Focused pupil reflex injury (RAPD) (Marcus Gunn pupil)

2021-01-26 12:00 AM

The radial reflex damage caused by the incoming Edinger-Westphal nucleus is asymmetric due to the radial band structure. Symmetrical disorders do not cause pupil-centred reflex.

Description

Paradoxical dilatation of both pupils occurs when the light source moves from the naked eye to the diseased eye (eyes with radial reflex lesions) during the rotation of the light source. Radial pupil reflex injury is a disorder of the afferent optic band of the pupil light response pathway (eg, optic nerve, retina).

Reason

Common

Neuritis (eg. Multiple sclerosis).

AION of the optic nerve (AION).

Less common

Glass haemorrhage.

Retinal detachment.

Retinoblastoma.

Mass lesions (eg. Tumor, abscess).

Figure. Describe the right radial pupil reflecting injury with light source rotation test. A, Shine the light in the right eye; The pupil is poorly contracted and has a sympathetic reaction; B, pupil shrinks well and has empathy response when shining the light on the left eye; C, moving the light from left to right causes the eyeballs to dilate again.

Figure. The pupil response is related to RAPD.

CG = Lymph nodes; EW = Edinger-Westphal Human; LGN = Human body pillow; Lab = Multiply in front of roof; RN = Red multiplication; SC = Upper central tuber.

Mechanism

Concentric reflex damage caused by the asymmetrical input to the Edinger-Westphal nucleus due to the radial optic band structure (eg, optic nerve, retina). Symmetric disorders (bilateral symmetrical optic neuropathy) do not cause the pupil-centred reflex. The light source rotation solution can only determine the difference between the two radial bands. Mechanisms of RAPD include:

Visual nerve disorders.

Retinal disorders (rare).

Visual nerve disorders

Asymmetric disorders of the optic nerve are the most common cause of the pupil-centred reflex. The patient may have clinical evidence of optic nerve dysfunction (eg, papular oedema, vision loss, vision loss, colour blindness). Causes include inflammation of the optic nerve, the tip of the optic nerve (AION), and tumours of the optic nerve (eg. Gliomas). Idiopathic increase in intracranial pressure and other causes of increased intracranial pressure can cause RAPD if the neurological dysfunction is asymmetric.

Retinal disorders (rare)

Severe unilateral retinopathy is rarely the cause of the afferent reflex damage. Typically, the degree of paradoxical pupil dilatation is usually worse than neurological dysfunction. Causes include ageing macular degeneration, diabetic retinopathy, high blood pressure retinopathy, and central retinal artery obstruction.

Meaning

The sensitivity of RAPD in determining unilateral optic neuropathy was 92 –98%.