TBI linked to range of vision problems
November 28, 2012
FORT BENNING, Ga. (Nov. 28, 2012) -- Traumatic brain injuries can result in many visual problems such as binocular vision dysfunction, light sensitivity, and visual field defects. Although progress has been made in recent years, the pathophysiology of these injuries is not well understood and continues to affect soldiers in their activities of daily living.
Binocular vision is essentially how the eyes work together as a "team". Binocular vision disorders have been reported to be among the most common vision problems in traumatic brain injury patients.
The degree of binocular or accommodative dysfunction can range from mild to severe, but the effects on activities of daily living, such as reading, studying and administrative tasks, may be dramatic. Many of the issues associated with these injuries can be managed or eliminated with lenses.
Another common finding in the TBI population is photophobia or light sensitivity. Many individuals with a TBI report increased sensitivity to light, and some so severe that even normal room illumination causes considerable visual discomfort. This photosensitivity remains in absence of ocular inflammation and ocular pain: 74 percent of patients with TBI have self-reported visual complaints.
Not much was known about TBI 10 years ago, and knowledge in the healthcare realm continues to grow each day. Injuries associated with TBI can cause many issues with the visual system ranging from poor near vision to vision threatening complications.
Eyes account for about 0.10 percent of the surface area of the body, yet the injuries related to them from TBI are almost 50 times more than what would be expected. Vision is very complex and the pathways involved in the brain even more so. Pathways in the brain relating to vision aren't completely understood yet and may never be.
The neural circuitry involved to have the eyes track a moving object, fixate, focus on a near object, have the eyes align properly, and depth perception requires many brain structures working together in a coordinated and efficient manner.
When a blast or blunt trauma occurs to the head, it results in a coup contrecoup injury. This means the brain essentially becomes bruised. The head will strike an object and will suffer trauma at the point of impact (coup), then injury will also occur at the opposite side upon recoil (contrecoup). This excessive movement and bruising of the tissues leaves the possibility of extensive damage to many structures. The visual system takes up many connections and pathways in the brain, which makes it vulnerable to this type of injury.
One 2007 TBI study evaluated 50 patients with diagnosis of a TBI. Seventy-four percent of subjects complained of vision problems. Common complaints of these subjects included blurred distance vision, sensitivity to light, scotoma or field loss, bumping into objects or walls, blurred near reading, and inability to sustain reading.
In this study the incidence of binocular vision dysfunction (accommodation and convergence) was 30 percent among subjects yet the median best corrected visual acuity (distance and near) for these patients was 20/20.
With refraction and ocular health appearing normal, many of these binocular vision problems go undiagnosed. Accommodative dysfunctions are one of the most common side effects of head injuries, yet are often undetected despite causing significant interference with the comfort and efficiency of a person's ability to carry out daily activities.
Fort Benning Optometry is currently involved with two TBI studies with over $3 million in funding. These studies are focusing on eye movements shortly after a concussive event and will hopefully to lead to more quickly and accurately diagnosed TBIs.
The healthcare realm doesn't have a great objective way to tell if someone has a TBI. Healthcare providers typically depend on subjective responses from patients to make a diagnosis. With these eye-tracking studies objective measurements -- such as how the eye tracks a moving object, how the eye fixates and pupil reactions -- show very promising results in the early phases.