Week 8 - Strabismus Surgery Flashcards
Surgical principles:
• Only operate when:
- Conservative treatment ineffective
- Conservative treatment cannot succeed
• Conservative options:
- Do nothing
- Occlusion
- Spectacles
- Prisms
- Botox
• Aims of surgery are:
- Straighten the eye : functional or cosmetic
- Restore/maintain concomitance
- Relieve symptoms
• Minimal number of procedures
• Reversible surgery if possible
Muscle weakening
• Weaken muscles but DO NOT cause limitation of movement
• Recession commonest
• Hangback and /or conjuctival recession to augment
Posterior fixation suture - Faden
• Muscle tethered to the globe
•12-14mm posterior to insertion
• Little effect in the primary position
• Weakens the muscle progressively as eye moves
Muscle strengthening
• Muscle is shortened (resection)
• Therefore more powerful
• Maintains action through point of insertion
• Avoid mechanical limitations
Unilateral vs bilateral surgery
• Tends to be unilateral for most horizontal strabismus
• Convergence excess
• True distance exotropia
Vertical muscles:
• Inferior Oblique
• Superior Oblique
INFERIOR OBLIQUE surgery indications
• Surgery on the inferior oblique muscle is virtually always undertaken to weaken it.
The most common indications are:
• Primary IO overaction
• Secondary due to ipsilateral superior oblique weakness
• IOOA in association with dissociated vertical deviation (DVD)
IO weakening:
• Disinsertion (MOST COMMON)
• Recession
• Myectomy (seldom done)
• Anteropositioning
IO Recession types:
Re-attach the muscle to the sclera at a pre-determined point depending on the amount of recession
• Parks (point A) described the point of reattachment at 2 mm lateral and 3 mm posterior to the lateral border of the inferior rectus insertion equating to approximately 10mm of recession
•Fink (point B) reattached the IO at a point 6mm below and 6mm posterior to the lower border of the LB (LR) insertion equating to арргохmately 8mm of recession
Superior oblique insertion
• The insertion is quite variable but the
SO usually inserts under the SR muscle, posteriorly on the globe. The insertion is broad as the tendon spreads out at the distal end.
• The angle between the trochlea and insertion is about 50. When the eye is looking straight ahead the SO functions as an incyclotorsion muscle. When the eye is adducted by 50, the SO acts as a depressor of the eye.
Latrogenic causes mechanical restriction:
• Retinal detachment surgery
• Glaucoma surgery - especially valves
• Ocular oncology surgery / radiation
• Cataract surgery
• Trauma
Why do people get surgery?
• First described in 1941
• May improve accuracy of alignment
• Position of muscles changed postoperatively
• Improves the chance to maintain alignment
• Patient should be alert and co-operative
• Able to fixate on an accommodative target
• Measurements should be obtained not only in primary gaze but on left and right gaze
Successful adjustment surgery:
• Deviation > near = medial rectus
• Deviation > distance = lateral rectus
• Position field of BSV centrally and below midline
• In secondary exo could restrict abduction of squinting eye
• Leave vertical under corrected especially with TED and IV
• Adjust in stages
• Ensure cosmetically acceptable before tying off
Botulinum Toxin
• Temporarily paralyses the muscle injected
• Reduces the angle of the squint, allows assessment of risk of diplopia post op
• Pts who have a risk on orthoptic testing may not necessarily have diplopia when their eye is straightened with BT
What does surgery do + types of surgery:
• Surgery alters muscle balance around one of three axes of rotation
• Changes in position of insertion or muscle length results in change in magnitude or direction of force
3 main types of surgery:
• Weakening
• Strengthening
• Transposition
