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    . A 20 year old patient attends for his first eye examination. He complains that his vision is blurred in both eyes and that the blur is more noticeable for near vision than for distance vision. You find he has Snellen acuities of 6/60 right and left. With spherical correction, his acuities are 6/18 right and left.

    a) Starting from the uncorrected state, discuss how you would subjectively refract this patient using the fan and block technique (10 marks)
    b) Suggest what the patient’s refractive error might be (6 marks)
    c) Use ray diagrams to illustrate your answer where necessary (4 marks).
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    Hi,

    Depending what year you are in in your Optometry course, I hope the below helps:

    A) a) take a full optical, medical, family and drug history; particularly, find out how long he has noticed his symptoms; if very acute, ask further questions to exclude pathology.
    b) put on testing frame and adjust. Perform retinoscopy.
    c) description of refractive technique including determination of spheres [and +1 blur test as well as duochrome) - describe possible results and what you would do in response e. g. when duochrome red/green , chk with appropriate 0.25/0.50 trial lenses.
    d) determine cyls using cross-cyl to determine, first power needed, then axis. Description of logic behind responses of patient to 1 or 2 in cross-cyl technique, etc.

    B) The initial spheres brought acuity from 6/60 to 6/18; the sphere must be around +4-5 D (probs hypermetropic as near worse), in a 20 year old whose accommodation would be maximum, assuming no problems with parasympathetic innervation to cilary muscle, etc. If initial spherical correction gives acuities of 6/18 and this is the full spherical correction, then there must be a cyl of approx. 3 dioptres (you will remember that a cyl has a lesser negative impact on acuity than a sphere. Astigmatism more likely to be with-the-rule so axis closer to horizontal.

    So overall: +3.00/-3.00 X 180

    C) i) Draw a ray diagram showing potentially rays focusing behind retina (too much divergence)
    ii) A diagram showing correction with a plus lens; show how the extra convergence brought about by the plus (convex) lens, pulls the focus point forward onto the retina.

    Best Wishes
 
 
 
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