American Academy of Ophthalmology Web Site: www.aao.org
Ophthalmic Pearls: Strabismus
Diagnosis and Treatment of Strabismus in Seniors
While everyone recognizes that special tricks are often required to examine children, unique skills are also helpful for the evaluation and management of more senior patients who have eye muscle disorders. As our population ages and life expectancy increases, ophthalmologists will need to be comfortable handling strabismus in senior citizens.
With pediatric patients, we are accustomed to parents as the caregivers and source of historical information. For a geriatric patient, however, the child is often the caregiver and may be your best source of information. When children are the patients, there are rarely ocular degenerative conditions to consider, and usually few medical problems and medications. But in seniors, the opposite is true.
In general, for pediatric patients, the mindset of the ophthalmologist is to provide lifetime treatments, such as the reversal of amblyopia. For the senior patient, attention will be focused on lifestyle treatments; for example, a simple pair of prism spectacles may allow the patient to drive again.
History: Three Key Questions
Obtaining a good history gives a jump start on the upcoming examination. It’s important to realize that many patients may not actually complain of diplopia per se but may relate a history of closing one eye to read or to watch TV. This is a tip-off that the patient may have a binocular disturbance.
Three key questions can narrow the diagnostic field considerably.
2. Is the diplopia monocular or binocular? For monocular diplopia, think about cataracts or astigmatism.
3. Is diplopia vertical or horizontal? For vertical double vision, consider common etiologies such as fourth nerve paresis and skew deviation. For horizontal diplopia, the differential diagnosis includes such entities as sixth nerve paresis, divergence palsy and convergence insufficiency. Asking whether the horizontal diplopia is worse at near or distance can further narrow the possibilities. If horizontal diplopia is worse in the distance, this usually points toward a sixth nerve palsy or divergence paresis. If the horizontal diplopia is worse at near, often the culprit is convergence insufficiency.
A good refraction needs to be performed to be sure that vision is maximized. The presence of cataracts and/or macular degeneration can threaten fusion in susceptible patients. Patients with tenuous fusion may lose their control as their vision worsens in one eye.
In seniors, despite a vigorous complaint of diplopia, there may be minimal visible strabismic deviation. These small deviations—especially vertical—can be difficult to measure. Adequate lighting in the examining room is crucial. Prolonged alternate cover testing will often elicit the strabismus, but not always. In some patients, a Maddox rod will be necessary. We have found that tiny corrections, even 1 or 2 prism diopters, will often provide significant relief. It is important to be meticulous with these measurements and to have patience when eliciting the deviation.
Red flags. In patients with new-onset strabismus or diplopia, consider more serious underlying neurological disease if there are multiple cranial nerve palsies, other neurological signs or an isolated nerve palsy in a nonvasculopathic patient. Transient diplopia can be evidence of a transient ischemic attack. New-onset nystagmus can be related to medication toxicity or brain stem pathology. Neurological consultation is warranted if these red flags arise.
Convergence insufficiency. One of the common clinical scenarios in seniors is convergence insufficiency, especially in patients with Parkinson’s disease. Common findings on examination include a remote near point of convergence and exotropia at near. Most patients can be managed with a pair of base-in prisms in their reading glasses. Also consider reducing the plus in the reading add, if possible, to move the focal point farther away. Surgical correction may be considered for those patients who also have more than 10 prism diopters of exodeviation in the distance.
Divergence paralysis. Another common source of horizontal diplopia is divergence paralysis. These patients will have sudden-onset esotropia in the distance with little or no deviation at near. The deviation is comitant (in contrast to a sixth nerve palsy). There may be a subtle limitation of abduction in both eyes. Base-out prisms are useful for these patients so they can drive. Surgery (bilateral lateral rectus resection) is also a viable alternative. Although divergence paralysis is generally a benign condition, neurological consultation should be considered if other neurological signs or symptoms are present.
Learn to love the trial frame. A trial frame is a vital tool for evaluating strabismus in seniors. Placing prisms in the phoropter is often inadequate to determine whether the correction will satisfy the patient under “real world” conditions. For example, in a patient with convergence insufficiency, we will give the patient his or her full reading prescription with prisms in the trial frame. We will have the patient read a magazine in the waiting room to be sure that he or she is happy. Once this is accomplished, we can truly assure the patient that “what you see is what you get!”
Always remember your good friend Fresnel. For seniors, especially those on a fixed budget, a pair of prism glasses can be an expensive proposition. Fresnel prisms are an inexpensive alternative, and they can be used for several months or even longer as needed. These stick-on prisms can also be a useful short-term solution for patients with ischemic-related strabismus that generally resolves over time. For example, many patients with fourth and sixth nerve paresis will require the use of a prism for a few months to alleviate their diplopia, and when their symptoms have resolved they can simply peel off the prism.
Incomitant strabismus does not preclude the use of a Fresnel prism. The prism can still be valuable to relieve diplopia in primary and reading positions.
Last, in some patients with sizable deviations who aren’t surgical candidates, a Fresnel prism can provide a potential alternative. Generally, 10 to 12 prism diopters is the maximum that can be incorporated into a pair of spectacles without inducing significant prismatic distortion. We recently saw an 86-year-old man (whose nephew is a pediatric ophthalmologist!) who had 20 prism diopters incorporated into his glasses by a local optometrist. His blurring and prismatic distortion were so great that he fell down the stairs. As he didn’t want surgery, we managed him successfully for nearly a year with a Fresnel prism. Note that higher-numbered Fresnel prisms may blur the vision slightly, but this is usually an acceptable trade-off for the diplopic patient.
Are Seniors Too Old for Surgery?
Many patients may think they are “too old” for strabismus surgery, but in fact the surgery is well-tolerated. Generally, patients with deviations greater than 10 prism diopters can be considered as surgical candidates. With advances in intraocular lens technology, we have encountered seniors who have undergone cataract surgery and enjoy excellent uncorrected visual acuity, but who suffer from small-angle strabismus (less than 10 prism diopters). This subset of patients is highly motivated for surgical correction so they can go without glasses. The adjustable suture provides an outstanding tool for accurate results.
In the OR, the use of a laryngeal mask airway often enables a quick induction and recovery from anesthesia with minimal discomfort. The conjunctiva of older patients is especially thin and requires gentle manipulation. The use of “marking sutures” to tag the ends of the conjunctival peritomy is helpful. Similarly, the muscles can be fragile, especially the inferior rectus, and careful attention should be paid to avoid excess traction. The Apt clamp (Storz) is a useful tool to hold the muscle without causing undue stress.
Fusion: Putting It All Together
Strabismus in seniors requires special skills in the ophthalmologist. After obtaining the pivotal historical points, a meticulous sensorimotor examination can identify the underlying problem. In the office, trial frames and Fresnel prisms are essential tools. In the operating room, gentle manipulation is paramount to surgical success. By alleviating diplopia, you can make the golden years truly rich for your patients.