In contrast, internuclear ophthalmoplegia (INO), aka medial longitudinal fasciculus syndrome (MLF syndrome) is pathognomonic of MS (i.e., you only see it in MS). In MS, although optic neuritis is common, it is non-specific, and can be caused by other pathologies (e.g., sarcoidosis) and drugs (e.g., ethambutol). I don’t even think I totally understood MG pupil until now truthfully.” Yeah, I know. Therefore, when you go back to the affected side with the light, the lesser degree of direct response will make it appear as though the pupil is dilating, when in reality it’s just constricting less relative to the robust level of constriction from the previous consensual response.įor instance, if we have a Marcus Gunn pupil in the right eye (left side of following diagram), this is what we’d see: However, the right eye is normal, so if you shine the same light into it, the afferent signal will be much stronger, so the degree of constriction, as received via the efferent response, will also be stronger bilaterally. If CN II of the left eye is affected by optic neuritis, the left CN II is essentially communicating, “we don’t need to constrict either pupil that much because there’s not much light here let’s constrict both pupils just a little.” So the result is, the direct and consensual constrictive response is weak. When CN II from one eye receives a light stimulus, that is transmitted in the form of an afferent signal to the Edinger-Wesphal nucleus of the midbrain, which will then relay an efferent signal back to both eyes via CN III, yielding both a direct and consensual response. When you shine a light into one eye, the resultant constriction of that eye’s pupil is called a direct response. The constriction of the contralateral pupil is called the consensual response. In order to understand this, you must first know that optic nerve (CN II) afferent input from either eye will cause a bilateral efferent response via the oculomotor nerve (CN III), causing both eyes to constrict. In reality, it doesn’t dilate it just doesn’t constrict as much as the unaffected side. In RAPD, shining a light in the eyes and moving it side to side will make it appear as though the affected eye’s pupil dilates, rather than constricts, in response to light. Optic neuritis causes a Marcus Gunn pupil, which is also known as a relative afferent pupillary defect (RAPD). Essentially in the vignette they’ll say a woman 20s to 30s who has an episode of blurry vision + urge incontinence + other sensory or motor dysfunction –> answer = MS with optic neuritis. Optic neuritis literally means inflammation of the optic nerve –> classically seen in multiple sclerosis –> can present with a wide array of visual changes, e.g., blurry vision, loss of color vision, and central scotoma. Treatment for diabetic retinopathy is with injections of VEGF inhibitors or laser photocoagulation. HTN is the other common cause of cotton wool spots. In addition, they can also grow into the vitreous humor, eventually leading to vitreous hemorrhage.Ĭotton wool spots may be seen on fundoscopy, which are axonoplasmic aggregates from neuronal degeneration. The tiny new blood vessels are fragile and can easy rupture, causing blindness. Initially it is non-proliferative, meaning there is no neovascularization of the retina, and many patients won’t notice any visual changes.Īs retinal ischemia progresses, neovascularization occurs this is called proliferative diabetic retinopathy. Caused by non-enzymatic glycosylation of retinal microvessels –> vascular damage with degeneration of capillaries –> reduced retinal blood flow + ischemia + damage to neurons of inner retina.
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