Blindness is a complex condition that can manifest in various ways. Understanding the differences between different types of blindness is crucial for both medical professionals and individuals affected by these conditions. Two terms that are often used interchangeably but have distinct meanings are “cortical blindness” and “ocular blindness.” In this blog post, we will describe both conditions and unravel their differences.
Table of contents
What is 20/20 Vision?
Before delving deeper into ocular and cortical blindness, it’s important to understand the concept of 20/20 vision, a term often associated with optimal visual acuity.
20/20 vision is a measurement of visual acuity, which represents the clarity and sharpness of one’s vision at a standard distance. In this context, the term “20/20” means that a person can see at 20 feet what should normally be seen at that distance. It’s considered the standard for normal, healthy vision.
If you have 20/20 vision, it means that you can read the same line of letters on an eye chart at 20 feet that a person with normal vision should be able to read at that distance. The top number (20) is the test distance, and the bottom number (20) is the distance at which a person with normal vision should be able to read the same line.
However, it’s important to note that having 20/20 vision doesn’t necessarily mean you have perfect vision in all aspects. It primarily measures clarity at a distance and doesn’t account for other aspects of visual health, such as peripheral vision, color vision, or depth perception.
What is Ocular Blindness?
Ocular blindness, also known as blindness, is a condition in which an individual experiences a significant loss of vision or the complete inability to see.
It is important to note that ocular blindness is a term specifically used to describe vision loss caused by issues within the eye itself, such as damage to the retina, optic nerve, or other structures involved in the visual pathway. It does not include blindness caused by conditions or diseases that affect the brain or other parts of the visual processing system.
”Vision loss can affect people of all ages; however, most people with vision impairment and blindness are over the age of 50 years.”
Symptoms of Blindness
- Blurred vision.
- Eye pain.
- Light sensitivity.
- Difficulty focusing on objects.
- Visual distortion.
- Floaters (spots or specks in the field of vision).
- Sudden loss of central or peripheral vision.
Causes of Blindness
- Eye injuries: Eye injuries can happen during work, sports, traffic accidents, exposure to toxins, and due to pyrotechnic means. Severe eye injuries can result in blindness if they damage the eye’s critical structures.
- Infections: Some eye infections, if left untreated, can lead to vision loss.
- Cataracts: Cataract results in clouding of the eye’s natural lens.
- Diabetic retinopathy: Damage to blood vessels in the retina due to diabetes.
- Age-Related Macular Degeneration: Deterioration of the macula, affecting central vision.
What is Cortical Blindness?
Cortical blindness happens due to the brain damage which makes processing the signals sent from the eyes difficult. More specifically, it refers to the damage in the primary visual cortex. It can result in partial or complete vision loss.
Being cortically blind is often commonly labelled as cerebral visual impairment (CVI). CVI more often happens in children than adults. However, it can affect individuals of all ages.
”The eyes are able to see, but the brain cannot understand what they see.”
CVI affects 30-40% of children with visual impairments. According to the National Institutes of Health website, CVI affects 10.5% of all children with developmental impairments.
Symptoms of CVI
Symptoms of cerebral visual impairment include:
- Abnormal light response: They might be overly sensitive to light (photophobia) or appear to be unfazed by bright lights.
- Distinct color preferences: Some children with CVI may have a preference for or react strongly to certain colors, while being indifferent to others.
- Poor visual acuity.
- Visual Field Deficits: Children with CVI may have blind spots or reduced peripheral vision.
- Delayed visual response.
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How To Recognize A Child Might Have Cerebral Visual Impairment
There is no single test to diagnose CVI, and the first step is to have a comprehensive eye examination. However, there are some behaviors in children that parents or other caregivers can recognize that may signal a CVI condition.
- Unusual Visual Behaviors: Children with CVI may exhibit unusual visual behaviors such as light gazing, excessive eye rubbing, or poor eye contact. They may also have difficulty tracking objects or people with their eyes.
- Difficulty Recognizing Faces: Children with CVI might struggle to recognize familiar faces, even those of close family members.
- Preference for Certain Colors: Some children with CVI may have a preference for or react strongly to certain colors, while being indifferent to others.
- Inconsistent Visual Responses: CVI often results in inconsistent visual responses. The child may respond well in some situations and poorly in others.
- Visual Fatigue: They may become easily fatigued or overwhelmed by visual stimuli. Bright lights, complex patterns, or crowded environments might be particularly challenging for them.
- Difficulty with Visual-Motor Tasks: Children with CVI may have difficulty with tasks that require hand-eye coordination, such as reaching for an object, catching a ball, or drawing.
- Atypical Gaze Patterns: They may exhibit atypical gaze patterns, like staring at an object for an extended period or failing to fixate extraocular eye muscles on an object.
- Nystagmus: Some children with CVI may have nystagmus, which is a rhythmic, involuntary movement of the eyes.
- Difficulty in Complex Visual Tasks: Children with CVI may have trouble with tasks that require complex visual processing, such as recognizing objects in a cluttered environment or understanding spatial relationships.
- Visual Inattention: They may not pay attention to objects or people in their visual field, which can be mistaken for inattentiveness or behavioral issues.
Causes of BVI
- Stroke: Damage to the cortex resulting from a stroke.
- Traumatic Brain Injury (TBI): Head injuries that affect the brain’s visual processing centers.
- Infections: Infections like encephalitis or meningitis can damage brain tissue, including the visual processing centers.
Key Differences Between Ocular and Cortical Blindness
The primary difference between ocular blindness and cortical blindness lies in the origin of the condition. Ocular blindness originates in the eyes themselves, while cortical blindness results from damage to the brain, specifically the visual cortex.
In ocular blindness, the eyes may have structural issues or damage that impede the transmission of visual information to the brain. In cortical blindness, the eyes themselves are often structurally healthy, but the brain cannot process the visual information it receives.
Ocular blindness often has more treatment options, ranging from eyeglasses, contact lenses, and surgery to correct or improve vision. Cortical blindness, being a neurological condition, is generally more challenging to treat, and the focus is often on rehabilitation and adaptation strategies.
It’s important to note that the specific symptoms and causes may vary from one individual to another. Proper diagnosis and a multidisciplinary approach involving ophthalmologists, neurologists, rehabilitation specialists, and support networks are often essential for individuals with both ocular and cortical blindness to effectively manage their conditions and improve their quality of life.
Frequently Asked Questions
The key distinction lies in the origin of the condition. Ocular blindness results from issues with the eyes themselves, while cortical blindness is caused by damage to the brain’s visual processing centers.
Common symptoms of ocular blindness include blurred vision, eye pain, light sensitivity, difficulty focusing on objects, visual distortion, floaters, and sudden loss of central or peripheral vision. Symptoms can vary depending on the underlying eye condition.
Cortical blindness often presents as either complete or partial loss of vision. Individuals with this condition may also experience visual neglect, where they ignore or do not perceive objects or stimuli in a specific area of their visual field. Difficulty recognizing objects is another common symptom.
Providing emotional support, helping with daily tasks, and encouraging individuals to seek professional help and rehabilitation services are crucial ways to support someone with ocular or cortical blindness. Additionally, fostering a positive and inclusive environment is important in facilitating their adaptation and well-being.