Postoperative decompensated strabismus is a condition in which a previously well-controlled asymptomatic or intermittent strabismus becomes manifest after uncomplicated ophthalmic surgery.
Strabismus affects approximately 4% of the US population. Up to 3% of patients experience diplopia after cataract surgery, with decompensation of pre-existing strabismus accounting for 34% of 150 cases of postoperative diplopia—the most common cause—followed by refractive diplopia (8.5%) and disruption of central fusion (5%). The incidence of diplopia after cataract surgery is reported to be less than 1% 1), and decompensated strabismus is one of the most common neuro-ophthalmic visual disturbances after cataract surgery. Decompensation of pre-existing strabismus is also the most common cause of binocular diplopia after LASIK.
This condition can be prevented by thorough preoperative evaluation, and it is important to include the possibility of fusional decompensation and postoperative diplopia in informed consent.
The main mechanism of postoperative decompensated strabismus is that temporary visual blur after surgery disrupts fusion, causing previously controlled strabismus to become manifest.
Cataract surgery, LASIK, glaucoma filtration surgery, scleral buckling, pterygium surgery, and blepharoplasty can cause this condition 2).
There are risks of diplopia after cataract surgery at each stage: preoperative, intraoperative, and postoperative.
| Timing | Main Risk Factors |
|---|---|
| Preoperative | Pre-existing ocular muscle disease, previous ophthalmic surgery history, neurological or systemic diseases |
| Intraoperative | Retrobulbar/peribulbar anesthesia (higher risk of diplopia than topical anesthesia), inadvertent damage to extraocular muscles or nerves |
| Postoperative | Inflammation, cystoid macular edema, delayed muscle palsy |
Additionally, retrobulbar/peribulbar anesthesia without hyaluronidase, injection by non-ophthalmologists, and injection into the left eye increase the risk of diplopia2).
It is important to rule out thyroid eye disease and myasthenia gravis. Check for systemic symptoms such as weight changes, heat/cold intolerance, difficulty swallowing, and easy fatigability, and consider blood tests when appropriate.
The main differential diagnoses include decompensated childhood strabismus (most common), thyroid eye disease, myasthenia gravis, diabetic microvascular disease, trauma, stroke, and tumor.
If diplopia does not improve 6 months after surgery, consider referral to a strabismus specialist2).
Conservative Treatment
Observation: If symptoms are mild or transient, observation is chosen. Transient postoperative strabismus may resolve spontaneously 2).
Prism glasses (first-line): Fresnel prisms or built-in prisms can manage most cases. Dose adjustment may be needed as the deviation angle changes 2).
Occlusion therapy: Monocular occlusion with a patch, Bangerter filter, or satin tape. Used when prisms are insufficient 2).
Surgical Treatment
Indications for strabismus surgery: Considered when prism correction is not possible. Surgical procedures (e.g., recession, resection, marginal myotomy) are selected based on the amount of deviation 2).
Timing of surgery: Plan surgery after confirming stable ocular alignment for at least 4–6 months preoperatively 2).
Surgical prognosis: Generally good, but reoperation is required in 20–30% of cases.
For deviations that cannot be corrected with prisms, strabismus surgery is considered. Surgery is planned after the eye position has been stable for 4 to 6 months 2). The prognosis is generally good, but reoperation is needed in 20–30% of cases. Occlusion therapy may be used to manage double vision until surgery.
Normal binocular single vision is maintained by two processes: sensory fusion and motor fusion.
Sensory Fusion
Definition: The process by which the visual cortex integrates images of similar size, shape, and clarity formed on corresponding retinal points of each eye.
Inhibitory factors: Asymmetry in image size or clarity (due to changes in refractive error, opacity of the ocular media, or optic nerve lesions) makes fusion difficult.
Effect of aniseikonia: When the difference in image size between the two eyes is 5–7% or more, maintaining fusion becomes difficult.
Motor Fusion
Definition: The ability to adjust the eyes to a position that maintains sensory fusion. Single vision is achieved by keeping the image within Panum’s fusional area.
Panum’s fusional area: The area near the fixation point is narrow in depth, while it becomes wider peripherally. Within this area, single vision is possible even for non-corresponding points.
Inhibitory factor: When an image deviates outside Panum’s fusional area, diplopia occurs.
The following three conditions are necessary to maintain fusion.
It is not a complication of the surgery itself, but rather a temporary visual blur (e.g., refractive changes) after surgery that disrupts fusion. A latent strabismus previously controlled by fusion becomes manifest, and diplopia persists even after the visual blur resolves if fusion does not recover. Details are provided in the “Pathophysiology and Detailed Mechanism” section.
