vorc

How to refine the sphere

Who - routine, vision complaints, new prescription. Not on uncooperative pts (eg young children, mentally impaired)

Why - to give best VA and correct RE, can reduce eyestrain. Move CLC onto retina

How -

1. measure VA with ret result

2. Direct pt to look at smallest line of letters

3. Offer +0.50 for 1 second ‘do the letters look clearer with this lens, without this lens or about the same’

   Regardless of response repeat with -0.50 for half a second

   If pt responses are contradictory or overly hesitant repeat with 0.75/1.00

4. If ‘better with’ +0.50 add +0.50 to TF

   If ‘same with’ +0.50 add +0.25 to TF

5. If ‘better with’ -0.50 check for VA improvement

   If acuity improves by 1 line add -0.25

   If acuity improves by 2 lines+ add -0.50

6. Repeat but if you added +ve power, only offer +ve and vice versa for -ve

   Continue to add +ve power until pt is certain its ‘better without’

   Continue to add -ve power until pt says ‘its better without’, ‘its the same’, ‘its better’ but no improvement in va

7. When close to endpoint switch to +- 0.25 flippers offer both

   Measure VA with the BMS/BVS

   Expected results - Reached the end when +0.25 makes VA ‘worse’ and -0.25 is ‘the same’ (no improvement in VA) or ‘worse’

   If only a sphere is present in trial frame its the best mean sphere. If VA is close to 105 theres little/no astigmatism

   If theres a sphere and cyl in trial frame its the best vision sphere if theres cyl is correct, VA should be good

   If results differ - if pts VA doesnt it could be due to underlying issue eg cataract, corneal irregularities etc, practitioner measurement error, incorrect cyl, presbyopia

   Recheck measurements ensure proper alignment of trial frame or phoropter, pinhole to differentiate between refractive error or other eye conditions, investigate eye health on slit lamp (cornea, lens, volk)

JCC Axis determination

Who - routine, vision complaints, new prescription. Not on uncooperative pts (eg young children, mentally impaired)

Why - give best VA by correcting astigmatism, correct cyl axis to make interval of sturn smaller circles appear rounder and clearer when theres less residual ametropia

How -

1. Pt looks at vernhoeff rings, adjust to appropriate size

If starting with no cyl in place:

1. Hold handle at 180 (markings will be at 45/135) - ask pt ’do the circles look rounder and clearer with 1 or 2 or the same’. Note where negative markings are

Repeat with handle at 45 (markings will be at 90/180)

2. Place -0.25 cyl in TF with its axis in the middle of the 2 preferred positions

3. Hold handle at the axis - ask q and rotate cyl towards minus axis of JCC

4. Repeat until you get a reversal, then rotate cyl by half the previous amount until 1 and 2 are the same. Always get atleast 1 reversal. Even if pt says ‘same’ move cyl more to see if it goes back to where it was the same.

How much to rotate?

-0.25 = 30

-0.50 = 20

-0.75 = 15

-1.00-2.00 = 10

-2.25+ = 5

Expected results - move axis until you get a reversal then move it by half each time until circles are the same

Different from expected - when starting jcc without a cyl and showing 45/180 - If no preferred position (same for all) - dont add cyl - little/no astigmatism

Pt could be indecisive, dry eye, cataracts

JCC power determination

Who - routine, vision complaints, new prescription. Not on uncooperative pts (eg young children, mentally impaired)

Why - give best VA by correcting astigmatism, When changing cyl power by changing the trial lens, it only moves the front focal line back (only power in one meridian), CLC also moves back. Smaller IoS. we need to sphere compensate to move CLC onto retina.

How -

1. Show pt vernheoff rings at an appropriate size

2. Hold axis markings of the along the axis of cyl in trial frame

(If VA is good (6/12, 85+) use 0.25 JCC. If its worse than that use 0.50)

3. Ask pt ‘do the circles appear rounder and clearer with 1 or 2 or the same’

4. Note position of negative markings (1 or 2) and change cyl power accordingly - if they prefer when negative markings are along the axis then add -0.25, if they prefer +ve and +0.25

5. If cyl power is changed by -0.50 recheck VA to make sure its improving

If its changed by ±0.50 recheck cyl axis, sphere compensate with half the opposite powered sphere (+0.25DS for every -0.50DC)

If power changed by 0.50 and/or axis changed by more than 30º Do BVS again at the end with ±0.25 flippers

Expected results - endpoint when 1 and 2 are the same (dont need reversal)

When pt says JCC positions are the same the jcc is introducing RE. This is why at the end point the circles arent clear theyre equally blurred

Cyl power should align with how many lines away from the bottom of the chart eg VAR 95 (2 line reduction) suggests -1.00 DC (-0.50DC for 1 line)

If different from expected - pt may be indecisive so you may be close to the endpoint and its getting difficult to judge - can check VA to see if youre close to endpoint

Consider rechecking the axis, checking eye health

Duochrome

Who - younger patients. Tends to work less well in older pts (the absorb blue blue) and pts with considerable blur (bigger sphere changes needed). However young pts can be unreliable too (always red) or need 1D change to change colour

Why - helps to refine sphere power, can be used throughout subjective refraction but mostly used to check sphere power before JCC and at the end of subjective refraction

How -

Room lights should be dimmed so the eye dilates for more chromatic abberation

1. Show duochrome target and ask pt ‘do the circles look rounder and darker on the red or the green or about the same’

2. Can check is responses are reliable if they say circles are the same - show +0.25 red should be clearer, shower -0.25 green should be clearer.

Expected result - (if BVS is correct) circles should be the same (CLC is on retina) or slightly clearer on green (pt can accomodate)

If results differ -

If clearer on red (overplussed) : show -0.25 (only leave in if it improves VA)

If clearer on green (overminused) - show +0.25 (dont leave in if it reduces VA)

If 0.25 change doesnt make them the same try 0.50 and 0.75 - if no colour change then duochrome unreliable or BVS incorrect

+1.00 blur test

Who - younger pts. Not on older pts bc they cant accomodate so if you under plus/over minus an older pt, VA will be bad bc they cant accomodate over it

Why - at the end of subjective refraction, eye should be emmetropic so +1.00 generates 1D of myopia and for every 0.25 = 1 line reduction (4lines)

Check if we have over minused or underplussed the pt

How -

1. Measure VA - should be around 105

2. Ask pt ‘your vision may not be as good with this lens but try tell me what the smallest line is that you can read’

Expected results - VA should be reduced by 4 lines (2-7)

If results differ - offer +0.25 only leave in if it doesnt make VA worse

Binocular refraction

Who - younger pts. Not on pts with highly dominant eyes, pts who arent binocular (strabismus/amblyopia)

Why - more accurate/natural refraction - no occluder so no dissociation no stimulus to accomodation, peripheral fusion and binocular lock, quicker as you dont need to binocularly balance

How -

1. Need an accurate ret result that gives good VA

2. Introduce fogging lens (+0.75 (younger) or +1.00 (older) in left eye which should reduce VA by 3-4 lines (6/9)

3. Do subjective refraction as normal

Expected results - accept more plus power (accomodation is relaxed) - prevents over minusing or underplussed plussing

If results differ -

more minus than expected - pt may still be accomodating so use a higher powered fogging lens

Pt may have a highly dominant eye or arent binocular

Binocular balancing

Who - younger pts. Not on older pts, pseudophakes, or pts with a highly dominant eye

Why - done after monocular subjective to relax and balance accomodation in both eyes. See if pt accepts more plus power - prevents over minusing or underplussing. Fogging avoids complete dissociation and accomodation that occulder stimulates. Conditions more close to normal viewing situation

How -

1. Complete monocular subjective refration in both eyes up to an including +1.00 blur test which should reduce VA by 3-4 lines

2. Fog left eye (+0.75/+1.00) tell pt ‘this is going to make the LE blurry’

3. Repeat BVS using +0.25 in right eye

If pt says ‘better with’ add +0.25 and repeat until ‘better without’

4. Remove fog from left eye and put on right eye and repeat BVS

5. Measure binocular VA

Expected results - usually no change from monocular refraction results or sometimes a small amount of additional positive lens power in one eye - rarely both eyes

If results differ -

Eye may be accomdating - add move +ve to fogging lens

may have a dominant eye

Near add

Who - pts that cant accomodate - older pts 40+ (presbyopes), younger pts too. Pts struggling to see at near. Not on younger pts who can accomodate. (Must ask everyone about near vision)

Why - help pt focus at near

How -

1. Add pts distance Rx into trial frame

2. Ask pt if they read in normal room lighting or with a reading lamp - only use if they do

3. Ask pt to ‘hold reading card where youd like to read/work even if its blurry there’ - measure the distance(s)

4. Explain to pt im going to determine the power you need for your reading glasses’

5. Use table and age to determine tentative add or if 60+ 1/WD

45 = +1.00

50 = +1.50

55 = +2.00

60 = +2.25

Put add into trial frame

6. Direct pt to look at best acuity paragraph which is held at their preferred working distance

Using ± 0.25 flippers

Show -0.25 ask ‘do letters become better/sharper with the lens, without, or the same’ - if better or the same add -0.25 and repeat until better without

If pt prefers +0.25 only add if VA improves (maximum minus - range of clear vision decreases with higher add powers)

7. Determine range of clear vision - ask pt to look at best acuity paragraph and ‘move reading card closer until they first notive blur’ - measure this distance. And then ‘move the card slowly away until first notice blur’ measure this

8. Ask pt about hobbies and determine if the range is adequate for it. If not suggest: progressive addition lenses, compromise addition, several pairs of single vision glasses or multifocals

Expected results - pt has good acuity for tasks they wish to complete at near at their working distance

If results differ: if they cant read N5 with optimal near correction suggest a reading lamp at home

Unequal reading adds in each eyes require further testing - retest near add endpoints for each eyes or recheck distance binocular balance