What does APD stand for in medical terms?
Afferent Pupillary Defect (“APD”) Also known as a “Marcus-Gunn Pupil,” the Afferent Pupillary Defect is due to dysfunction of Cranial Nerve 2 (Optic Nerve).
Is APD the same as glaucoma?
APD and Glaucoma. Determining the presence or absence of an APD is of great clinical value, particularly in guiding the practitioner in the course of treatment for their glaucoma patients. Though glaucoma is typically a bilateral condition, it often initially presents unilaterally or bilaterally with variation in severity between the two eyes.
What is relative afferent pupillary defect (Rad)?
The relative afferent pupillary defect is the most common abnormal pupillary finding, more common than all other pupillary defects combined.4 Although the relative afferent pupillary defect was described by R. Marcus Gunn in 1904, it is clear from his report that the sign was generally known to clinicians of his time.
What is the pathophysiology of right APD?
Patient has a Right APD. Pathology: CN-2 carries the impulse to the brain (occipital lobe). But en route, it synapses to the Edinger-Westphal nucleus in mid-brain. There, CN-3 (Oculomotor Nerve) travels back to constrict the pupil (direct response), and also to the contralateral pupil (consensual response).
What is the difference between RAPD and APD?
RAPD vs APD In literature, and clinical practice, RAPD, and APD, or afferent pupillary defect, may be used synonymously. However, RAPD is technically describing the relative response of one pupil so there is no such thing as bilateral RAPD and, for a RAPD to exist, the damage must be asymmetric between the eyes.
What is a positive APD?
A positive RAPD means there are differences between the two eyes in the afferent pathway due to retinal or optic nerve disease. If the light used is sufficiently bright, even a dense cataract or corneal scar will not give a RAPD as long as the retina and optic nerve are healthy.
What can cause an APD?
CausesIllness. APD can happen after chronic ear infections, meningitis, or lead poisoning. Some people who have nervous system diseases, such as multiple sclerosis, also develop APD.Premature birth or low weight.Head injury.Genes (APD may run in families).
Can you have APD in both eyes?
In case if both pupils do not show a similar response to the light stimuli, shone in one eye at a time, the patient will be diagnosed with RAPD or Marcus Gunn pupils. off note if the condition is bilateral and symmetrical, there will not be a RAPD but bilateral APD.
How do you test for relative afferent pupillary defect?
In a normal patient without afferent pupillary disease, shining a light in either eye will produce constriction of both eyes equally. In the case of an afferent pupillary pathway lesion, the light response is tested individually in each eye and then the light swings between the two eyes in order to detect an RAPD.
What cranial nerve is responsible for afferent pupillary reflex?
The optic nerveThe optic nerve, or more precisely, the photosensitive ganglion cells through the retinohypothalamic tract, is responsible for the afferent limb of the pupillary reflex; it senses the incoming light.
Why is the pupillary reflex important?
The pupillary light reflex allows the eye to adjust the amount of light reaching the retina and protects the photoreceptors from bright lights. The iris contains two sets of smooth muscles that control the size of the pupil (Figure 7.2).
How do you test for pupillary light reflexes?
Gently point the focal light into one eye, this is known as the direct pupillary light reflex. Then, withdraw the light for few seconds, followed by stimulating the same eye again but this time observe the indirect, or consensual, PLR in the opposite eye.
Does macular degeneration affect pupil response?
The study showed that AMD significantly affects the pupil's response to light stimulus (20 msec duration and 24.6 cd/m2 intensity), when compared to normal subjects.
Does amblyopia cause an APD?
Pathology responsible for causing an APD can include significant amblyopia, major retinal issues and optic neuropathy.
What does unequal pupil size mean?
Unequal pupil sizes of more than 1 mm that develop later in life and do not return to equal size may be a sign of an eye, brain, blood vessel, or nerve disease.
What is APD in the left eye?
An Afferent Pupillary Defect (APD) is caused by damage to the neuropathway connecting the eyes and the brain. Your doctor or technician will check for this by shining a handheld light into your eyes and looking for an equal response.
What is a Marcus Gunn pupil?
Marcus Gunn pupil (MGP) is the term given to an abnormal pupil showing aberrant pupillary response in certain ocular disorders. In literature, the term is often used synonymously with Marcus Gunn phenomenon or relative afferent pupillary defect (RAPD). [1] After exposure to bright light, a normal pupil constricts.
What is ischemic optic neuropathy?
Ischemic optic neuropathy is the sudden loss of vision due to an interruption in blood flow to the optic nerve. The optic nerve carries visual information from the eye to the brain, where images are interpreted. When blood flow to the nerve is interrupted, the nerve is deprived of oxygen and nutrition.
What is a tonic pupil?
The tonic pupil, sometimes called Adie tonic pupil or simply the Adie pupil, is the term used to denote a pupil with parasympathetic denervation that constricts poorly to light but reacts better to accommodation (near response), such that the initially larger Adie pupil becomes smaller than its normal fellow and ...
How is APD measured?
6,7 By adjusting the stimulus between the two eyes until they reach the same amplitude, an APD can then be measured quantitatively by comparing the difference or latency between eyes. 6 The precise calculation uses the ratio of the amplitude to the latency of the light reflex in each eye. 7
How to measure APD?
Once the APD is neutralized, the endpoint is reached as measured by the log unit necessary to achieve neutrality. 5 Even in the case of a unilateral, fixed pupil, an APD is detectable through observation of the direct or consensual response of the reactive pupil. 5 Animal studies show that a 0.6 log unit APD is observed in response to an approximate unilateral loss of 25% to 50% of RGCs. 2,6
What is pupillary response?
The testing of the pupillary response to light is routinely performed by the eye care practitioner and imparts valuable information regarding the presence, laterality or magnitude of diseases that mainly affect the optic nerve, such as glaucoma. 1 A relative afferent pupillary defect (APD), when present, is an important marker in the evaluation of unilateral or asymmetric function of the anterior visual pathway. 1-4 It serves as an indication of reduced afferent input from the retina or optic nerve when compared with the fellow eye. 3
What is RAPDX used for?
The RAPDx (Konan Medical) device is used most often in clinical studies to objectively calculate an APD using log units. 8 This high resolution device has demonstrated greater sensitivity in the detection of smaller APDs when compared with the swinging flashlight method. 6 The machine’s duration, interval and intensity of the stimulus are fixed, maintaining a stable light reflex and eliminating examiner discrepancy. 7
How to test for APD?
Swinging flashlight test. Most commonly, the presence of an APD is evaluated in office using the swinging flashlight test, in which each pupil is illuminated and the velocity and amplitude of the pupillary response is compared. 2 In a healthy patient, light stimulation into one pupil results in equal constriction of both. In a patient with an APD, the affected eye will have less pupillary constriction or will dilate in significant defects. 6
What is the afferent portion of the optic nerve?
As the first arm, the afferent portion signifies the nerve impulse sent from stimulation of the retinal ganglion cells (RGCs) to the optic nerve by light, continuing down the optic tract, decussating at the chiasm and ultimately reaching the pretectal nucleus of the midbrain.
When is pupillography used?
Besides the detection of an APD, pupillography may be used in other cases when pupil size is of diagnostic importance, such as differentiating physiological anisocoria from Horner’s syndrome or measuring pupil size for refractive surgery. 9
Which direction does the pupil constrict?
Swing back to the Left, pupil constricts.
Which eye does the penlight go to?
Quickly swing the penlight to the Right Eye. The diseased CN-2 senses less light, so the Right Pupil dilates. Left Pupil also dilates, but you don’t see it [dark room].
How to check for a pupillary defect?
1. Look for a relative afferent pupillary defect using the swinging light test, which accentuates the difference between the direct light reflex of each eye. Ask the patient to look at a distant object and shine the light into the affected eye: both pupils constrict sluggishly.
Who discovered the relative afferent pupillary defect?
Although the relative afferent pupillary defect was described by R. Marcus Gunn in 1904, it is clear from his report that the sign was generally known to clinicians of his time.
What causes afferent pupillary defects?
Afferent pupillary defects are caused by lesions in the ‘front end’ of the pupillary light reflex pathway and most commonly by lesions in the retina and optic nerve.
What is the defect of the pupillary reflex?
A defect of the pupillary reflex caused by a lesion along the pathway of either the parasympathetic supply from the Edinger–Westphal nucleus to the sphincter pupillae muscle of the iris (Adie's pupil) or the ocular sympathetic supply from the ciliospinal centre to the dilator pupillae muscle of the iris (Horner's syndrome).
What does decreased direct light reflex mean?
Pupils: if the parasympathetic pathway for pupillary constriction is normal (efferent pathway), a decreased direct light reflex indicates anterior visual pathway (afferent pathway) disease.
Can RAPD be seen without visual field defect?
There are a few cases reported with clear RAPD in the absence of any visual field defect or any other sign of visual loss on the involved side ( Ellis, 1984; Johnson and Bell, 1987; Eliott et al., 1991 ). The magnetic resonance (MR) scans of these patients showed lesions contralateral to the RAPD, always close to the pretectal area or the LGN involving the brachium of the superior colliculi. This is a rare case, where a RAPD may exist without any defect of the afferent visual system. Even retrogeniculate lesions may show RAPD. In these cases the lesion is almost always located anteriorly close to the LGN and brachium of the superior colliculi ( Papageorgiou et al., 2008 ). It is therefore likely that a lesion of those structures is responsible for the RAPD. This would also indicate that there are more crossed than uncrossed fibers in the afferent pupillary pathway.
Can retinal disease cause a pupillary defect?
Severe retinal disease may cause a relative afferent pupillary defect, although the retinal disease must be markedly asymmetric to produce the finding and, once the finding appears, it is subtle compared with that seen in optic nerve disease.14.
Background
Relative Afferent Pupillary Defect (RAPD) is a condition in which pupils respond differently to light stimuli shone in one eye at a time due to unilateral or asymmetrical disease of the retina or optic nerve (only optic nerve disease occurs in front of the lateral geniculate body).
Conditions Leading to a RAPD
Any disorders that affect the optic nerves regardless of the its pathology can lead to a RAPD. Common causes of unilateral optic neuropathies that lead to RAPD are:
RAPD Diagnosis and Challenges with the Swinging Flashlight Test
Pupils are inspected for size, equality, and regularity during an eye exam. Each pupil should constrict quickly and equally during exposure to direct light and to light directed at the other pupil (the consensual light reflex).
Quantification of RAPD
Various techniques have been described to quantify or measure APDs. These include the use of neutral density filters , cross-polarized filters , and subjective grading based on the amount of initial contraction and subsequent re-dilation of each pupil as the light is swung .
Digital Marcus Gunn Test as an Alternative Solution
The development of personal computer-based infrared video instruments has allowed pupillography to enter the clinical arena.
Extraocular muscles
Hirschberg Have the patient look at a light shining from directly in front. In a non-strabismic patient, the corneal light reflex should be close to the center of the pupil. If the light reflex is deviated, you can estimate the degrees of deviation using the table below.
Disease Severity Staging
Cataract Grading: Thylefors B, Chylack LT, Konyama K et al. A simplified cataract grading system. Ophthalmic Epidemiology 2002. http://www.ncbi.nlm.nih.gov/pubmed/11821974
Exam Findings
Scheie Gonioscopy: Scheie HG. Width and pigmentation of the angle of the anterior chamber; a system of grading by gonioscopy. AMA Arch Ophthalmology 1957. http://www.ncbi.nlm.nih.gov/pubmed/13457548
