Solving Sight #2- What Happens When the Eye Fails

Intro

Welcome back and welcome to part two of our three part series; Solving Sight! In today’s article we are going to be talking about the most common visual disorders and how they affect daily life! Since a lot of eye terminology will be used, I recommend checking out part one of the Solving Sight series, to increase your ability of comprehension for this article. Now that you know how the eye is supposed to function, let’s bring you into the world of everything that can go wrong.

Disorders

Retinitis pigmentosa: (hereditary degeneration of rod photoreceptors)

Retinitis pigmentosa (RP) is a group of inherited eye disorders characterized by the progressive degeneration of the retina, particularly affecting the rod photoreceptors — the cells responsible for vision in low light. Individuals with RP often first notice difficulty seeing at night, followed by a gradual loss of peripheral (side) vision, which can progress to tunnel vision and, in severe cases, complete blindness. Since rods are primarily responsible for night and peripheral vision, their degeneration significantly impairs visual function over time. RP is genetically diverse, with mutations in over 60 different genes identified as potential culprits. RP is especially mentioned during the documentary Pick of the Litter, a documentary on the process of guide dogs being matched with their owners. If you are like me, and LOVE dogs, I highly recommend checking it out! There’s also a TV show (on Disney) which is equally good! 

Macular degeneration: (damage to macula)

Macular degeneration is a common eye condition that primarily affects people over the age of 50, leading to progressive damage of the macula—the central portion of the retina responsible for sharp, detailed vision. This condition can severely impact daily activities such as reading, driving, and recognizing faces. There are two main types: dry (atrophic) and wet (neovascular). The dry form involves gradual thinning of the macula, while the wet form is characterized by abnormal blood vessel growth that leaks fluid or blood, causing rapid vision loss. Though macular degeneration doesn’t typically lead to complete blindness, it can cause significant central vision loss. 

Glaucoma: (optic nerve damage due to high eye pressure)

Glaucoma is a group of eye diseases that damage the optic nerve, often due to abnormally high pressure inside the eye—a condition known as intraocular pressure. This damage can lead to gradual and irreversible vision loss, starting with peripheral  vision and, if left untreated, potentially progressing to total blindness. Glaucoma typically develops without noticeable symptoms until significant vision loss has occurred. There are several types of glaucoma, with open-angle glaucoma (sharing the symptoms I just described) being the most common. 

 Cataracts: (clouding of the lens)

Cataracts are a common eye condition characterized by the clouding of the eye’s natural lens, leading to blurred or impaired vision. This cloudiness develops gradually and can make everyday activities like reading, driving, or seeing at night increasingly difficult. Cataracts are most often age-related but can also result from injury, certain medications, or underlying health conditions such as diabetes. Symptoms may include faded colors, glare or halos around lights, and the need for frequent prescription changes.

Visual aphasia 

Visual aphasia, also known as visual agnosia, is a neurological condition in which a person loses the ability to recognize or understand written words, despite having normal vision and the ability to write or speak. This condition typically results from damage to specific areas of the brain, often in the left occipital or temporal lobes, which are responsible for processing visual language. Individuals with visual aphasia may look at printed text but be unable to comprehend it, even though they can still read aloud or recognize objects and faces. This can be particularly frustrating, as the person’s eyesight remains intact, but their brain can no longer link written symbols to their meaning. Visual aphasia is most commonly caused by stroke, traumatic brain injury, or certain neurological diseases.

Myopia (nearsightedness) 

Myopia, or nearsightedness, is a refractive vision condition where objects up close appear clear, but distant objects look blurry. The main causes of this are when the eyeball is too long or the cornea is too curved, ultimately causing light to focus in front of the retina instead of directly on it. Generally, Myopia starts in your childhood years and will progress with age. Especially during school years when visual demands increase, you are constantly sitting at the back of the room having to stare at the board, or focusing on small text for homework assignments. A lot of the visual signs of Myopia are squinting, eye strain, and difficulty seeing road signs or classroom boards from a distance. Fortunately, Myopia is easily diagnosed through an eye exam and is typically corrected with glasses, contact lenses, or in rare cases, refractive surgery such as LASIK. If you are curious on how this works, stay tuned for the next article!

Hyperopia (farsightedness)

Hyperopia, or farsightedness, is also a common refractive error where objects further away are more visible than up close. The main causes are similar to those in Myopia, where it has to do with the eyeball being too short, or the cornea lacking curvature, causing light to focus behind the retina instead of directly on it. Hyperopia makes close-up tasks like reading, writing, or using a smartphone more difficult, often leading to eye strain, headaches, or blurred vision after prolonged near work. Hyperopia can be present from birth and may improve as the eyes grow. While Myopia typically starts in childhood years, Hyperopia is much more common to occur with age, hence why reading glasses are so popular, and less often seen in kids. When my brother was 6, he had glasses for visual processing disorder. Essentially, his individual eye function was fine, but they weren’t working together, causing symptoms of both Hyperopia and Myopia. The glasses were to correct the individual eye function and coordinate them to work together.

Astigmatism (distorted vision at all distances)

Astigmatism is a common vision condition caused by an irregular curvature of the cornea or lens, leading to distorted or blurred vision at all distances. Instead of having a perfectly round shape like a basketball, the eye’s surface is shaped more like a football, causing light to focus unevenly on the retina. This results in symptoms such as blurred or double vision, eye strain, headaches, and difficulty seeing clearly at night. Astigmatism can occur on its own or alongside other refractive errors like myopia or hyperopia. 

Diabetic retinopathy (Diabetic complication leading to damaged blood vessels)

 Diabetic retinopathy is a serious eye condition that can occur in people with diabetes, resulting from damage to the small blood vessels in the retina (the light-sensitive tissue at the back of the eye). High blood sugar levels over time can weaken or block these vessels, leading to leakage, swelling, or the growth of abnormal new vessels, all of which can impair vision. In its early stages, diabetic retinopathy may not cause noticeable symptoms, but as it progresses, it can lead to blurred vision, dark spots, or even complete vision loss if left untreated. This condition is one of the leading causes of blindness in adults.

Color blindness (all three types)

Color blindness, or color vision deficiency, is a condition where a person has difficulty distinguishing between certain colors, most commonly reds and greens. It occurs when the cone cells in the retina are absent, not functioning properly, or sensitive to the wrong wavelengths of light. There are three main types: red-green color blindness, which is the most common form; blue-yellow color blindness, a rarer form that affects the ability to distinguish between blues and yellows; and complete color blindness (achromatopsia), the rarest type, where individuals see only shades of gray. Color blindness is usually inherited and present from birth, although it can also be acquired later in life due to disease, injury, or certain medications. If you want to learn about your current vision spectrum, there are several tests online which provide you with a small scope of your color vision! These tests, as seen above, require you to distinguish a number from a circle, and they get progressively harder as the test goes on. In my neuroscience course last summer, we were able to use and try out the tests, resulting in a surprising color blindness diagnosis for a student!

Blindness (causes)

Blindness is the complete or nearly complete loss of vision, significantly impacting a person’s ability to carry out everyday activities. It can result from a variety of causes, including eye diseases like glaucoma, cataracts, and diabetic retinopathy; injuries to the eye or brain; infections; and genetic conditions. Age-related macular degeneration and severe refractive errors that go untreated can also lead to vision loss. In some cases, blindness occurs due to damage to the optic nerve or parts of the brain responsible for processing visual information. While some causes of blindness can be prevented or treated with timely medical care, others are irreversible.

Thank you for tuning in to part two of Solving Sight! Make sure to stick around for the final article, which touches on the solutions for these problems, and how people adapt  when faced with these conditions. As always, here’s the annual neuroscience pun!

What do you call a fish with no eyes?

Fishually impaired.

Okay, okay, I get it, that joke was really cornea, but I do hope it encouraged you to read article #5 and stay tuned for the final part in Solving Sight- the solutions and treatment options!