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Squint/Neuro-ophthalmology

Rohit Saxena1 MD, Ankur Sinha2 MD

1. Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi

2. Max Vision Eye Care Centre, Vaishali Nagar, Jaipur, Rajasthan

Tips and Tricks for Successful Outcome in Squint


Rohit SaxenaMD

The outcome of squint surgery can be very tricky in view of considerations of both anatomical allignment as well

as functional improvement.

Pre- operative factors affecting the outcome of strabismus surgery:

Assessment of Refractive status of the eye - The first step in all cases of squint is to have a full cycloplegic refraction. The cycloplegic agent to be used should be according to the age of the child (ointment atropine for children less than 5 years of age and even in older children if refracting an esotropic child for the first time, homatropine for older children). Full refractive correction (remove only the distance correction from the retinoscopic value obtained at the time of refraction) is to be prescribed. Both hypermetropia and myopia needs to be corrected (hypermetropic correction reduces the dynamic component of esotropia and myopic correction leads to accommodative convergence helping control of exophoria. Refractive correction also improves the clarity of vision stimulating fusion in divergent squints. (Figure 1a,b). However use of atropine even in the ointment form may lead to rise in temperature and fever in children less than 6 months of age, hence parents need to be well informed of same and in case of fever anti-pyretic needs to be added. If the fever is of high grade the refraction under atropine needs to be deferred till the child is around one year of age.

Assessment of visual acuity - It is essential that both the eyes should have equal vision prior to surgical intervention and amblyopia has been ruled out. If amblyopia is present then proper treatment is to be instituted (refractive correction, occlusion full time/ part time or penalization). In

children where assessment of visual acuity is difficult, free alternation of the deviation shows absence of amblyopia. Alternatively covering of either eye can show presence of amblyopia. (Figure 2). The advantages of giving amblyopia

Figure 1 (a,b): Accommodative esotropia showing full correction of the deviation with glasses.

30 l DOS Times - Vol. 19, No. 6 December, 2013


therapy prior to surgery are that in small children it is easier to assess for equalization of visual acuity by using free alternation as the end point of amblyopia therapy as it is difficult to measure visual acuity in small children. Also younger the child more successful and faster is amblyopia therapy. It is very important to treat amblyopia before the surgical intervention as firstly, it keeps the parents motivated to complete the amblyopia therapy, secondly a good binocular visual acuity has a chance for the patient to develop peripheral fusion, which may keep the alignment permanent.

Assessment of fundus–This is a very important part of examination, it is imperetive to look for cause of poor vision

and to ensure that the fundus is normal before diagnosing amblyopia. Unnecessary occlusion therapy in the presence of obvious organic pathology explaining sub-normal vision should be avoided. The fixation pattern also needs to be evaluated. It can be assessed using the fixation star of the direct ophthalmoscope. Presence of eccentric fixation may be a contra-indication for conventional occlusion therapy. In very young children indirect ophthalmosope may be a good instrument to look at the gross view of fundus and to rule out retinal pathology

Assessment of head posture: Assess the head posture of the child as he/she comes to the clinic or when the child is playing. This needs to be assessed at the presentation when

Figure 2(a): LCS with Left amblyopia. Child is comfortable on covering of the left eye but strongly resists the covering of the right eye showing the left eye to be amblyopic.

Figure 2(b): Intermittent Divergent squint showing improvement in fusional control of the deviation with glasses.



the child is looking at the vision chart and is unaware of his/her head d posture, as later the child may get conscious and may correct the head posture. A mild head tilt in superior oblique palsy can easily be overlooked and unless it is corrected, a SO palsy can be missed (Figure 3).

Assessment of deviation - Proper evaluation of deviation should be done using corneal light reflex (Figure 4), PBCT or synaptophore,with and without proper refractive correction. The difference between the two readings gives

Figure 3: Left head tilt in a case of Right superior oblique palsy. Head posture is also seen in paralytic

squint, restrictive squint, nystagmus and A-V pattern

Figure 4: Hirschberg corneal reflex test: It is performed by shining a light on the eyes and observing the reflection. In normal ocular alignment the light reflex lies slightly nasal from the centre of the cornea. During the test, compare the light reflexes of both eyes for symmetry. The child below has an appearance of squint from a distance but on closer inspection

the light reflex is falling on symmetrically on both corneas and so the child has a Pseudo-esotropia or false squint.

us the dynamic component of the squint, which should not be addressed to in surgical dosage. After proper refractive correction for the distance is given then PBCT should be performed for distance using accommodative target i.e. 6/9 Snellen’s target for distance and accommodative target for near.

Assessment of ocular motility- Motility in all direction, versions and ductions to be carefully examined (Figure 5) and all 9 gazes should be evaluated to look for presence of overaction of obliques and A or V phenomenon (Figure 6a & 6b), which have to be operated in the same sitting. In cases of paralytic squint it gives idea about the muscle function. In adults often an assessment of saccadic velocity is possible in more experienced hands

Assessment of binocularity and stereopsis – Presence of binocularity or stereopsis is a good prognostic factor for the management of strabismus. Falling stereopsis may point towards poor control of intermittent exotropia and is an indication for surgery. A simple “worth four dot test” may give us a clue towards binocularity and “two pencil test” may help us assess the gross stereopsis for near.

Assessment of stability/variability of deviation – In cases of paralytic squint at least 2-3 monthly follow up should

Table 1: Minimum and maximum recession of various recti muscle from their respective site of insertions1

S.No. Muscle Minimum limit of recession (mm)

Maximum limit of recession (mm)

1 Medial Rectus 2.5-3.0 5.0-5.5

2 Lateral Rectus 4 8.0-9.0

3 Superior Rectus 2.5-3.0 5.0

4 Inferior Rectus 2.5-3.0 5.0

Table 2: Minimum and maximum resection of various recti muscle1

S No. Muscle Minimum limit of recession (mm)

Maximum limit of recession (mm)

1 Medial Rectus 3.0 6.0

2 Lateral Rectus 4.5 9.0

3 Superior Rectus 2.5-3.0 5.0

4 Inferior Rectus 2.5-3.0 5.0



Figure 5: Check for both version and duction. The child appears to have bilateral lateral rectus palsy as the eyes are not abducting. But on uniocular motility examination the eyes abduct fully. The child was using cross fixation and that gave the appearance of a palsy.

Figure 6a: The 9 gaze examination shows an exodeviation in primary gaze along with a “V” pattern. In the tertiary positions of gaze we can see the presence of bilateral IOOA. We need to

operate the Inferior obliques along with the horizontal recti.



be done and once the follow up deviations are stable surgery may be planned. Increase of eso-deviation without glasses suggests improper refractive correction or non accommodative component of squint. As stressed earlier, proper refractive correction is the key to differentiate the two. Increase in eso-deviation for near may suggest high AC/A ratio (bifocals may be needed as treatment, do not operate for it).

Assessment of muscle function, forced duction test and force generation test (FDT/ AFGT)2– The contracture in cases of long standing, paralytic and restrictive strabismus may need to be freed during the surgery. Forced Duction Test (FDT) should be performed in the direction of underaction of muscle (for recti lift the globe in FDT, while for obliques push the globe in). For Active Force Generation

Figure 7: Palpabral fissure changes are observed after a large recession –resection procedure is done in one eye.

Figure 6b: The 9 gaze examination shows an exodeviation in primary gaze along with an “A” pattern. In the tertiary positions of gaze we can see the presence of bilateral SOOA. We need to weaken the superior obliques along with the horizontal recti.

Test (AFGT) ask the patient to look in the direction of the action of muscle and feel the tuck (force) generated by the muscle.

While planning for surgery use standard nomograms available in textbooks. Always be consistent in the surgical steps so that predictability is there in the surgery. Modification of the surgical doses to suit your results can be done as one gets more experienced. Do not resect or recess the recti muscle more than the recommended values (Table 1&2) else significant palpabral fissure changes are observed (Figure 7) or there is significant limitation of movement.

Intra-operative factors3

1. Use microscope during the surgery as better visualization helps in preventing complications

2. Vasoconstrictor drops like Naphazolin should be used as these drops significantly reduce the intraoperative bleed and keep the surgical area clean.

3. Clean and smooth incision of conjunctiva is a prerequisite for good surgical outcome. In cases where fornix incision is used, try and avoid extension to the caruncle.

4. The dissection around the muscles should be sharp and clean, do not strip the muscle or use blunt dissection. The muscle sheath should not be breached as this can lead to fibrosis and contracture around the muscle.

5. Cautery may be used to coagulate the bleeders, however it should be minimally used as its excessive use can lead to fibrosis.

6. As the insertion of the muscle is C shaped, the measurement of recession or resection should be done



from either ends, else there the surgery done would be less than planned leading to less correction then desired.

7. One should be careful while passing the sutures through the sclera. One should be more careful in cases of anisomyopia or high myopia where the sclera is thin and can lead to inadvertent perforation. Always keep an eye on the tip of the needle to avoid inadvertent perforations

8. In cases where the perforation has occurred or suspected, put the pressure on the globe with a cotton swab, so that the bleed if sub retinal does not enlarge and goes below the fovea. Following which ensure that the IOP is maintained, in this case one can carry on with the surgical plan, however pupil need to be dilated and post surgery indirect Ophthalmoscopy and if needed laser delimitation (using laser indirect ophthalmoscope, preferred modality) or cryo should be applied to prevent retinal complication. In cases where the IOP is low due to the perforation the surgery may need to be abandoned and reassessment should

be done later in the follow up, the pupil needs to be dilated and laser (preferred) or cryo should done.

9. Try to have the insertion as wide as the original, while recessing the muscle keep the recession directly behind the previous insertion unless a supra or infraplacement of the muscle is planned.

10. At the end of the surgery end to end closure of conjunctiva to be performed and care should be takes so that there is no tenon prolapse.

11. In the post-operative course steroid and antibiotic drops should be used 4-6 times a day which may be tapered over 4-6 weeks.

References

1. Kenneth W. Wright Color Atlas of Strabismus Surgery: Strategies and Techniques. Springer. Am Orthopt J. 2007;57:145-7.

2. Gunter K. von Noorden, Emilio C. Campos. Mosby Binocular Vision and Ocular Motility: Theory and Management of Strabismus, 6th edition. Am Orthopt J. 2001;51:161-2.

3. Parks MM, Mitchell P: Concomitant exodeviations. In Duane TD ed: Clinical Ophthalmology, Vol 1. Philadelphia, JB Lippincott, 1988.

squint/neuro-ophthalmology tips and tricks for … · www. dosonline.org l 31...

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