There are 4 techniques to modify astigmatism correction for first time wearer, please discuss all of the 4 techniques in details. 1. Reduce cylinder power and maintain spherical equivalent This option places the “circle of least confusion” of the remaining astigmatic interval on the retina, allowing for the clearest vision possible. For every 0.50D decrease of minus cylinder, the sphere must be increased -0.25D. This modification provides relatively clear vision and decreases the spatial distortion associated with the meridional magnification that occurs with high cylindrical prescription. 2. Under prescribe (undercorrect) the cylinder initially then increase cylinder power over time. This option is best tried in a trial frame with the sphere lens from the refraction in place and the axis of the cylinder set to that required. Cylinder power is added 0.25D at a time until acceptable vision is obtained without the symptoms of spatial distortion. This technique may be more successful than the spherical equivalent when one deals with corrections of large amounts of anisometropia. 3. Use the old cylinder axis and modify the cylinder power. For a patient who has had problems adapting to changes in cylinder axis, this is a very good option. Using the old cylinder axis, one performs a Jackson crossed-cylinder (JCC) power refinement and then adjusts the spherical component until the patient achieves best visual acuity. 4. Move the axis toward 90◦ or 180◦ This technique is based on the fact that adaption occurs more rapidly for cylinders that are close to axis 90◦ or 180◦. In fact, the earlier literature mentions this option frequently. Because this technique creates residual astigmatism due to obliquely crossed cylinders, it is not recommended.
Reference: Kenneth E B (1996). Refractive Management of Ametropia, Butterworth-Heinemann, pg 78
a) THERE ARE 4 TECHNIQUES TO MODIFY ASTIGMATIC CORRECTION FOR FIRST TIME WEARER, PLEASE DISCUSS ALL THE TECHNIQUES IN DETAILS
In order to reduce spatial distortion for first time wearer, there are 4 techniques to modify astigmatic correction.
The first technique is reducing the cylindrical power while maintaining the spherical equivalent. This option places the “circle of least confusion” of the remaining astigmatic interval on the retina, allowing for the clearest vision possible. For every 0.50D decrease of minus cylinder, the sphere must be increased -0.25D. This technique provides relatively clear vision and decreases the spatial distortion associated with the meridional magnification that occurs with high cylindrical prescription.
The second technique is undercorrect the cylinder initially then increase it over the time especially for anisometropia case. This option is best tried in a trial frame with the sphere lens from the refraction in place and the axis of the cylinder set to that required. Cylinder power is added 0.25D at a time until acceptable vision is obtained without the symptoms of spatial distortion. This technique may be more successful than the spherical equivalent when one deals with corrections of large amounts of anisometropia.
The third technique is using the old cylinder axis while modify the cylinder power. For a patient who has had problems adapting to changes in cylinder axis, this is a very good option. Using the old cylinder axis, one performs a Jackson crossed-cylinder (JCC) power refinement and then adjusts the spherical component until the patient achieves best visual acuity.
The last technique is move toward 90 & 180, so that adaptation can occur more rapidly. This technique is based on the fact that adaption occurs more rapidly for cylinders that are close to axis 90◦ or 180◦. In fact, the earlier literature mentions this option frequently. Because this technique creates residual astigmatism due to obliquely crossed cylinders, it is not recommended.
Reference: • Kenneth E. Brookman (1996). Refractive Management of Ametropia, Butterworth-Heinemann, page 78.
b) DISCUSS ABOUT 5 DIFFERENCES OF SYMPTOMS AND SIGNS FOR MYOPIA AND HYPEROPIA
SIGNS :
MYOPIA
1. Distant vision appear blurry 2. Good near vision 3. In high myopia, in addition to distance problems, there is also a problem for near work 4. Blurred vision can be worse at night 5. Poor school performance, which is often the first clue in young children, who rarely complain about vision problems
HYPEROPIA
1. Difficulty concentrating or focusing on nearby objects 2. Good distant vision 3. Blurred distance vision (occurs with higher amounts of hyperopia) 4. Blurred vision can be worse at night 5. Difficulty tracking from one line to the next while reading, or a tendency to read the same line over and over again
SYMPTOMS:
MYOPIA
1. Having headache caused by excessive eyestrain 2. Eyestrain due to more concentration to get the vision details 3. Scratchy or tired eyes in children 4. Squinting of eye due to too much eye strain and to receive better image 5. Placing books or objects very close to the face during reading
HYPEROPIA
1. Fatigue or headache after performing a close task such as reading 2. Eyestrain due to more concentration to get the nearer object details 3. Pulling sensation and burning eye 4. Crossed eye in children 5. Feel comfortable to hold newspaper further away from the eyes
The signs and symptoms of myopia and hyperopia The primary symptom of myopia is distance blur. Children are often unaware of difficulty in distance viewing until they compare what they can see with what one of their friends or classmates sees. It is important to differentiate constant distance blur from intermittent distance blur. Intermittent distance blur s often a symptom of accommodative infacility. Asthenopia is usually not a problem in myopia unless the myopia is accompanied by astigmatism, anisometropia, accommodative dysfunction, or a vergence disorder. Symptoms of astigmatism may include distance and near blur or asthenopia. The primary sign of myopia is reduced distance visual acuity. There is close relation between unaided distance visual acuity and amount of myopia. Unaided near visual acuity is normal in myopia unless the amount is high enough that the nearpoint test distance is beyond the patient’s far point of clear vision. In hyperopia, visual acuity is frequently unaffected but patients are often uncomfortable or exhibit functional problems if the hyperopia is not corrected. Because persons with hyperopia habitually accommodate and often have difficulty relaxing accommodation in response to plus lenses, the optometrist cannot simply perform a refraction and prescribe lenses. Visual acuity is unaffected in hyperopia if the amount of hyperopia is low or if the patient’s of accommodation is enough to neutralize the error. The effort of accommodation however may cause the patient to experience discomfort, particularly when performing near work, so that even low amount hyperopia may need to be corrected. High amount of hyperopia decrease the visual acuity, the decrease in acuity always being larger at near than at distance. High hyperopia that is not corrected at a young age can lead to unilateral or bilateral refractive amblyopia.
Reference: Kenneth E B (1996). Refractive Management of Ametropia, Butterworth-Heinemann, pg 78
There are 4 techniques to modify astigmatism correction for first time wearer, please discuss all of the 4 techniques in details.
ReplyDelete1. Reduce cylinder power and maintain spherical equivalent
This option places the “circle of least confusion” of the remaining astigmatic interval on the retina, allowing for the clearest vision possible. For every 0.50D decrease of minus cylinder, the sphere must be increased -0.25D. This modification provides relatively clear vision and decreases the spatial distortion associated with the meridional magnification that occurs with high cylindrical prescription.
2. Under prescribe (undercorrect) the cylinder initially then increase cylinder power over time.
This option is best tried in a trial frame with the sphere lens from the refraction in place and the axis of the cylinder set to that required. Cylinder power is added 0.25D at a time until acceptable vision is obtained without the symptoms of spatial distortion. This technique may be more successful than the spherical equivalent when one deals with corrections of large amounts of anisometropia.
3. Use the old cylinder axis and modify the cylinder power.
For a patient who has had problems adapting to changes in cylinder axis, this is a very good option. Using the old cylinder axis, one performs a Jackson crossed-cylinder (JCC) power refinement and then adjusts the spherical component until the patient achieves best visual acuity.
4. Move the axis toward 90◦ or 180◦
This technique is based on the fact that adaption occurs more rapidly for cylinders that are close to axis 90◦ or 180◦. In fact, the earlier literature mentions this option frequently. Because this technique creates residual astigmatism due to obliquely crossed cylinders, it is not recommended.
Reference:
Kenneth E B (1996). Refractive Management of Ametropia, Butterworth-Heinemann, pg 78
ASSIGNMENT 1
ReplyDeletea) THERE ARE 4 TECHNIQUES TO MODIFY ASTIGMATIC CORRECTION FOR FIRST TIME WEARER, PLEASE DISCUSS ALL THE TECHNIQUES IN DETAILS
In order to reduce spatial distortion for first time wearer, there are 4 techniques to modify astigmatic correction.
The first technique is reducing the cylindrical power while maintaining the spherical equivalent. This option places the “circle of least confusion” of the remaining astigmatic interval on the retina, allowing for the clearest vision possible. For every 0.50D decrease of minus cylinder, the sphere must be increased -0.25D. This technique provides relatively clear vision and decreases the spatial distortion associated with the meridional magnification that occurs with high cylindrical prescription.
The second technique is undercorrect the cylinder initially then increase it over the time especially for anisometropia case. This option is best tried in a trial frame with the sphere lens from the refraction in place and the axis of the cylinder set to that required. Cylinder power is added 0.25D at a time until acceptable vision is obtained without the symptoms of spatial distortion. This technique may be more successful than the spherical equivalent when one deals with corrections of large amounts of anisometropia.
The third technique is using the old cylinder axis while modify the cylinder power. For a patient who has had problems adapting to changes in cylinder axis, this is a very good option. Using the old cylinder axis, one performs a Jackson crossed-cylinder (JCC) power refinement and then adjusts the spherical component until the patient achieves best visual acuity.
The last technique is move toward 90 & 180, so that adaptation can occur more rapidly. This technique is based on the fact that adaption occurs more rapidly for cylinders that are close to axis 90◦ or 180◦. In fact, the earlier literature mentions this option frequently. Because this technique creates residual astigmatism due to obliquely crossed cylinders, it is not recommended.
Reference:
• Kenneth E. Brookman (1996). Refractive Management of Ametropia, Butterworth-Heinemann, page 78.
ASSIGNMENT 2
ReplyDeleteb) DISCUSS ABOUT 5 DIFFERENCES OF SYMPTOMS AND SIGNS FOR MYOPIA AND HYPEROPIA
SIGNS :
MYOPIA
1. Distant vision appear blurry
2. Good near vision
3. In high myopia, in addition to distance problems, there is also a problem for near work
4. Blurred vision can be worse at night
5. Poor school performance, which is often the first clue in young children, who rarely complain about vision problems
HYPEROPIA
1. Difficulty concentrating or focusing on nearby objects
2. Good distant vision
3. Blurred distance vision (occurs with higher amounts of hyperopia)
4. Blurred vision can be worse at night
5. Difficulty tracking from one line to the next while reading, or a tendency to read the same line over and over again
SYMPTOMS:
MYOPIA
1. Having headache caused by excessive eyestrain
2. Eyestrain due to more concentration to get the vision details
3. Scratchy or tired eyes in children
4. Squinting of eye due to too much eye strain and to receive better image
5. Placing books or objects very close to the face during reading
HYPEROPIA
1. Fatigue or headache after performing a close task such as reading
2. Eyestrain due to more concentration to get the nearer object details
3. Pulling sensation and burning eye
4. Crossed eye in children
5. Feel comfortable to hold newspaper further away from the eyes
The signs and symptoms of myopia and hyperopia
ReplyDeleteThe primary symptom of myopia is distance blur. Children are often unaware of difficulty in distance viewing until they compare what they can see with what one of their friends or classmates sees. It is important to differentiate constant distance blur from intermittent distance blur. Intermittent distance blur s often a symptom of accommodative infacility. Asthenopia is usually not a problem in myopia unless the myopia is accompanied by astigmatism, anisometropia, accommodative dysfunction, or a vergence disorder. Symptoms of astigmatism may include distance and near blur or asthenopia.
The primary sign of myopia is reduced distance visual acuity. There is close relation between unaided distance visual acuity and amount of myopia. Unaided near visual acuity is normal in myopia unless the amount is high enough that the nearpoint test distance is beyond the patient’s far point of clear vision.
In hyperopia, visual acuity is frequently unaffected but patients are often uncomfortable or exhibit functional problems if the hyperopia is not corrected. Because persons with hyperopia habitually accommodate and often have difficulty relaxing accommodation in response to plus lenses, the optometrist cannot simply perform a refraction and prescribe lenses.
Visual acuity is unaffected in hyperopia if the amount of hyperopia is low or if the patient’s of accommodation is enough to neutralize the error. The effort of accommodation however may cause the patient to experience discomfort, particularly when performing near work, so that even low amount hyperopia may need to be corrected. High amount of hyperopia decrease the visual acuity, the decrease in acuity always being larger at near than at distance. High hyperopia that is not corrected at a young age can lead to unilateral or bilateral refractive amblyopia.
Reference:
Kenneth E B (1996). Refractive Management of Ametropia, Butterworth-Heinemann, pg 78