Strabismus and the Refractive Surgery Patient

The strabismologist is often faced with one of two scenarios: the patient who has previously undergone strabismus surgery and now wants refractive surgery, or the strabismic patient who has had previous refractive surgery and now wants to be considered for strabismus surgery. With careful assessment, strabismologists can help these patients achieve the best possible visual outcomes. In this article, I touch on some of the considerations and issues that the strabismologist must address in managing the strabismus and refractive surgery patient.

Strabismus following refractive surgery may be the result of decompensation of a preexisting phoria or change in accommodative control. With new-onset strabismus, it is important to wait a minimum of 3 months, and preferably 6 months, until two consecutive measurements demonstrate stability of deviation 2 months apart, before considering strabismus surgery.

After refractive surgery, patients often experience a brief period of disruption of binocular vision. This can be the stimulus for decompensation of a phoria to a tropia. Longer periods of disruption, as experienced with surface ablation (compared with flap-based procedures), with sequential uniocular rather than binocular surgery, or with planned monovision will increase the chance of such events, and should be considered when deciding the type of refractive surgery procedure to be performed.

HYPEROPIC VERSUS MYOPIC CORRECTIONS
Hyperopic patients who have a prominent exophoria or intermittent exotropia are at risk of manifesting a full-blown exotropia after refractive surgery, as there is often an element of accommodative control that is lost when the hyperopia is corrected. The converse may be true of the young myopic patient with a high accommodative convergence-to-accommodation ratio, in whom even a small degree of over-correction may result in manifestation of an accommodative esophoria after refractive surgery. However, myopic patients with exophoria or intermittent exotropia may actually gain the accommodative stimulus required to maintain better control of their strabismus tendencies once their myopia is corrected.

The same principles applied in spectacle or contact lens management of such patients offer the potential for freedom from optical aids for the hyperope with a fully accommodative strabismus or for the patient with partially accommodative esotropia, when performed as part of a combination strategy prior to planned strabismus surgery. If this strategy can be further applied to that portion of the strabismic pediatric population that is poorly compliant or intolerant to spectacles or contact lenses, it could potentially enhance our armamentarium in the fight against avoidable amblyopia. It is my belief that this area represents tremendous potential for improving the lives of this subset of pediatric patients in the foreseeable future.

PATIENT ASSESSMENT
Awareness of strabismus as a risk of refractive surgery has increased, and screening for anomalies of ocular alignment or deviation is becoming part of the refractive surgery patient selection process. When assessing patients with a history of strabismus surgery or those who display marked phorias, the refractive surgeon must explore further. If the patient previously underwent strabismus surgery, it is important to learn the type of strabismus they had, the type of surgery that was performed, and their clinical course thereafter. Admittedly, it is not always possible to ascertain this type of history. Information regarding the frequency of phoria decompensation to tropia or intermittent manifestation of a larger angle of deviation in manifest deviations (ie, when the patient is tired or unwell) can augment appropriate counseling of patients regarding the likelihood that refractive surgery will disrupt their control mechanisms and manifest strabismus after the procedure.

Individuals who have a manifest strabismus will generally benefit from undergoing strabismus surgery before considering refractive surgery. Despite preoperative testing, some strabismus patients may experience intractable diplopia after correction of a deviation. In such cases, refractive surgery may increase awareness of their diplopia by enhancing their vision and thus be undesirable. Strabismus surgery is also associated with changes in refraction. Once vision is stabilized, treating the overall refractive error with refractive surgery maximizes the chances of optimal patient outcomes.

As an additional point of caution, patients with small angle deviations corrected by the use of prisms in spectacles may often forget or be unaware of this prismatic component of their normal correction. Routinely measuring the patient's current spectacles prior to surgery will identify any prismatic component and hopefully reduce the chances of surprise outcomes.

COUNSELING PATIENTS
Many surgeons may choose not to perform surgery in these types of patients, who undoubtedly require investment of much greater time and emotional energy and are therefore less economically rewarding. However, these conditions should not be an absolute contraindication to refractive surgery in all cases. Every patient should be assessed individually; if patients demonstrate appropriate understanding of the implications and risks of needing further medical or surgical intervention and are willing to accept those risks, it is reasonable to proceed. As ever, it is the patients who present with more than one problem whose lives we have the greatest potential to help transform.

Following the under-promise and over-deliver ethos, I generally advise strabismus patients who are considering refractive surgery to make their decisions based on the assumption that they will have a recurrence or breakdown postoperatively, and that this will require further surgical intervention. If this is an acceptable path for the patient, then I am happy for them to proceed with refractive surgery. As always, clear documentation of discussion and awareness of all relevant issues is imperative, and I often ask patients to countersign the record of discussions in the medical notes in addition to their consent form. Conversely, if the patient decides that experiencing decompensation of strabismus or needing another strabismus surgery is not acceptable, then refractive surgery may not be an appropriate option for that patient.

SURGICAL TECHNIQUE
Minor modifications to surgical techniques can reduce the risk of adverse events and maximize achievement of the desired outcomes in these patients. Strabismus surgeons commonly use corneal traction sutures to aid positioning of the eye during surgery. This technique may pose a risk to post-LASIK patients because there is a risk that the suture will go into the flap interface and potentially lift the flap. Also, as corneal traction sutures always involve suture traction and compression over the cornea, there is an increased risk of trauma and epithelial defects in post-LASIK patients. Therefore, it is best to position the sutures at the limbus and orient them so that the traction is not directly over the cornea. As with standard strabismus surgery, the surgeon should aim to keep the cornea well lubricated to reduce the risk of epithelial defects or postoperative soreness.

Saj Khan, MB, BS, FRCSEd(Ophth), is a Consultant Ophthalmic Surgeon, Centre for Sight, London. Mr. Khan has no financial interest in products or companies mentioned. He may be reached at tel: +44 1342 321 201; fax: +44 1342 325873; e-mail: skhan@centreforsight.com.