Visual Field Loss: Key Questions and Insights

Q: Visual Field Loss: Key Questions and Insights

Hello, Xin： Is a visual field defect of 18.14 dB indicative of a total decrease in sensitivity within a 30-degree central visual field? -> Yes, it is possible that there are certain areas where light points are completely unperceived. <br>It may also be that many areas cannot det

Visual field issues

Hello, is a visual field defect of 18.14 dB indicative of a total decrease in sensitivity within a 30-degree central visual field? It is possible that there are areas where light points are completely unperceived.
There may also be many areas where smaller, weaker light points are not perceived, but brighter light points can still be detected, although with reduced sensitivity compared to normal vision, resulting in the accumulated value, correct?
Additionally, the Amsler grid test assesses the visual field within 10 degrees; if the visual field within 10 degrees is normal, there should be no abnormalities when viewing the grid, right? Furthermore, if there are several instances during the visual field test where the patient does not respond or press the button, will this affect the test results? Or is it acceptable as long as it is not too many times?
Does the inability to perceive light points during the visual field test indicate a visual field defect? Is it true that within a normal 30-degree visual field, one can perceive stationary objects and distinguish colors? Beyond 30 degrees, does one need moving objects to perceive them, and is color distinction more challenging?
If the visual field defect is located medially, but the eyes are habitually turned slightly inward, is it less likely to notice the defect? If the eyes are habitually turned slightly inward, does this make it more difficult to notice objects on the outer side, but does not necessarily indicate a defect in that area?
In general, do people tend to turn their eyes towards areas with a larger visual field? For example, if there is less defect in the outer visual field or if the defect is only peripheral, do they prefer to look outward? However, if focusing while turning the eyes outward is difficult, even with a more severe defect in the inner visual field, will they still look inward because it is clearer and requires less effort?
If the prescription for glasses is adequate, and wearing glasses allows one to see without needing to get too close, why is there still an unconscious tendency to look without the lenses, with the eyes turning inward and upward to see things up close? Is this because looking without glasses requires less accommodation? Or is it due to nystagmus, making it easier to focus on nearby objects, while focusing on distant objects becomes more challenging?
Is nystagmus characterized by noticeable, small, rapid back-and-forth movements and rotations of the eyeball, without any angle appearing to slow down, even in severe cases? Does nystagmus cause visual field instability? Thank you for your response.

Xin, 10~19 year old female. Ask Date: 2022/05/24

Dr. Gao Pilin reply Ophthalmology

Hello, Xin: Is a visual field defect of 18.14 dB indicative of a total decrease in sensitivity within a 30-degree central visual field? -> Yes, it is possible that there are certain areas where light points are completely unperceived.
It may also be that many areas cannot detect smaller, weaker light points, but can still perceive brighter light points, although they are less sensitive compared to a normal visual field, resulting in the accumulated value, correct? -> Yes, that is an average value.
Additionally, the Amsler grid test assesses the visual field within 10 degrees; if the visual field within 10 degrees is normal, there should be no abnormalities when viewing the grid, correct? -> The Amsler grid test evaluates the condition of the central visual field.
As for whether it is precisely 10 degrees, that is not so accurate.
Furthermore, if there are several instances during the visual field test where the patient does not respond or press the button, will that affect the test results? Or as long as it’s not too many times, it won’t have an impact? -> It should not be too many times, as it may lead to repeated occurrences.
If there are light points that cannot be perceived during the visual field test, does that indicate a visual field defect? -> Yes, it indicates insensitivity.
The degree of sensitivity reduction corresponds to the severity of the visual field defect.
Is it true that within a normal 30-degree visual field, one can perceive stationary objects and distinguish colors? Outside of 30 degrees, does one need moving objects to perceive them, and is color discrimination more difficult? -> The further out, the less sensitive one may be, making it harder to discern objects and colors.
If the visual field defect is located inward but the eyes are habitually turned slightly inward, is it less likely to notice the defect? If the eyes are habitually turned slightly inward, does that make it harder to notice objects in the outer field, but does not necessarily indicate a defect in the outer field? -> As long as the eyes are turned, one may not notice because they are using the central vision.
Generally, do people tend to turn their eyes towards a wider visual angle to see things? For example, if there is less defect in the outer visual field or if the defect is only in the periphery, do they usually prefer to look outward? -> People primarily use their central vision to see; peripheral vision is just for sensing.
However, if focusing while turning the eyes outward is difficult, even if there is a more severe defect in the inner visual field, one will still look inward because it is clearer and requires less effort? -> Vision is primarily through central vision, not peripheral vision.
If the prescription is adequate, wearing glasses allows one to see without needing to be so close, but there is still an unconscious tendency to look without the lenses, turning the eyes inward and upward to see things up close, because viewing without glasses requires less adjustment.
Is it also due to nystagmus, where focusing on close objects is easier, while distant objects are harder to focus on? -> It may be that viewing without glasses feels more comfortable and habitual.
Perhaps this way of seeing minimizes the tremors.
Is nystagmus visibly apparent, showing small, rapid back-and-forth movements and rotations of the eyeball, with no angle appearing to slow down even in severe cases of nystagmus? Does nystagmus cause visual instability? -> Sometimes, there may be an angle where the tremors are less pronounced; one can try to find that angle for more stable images.
Nystagmus will definitely cause visual instability due to the shaking.

Reply Date: 2022/05/24

More Info

Understanding visual field loss is crucial for diagnosing and managing various ocular conditions. Your inquiry touches on several important aspects of visual field sensitivity and the implications of visual field loss, particularly in relation to measurements like decibels (dB) and the functionality of visual tests such as the Amsler grid.

1. Visual Field Sensitivity and Decibel Measurement: A measurement of 18.14 dB indicates a significant reduction in sensitivity within a specific area of your visual field. This means that certain areas may not perceive light at all, while others may only detect brighter stimuli. The decibel scale is logarithmic, so a decrease in dB corresponds to a substantial increase in the threshold of light required for detection. This can indeed accumulate from multiple areas of reduced sensitivity, leading to a composite score that reflects overall visual field performance.

2. Amsler Grid Testing: The Amsler grid primarily assesses the central 10 degrees of vision. If your central vision appears normal when using the grid, it suggests that there are no significant distortions or scotomas (blind spots) in that area. However, it is essential to understand that this test is limited to central vision and does not provide a complete picture of peripheral visual field loss.

3. Impact of Response During Visual Field Testing: If you miss responding to certain stimuli during a visual field test, it can affect the accuracy of the results. However, a few missed responses typically do not invalidate the entire test. Consistency and attentiveness during the test are crucial for obtaining reliable data. If you are frequently missing responses, it may indicate fatigue or difficulty concentrating, which could skew the results.

4. Detection of Visual Field Loss: The inability to perceive light in specific areas during a visual field test does indicate a loss of vision in those regions. Normal visual function within 30 degrees should allow for the perception of stationary objects and color. Beyond this range, movement is often necessary to detect objects, and color perception may diminish.

5. Eye Position and Perception of Visual Field Loss: If your eyes habitually turn inward, you may be less aware of visual field loss in the outer regions. This is because your focus is naturally directed toward the center, potentially masking peripheral deficits. People often adjust their gaze to maximize their visual field, favoring areas with less impairment.

6. Visual Habits and Eye Strain: The tendency to look closely at objects without glasses may stem from a desire to reduce the effort needed for focusing. This behavior can be exacerbated by conditions like nystagmus (involuntary eye movement), which can make distant focusing more challenging. Nystagmus can indeed cause visual instability, leading to difficulties in maintaining a clear image.

7. Nystagmus and Visual Stability: Nystagmus is characterized by rapid, involuntary movements of the eyes, which can disrupt visual stability and clarity. Individuals with nystagmus may experience challenges in maintaining focus on stationary objects, leading to a perception of blurred or unstable vision.

In summary, visual field loss can manifest in various ways, and understanding the nuances of your symptoms is vital for effective management. If you are experiencing significant changes in your vision, it is essential to consult with an eye care professional for a comprehensive evaluation. They can provide tailored recommendations based on your specific condition, including potential treatments or interventions to help manage your symptoms and improve your quality of life. Regular monitoring and follow-up are crucial, especially if you notice any progression in your visual field loss or associated symptoms.

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