Written By: Dr. Sarah Mireles Jacobs
Melvin*had served honorably in the military for 30 years. Standing 6’3” with a muscular build, he carried himself with a self-assurance that put people around him at ease. You just felt safer with him by your side. After retirement, he decided to stay active by giving people rides around town via an app-based service. He liked the extra income, the casual back-and-forth conversations, and seeing the city life. Late one Saturday night, he was parked waiting for someone to order a ride when he saw a woman get accosted by two men. He jumped out of his car and rushed to her aid. When the woman ran away, the men turned their attention to Melvin. He was hit hard in the face by a fist wearing a heavy ring, and felt a sickening gush of fluid as his left eyeball ruptured open. That moment changed the way he would see for the rest of his life.
Vision is Multifaceted
When people think of having their vision tested, they usually imagine sitting in a dim room looking at a Snellen chart on a bright white screen, reading random alphabet letters as the font size gets smaller and smaller. While visual function does include visual acuity (how clearly you can see an object of a certain size from a certain distance away), it also encompasses several other capabilities. Severe ocular trauma can impact any or all facets of visual function.
Visual Acuity
The clarity of your vision depends on the optics of your eye. You need 3 things: unobstructed light entering the eye, good refraction to focus the light onto the retina, and the capacity to turn that light into nerve impulses to transmit to the brain’s visual cortex. For unobstructed light to reach the retina, the eye needs a smooth layer of tears on its surface, a healthy clear cornea, clear lens, and clear fluids (aqueous and vitreous) that allow the light to pass through. Merely permitting light into the eye is not enough, though. The light must be redirected (refracted) to reach a sharply-focused point exactly on the retina. Eyeglasses, contact lenses, or laser refractive surgery can be used to make your refraction as focused as possible. However, even the most perfectly-refracted light cannot make a damaged eye see. When the focused image falls on the retina, it needs healthy photoreceptors to translate the light into nerve impulses then transmit those signals from the eye, through the optic nerve, to the brain.
The blow to Melvin’s face caused his eye to split open in a line extending across the cornea and sclera. The compressive force pushed the lens, iris, and part of his retina out through the wound. He underwent one surgery to repair the rupture and another to place a new lens in the eye, but he still had an opaque corneal scar partially obstructing his vision, and an irregular corneal shape (astigmatism) that prevented the light from sharply focusing on his retina. His vision was a foggy, distorted blur.
Visual Field
An average person with healthy eyes has a broad swath of peripheral vision—typically 140 degrees horizontally (90 degrees temporally, 50 nasally), and 110 degrees vertically (50 degrees superiorly, 60 inferiorly). Severe eye injuries can reduce the size of the visual field (field constriction) or cause regions of the vision to be missing (scotoma). The most common sites of injury resulting in field loss are the retina and the optic nerve.
A portion of Melvin’s retina was forcibly expelled from the eye, and the retina remaining within the eye was detached. Although surgical repair of a detached retina is possible, restoring it to a normal anatomic position does not always restore vision since the connections between the retina and the optic nerve have been disrupted. The vision in the injured retinal region is often warped, dim, or blacked out. After Melvin underwent retinal detachment repair surgery, more than half of his peripheral vision was still just a dark gray shadow.
Contrast Sensitivity
Although vision is typically tested with dark black letters against a pure white background, the real world is full of low-contrast imagery. Injuries to the cornea, lens, retina, and/or optic nerve often make it more difficult to see in situations with dim lighting, faded colors, or gradients of gray. The Pelli-Robson chart is a common method for assessing impairment in contrast sensitivity.
Depth Perception
The brain relies on binocular vision for depth perception, using visual inputs from both eyes to gain a sense of distance away from objects. Because the eyes are spaced apart by about 2.5 inches, each eye delivers a slightly different view of the object you are looking at. As an object gets closer to your face, the left and right eyes get increasingly different views of it. The brain uses the differences between the two views to calculate the object’s size, surface curvature, and distance away, allowing you to perceive the object in “3D.” For any object within 20 feet, someone with intact binocular vision will have an easier sense of its position in space.
Melvin maintained excellent vision in his right eye, but the visual deficits in his injured left eye kept him from having depth perception. Pouring coffee in the morning, the cup overflowed since it was hard to see how deep he filled it. He could no longer reliably catch a ball. When he walked down stairs or stepped up onto a curb, it was hard to tell where his foot would meet the next step. If he tried to shake hands, he might reach out embarrassingly early, too late, or miss entirely.
Low Vision Services
Specially trained optometrists and ophthalmologists care for patients who have lost significant vision in one or both eyes. Adaptive technology including magnifiers, telescopic lenses, closed-circuit televisions, text-to-speech software, and task lighting can optimize the use of any residual vision. Physical/occupational therapists can help patients relearn how to do daily tasks despite visual impairment. By relying on professionals for supportive training, and using the same self-discipline that had made him an excellent soldier, Melvin relearned how to safely walk, pour coffee, and even legally drive again with his remaining good eye.
Meet the Author Dr. Sarah Mireles Jacobs
Dr. Sarah Mireles Jacobs is an Oculoplastic Reconstructive Surgeon who graduated from Mayo Clinic School of Medicine, completed Ophthalmology residency at Washington University in St Louis, then Oculoplastic Surgery fellowship at the University of Washington in Seattle. She is on faculty at the University of Alabama Birmingham Callahan Eye Hospital. Learn More About the Author.
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