Subjective Refraction- Refining Sphere Flashcards
How to refine sphere
Ask the patient to fixate on one of the letters on the lowest line of the acuity chart that they can see comfortably.
How would you ask the patient to fixate on lowest line of the chart they can see comfortably
Is that letter clearer with [place a +0.25 sphere in front of their eye] or without the lens [remove the +0.25 sphere] or about the same?
If a response is not immediately given after asking the patient if the vision is better with the +0.25 sphere what do you do?
after only a couple of seconds, remove the lens, wait a couple of seconds, then re-offer them the lens and repeat the question. Do not simply hold the lens up waiting for a decision, since the quality of the answer diminishes rapidly with time. If no response is succinctly given, it is likely that the letter remains about the same.
If the patient reports that the letter is clearer or about the same what do you do?
add the plus lens to the frame and repeat.
If the patient reports that the letter is worse with the plus lens what do you do?
do not give the plus lens. Instead, offer them a -0.25 sphere and ask them:
Is that letter better, or just smaller and darker?
If the patient immediately reports that the letter is better with a -0.25 spherical lens what do you do?
add the -0.25 sphere to the trial frame and repeat. If they report that the letter is smaller and darker, check the acuity and move onto refining the cyl. If they report that the letter is worse (even though you did not ask them this), check the acuity and move onto refining the cyl.
When refining sphere would you ever use a +/- 0.50 sphere
Using a +0.25 sphere to refine the sphere is appropriate if the acuity is 6/9 or better. If the acuity is between 6/12 and 6/18, use a +0.50 sphere, and consider using a +1.00 sphere if it is worse than 6/18.
How to avoid inducing accommodation?
When adding a plus lens: for hypermetropes, do not remove the lens from the trial frame before adding the new lens. For myopes, remove the original lens before adding the new lens
Only add a minus lens to a myope if it makes the vision better, rather than just smaller and darker
What if the vision cannot be improved?
do not panic if the acuity is poor and cannot be improved. It may be that the patient has a large cyl (a high degree of astigmatism). Therefore, move onto refining the cyl when an end point is reached, rather than persevering only with spheres in the pursuit of perfect acuity.
