• Unaided VA
  • Cover test (ask them to look at letter on worst line, or line above if both same) – record either exo/eso phoria, tropia or NMD & recovery
  • Prelims (fields, Hirschberg/kappa, motility, pupils)
  • PD
  • Fit trial frames
  • Do pinhole if necessary
  • Retinoscopy – dim lights, put in working distance at back, check that there is against movement in LE before starting RE, if necessary add more plus but REMEMBER to REMOVE this once done with RE
  • Take out working distance, check VA on Snellen one eye at a time
  • ONLY DO BEST SPHERE WITH F&B – do F&B with harder cyl
  • F&B – occlude other eye, take out cyl from ret. & put in fogging (half estimated cyl + 0.50DS – half estimated cyl is part of Rx!)

Ask them to look at fan & point to clearest line (= axis) “Are two limbs of V equally blurred?” “Which block of lines is clearer?”

Start off by putting estimated cyl in at that axis, if block that is clear is same as before, need more negative cyl & if other block is clearer, need more positive cyl. Remember to compensate for every -0.50DC give +0.25DS

When both blocks & all lines appear equal, hold +0.50DS over as a check – everything should still be equal

Now check VA on Snellen chart – remove +0.50DS from fogging slowly (want to push the plus)

  • Now do +1.00 & duochrome, & write final result
  • Cross Cyl – make sure eye is on green on duochrome! Take out after

Leave cyl in & turn on bright circles/drum – ask them to focus on inner circle

Find axis first – hold handle at axis of cyl & twirl “Is the circle clearer, blacker & rounder with lens 1 or lens 2?” – & move the axis towards the -0.25 (negative) – repeat until “about equal”

Now find power – align markings of power on cross cyl with axis & ask “is the circle clearer blacker & rounder with lens 3 or lens 4?” – repeat until about equal

Check VA & optimise sphere (with cyl in)

Do +1.00 & duochrome, & write the final result

  • Binocular Balancing – HIC: fog one eye with +0.75DS & do best sphere on the other eye – exactly the same as BS “do you prefer it with this lens or without/is it easier to read with this lens or without?”

Switch eyes & do the same

Then check with twirl binocularly & if they say they prefer with extra plus add extra +0.25DS in both eyes

  • Maddox Rod – turn OFF lights, put in RE horizontal first so they see a vertical line – if line is to the left of the spot it is EXOphoria (opposite side), if on right side then ESOphoria (same side)

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How do these factors affect visual acuity?

  • The object and its illumination
  • The optical system including the pupil
  • Detection
  • Processing

The object and its illumination

The distance of the object affects visual acuity – the further away the object, the image projected onto the retina is smaller and of lower minutes of arc.

The contrast of the image also has an effect – the higher the contrast of the image, the better the visual acuity as the image stands out more against the background. The lower the contrast ratio, the lower the visual acuity.

Visual Acuity also increases as luminescence increases, because they are similar in ratio.

We ran a study with all members of staff at Gordon’s Glazing Windows Glasgow and found that many people had fantastic vision. Great news!

The optical system including the pupil

The pupil size affects visual acuity and resolution of the image. In low-light conditions, the pupil increases in size and this decreases visual acuity by projecting the image onto the retina as blurred and not sharp. However low visual acuity is also the case if the pupil is too small, where diffraction occurs (not all of the image is sharp/clear, causes a blur at the edge of the shadow of the object).

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