Download another way to check afferent pupillary defect (apd) with slit lamp

ALTERNATE METHOD TO EVALUATE RELATIVE
AFFERENT PUPILLARY DEFECT (RAPD) WITH SLIT LAMP
MEASUREMENT
Fuxiang Zhang, MD
Department of Ophthalmology, Henry Ford Health System, Taylor,
Michigan
PURPOSE: To demonstrate a new, easy to use, method of
checking RAPD with results that are quantitative and comparable
to those obtained with the conventional swinging flashlight
technique.
SETTING: Suburban Comprehensive Ophthalmology Clinic.
METHODS: A prospective study of 15 consecutive patients with
RAPD seen at a single general ophthalmologist’s office. The pupil
size of each eye was measured with a penlight in dim light. The
presence of an RAPD was determined with conventional swinging
flashlight technique. The pupil size was re-measured quantitatively
using the slit lamp beam. Digital camera photos were taken to
demonstrate that there was no preexisting anisocoria.
RESULTS: The pupil size of the affected eye in all 15 patients was
larger than the fellow eye with the slit lamp beam measurement.
The percentage difference in pupil size between the two eyes of
each patient measured using the slit lamp beam correlated with the
extent / depth of RAPD.
CONCLUSION: Slit lamp beam measurement of pupil size is a
new and easy way to check for the presence of an RAPD and also
provides a quantitative measure that is related to the intensity of
the defect.
FINANCIAL DISCLOSURE: The author has no financial or
proprietary interest in any material or method mentioned.
The afferent papillary defect (APD) better referred to as relative
afferent pupillary defect (RAPD), also known as Marcus-Gunn
pupil, is a very significant and highly objective finding in the
clinical examination of the visual system1. A broad range of visual
system anomalies, including advanced asymmetric glaucoma,
extensive retinal disease, optic neuritis or other optic neuropathy,
can produce an objective RAPD. An RAPD can be detected even
in an unconscious patient. In contrast, many significant ocular
problems with severe vision loss, such as advanced cataract,
vitreous hemorrhage, functional vision loss, or lesions of the optic
radiations and visual cortex, do not have an RAPD. Efferent
pathway abnormities, such as third nerve palsy, Horner’s syndrome
and Adie’s pupil, will produce anisocoria but will not show an
RAPD.
Personal observations of pupil size during routine slit lamp
examination of patients with RAPD revealed an apparent
difference in diameter, if the patient had an RAPD. When the
affected eye was examined with the slit lamp light, the pupil
diameter appeared larger than that of the fellow eye when it was
examined with a beam of the same intensity. Based on this
observation, this study was designed to determine whether
measurement of pupil size at the slit lamp could provide a reliable
means to demonstrate the presence of RAPD and estimate its grade
or depth. To the best knowledge of the author, this new method of
checking RAPD was never published in our ophthalmology
literature.
PATIENTS AND METHODS
Fifteen consecutive patients with an RAPD confirmed by swinging
flashlight test were enrolled in this study between August 2008 and
February 2011. All patients were evaluated by a single
comprehensive ophthalmologist at the suburban Taylor branch
office of the department of ophthalmology, Henry Ford Health
System, Michigan. The Henry Ford Health System Institutional
Review Board (IRB) approved the study design and protocol, and
all participants signed an informed consent form.
Inclusion and Exclusion
All patients with an RAPD as demonstrated by the swinging
flashlight test who also had normal iris structure and equal, round,
regular shaped pupils in both eyes, who were willing to participate
in the study were included.
Patients with any one of the following conditions were excluded:
Anisocoria, irregularly shaped pupil or iris, history of open wound
intraocular surgery, history of laser surgery involving the iris,
history of iritis, and history of any ocular trauma. One patient was
excluded because the quality of ocular photographs was not clear
enough to role out pre-existing anisocoria.
Routine Eye Examination
All patients underwent a comprehensive routine eye examination
prior to the study day. The presence of RAPD had been confirmed
at that prior exam and the patient was invited to participate in the
study if they satisfied both inclusion and exclusion criteria. After
signing the informed consent form, the swinging flashlight test was
repeated, with RAPD graded as 1+ or less, 2+ and 3+, according to
the following subjective criteria:
1+ or less (mild): the affected pupil shows a weak, but
noticeable initial constriction and then weakly dilates to a
slight larger size.
2+ (moderate): the affected pupil shows a more noticeable
dilation to a larger size when the direct light is shined into
the affected eye.
3+ (severe): the affected pupil shows an immediate dilation
to a larger size.
Digital photographs showing both eyes were taken at 6 inches to
document that there was no pre-existing anisocoria.
Pupillary Size Measurement at the Slip Lamp
All pupil measurements made at the slit lamp (Haag-Streit BQ 900,
Switzerland) using the beam length gauge with the transformer
power set at level one (dimmest light, for patient comfort) using a
narrow slit beam (wide enough to view the pupil), angled
perpendicular to the iris (i.e., straight, at 90 degrees). The vertical
diameter of each pupil was measured along the12:00 to 6:00
o’clock meridian. When pupil oscillation (hippus) was present, the
smallest pupil diameter was recorded. While measuring the right
pupil, the patient was instructed to use the left eye to look in the
direction of the examining doctor’s right ear (while fixating at a
distance). The same approach was used to measure the left pupil,
with the patient using the right eye to look in the direction of the
examiner’s left ear, keeping the eyes straight and fixating at a
distance. The slit beam settings and incident angle remained
unchanged when measuring both pupils.
RESULT
Table 1 summarizes the main study data.
In this study, the affected pupils of all 15 patients were larger than
the pupils in their respective fellow eyes. The percentage
difference in pupil size was calculated using the following
formula:
Percentage Difference = (larger pupil diameter-small pupil
diameter)/small pupil diameter x 100.
The pupil size difference as a percentage had a mean of 12.5 % and
standard deviation of +6.7 within the first group of 6 patients who
had a 1+ or less RAPD, by swinging flashlight test. The second
group of 5 patients who had 2+ RAPD by swinging flashlight test
had a mean pupil size difference of 43.0% and standard deviation
of +15.3. The third group of 4 patients who had a 3+ RAPD had a
mean difference in pupil size of 75.2% with a standard deviation of
+65.4. (See Table 1) The resulting association between the
swinging flashlight test and the pupil size difference was
statistically significant, with a Spearman correlation coefficient of
+0.76 and corresponding p-value of 0.001.
In summary, there was a statistically significant tendency of the
pupil size difference to become larger as the grade of RAPD by
conventional swinging flashlight test result became larger.
DISCUSSION
The pupillary light reflex is a four neuron arc. The first neuron
connects the retina to the pretectal nucleus in the midbrain, from
where the second (internuncial) neuron connects each pretectal
nucleus to both Edinger-Westphal nuclei, thus explaining why a
unilateral light stimulus evokes bilateral pupil constriction. The
third neuron connects the Edinger-Westphal nucleus to the ciliary
ganglion. The fourth neuron connects the ciliary ganglion to the
sphincter muscle of the pupil.
In a patient with normal intact afferent fibers, both pupils constrict
equally and re-dilate slightly when either eye is stimulated, and the
direct response should be equal to the consensual reflex. In an
individual with a compromised afferent nerve system, the affected
eye responds as if the light is dimmer and so it constricts less and
re-dilates more than the fellow normal eye. The normal eye will
have a greater direct response than the consensual response, and
the affected eye will have a greater consensual response than its
own direct response, an RAPD. An RAPD occurs with significant
retinal or optic nerve disease, when there is a difference in the
disease process severity between the two eyes. If each eye has
equally severe pathology, there will be no RAPD. A patient with a
deficit in one eye leading to an RAPD will not present anisocoria
since the pupil of the affected eye will appears to be of equal size
to the fellow eye due to the consensual light reaction.
The Swinging Flashlight Test is the traditional and most
commonly used clinical test to detect and grade an RAPD. It is
easy and straightforward, but it has the following minor
downsides:
1. It is hard to detect a mild RAPD, unless a bilateral indirect
ophthalmoscope light is used.
2. The grading of the RAPD by this method is subjective. The
established method of measuring the severity of the RAPD
quantitatively involves using neutral density filters. This
technique involves placing filters of graduated logarithmic
density before the more normal afferent system until the
pupil responses to the swinging flashlight test are
symmetric2. This technique is time consuming and not
practical for most general ophthalmologists.
More sophisticated methods of testing RAPD have been described
in the literature. Computerized portable pupillometer3, various
pupillography for RAPD tests4-5, and magnifier assisted swinging
flashlight test6-7 were well studied in the past. These tests certainly
provide more accurate information, but they are time consuming
and not practical for most general ophthalmologists.
This study illustrates an alternative way of checking RAPD by
measuring pupil diameter with the slit lamp beam. As long as the
brightness of the slit lamp beam and the incident angle of the light
to the eyes remain equal for both eyes, as mentioned in the
Methods section, the affected pupil should be larger in size than
that of its fellow eye. The size difference between the two eyes
also seems to correlate with the conventional swinging flashlight
grading of the RAPD. Because this method is quantifiable, it is
also potentially more useful as an objective clinical evaluation.
One difficulty with this method occurs when pupil oscillation
(hippus) is present. In that circumstance it may not be as easy to
obtain an exact, accurate measurement of pupil diameter.
However, by using a slit lamp beam that is dim and narrow, and by
using the same endpoint for both eyes, the measurement can still
be very accurate in providing useful information to the clinicians.
This study is a preliminary one and only one observer for all the
measurements. Further investigation with more cases, better with
controlled group, is recommended to test the validation of this test.
Acknowledgment: Barry Skarf, MD, PhD and Alan Sugar,
MD provided assistance with the manuscript and Gordon
Jacobsen MS provided assistance with statistical analysis.
Steve Ogilvy, BFA, CRA provided assistance for video
design and recording.
REFERENCES
1. Bajandas FJ, Kline LB, Neuro-Ophthalmology Review Manual,
Third Edition. Thorofare, NJ: Slack, Inc; 1988: 118.
2. Albert D, Jakobiec F, Principles and Practice of Ophthalmology,
Clinical Practice, Philadelphia: W.B. Saunders; 1994: Vol 4: 2476.
3. Volpe NJ, Plotkin ES, Maguire MG, Hariprasad R, Galetta SL.
Portable Pupillography of the Swinging Flashlight Test to Detect Afferent
Pupillary Defects. Ophthalmology 2000 Oct; 107(10):1913-21; discussion
1922.
4. Kawasaki A, Moore P, Kardon RH. Variability of the Relative Afferent
Pupillary Defect. Am J Ophthalmol. 1995 Nov;120(5):622-33.
5. Cox TA. Pupillography of a Relative Afferent Pupillary Defect. Am J
Ophthalmol. 1986 Mar 15;101(3):320-4.
6. Lankaranian D, Altangerel U, Spaeth GL, Leavitt JA, Steinmann WC.
Trans Am Ophthalmol Soc. 2005; 103:200-7; discussion 207-8.
7. Ichhpujani P, Rome JE, Jindal A, Khator P, Leiby BE, Gordon
H, Chen B, Spaeth GL. Comparative Study of 3 Techniques to
Detect a relative Afferent Pupillary Defect. J Glaucoma. 2010 Sep
16. (EPub ahead of print)