best vision sphere fan and block Flashcards
(20 cards)
What is the Best Vision Sphere (BVS)?
The Best Vision Sphere (BVS) is the most plus or least minus spherical lens that gives the best visual acuity, typically found by adjusting the Circle of Least Confusion (CLC) onto the retina.
How do you determine the Best Vision Sphere (BVS)?
The BVS is determined by using the plus/minus technique to find the most plus or least minus spherical lens that gives the best visual acuity for the patient.
Describe the plus/minus technique used to determine the Best Vision Sphere (BVS).
Step 1: Start with the best possible correction for the patient and add +0.25 DS lenses.
Step 2: Ask the patient, “Is it clearer with the lens or without it?”
Step 3: Keep adding +0.25 DS until the patient reports no further improvement in clarity
What does BVS aim to do in astigmatic correction?
In astigmatism, BVS brings the Circle of Least Confusion (CLC) onto the retina by adjusting the spherical power, which optimizes the image clarity.
How do you measure the Best Vision Sphere when the patient’s vision improves with plus lenses?
: When the patient’s vision improves with plus lenses, you continue adding +0.25 DS lenses until their vision no longer improves, indicating that the BVS has been reached.
: What happens when the BVS is overcorrected with too many plus lenses?
If the BVS is overcorrected, the image will begin to blur due to the increase in positive power beyond the point of optimal visual acuity.
: What is the Maximum Plus to Maximum Visual Acuity (MPMVA) method?
MPMVA involves using plus lenses to relax accommodation until the visual acuity decreases by four lines. Then, reduce the fogging by 0.25 DS steps to improve vision.
How do you fog the patient’s vision in the MPMVA technique?
In the MPMVA technique, +1.00 DS is added to relax accommodation, causing a four-line reduction in visual acuity. The fogging is then progressively reduced.
Why is fogging done in the MPMVA technique?
Fogging is done to induce accommodation relaxation and provide the patient with a comfortable starting point for adjusting the lens to their optimal power.
How do you remove the fog after the MPMVA method?
After fogging with +1.00 DS, you gradually remove 0.25 DS to improve vision and find the maximum plus that gives the best visual acuity.
What is the Fan and Block Technique used for in refraction?
The Fan and Block Technique is used to determine the axis and amount of astigmatism, especially when Jackson Cross Cylinder (JCC) cannot be used.
How does the Fan and Block Technique work for astigmatism measurement?
The Fan chart helps identify the meridian with the posterior focal line of the astigmatic eye, while the Block method is used to refine the cylinder power by determining which block appears clearer.
What are the steps involved in using the Fan and Block technique?
Step 1: Use the Fan chart to locate the principal meridian of the astigmatism.
Step 2: Use the Block chart to refine the cylinder power by determining which block appears clearer.
What is the purpose of the Maddox V in conjunction with the Fan and Block technique?
The Maddox V is used to identify the principal meridians of the eye by placing the Maddox V in front of the patient and aligning the principal meridians with the fan lines.
How is the principle meridian found using the Fan and Block technique?
The principle meridian is determined by observing the alignment of the fan lines and adjusting the Maddox V until the lines are equally blurry, identifying the meridian of astigmatism.
How does the Maddox V work for determining the axis of astigmatism?
The Maddox V is rotated until the two limbs of the V appear equally blurred, indicating the correct axis of the astigmatism.
How is the Maddox V technique used in combination with Fan and Block?
The Maddox V helps to pinpoint the axis by aligning the lines with the principal meridians. Once the meridians are located, Fan and Block helps determine the cylinder power for correction.
What is the circle of least confusion (CLC) in astigmatism?
: The Circle of Least Confusion (CLC) is the point where the two focal lines of an astigmatic eye meet, and placing the BVS ensures that the CLC is positioned on the retina for optimal clarity.
Why is the BVS important for image formation in astigmatism?
The BVS is essential because it ensures that the Circle of Least Confusion (CLC) is aligned with the retina, providing the sharpest possible image for the patient with astigmatism.
How does the Maddox V help in correcting astigmatism?
The Maddox V identifies the principal meridians of the eye, allowing the clinician to refine the axis and cylinder power needed for accurate astigmatism correction.
