Strabismus Associated With Other Ocular Surgery
Refractive surgery that produces monovision, facilitating visual clarity at distance and near without optical aids (performed mainly in adults of presbyopic age; see BCSC Section 13, Refractive Surgery), can result in dissimilar sensory input to the 2 eyes. The dissimilarity can impair motor fusion, particularly in patients with marginally controlled heterophorias.
Retinal distortion due to an epiretinal membrane or after retinal detachment repair can also distort the retinal image (metamorphopsia, micropsia, or macropsia) to impair motor or sensory fusion. The diplopia rarely improves with surgery for the epiretinal membrane; fogging the eye with a translucent filter or tape (Bangerter; Ryser Optik AG, St Gallen, Switzerland) is the main treatment option.
The dragged-fovea diplopia syndrome occurs when an epiretinal membrane displaces the fovea, placing foveal fusion in conflict with peripheral fusion. Prism and alternate cover testing shows a small heterotropia corresponding to the foveal displacement. But under binocular conditions, that prism eliminates the diplopia only briefly, until a fusion movement brings the peripheral retinae back into alignment. Treatment involves fogging the eye, sometimes in combination with a small amount of prism.
Surgery for retinal detachment can lead to restricted rotations and scarring from dissection of the EOMs and the application of devices (such as a scleral buckle) required to bring about reattachment (see BCSC Section 12, Retina and Vitreous). Surgical correction of the resultant strabismus is often difficult. Consultation with a retina surgeon is recommended if removal of a scleral buckle is contemplated.
Tube shunts are another potential source of scarring and interference with ocular rotations (see BCSC Section 10, Glaucoma). Treatment may require removal, relocation, or substitution of the device, which creates a dilemma if it has been functioning well.
The EOMs can be damaged from retrobulbar injections, either by direct injury to the muscles or from toxicity of the injected material. Because of the usual site of these injections, the vertical rectus muscles are the most vulnerable.
Injection of botulinum toxin into the eyelids can result in diffusion of this substance and a transient paralyzing effect on any of the EOMs.
Laceration or inadvertent excision of an entire section of the medial rectus muscle is one of several serious ocular and orbital complications of pterygium removal or endoscopic sinus surgery. Restoration of function can be an extremely difficult surgical challenge.
Conjunctival scarring and symblepharon can also result in restrictive strabismus after pterygium surgery or other surgery or trauma involving the conjunctiva, particularly in the lateral canthal area. Treatment involves lysis or excision of the fibrotic band. The resulting defect can be managed with conjunctival recession, conjunctival transposition, or an amniotic membrane graft.
Kushner BJ, Kowal L. Diplopia after refractive surgery: occurrence and prevention. Arch Ophthalmol. 2003;121(3):315–321.
De Pool ME, Campbell JP, Broome SO, Guyton DL: The dragged-fovea diplopia syndrome. Ophthalmology. 2005;112(8):1455–1462.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.