Tuesday, March 25, 2008

Myasthenia Gravis

  • autoimmune disorder in which antibodies prevent the neurotransmitter acetylcholine from attaching to muscle receptors, thereby interfering with muscle contractions
  • characterized by fatigability of voluntary eye movements (diplopia worsens as day progresses, improves with sleep)
  • can present with diplopia, ptosis or both

Tests

  • sustained upgaze: patients will show a gradual worsening as the levator muscle fatigues
  • ice pack test: apply a cold pack to the eyelid for 5 minutes (cold temp allows Ach to have more time to react with the muscle receptors), check for improvement in ptosis
  • sleep test: have the patietn take a nap in the exam chair for 30-45 minutes, check for improvement in ptosis
  • Tensilon is an IV cholinergic drug that typically shows improvement in muscle function within seconds

Treatment

  • Mestinon (cholinergic drug) and immunosuppresive therapy (neurophthalmology)
  • if medications don't eliminate ptosis/diplopia, may try prismatic corrections and ptosis crutches

Differentials
  • 3rd nerve palsy: has vertical and horizontal component
  • skew deviation: usually appears with concomitant hypertropia and other abnormal eye movements such as nystagmus
  • disease of the orbit: neoplastic, inflammatory, infectious, traumatic can cause proptosis, lid retraction, periorbital edema, conjunctival hyperemia, disc edema

Thursday, March 6, 2008

Determining Prism

Sheard's criterion
  • Prism needed = 2/3 (phoria) - 1/3 (compinsating fusional vergence)
  • eg: pt has 6 XP and BO to blur is 6, the prism needed is 2/3 (6) - 1/3 (6) = 2 BI

Percival's criterion

  • Prism needed = 1/3 (greater limit of BI or BO range) - 2/3 (lesser limit of BI or BO range)
  • eg: pt has 6 XP and BO ranges of 6/10/8 and BI range of 21/26/22, prism needed = 1/3 (21) - 2/3 (6) = 3 BI

Parks-Bielschowsky Three Step Test (for head tilts "torticollis")

  • Which eye is hyper in primay gaze?
  • In which horizontal gaze does hyperdeviation increase?
  • In which direction of head tilt does the hyperdeviation increase?
  • right hyper --> right gaze --> right tilt = LIO
  • right hyper --> right gaze --> left tilt = RIR
  • right hyper --> left gaze --> right tilt = RSO (most common cause of vertical dipl.)
  • right hyper --> left gaze --> left tilt = LSR
  • right hyper --> right gaze --> right tilt = RSR
  • right hyper --> right gaze --> left tilt = LSO (most common cause of vertical dipl.)
  • right hyper --> left gaze --> right tilt = RIR
  • right hyper --> left gaze --> left tilt = RIO

Postures and Treatments

  • Left head turn --> Right gaze preferred --> LLR or RMR paresis --> give yoked prism base left
  • Right head turn --> Left gaze preferred --> RLR or LMR paresis --> give yoked prism base right
  • Left head tilt --> Right hyperdeviation --> RSO paresis (most common cause of vertical diplopia)--> BD over right eye if longstanding
  • Right head tilt --> Left hyperdeviation --> LSO paresis (most common cause of vertical diplopia)--> BU over left eye if longstanding
  • Head tip back --> Downgaze preferred --> V-pattern exotropia or A-pattern esotropia --> BU yoked prism
  • Chin depressed --> Upgaze preferred --> A-pattern exotropia or V-pattern esotropia --> BD yoked prism

Coding Dry Eye

Ocular findings:

  • Tear film insufficiency (375.15) -- test show decreased TF; for punctal plugs diagnosis
  • Keratoconjunctivitis sicca, not specified as Sjogren's (370.33) -- observation of "inflammation of the conjunctiva and cornea, characterized by "horny"-looking tissue and excess blood in these areas"
  • Punctate keratitis (370.21)
  • Exposure keratitis (370.34)
  • Sjogren's syndrome (710.2)

Patient symptoms:

  • Eye pain (379.91) -- may be used for all levels of eye discomfort, e.g. burning/stinging
  • Redness of eyes (379.93) -- r/o episcleritis (379.01) and scleritis (379.00)
  • Epiphora (375.20) -- dry eye due to reflex tearing

Procedure diagnastic codes:

  • External ocular photography (92285) -- photos need to document the efficacy of treatment or the progression of the disease, and not just enhance the medical record or billable procedures
  • Bandage contact lenses (92070) -- covers fitting and supply of lens