High Myopia, Astigmatism, and Visual Field Defects in Ophthalmology

Q: High Myopia, Astigmatism, and Visual Field Defects in Ophthalmology

Hello, Xin： Since the degree is a numerical value, it can have various different values. <br>The term "height" refers to a large value, so its definition can vary. <br>There is no need to be overly strict about the terminology, but it can all be referenced. <br>The physiological

Visual field concerns?

What are the definitions for high myopia, high astigmatism, and high hyperopia in terms of diopter measurements? It seems that different websites provide varying definitions.
Is the physiological blind spot located on the nasal side of the retina, meaning that the actual perceived blind spot would be on the temporal side? (For instance, damage to the nasal retina would cause a loss of vision in the temporal visual field, while damage to the temporal retina would result in a loss of vision in the nasal visual field?) What are the implications of having retinal blood vessels that are more dispersed and have a more outwardly spreading shape? Is it true that the grid lines in the Amsler grid are inherently more difficult to notice in the upper and lower sections? For individuals with nystagmus, do the grid lines in the Amsler grid appear to move? After experiencing various directions of visual field oscillation, do peripheral areas start to become blurry? Is it possible for the lines to appear to alternate between faint and bold, and does the sensation of nystagmus sometimes feel like rapid flickering lights? In the visual field map of the right eye, is the left side nasal and the right side temporal? Is it possible that within a certain range of the visual field, one can see and feel movement, but it appears significantly more blurred, which could indicate a visual field defect? Is it sometimes possible to identify areas of visual field loss during a visual field test, such as a noticeable area on the inner side where one can hardly see or feel any movement from top to bottom? Does being able to identify the area of loss indicate a more severe condition, suggesting a larger area of loss and greater sensitivity decline? If the eyes are turned inward, does that mean one would no longer perceive a defect in the inner visual field? Thank you.

Xin, 10~19 year old female. Ask Date: 2022/08/08

Dr. Gao Pilin reply Ophthalmology

Hello, Xin: Since the degree is a numerical value, it can have various different values.
The term "height" refers to a large value, so its definition can vary.
There is no need to be overly strict about the terminology, but it can all be referenced.
The physiological blind spot is located at the optic nerve position, which is on the temporal side.
Regarding the retinal blood vessels appearing more dispersed and having a shape that spreads outward, what impact could this have? -> It could indicate a retinal issue, so the condition of the retina needs to be examined.
The Amsler grid is designed to assess central vision, so peripheral vision is naturally less emphasized.
For individuals with nystagmus, does viewing the Amsler grid make the grid lines appear to move? Additionally, does the sensation of the visual field constantly swaying in various directions lead to peripheral areas becoming blurry? Or do the lines appear to fluctuate in intensity, with a sensation of rapid positional changes? -> This is possible.
The images may appear unstable due to nystagmus.
Does the oscillating sensation from nystagmus sometimes feel like lights are flickering rapidly? -> Perhaps not; it may just be the image shaking.
Regarding the visual field map for the right eye, is the left side nasal and the right side temporal? -> Yes, that is how the visual field map is structured.
Is it possible that in certain areas of the visual field, one can see objects but they appear noticeably blurrier, which could indicate a visual field defect? -> It could indicate reduced sensitivity.
Is it sometimes possible to identify areas of visual field loss during a visual field test, such as feeling a significant lack of vision and movement in a specific area from top to bottom? However, being able to identify the defect also suggests that it is more severe, indicating a larger area of loss and greater sensitivity reduction? -> Yes, this allows for an approximate assessment of the defect.
When the eyes turn inward, does it eliminate the sensation of a defect in the inner visual field? -> Yes.

Reply Date: 2022/08/08

More Info

Understanding high myopia, astigmatism, and visual field defects is crucial for managing eye health, especially for individuals with significant refractive errors. Let's break down your questions regarding these conditions.

Definitions of High Myopia, Astigmatism, and Hyperopia
1. High Myopia: Generally, myopia (nearsightedness) is classified as high when the refractive error exceeds -6.00 diopters. This level of myopia significantly increases the risk of complications such as retinal detachment, glaucoma, and cataracts.

2. High Astigmatism: Astigmatism is considered high when the cylindrical component of the prescription is greater than -2.00 diopters. This condition occurs when the cornea or lens is irregularly shaped, leading to blurred or distorted vision.

3. High Hyperopia: Hyperopia (farsightedness) is categorized as high when the refractive error exceeds +6.00 diopters. Individuals with high hyperopia may experience difficulty focusing on near objects, and they are at risk for eye strain and fatigue.

Physiological Blind Spot
The physiological blind spot, or the area of the retina where the optic nerve exits, is indeed located on the nasal side of the retina. Consequently, when there is damage to the nasal retina, it can lead to a corresponding loss of vision in the temporal visual field. This means that if the nasal retina is affected, the individual may experience a loss of vision on the temporal side, and vice versa.

Retinal Vascular Patterns
When retinal blood vessels appear more scattered and spread out, it can indicate various underlying conditions. This pattern may suggest retinal ischemia or other vascular issues that could lead to complications such as diabetic retinopathy or retinal vein occlusion. Regular monitoring and assessment by an ophthalmologist are essential to determine the significance of these findings.

Amsler Grid and Visual Perception
The Amsler grid is a tool used to detect visual distortions, particularly in individuals with macular degeneration. It is common for the lines at the edges of the grid (upper and lower) to be less noticeable due to peripheral vision limitations. Individuals with nystagmus (involuntary eye movements) may perceive the lines as moving or distorted, which can complicate their ability to assess their central vision accurately.

Nystagmus and Visual Distortion
For individuals with nystagmus, visual perception can be significantly affected. They may experience fluctuating clarity, where lines on the Amsler grid appear to move or change in intensity. This can lead to a sensation of instability in their visual field, where peripheral vision may become blurred or distorted. The perception of flickering lights may occur, but this is typically more related to the instability of the visual image rather than actual light flickering.

Visual Field Mapping
In terms of visual field mapping, the right eye's visual field does indeed extend to the left (nasal side) and the right (temporal side). If there is a defect in the visual field, it may be more pronounced in one area, indicating potential retinal or neurological issues. If a person can identify areas of visual loss during a field test, it may suggest that the defect is significant and warrants further investigation.

Eye Movement and Visual Perception
When the eyes are turned inward (converged), it may alter the perception of visual field defects. This is because the brain compensates for the eye's position, potentially masking certain visual field losses. However, this does not eliminate the underlying defect; it merely changes how it is perceived.

Conclusion
In summary, understanding the definitions and implications of high myopia, astigmatism, and hyperopia is vital for managing eye health. Regular eye examinations are essential for monitoring changes in vision and addressing any complications that may arise. If you have concerns about your vision or experience any unusual symptoms, it is crucial to consult with an eye care professional for a comprehensive evaluation and tailored management plan.

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