W3: Near Visual acuity Flashcards

1
Q

Importance of Near Vision

A

o Detection and monitoring of ocular disease
o Presbyopia- physiological changes in near vision with age
o Assessment of functional & quality of life

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2
Q

Reduced Snellen Chart

A

o For use at specified distance only (usually 40cm or 16” (in US)
o Typically record as Snellen Fraction e.g. 6/6 at 40 cm
o Must record the distance tested
o Can correlate distance and near acuities

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3
Q

Jagear notation

A

o Near acuity recorded with a J followed by
the ‘size’ – smaller numbers indicate smaller
print sizes (J1 – J20)
o Not standardized–different sizes between
different manufacturers even with the same
‘J’ number

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4
Q

Snellen fraction

A

Distance/ smallest M unit can be read

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5
Q

Adv and Dis of Bailey Lovie, Snellen, EDTRS, continuous text. pg21

A
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6
Q

Point spread function

A

Consider if tiny light point
If visual system had perfect optics the image on the retina would be identical to the original point of light.
o The relative intensity of this point of light were plotted as a function of distance, on the retina, such a plot would look like the dashed red line.

If visual system had perfect optics the image on the retina would be identical to the original point of light.
o The relative intensity of this point of light were plotted as a function of distance, on the retina, such a plot would look like the dashed red line

o To be able to resolve two stars, images on the retina
have to be a certain distance apar

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7
Q

Rayleighs criteria

A

Two points or lines are just resolved if the peak of one point spread function lies on the first trough of the other point spread function

radians = 1.22 λ/d

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8
Q
A
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