Subjective refraction Flashcards
what is subjective refraction used for
subjective refraction is used for finding the spherical endpoint e.g. duochrome
others are used for closing the astigmatic interval aka correct astigmatism
best vision sphere - most positive sphere that gives the optimum level of va
+ tells us that the patient is accommodating
if patient has no astigmatism best vision sphere will be their correction - Plano is a possibility - if there is astigmatism the best vision sphere places the circle of least confusion on to the retina
circle of least confusion - circle of least confusion dioptriclally is halfway across the astigmatic interval
circle of least confusion is the halfway point across the astigmatic interval
how to close the astigmatic interval
spheres do not close the astigmatic interval
- spheres move the astigmatic interval back
+ spheres move the astigmatic interval forward
in order to close the astigmatic interval , we have to find the orientation of the astigmatism and the size of the astigmatism
step 1 - find best vision sphere
step 2 - estimate astigmatic interval
1 diopter of spherical blur = 6/18 = 2 diopter
what is the Jackson cross cylinder
The average power of the Jackson cross cylinder = 0 (mean strength)
used to refine an objective measurement
action relies on having the circle of least confusion on the retina
it won’t move with the lens 1 + 2 does not move the circle of least confusion
refine the axis
align handle with working cylinder axis
ask if letters are clearer with lens 1 or lens 2
roatate towards negative sign they have chosen
The Jackson cross cylinder is a tool used during a refraction exam to determine the amount and axis of astigmatism in an individual’s eyes. The tool consists of two cylindrical lenses with opposite signs, placed in a cross configuration.
During the exam, the person being tested looks through the Jackson cross cylinder at a chart with letters or symbols. The examiner then rotates the cross cylinder to different axes, and the person being tested is asked to compare the visual acuity at each axis. The examiner can use this information to determine the axis of astigmatism and the strength of the cylindrical lens needed to correct the astigmatism.
The Jackson cross cylinder is a valuable tool because it allows the examiner to determine both the axis and the power of astigmatism with a high degree of accuracy. This information is essential for prescribing the correct corrective lenses, such as toric contact lenses or eyeglasses with cylindrical lenses, to provide clear and comfortable vision.
what is binocular balance
presence of occluder = non naturalistic viewing
presence of occluder can act as an accomodative stimulus for the eye under the occluder
won’t be corrected
need to create naturalistic viewing systems
approx 0.75ds encourages the eye to not accommodate
relaxing the eye that has been accommodating
If your relaxing accomodation in 1 eyes you are relaxing accomodation in the other eye
