Content Reviewers:Antonella Melani, MD, Lisa Miklush, PhD, RNC, CNS, Ashley Mauldin MSN, APRN, FNP-BC, Viviana Popa, MD, Gabrielle Proper, RN, BScN, MN
Legal blindness is defined as having a central visual acuity of 20/200 or less in the better-seeing eye, or having a peripheral visual field of 20 degrees or less. So, many people who are legally blind in some sense can still see, but they have severe visual impairment.
First, let’s quickly review the physiology of vision. Okay, now, the visual pathways begin in the eye. If we zoom into the wall of the eye, there's an outer fibrous layer, which contains the cornea and sclera, and helps control and focus the entry of light. So the light that passes through the cornea is directed to the lens, which in turn collects light arrays and focuses them into the retina at the back of the eye. The retina houses photoreceptors that translate light into electrical impulses, which are then carried by the optic nerve into the visual cortex of the brain. Finally, the visual cortex processes the impulses coming from both eyes, and fuses them into one clear image.
Now, common causes of legal blindness include eye conditions like cataracts, age-related macular degeneration, glaucoma, diabetic retinopathy, eye infections like trachoma, or it can be congenital. Lastly, the cause of legal blindness may also be idiopathic or unknown. Risk factors for legal blindness include being assigned female at birth or over the age of 50, as well as having a systemic disease like diabetes mellitus, or undergoing eye surgery.
Okay, so the pathology of legal blindness can have two main origins. On the one hand, it can originate from abnormalities or damage involving a structure within the eye, such as the lens or retina. If any of these structures isn’t properly functioning, the eye is not able to perceive light and images, and thus fails to translate it to electrical impulses for the brain.
On the other hand, the eye might be fine, but a part of the central nervous system, such as the optic nerve or the brain, can be affected. As a result, either the optic nerve is unable to carry the electrical impulses from the eye to the brain; or the brain isn’t able to process the impulses into images. Ultimately, regardless of the origin, the outcome is the same, meaning vision loss.
Additionally, vision loss can also lead to circadian rhythm disorders, such as non-24 hour sleep-wake disorder. This means that, in the absence of visual cues of light and dark, individuals are unable to maintain a relatively regular sleeping pattern, so they gradually go to sleep and wake up at later times throughout the day, until their sleep times eventually go all the way around the clock.
Typically, the clinical manifestations of legal blindness include blurred or cloudy vision; the inability to see shapes; tunnel vision or seeing only shadows; as well as seeing wavy spots in the center of vision, and even difficulty seeing colors. In addition, clients may experience poor night vision, and in severe cases, even complete blindness.
Diagnosis of legal blindness begins with the client’s history and physical assessment. This includes visual acuity testing, using the Snellen eye chart. Other tests include perimetry or visual field testing to measure all areas of the client’s eyesight, including peripheral vision; as well as tonometry to check the intraocular pressure; dilated-pupil fundus examination and fundoscopy; and color vision testing.
Treatment of legal blindness typically includes addressing the underlying cause, when possible. In addition, clients are often monitored with routine comprehensive eye exams. Low vision rehabilitation is typically recommended to learn techniques to perform daily tasks with their visual acuity and may include glasses or contacts, magnification devices, and assistive technology.
Alright, let’s look at the nursing care you’ll provide for a client with legal blindness. Your nursing goals are to maintain the safety of your client and provide supportive care.