W3: Near Visual acuity

Question 1

Importance of Near Vision

Answer 1

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

Question 2

Reduced Snellen Chart

Answer 2

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

Question 3

Jagear notation

Answer 3

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

Question 4

Snellen fraction

Answer 4

Distance/ smallest M unit can be read

Question 5

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

Question 6

Point spread function

Answer 6

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

Question 7

Rayleighs criteria

Answer 7

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