THE CLINICAL CHALLENGE
There are a number of challenges with ectopia lentis, more commonly known as lens dislocation. The symptoms of dislocation of a patient’s natural lens or an implanted lens may vary. Patients may report immediate or gradual vision loss and may have associated large floaters or diplopia—either monocular or binocular. Depending on the etiology, the vision loss may or may not be accompanied by pain.
As such, lens dislocation becomes a part of the differential in a patient that presents with sudden loss of vision. When the lens is not in place, there is a major loss of refraction, and the eye becomes severely hyperopic, causing difficulty with distance vision. When the lens becomes partially dislocated, this is referred to as lens subluxation. A subluxated lens can also impair vision by causing irregular refractive surfaces when the lens is tilted. The lens can split the visual axis and lead to an optical defect where two or more blurred images are formed, leading to monocular diplopia.
The lens is located posterior to the iris and supported in 360° by zonules, tiny threadlike fibers, which attach the lens to the ciliary body. The tightening and relaxing of the zonules adjust the lens for near or far vision. Disruption of the zonules can lead to subluxation (partial dislocation), where the lens either hangs from the ciliary body, or dislocation, where the lens lies in the posterior segment of the eye.
Traumatic injury of the eye is the most common cause of lens dislocation. The lens usually dislocates posteriorly because the iris limits the lens’s movement anteriorly. It may float in the vitreous humor if it is tethered to intact zonules or settle onto the retina.1 However, other rare causes of anterior lens dislocation have been reported, such as a 51-year-old male with no history of eye or systemic disease who presented with painless vision loss in his right eye after vomiting for 4 hours. It was theorized that the increased neck and chest pressure from vomiting with subsequent increased intraocular pressure from the back to the front of the eye caused disruption of the zonules and led to anterior dislocation.2 The severity and location of the zonular disruption will dictate the degree of dislocation the lens will undergo anatomically. It is also worth noting that patients with connective tissue disorders, such as Ehlers-Danlos or Marfan syndrome, are at risk for lens dislocation even from minor trauma. Some conditions usually diagnosed in the pediatric years, such as homocystinuria or microspherakia (a congenitally spherical, smaller lens), also increase the risk of lens dislocation. In cases such as chronic uveitis or syphilitic uveitis, it has been theorized that the zonules become weakened by humoral and cellular effects of the disease.3
Rarely, iatrogenic trauma can cause lens dislocation (eg, after cataract surgery in 0.2% to 3% of cases).4 Intraocular lens (IOL) dislocation may be caused by asymmetric fixation, intraoperative complications, zonular weakness, inadequate capsular complex, pseudoexfoliation syndrome, myopia/increased axial length of the globe, retinitis pigmentosa, uveitis and Marfan syndrome, and other connective tissue disorders.
APPROACH/THE FOCUSED EXAM
A thorough medical history can be useful in ascertaining the underlying etiology of the vision loss along with a full ophthalmic exam. As lens dislocations seen in the emergency department (ED) are often caused by trauma, providers should perform complete primary and secondary surveys. During the secondary survey, the identification of any visual disturbance warrants further investigation.
When assessing past medical history, inquire whether the patient wears glasses or contacts and whether they were wearing them at the time of the injury in order to assess for other complicating factors such as corneal abrasions, foreign bodies, or globe rupture. Ask about history of connective tissue disorders, glaucoma, infections of eye, or any medical intervention to the eye preceding the injury. In assessing past surgical history, ask whether the patient has had any prior eye surgeries such as cataract removal, lens insertion, retinal surgery, and/or glaucoma surgery.
Note any facial swelling, ecchymosis, lacerations to the eyelid or surrounding structures. If there is significant eyelid edema, a second person may be required to help hold the eyelids open for a full examination of the eye. Note pupillary responses and extraocular movements, and complete a visual acuity test with a Snellen chart. Perform a fluorescein exam to assess for Seidel sign in globe rupture and presence of corneal abrasions. Intraocular pressures should be obtained provided there is no concern for globe rupture. These assessments may help lead to the cause of vision loss but are inadequate alone to diagnose lens dislocation. All of this is predicated on patient cooperation, because one prospective study was unable to perform visual acuity evaluation in 60% of over 300 ED patients, and is a possible issue in trauma patients presenting with pain.5
If available in the ED and if the patient can cooperate, a slit-lamp examination can aid in the diagnosis of lens dislocation. The patient’s chin should be placed on the chin rest, with the forehead touching the top band and the eyes aligned with the black markings on the side of the stabilization frame. Adjust the width of the beam and angle the slit lamp to 45° to get an adequate view of the anterior chamber. The lens can dislocate within the lens plane, posteriorly into the vitreous cavity, or, less commonly, anteriorly into the anterior segment. When examining a patient with a subluxated lens via slit-lamp biomicroscopy, the observer can usually appreciate a deep anterior chamber and phacodensis (tremulousness of the lens during eye movement), signaling instability of the zonular fibers. A subluxated lens will often, but not inevitably, dislocate.
Phakia/phakic refers to the presence of the natural lens. Pseudophakia/pseudophakic refers to the presence of an artificial lens in place of the natural lens, such as those seen after cataract surgery. The following figures show patients with a normal phakic lens (Figure 39.1A), an intraocular/implant lens (Figure 39.1B), a partially dislocated phakic (Figure 39.1C) and pseudophakic lens (Figure 39.1D).