will cause a constriction and a pupillary escape in both eyes. Swinging the light to the fellow eye will cause it to constrict from the intermediary position and also dilate back to the intermediary position.

• patient, room illumination, stimulus same as above
• the light is shined directly into one eye for 2-3 sec
• observe the initial constriction and subsequent escape to an intermediate size
• quickly swing the light to the other eye
• observe the pupil constrict from the intermediate size & escape back to that size
• quickly swing the light to the first eye…
• repeat 3-4 times comparing the response and intermediate size in each eye
• switch to a 1 second per eye alternation and repeat 3-4 times
• phase #1, the 2-3 sec. phase, is used to assess the pupillary escape
• phase #2, the 1-sec. phase, is used to assess the constriction (more sensitive test!)
• the expected response is that the direct & consensual responses of both eyes are equal
•  The Key clinical observation for normals is that the:
• Constriction OD = Constriction OS
• Intermediate position OD = Intermediate position OS
• consensual pupil response
• direct pupil responseInternational Centre for Eyecare Education

Swinging flashlight test

The swinging flashlight test is conducted to compare the strength of the direct light reflex of one eye with that of the consensual light reflex from another eye (Fig. 6.4). An abnormality observed in this test is an indication of a problem in the afferent pupil pathway.

Procedure

1. The procedure is the same as that of the direct reflex test, except that the light source is alternated between one eye to the other and back and forth.

2. A handheld source of light (penlight, transilluminator) is directed toward the patient’s right eye for 2 to 4 seconds and is then quickly moved to the fellow eye which is illuminated for 2 to 4 seconds.

3. The exposure of the eyes to the light source must be of the same duration to avoid false positive results.

4. There must be a slight delay between the stimulation of the fellow eye so that it is able to respond to the consensual response of removing the stimulus from the other eye. Swing light source from one eye to the other and look to see if you get any dilation. You are comparing the afferent pathways of both eyes. The swinging motion must not be done in a horizontal direction from one eye to the next but rather from one to the next using a “U” pattern of movement of the light source. This provides a slight delay for the introduction of light source before the fellow eye.

5. If one observes a relative dilation (i.e. one eye dilates more than the fellow eye) it implies that a problem with the afferent neural pathway exists and this is referred to as a Relative Afferent Pupillary Defect (RAPD) or Marcus Gunn pupil (MG). When stimulating the good eye, one gets both the direct and consensual light reactions to light.

Upon withdrawal of the stimulus from the good eye, there is pupil dilation in response to the decreased light level.

When you introduce the stimulus before the poor eye (i.e. the eye with the afferent defect), the afferent stimulus of that eye is weaker than the fellow good eye producing effectively a lower efferent response, hence a dilation results. The efferent response being bilateral, both pupils will dilate. When the light is shone back on the good eye, the direct response being good, a more vivid efferent response will result, and a bilateral constriction ensues.

NB: A RAPD is not a diagnosis, but a sign of anterior visual system dysfunction such as retinal or optic nerve lesions that decrease the direct light reaction of the eye. It is important to realize that an RAPD is a relative defect where a smaller light signal is transmitted by one eye. The conduction defect must be unilateral or asymmetric for it to be observed at the Swinging flashlight test Figure 6.4 Swinging flashlight test with an abnormality detected in the left eye International Centre for Eyecare Education RAPD Grading

The RAPD is graded subjectively from Trace to 4+ according to the following observations following the light swing from the normal eye to the affected eye:

• immediate dilation of pupil ==> 3+ / 4+ RAPD
• (instead of normal pupil initial constriction)
• no change in pupil size initially ==> 1+ / 2+ RAPD
• (followed by dilation of pupil)
• initial constriction, but greater escape ==> Trace RAPD

to a larger intermediate size vs. other eye The RAPD can also be graded more objectively using Neutral Density Filters of 0,3 log units. The filters are added befpre the good eye until the RAPD is “canceled” or “equalized” by the reduced transmission caused by the filters in the good eye.

• RAPD – Tips for success!

1. Always look at the eye with the light on!

Many get confused as to which eye to look at during the RAPD testing. Just remember that throughout the whole pupil assessment, the eye of interest is the one with the light on.

2. Beware of physiologically induced RAPD i. Light induced RAPD: keeping the light too long on the same eye will blanch & desensitize the retina causing an apparent RAPD. Make sure both retinas are equally exposed to the light.

ii. Occlusion induced contralateral RAPD: eyes that are shut or covered for long periods (e.g. ptotic or patched eyes) will be highly sensitive to light and the swinging light test may reveal an apparent RAPD in the other eye.

iii. Cataract induced RAPD: the retina behind a unilateral cataract (e.g. pseudophakes) is more sensitive to light because of the natural occlusive effect of the cataract. When light is shone in the eye, the increased sensitivity coupled to the light dispersion caused by the cataract may cause it to respond more briskly and cause an apparent RAPD of the other eye.

3. Adjust the brightness or alternating speed of the stimulus when necessary Some pupils react very briskly to bright light and mild RAPD will be masked. Reducing the light intensity often facilitates the observation of an RAPD.

4. “Tilt” the RAPD if necessary

A 0,3-log unit neutral density filter will not change the pupil response when placed over a good eye but will markedly affect it over an affected eye. If an RAPD is suspected but difficult to confirm objectively, perform the International Centre for Eyecare Education swinging light test with the filter over the suspected eye. The filter will accentuate the RAPD & facilitate its observation.

5. Support the swinging light test with a subjective RAPD test Brightness or color comparison from one eye to the other will support “subjectively” the presence of an RAPD. An eye with a conduction defect will have a reduced stimulus input and therefore a reduced sense of color and light brightness when compared to the other.

6. Make use of the direct ophthalmoscope(DO)!

For infants and non-cooperative patients, the swinging light test can be performed by observing the red reflex through the DO in a dark room at a distance of 50 cm.

Reverse or Indirect RAPD

When 1 pupil is non-reactive or not visible because of trauma, synechia, drug effect, etc., an RAPD can still be detected using a modified alternating light test. In this test the reactive pupil is always observed as the swinging light test is performed. The direct and consensual responses of the working pupil are compared using the same principles described above.

If the direct response of the working pupil is greater than the consensual response obtained by flashing the other eye, an RAPD is present in the other eye (non-working or non-visible pupil).

If the direct response of the working pupil is less than the consensual response obtained by flashing the other eye, an RAPD is present in the eye with the working pupil.

Near reflex (Pupil response to accommodation) The near reflex involves the observation of the pupil reactions with the introduction of near accommodative stimulus. It is suggested that if the direct response is brisk and intact then the practitioner need not assess the near response since it is rare that the near reflex is abnormal, when the direct response is intact (Benjamin, 2006).

Procedure

1. The patient is directed to a distance target they can view clearly in normal room illumination.

• 2. No light stimulus must directed toward the eyes

3. The pupils are observed and their size noted.

4. A near target is introduced at a distance of 25 to 30 cm before the patient. The illumination of this near target must not differ from that of the distance target.

• 5. The patient’s fixation is alternated from the distance to the near target.

6. The pupils reactions are assessed for – Quantity & Quality as the direct response 7. The expected response is a brisk contraction similar to the direct response with equal constriction for both pupils 8. The Key clinical observation for normals is that the:

• near pupil response
• direct light responseInternational Centre for Eyecare Education

Recording pupil responses

Use the PERRLA +/- RAPD notation to describe the pupillary findings (size, shape, direct & consensual reactions, etc.) of the above tests:

P Pupils

E Equal

R Round

R Reactive

L Light

• A Accommodation (near)
• RAPD +/- Marcus Gunn

Examples:

OD 4 3+

E R R (-)RAPD

OS 4 3+

• 5 3+
• E R R (-)MG (Dim = Bright)
• 3 3+

4 0 3+

E R R A (-)RAPD

• 4 1+ 3+
• 4 2+

E R R (2+) MG OD

• 4 3+
• E R R (-) RAPD (OD pupil distorted)

4 3+

Pupil Test Summary

• 1. Comparison If Anisocoria, assess in Dim & Bright illumination
• 2. Direct Evaluate Quality/Quantity

3. Alternating Evaluate Consensual indirectly to Rule-out RAPD 4. Near Only necessary if direct reaction to light is weak International Centre for Eyecare Education Section A – PRELIMINARY EXAMINATION