Sensory/Secondary Strabismus Flashcards
What is a secondary strabismus?
Secondary – pathology led to the development of strabismus often due to the loss of vision which disrupts fusion mechanisms and thus affects strabismus (other causes possible but due to fusion breakdown). This is why it’s also often called Sensory Strabismus.
What else might result from a secondary strabismus?
Amblyopia may be present in addition to pathological reason for reduced vision.
What is the incidence rate of secondary strabismus?
The incidence of secondary strabismus is low approximately 6.7% of all strabismus types
Secondary ET more prevalent than Secondary XT
When vision loss is congenital (Havertape et al., 2001), what is more likely; ET or XT?
Havertape et al (2001) found where vision loss was congenital - 67% esotropic - 33% exotropic despite being roughly equal at birth
What type of secondary strabismus is more common in teens/adults?
XT
What was speculated to affect the direction of deviation in a secondary strabismus?
Worth speculated that the underlying refractive error of the sound eye may influence the direction of the deviation but unsupported
What are the types of Congenital defects that can cause secondary strabismus?
- Microphthalmos (when one or both eyes are abnormally small)
- Congenital Glaucoma & Cataract
- Persistent Hyperplastic Primary Vitreous (failure of the embryological primary vitreous and hyaloid vasculature to regress)
- Retinal Dysplasia (abnormal growth and differentiation of embryonic retina. Retinal dysplasia is characterized by folds or rosettes (round clumps) of the retinal tissue)
- Optic Nerve Hypoplasia (characterized by decreased number of optic nerve axons)
What are the types of Acquired defects that can cause secondary strabismus?
- Severe blunt or penetrating eye injury
- Corneal disease
- Glaucoma
- Cataract and uncorrected aphakia (aphakic means not having a lens inside of your eye)
- Retinal detachment
- Retinoblastoma (retinal cancer)
- Optic neuropathy
What are the signs of retinoblastoma relevant to orthoptists?
Sudden onset strabismus can be presenting sign of a serious condition (13% present with a strabismus)
Patients who presented with strabismus were significantly more likely to have foveal involvement than patients who presented with leukocoria alone (P= .001). Thirty-one percent of patients had strabismus as a component of their presentation; 63% had exotropia, 23% had esotropia, and 14% had variable strabismus. The percentage of patients with strabismus increased to 66% when small angle and variable strabismus were also considered.
How do we investigate a secondary/sensory strabismus?
- Case History e.g. trauma, sudden onset, GH, BH, OH, Family History (could have a genetic condition like congenital cataracts)
- VA (very poor VA = move forward, finger count, hand wave/movement, light check)
- Corneal Reflections & CT (CR if unable to take up fixation, Hirschberg’s)
- Fundus & Media
- Measure Deviation (PCT, Hirschberg’s, Krimsky, Maddox Rod)
- OM’s – check full movements i.e. inconcomitant opposed to comitant deviation
- Potential for BSV e.g. BSV tests & PAT(?)
No potential for BSV – PODT
How do we manage a secondary/sensory strabismus?
- Refractive correction if it helps
- Ensure underlying cause treated if possible – may only be possible in some conditions
- Treat any associated amblyopia
- Manage angle of deviation
How do we assess for potential BSV in secondary/sensory strabismus?
- Use prisms to correct angle of deviation and assess BV potential (PAT?)
- Synoptophore
- Botulinum Toxin A
How do we assess for potential Diplopia in secondary/sensory strabismus?
- PODT
- Botulinum Toxin A
- PAT
What are the aims for XT surgery in secondary/sensory strabismus?
- Aim for slight overcorrection when no potential for BV
- Aim for complete correction when potential for BV
What are the aims for ET surgery in secondary/sensory strabismus?
- Aim for slight undercorrection when no potential for BV
- Aim for complete correction when potential for BV
