Summary
The overuse of tests and consultants is a common problem in medicine, and the strabismus field is no exception. This may cost the patient time, possible unwarranted exposures, and money, and it adds to the overall burden of the medical system. A properly performed history and examination should allow the targeting of tests and use of consultants to those most likely to yield useful information.
Intraoperative inspection is an important step in surgical planning, and therefore part of preoperative data gathering. Forced duction testing, including torsional forced duction, and the exaggerated traction test of the oblique muscles are performed first, along with the spring-back balance test. Inspection of muscle belly paths (especially when magnetic resonance imaging is not possible), muscle capsule, perimuscular tissues, and pulley positions is quickly performed, and may lead to adjustment of the surgical plan. In reoperations, measuring actual muscle insertion positions, with comparison to previous operative reports, provides important information about the patient’s wound healing. Other features used to diagnose stretched scar include the separation of normal tendon from sclera by an interposed segment of scar tissue, longer-than-normal tendon length, and abnormal attachment at the new insertion position.
3 The Use of Testing, Consultants, and Intraoperative Assessment
3.1 Introduction
The purpose of this short chapter is not to create a list of each laboratory or imaging study to order for each disorder that may cause strabismus. These specifics are discussed in the separate chapters on each disorder or mechanism. The aim here is to provide a systematic framework for using testing and consultants to confirm and pinpoint diagnoses, with the least expenditure of time and money for the patients. With the history and office examination already completed, the strabismologist should already have a good idea of the diagnosis and should have ruled out other diagnoses that don’t fit the history and exam. This author has seen diplopic adult patients who arrive at the office with magnetic resonance imaging (MRI) scan of the brain in hand and pages of reports from laboratory testing. The history and examination indicates divergence insufficiency esotropia due to gradual lateral rectus pulley displacement, and the only test needed is an MRI scan of the orbits with detailed coronal sections, which are lacking in the brain MRI. The patients usually express anger and frustration over the unnecessary testing and the need for a repeat test. Even worse are the monocular diplopia patients with dry eyes who have undergone brain imaging and unnecessary sensorimotor consultation.
The most useful purpose of this chapter is to steer the reader back to Chapter 2, with the discussion of the history. This is the secret to making remarkable diagnoses. Then use the art of a good sensorimotor examination and general observation of the patient. Don’t think about ordering any tests until the first two steps have been performed well and the diagnosis is already surmised.
3.2 Preoperative Testing Useful to Strabismus Surgery
3.2.1 Laboratory
Laboratory testing should be targeted, based upon suspected diagnoses. Again, order tests that make sense with the history and exam. Diplopia gradually worsening over years, and controlled with prisms, does not need urgent testing. Acute diplopia in a nondiabetic elderly patient is another matter, and an easily done sedimentation rate may pick up giant cell arteritis and prevent blindness. A quick blood glucose test could pick up undiagnosed diabetes, as described in Chapter 2. It is a disservice to the patient and any needed consultants to order a battery of useless tests, possibly exhausting the patient’s insurance benefits or finances. This creates difficulty for the consultant, who may need particular tests, which are then denied.
3.2.2 Ancillary Office Testing
3.2.2.1 Forced Duction
Forced duction testing in the office can help sort out restrictive from paralytic causes of strabismus. The technique is described below, in Section 3.6, but requires gentler technique when performed in the awake patient. Ask the patient to look into the direction being tested (to relax the antagonist muscle) and then feel for restriction.
3.2.2.2 Force Generation
Although forced duction testing is easily performed under anesthesia at the beginning of surgery, force generation testing must, of course, be done awake. It is essential in order to confirm the presence of muscle weakness or paralysis, but it may also be positive with flap tear and muscle displacements, as the muscle’s pulling force is reduced. The eye is topically anesthetized, and the conjunctiva is grasped near the limbus, with the eye resting in primary position. The patient is then asked to look into the gaze direction served by the muscle that is suspected of weakness, and the muscle strength is felt with the forceps.
3.2.2.3 Axial Length
Axial length measurement is an easily performed office test when eye muscle displacement is suspected due to globe enlargement. In older adults, previous cataract surgery may have corrected high myopia, which may have been forgotten by the patient.
3.2.2.4 Iris Angiography
Iris angiography is sometimes used to assess the anterior ciliary vessels when anterior segment ischemia is of concern with planned strabismus surgery. This is mainly a research tool.
3.2.3 Imaging
Imaging is becoming increasingly important in strabismus, due to the newer procedures being developed to correct displaced muscles and pulleys. Accurate knowledge of muscle paths becomes essential to diagnose and manage these cases. Imaging is also required to confidently diagnose cranial nerve palsies and compartmental eye muscle palsies (Chapter 4). 1
3.2.3.1 MRI of Orbits
Contrast enhancement with an orbital MRI is only needed when a lesion is suspected. If the scan is ordered to assess muscle positions and rule out possible muscle atrophy due to palsy, then contrast adds an unnecessary and uncomfortable burden to the patient.
3.2.3.2 MRI and MRA of Brain
If the history and examination lead to serious consideration of an intracranial mass lesion, then of course MRI of the brain should be ordered, with intravenous contrast. Magnetic resonance angiography (MRA) may also be helpful if a vascular etiology, such as aneurysm, is a possibility. Both orbital and intracranial imaging may be performed on the same day as a convenience to the patient. Again, if you are also requesting consultation, contact the consultant in advance to determine what tests would be helpful prior to that visit. The consultant may insist on imaging from one particular center or may require specifics that need to be requested from the radiologist.
3.2.3.3 Computed Tomography Scan of Orbits, Sinuses
Computed tomography (CT) scans are better at detecting orbital fracture and sinusitis than MRI. If either of these diagnoses is high on your list of differential diagnoses, then consider CT scan rather than MRI. The significant X-ray exposure with CT scanning should be considered, and it is best to avoid these in children unless absolutely necessary. Again, ask for the scan to be done without contrast unless a lesion is suspected. Some patients are not permitted to undergo MRI due to a pacemaker, braces, or other metallic implants, making CT scanning their only option.
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