Asst. Prof. Dr. Rajendra Prasad for Ophthalmic Sciences
Certain principles have proven useful in the strabismus surgery, they will be presented in the form of guidelines. When properly applied to a specific case, these guidelines inteded to lead to the design of a surgical procedure that will be custom tailored to the individual and his or her strabismus problem.
Patient Evaluation :
The ophthalmologist must obtain and record a pertinent history. The following questions should be answered and the indicated tests performed and recorded during the process of patient evaluation before strabismus surgery.
History :
Why was the patient brought in for an examination?
What have the parents (Patient) noted about the eyes?
Esodeviation, Exodeviation, hyperdeviation, constant, intermittent etc.
Age of onset
Current Age
Birth weight (Premature?)
Growth of Development
Present weight
Physical mile stones
Subjective Complaints :
Diplopia (binocular, uniocular)
Oscillopsia
Asthenopia
Getting worse or better
Cosmetic problems
Family History :
Strabismus-parents, Siblings, Other
Other eye problems
Special Characteristics :
Head posture (face turn, chin elevation/depression, head tilt)
Variability of deviation
Preferred eye
Dancing eyes (Nystagmus)
Prior Treatment :
Glasses - when prescribed
prescription-bifocals/prisms etc.
Occlusion- which eye? how long? how well?
Orthoptics- types of exercises? how long? how well?
Ocular surgery- when? what was done? by whom?
Visual Acuity Testing
With an infant or a child too young to cooperate for visual acuity testing, reaction to the examiner's face, to a light, a toy and if poor vision suspected, an opticokinetic tape or drum should be observed. Teller Acuity Test is best for this age group.
An E chart or a STYCAR chart (HOTV) visual acuity test can usually be accomplished by the age of 3 years. Isolated E chart gives erroneously good vision in the presence of functional amblyopia because of the absence of the crowding phenomenon.
The grown up children and adults are tested by Snellen Acuity Chart.
Pupillary response to light is evaluated by moving a light from in front of one eye to in front of the other in reduced ambient light. A Marcus Gunn afferent pupillary defect, indicating decreased optic nerve function, can be demonstrated with this test by noting dilation of the pupil with the light shining in the eye (direct response) and constriction of the pupil when the light shines in the fellow the (consensual response).
Motor Evaluation :
Check for fixating eye, if either eye is used for fixation with free alternation or cross fixation free alternation may be present and should be recorded as such. Gross, wandering fixation may be present in the nonpreferred eye. Nystagmusm if present is noted and characterised as latent, manifest, horizontal, rotary, vertical, pendular and jerk. Frequency, amplitude, position of greater intensity, and null point should be noted.
Ocular Movements- Ductions (Monocular) and versions (binocular) should be evaluated. These should be checked in extreme diagnostic positions.
Sensory Evaluation :
Patients with any type of intermittent deviation and bifoveal or peripheral fusion should have their stereoacuity determined initially and then should be tested with the Worth four-dot test before resuming other examinations. The sensory testing is done on Synoptophore using slides for simultaneous macular perception (SMP), fusion and Stereopsis.
Bagolini straited glasses are the most physiological for testing retinal correspondence. Sensory testing is useful both preoperatively and postoperatively. The closer to normal the preoperative sensory testing is a check on surgical results and a guide to further nonsurgical treatment, which should be pursued vigorously i an undercorrection has been obtained in a potentially fusing patient.
Refraction :
In children less than 10 yeas age prolonged cycloplegic refraction under 1% atropine ointment has to be done. In children more than 10 years of age homatropine, tropicamide or cyclopentolate can be used. Fundus examinations should be done alongwith refraction.
Prism Bar Cover Testing :
Alternate prism and cover testing is carried out to measure the maximum deviation. This testing is performed at distance (6 meters) and near (13 inches), with and without glasses (if they are worn) while the patient views an accomodative target, viewing up and down by 30 degrees. PBCT should be performed in all nine diagnostic positions. Upgaze and downgaze are achieved by tilting the patient's head backward and forward. This maneuver uncovers an A or V pattern. A 10 prisms difference between upgaze and downgaze is significant for diagnosting an A pattern and a 15 prisms difference is significant for a V pattern. The double Maddox rod test is useful in the diagnosis of cyclodeviations. The 4 prisms base-out prism test may be used to uncover a scotoma in the macula of the one eye in patients with microtropia.
In blind or non-fixating eye, the Krimsky test determines the amount of prism that must be placed before the fixing eye to center the corneal light reflex in the pupil of the non-fixating eye.
Result to be Expected from Surgery
Horizontal rectus surgery for esotropia
No two procedures on the extraocular muscles will produce exactly the same results, even when proformed for the same magnitude of deviation and carried out in an identical manner. Nevertheless, it is possible to establish guidelines that can be used in planning and then carrying out successful strabismus surgery.
Single muscle procedures for esotropia __ for deviation between 10-15 prisms one medial rectus recession can be done. A single medial rectus recession is usually performed because the patient has diplopia and/or asthenopia and displays good potential for bifoveal fusion. Medial rectus recession upto 7 mm can be performed.
Two muscle surgery for esotropia __ A minimal bimedial rectus recession of 3 mm reduced an esodeviation approximately 15-20 prisms. A maximum bimedial rectus recession of 7 to 8 mm results in 50 prisms or more reduction in the esodeviation postoperatively, Slightly more effect may be obtained in infants.
Recession-Resection __ A minimum recession-resection procedure for esotropia is a 3 mm medial rectus recession and a 5 mm lateral rectus resection, which could be expected to correct 20-25 prisms of esotropia. A maximum recession-resection procedure 5mm medial rectus recession and 8 mm lateral rectus resection, corrects upto 50 prisms.
Three muscle surgery __ This should be used when the deviation is between 50-75 prisms. This maximum procedure consists of a bimedial 7 mm medial rectus recession and 8 mm resection of one lateral rectus.
Four muscle surgery __ Esotropia more than 75 prisms can be treated using this modality.
Horizontal rectus surgery for exotropia
Single muscle surgery __ No more than 15 prisms of deviation can be corrected with single muscle surgery for exotropia.
Two muscle surgery __ Bilateral recession __ A minimum bilateral lateral rectus recession of 5 mm will correct approximately 20-25 prisms. A maximum recession of 8+ mm can correct upto 50 prisms of deviation.
Recession-resection __ A minimum recession __ resection procedure for exotropia is 5 mm lateral rectus recession and 5 mm medial rectus resection. This approach will correct approximately 20-25 prisms. A maximum recession-resection of 8-10 mm recession and 8 resection of medial rectus will correct about 50 prisms exotropia.
Three muscle surgery __ This is used when the deviation is more than 75 prisms.
Four muscle surgery __ When the deviation is about 90-100 prisms four muscle surgery can be applied.
Vertical Rectus Surgery
A minimum 2.5 mm recession or resection of either the superior or inferior rectus will produce approximately 8 prisms of deviation. A maximum of 5 mm will produce upto 15 prisms of deviation. The normal maximums for recession and resection of the vertical recti can be exceeded in patients thyroid myopathy, blowout fractures, fibrosis syndrome, or previous surgery.
Surgery of the Oblique Muscles
Weakening procedures can be performed on both oblique muscles. The strengthening procedure of superior oblique should be done with caution as it can produce Brown's syndrome.
Surgery for Vertical Incommitant Horizontal
Strabismus (A and V Patterns)
If oblique muscle dysfunction is noticed they should be tackled to correct the A and V phenomenon. If oblique muscles are normal horizontal recti can be shifted __ medial rectus shifted towards the apex of A or V and lateral rectus towards open ends of A and V.
Adjustable Sutures
Indications for use of an adjustable suture are (1) restrictive strabismus in a patient with fusion potential (the patient with thyroid ophthalmopathy may be the prime example of such a patient), and (2) any strabismus in which the outcome of surgery cannot be readily predicted (including patients who had previous unsuccessful surgery).