Neuro-ophthalmology: Other Optic Neuropathies

Question 1

List the types of excavated optic disc anomalies?

Answer 1

• Optic disc pit
• Colobomas
• Optic nerve hypoplasia
• Morning glory disc anomaly
  Bits missing from optic disc

Question 2

Describe optic disc pit?

Answer 2

• Congenital (presumably from failure of foetal fissure) – leaves small hole
• Depression of disc surface
• Associated w/ VF defect
• Serous (fluid going in through hole) macular detachment:
  o Communication between optic pit & macula
  o Liquefied vitreous (going backwards into retina) or subarachnoid (from brain) fluid
  o Greyish appearance, temporal/inferior (last part to come together in foetus) disc
• Associated central vision loss when situated on maculopapular bundle
• Hospital Management:
  o Difficult – if affects macula then v dangerous to treat as could cause more vision loss
  o Observe – 25% spontaneously resolve (fibres merge into the hole), some develop macular involvement
  o If serous macular detachment & causing a reduction in vision & progressive – fluid going in then they may treat it
   Argon laser along temporal aspect of disc to stop fluid leaking further
   Pars plana vitrectomy – take out vitreous if it is the vitreous causing problem & leaking into retina – air/fluid exchange w/ posturing

Question 3

Describe coloboma?

Answer 3

• Congenital defect from incomplete closure of embryonic fissure
  o Eye developed from top round to bottom – not completely closed off & left gap at bottom
   Last part to join up during development
• Unilateral or bilateral
• Usually occur inferiorly
• Examination:
  o Visual Acuity:
   Reduced
  o Visual Fields:
   Superior field defect – due to inferior problem of disc
   Can mimic glaucomatous loss as affecting ONH – can get arcuate defects – not as severe
  o Fundus:
   Larger than normal optic discs
   Can involve uvea & retina if large
  o Associations:
   Microphthalmos – small eye
   Colobomas of iris, choroid, retina
  o Complications:
   Serous retinal detachment (fluid going in through areas that are missing & can push retina forward
   Rhegmatogenous retinal detachment – fluid seeping under retina pushing it up
   Progressive neuroretinal rim thinning

Question 4

Describe optic disc hypoplasia?

Answer 4

• Reduced number of nerve fibres
• In isolation (by chance), part of malformed eye (part of bigger problem w/ development) or associated with:
  o Midline structures of brain
  o Endocrine abnormalities – growth hormone & other pituitary hormones
  o Suprasellar tumours
• Predisposing Factors:
  o Maternal diabetes
  o Agents ingested by mother during pregnancy including alcohol, LSD, quinine, steroids, diuretics, anticonvulsants, cold remedies
• Presentation/Examination:
  o Spectrum of severity from asymptomatic to no perception of light – depending on how many nerve fibres have not developed
  o Unilateral or bilateral – depending on how it was caused
  o Bilateral cases:
   Roving eye movements – if someone has v poor vision due to not enough nerve fibres in the eye then they cannot fixate on something as macula has not developed problem
   Sluggish pupil responses – not many fibres there to take signals to brain
   Less severe bilateral cases:
• Squint
• Minor visual field defects
  o Unilateral cases:
   Squint in affected eye
   RAPD
   Unsteady fixation in affected eye
  o Visual Fields:
   Peripheral & arcuate defects – as affects ONH
  o Disc appearance:
   Small diameter of disc – comparison of 2 eyes useful if unilateral
   Grey disc colour & surrounding hypopigmentation
   Relatively large retinal vessel diameter
   Ratio of disc diameter: distance between disc & fovea
  >3:1  likely px has optic nerve hypoplasia
• Hospital Management:
  o MRI in all cases – for diagnosis
  o Need to find if systemic cause
  o Referral for endocrine opinion

Question 5

Describe morning glory anomaly?

Answer 5

• Rare congenital malformation, embryonic origin unclear – happens to embryo during development
• Funnel-shaped staphylomatous excavation of optic nerve
• Usually unilateral
• More common in females
• Examination:
  o VA <6/60
  o RAPD – since monocular
  o Visual Field loss
  o Fundus:
   Enlarged disc
   Disc pink or orange colour
   Chorioretinal pigmentation around excavation
   White glial tissue on central disc surface
   Retinal vessels appear at periphery at disc
   Serous retinal detachment