• Refractive Surgery and Diplopia: How to Do No Harm

    Diplopia, or double vision, can manifest after any type of surgery that changes a patient’s refractive error. It may be transient and improve over time or be persistent and require treatment with prisms or strabismus surgery.

    As a clinician, you’ll need to understand the factors that can contribute to diplopia. Here are the main causes that can lead to double vision after refractive or lens surgery:

    Monovision, an intentional correction of one eye for near vision and the other for distance vision. Monovision is a widely used strategy in the presence of presbyopia. However, in patients with an underlying strabismus, this approach can cause double vision. There are a few mechanisms by which this occurs:

    1. The prolonged monovision does not allow fusion and stereopsis. For this reason, previously compensated ocular deviations may become manifest (such as intermittent exotropia or fourth nerve palsy).
    2. Monovision in patients with paralytic strabismus leads to fixation with the paretic eye. The patient may be unable to compensate for the secondary deviation.
    3. Monovision in patients with constant strabismus of one eye can lead to diplopia when fixing with the nondominant eye, due to the absence of suppression scotoma. This is known as a diplopia fixation switch.

    Failure to obtain the appropriate refraction (accommodation problems). The aimed refraction may have not considered the patient's accommodation and convergence status and caused diplopia by decompensating a previously controlled deviation. 

    For example, a failure to identify patients using over minus lenses to control an intermittent exotropia or patients using a correction over the absolute hyperopia for the control of esotropia.

    Aniseikonia, a condition in which the size of the image seen by one eye is different from that seen by the other. Aniseikonia produces double vision not because the images are in different positions but because they have different dimensions. Care should be taken when planning refractive surgery in patients with a difference of more than 4 diopters between the eyes.

    History of prisms. It is very important to know if the patient wears or has already used prisms in their glasses. In patients using prisms, refractive surgery can correct the refraction, however, the patient may still need prism lenses or future strabismus surgery. The patient needs to be aware of this before the procedure.

    Problems associated with surgery, corneal scarring or opacity, target area smaller than recommended or decentralization of the treated area.

    Strategies to Minimize or Avoid Diplopia 

    Identify the risks:

    • Specifically ask about a personal history of strabismus, orthoptic exercises or using prisms or patching. 
    • Check patient’s eyeglasses for prisms or bifocals. 
    • Perform cover/uncover and alternate cover tests at far and near distances, especially when planning monovision.

    Tip: A contact lens test can be useful to determine how these patients will respond to an optical correction at the corneal plane.

    Be careful with hyperopia treatment. Refractive surgery to correct hyperopia is less accurate and more prone to postoperative fluctuations. It is also important to understand that hyperopia is not the mirror image of myopia. While the treatment of myopia focuses on a relatively fixed target (the cycloplegic refractive error), the treatment of hyperopia has a slightly less stable target due to the variable influence of accommodation. The planned degree in refractive surgery should weigh the accommodation and convergence status of each patient. It is not enough to consider the refraction observed during the examination.

    Tips:

    • Perform the dynamic and cycloplegic refraction.
    • Observe the absolute hyperopia (minimum amount of correction necessary for threshold visual acuity) and manifest hyperopia (maximum accepted hyperopia that permits the threshold visual acuity) before cycloplegia.
    • Use cyclopentolate hydrochloride as the cycloplegic agent. 
    • Determine the maximum degree that allows the threshold visual acuity at the cycloplegic refraction. 

    When to Consider a Strabismus Specialist Evaluation

    • Patients with a history of strabismus or diplopia or with prisms currently in their glasses
    • Patients with more than a minimal phoria or with tropia with the alternate cover test (ideally with the target refraction of the surgery for far and near distances)
    • Hyperopic patients, especially those with a difference greater than 2 diopters between static and dynamic refractions
    • Patients with strabismus or history of strabismus surgery, with fusion amplitudes of less than 5 prism diopters
    • Patients with accommodative esotropia that require correction greater than their absolute hyperopia to control their deviation
    • Planned monovision

    Other Concerns

    Astigmatism and Anisometropia 

    Corneal astigmatism must be assessed by topography in monocular and binocular conditions. If there is a large difference in the astigmatism axis between the two conditions, there is a risk of diplopia, and the axis should be reassessed in the office and in surgery. 

    Patients with more than 4 D of anisometropia and good fusion, are at high risk of developing symptomatic aniseikonia.

    Is the Risk of Diplopia an Obstacle to Refractive Surgery?

    In some situations, a moderate or high risk of diplopia is not an absolute contraindication for refractive surgery. Many patients may choose to undergo refractive surgery and treat diplopia, if it occurs, with strabismus surgery. In this case, it is recommended that strabismus surgery be performed after refractive surgery. It is important to note that this option will not be successful for patients in whom diplopia is caused by iatrogenic aniseikonia or if it results from monovision.

    The Academy’s YO Info Editorial Board is collaborating with YO leaders from our subspecialty society partners and thanks the American Association for Pediatric Ophthalmology & Strabismus’ (AAPOS) YO Committee Chair, Justin D. Marsh, MD, for recommending the author for this article.  AAPOS will hold its virtual annual meeting, April 9-11.

    Julia D. Rossetto, MD

    About the author: Julia Rossetto is a research fellow in pediatric ophthalmology and strabismus at the Bascom Palmer Eye Institute in Miami. She was a fellow in the pediatric ophthalmology and strabismus and oculoplastics department at the Federal University of Sao Paulo (UNIFESP, Brazil) and holds a master’s degree and PhD in ophthalmology from UNIFESP and post-doctorate associate from the Institute Fernandes Figueira, Oswaldo Cruz Foundation (IFF-FioCruz, Rio de Janeiro). She works as a pediatric ophthalmologist at the Institute of Childcare and Pediatrics Martagão Gesteira of the Federal University of Rio de Janeiro.