The document describes the procedures for performing subjective refraction to determine a patient's distance and near visual prescription. It involves first establishing the patient's best corrected and uncorrected visual acuity. The examiner then determines the patient's best vision sphere and estimates their astigmatism before refining the prescription with trial lenses to account for cylinder power and axis. Verification steps like binocular balance and range of clear vision are also mentioned. Near addition is calculated based on the patient's near point of focus and amplitude of accommodation. The document provides guidance on techniques, tools, and considerations for optimizing subjective refraction outcomes.

1. SUBJECTIVE
REFRACTION
OPTOM FASLU MUHAMMED

2. REFRACTION PROCEDURE: DISTANCE
2
1. Visual acuity (VA) with current Rx
VA versus spherical Rx table
• Spectacles
• AR
• Retinoscope
• Unaided
2. Perform Pinhole test
Unaided VA with existing Rx if aided VA is
worse than 6/12

3. REFRACTION PROCEDURE: DISTANCE
3. Determine Best Vision sphere
3
• Letter Chart
• Duochrome
4. Estimate Astigmatism
• VA with BVS
• Refractive Error Estimation table

4. 4
5. Refine Astigmatism (cylinder)
• Axis location
• Astigmatic power
- Fan & Block
- Jackson X-cyl
- Cyl trial lens Rotation & Letter
chart
6. Refine Sphere of Rx
• +1.00 DS Fog to blur vision
Refraction Procedure: Distance

5. REFRACTION PROCEDURE: DISTANCE
5
7. Bi-Ocular balance
• Simultaneous
• Alternating
- Prism Dissociation
- Polaroid
8. Final
Rx• Option
s

6. REFRACTION PROCEDURE: NEAR ADD
1. Establish Preferred Near Viewing Distance
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2. Determine Near Blur Point
• Binocular
• Monocular recheck
– near letter chart
– measuring tape
• Binocular
– measuring
tape

7. REFRACTION PROCEDURE: NEAR ADD
3. Calculate Near ADD required
7
• Maintain half (50%) the Amplitude of
Accommodation in reserve
- nomogram, nomograph (in the workbook)
4. Refine ADD
• Range of clear vision
- near letter chart
- trial lens

9. LOGMAR CHARTS
•The design principles
suggested by Bailey & Lovie
•More lines than a typical
Snellen chart, particularly at
poor VA levels
•Not truncated to 6/5 (20/15)
or similar.

10. TYPES
 ADULTS
– Bailey–Lovie Charts
– ETDRS charts
 CHILDREN
– The Glasgow Acuity Cards
 Keeler crowded logMAR charts

11. PROCEDURE
 The luminance of the chart should be between 80 and
320cd/m2.
 Seat the patient comfortably with an unobstructed view of
the test chart.
 You should sit in front and to one side of the patient in
order to monitor facial expressions and reactions.

13. •They should be pushed to
determine whether they can see
any more.
•If they make four or more
mistakes on a line of five
•Ask them to move closer if chart
not seen

14. If the patient cannot see the letters
even at the closest test distance
a) Hand Movements (HM) @ Y
cm
b) Light Projection (Lproj.):50 cm
c) Light Perception (LP):
Repeat measurements for the other
eye and binocularly.

15. Since each letter is
worth an equal 0.02
log units, you can
most accurately
determine visual acuity
by accounting for every
letter correctly identified.
Typically, an equation is
used to calculate VA:
logMAR VA = 1.1 - (0.02 x letters missed)

16. MOST COMMON ERRORS
1. Allowing cautious patients to decide their acuity (i.e. not pushing them to
guess).
2. Permitting the patient to screw their eyes up and improve their VA.
3. Permitting the patient to look around the occluder or through their fingers
and view binocularly when measuring monocular VA.
4. Taking distance VAs in a PAL or varifocal wearer when they are not looking
through the distance vision section of the lens.
5. Using an incorrect working distance.
6. Not recording the result immediately and guessing the result at the end of
the examination.

17. VA MEASUREMENT USING
SNELLEN CHART
 Procedure is similar to logMAR chart
 Vn is recorded as the smallest line in which the
majority of letters are seen,irrespective of
subjective blurr.
 Errors are recorded by appending a -1,-2, or -3 to
snellen fraction
Eg:6/9(-2),6/9(-3)…
If pt couldn’t see 6/60 letter @ 6m,but could @
2m,recorded as 2/60.

18. RECORDING
 The Snellen fraction is defined as:
 Test Distance
/Distance at which the letters subtend 5 min of arc.
1. Test distance can be provided in metres (metric) or
feet (imperial).
1. Snellen VA can be labelled in either decimal or
conventional Snellen notation

19. Snellen Fraction = Test Distance
Distance at which entire letter subtends 5’
The acuity test distance should be long enough to not stimulate the
accommodative system. By convention, the standard test distance in the
U.S. has been 20 feet. Everywhere else it is 6 meters:
20 is a Snellen fraction in feet
60
6 is the same Snellen fraction
18 in metric units
Measuring visual acuity: The Snellen Fraction

20. Measuring Distance Visual Acuity
Testing Sequence
By convention you always test in the following order
1st OD ocular dexter Right eye (cover left eye)
2nd OS ocular sinister Left eye (cover right eye)
3rd OU ocular utrique Both eyes

21. Measuring Distance Visual Acuity: Example 2
A P E O T F 20/25
E V O C T Z 20/20
O H P N T C 20/15
What is the visual acuity of this patient?
5/6 letters on the 20/25 line and only 2 letters on the 20/20 line
No reason to even test the 20/15 line
The visual acuity can be expressed as 20/25
However, accounting for the missed and identified letters...
The VA can be more descriptively expressed as 20/25-1/+2

22. MONOCULAR SUBJECTIVE RX
Letter Chart
Duochrome
test
Combination
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Spherical Correction
= Best vision sphere (BVS)
Obtain spherical correction giving best VA

23. MONOCULAR SUBJECTIVE RX
Starting point for BVS
 Sphere component of Spec Rx
 Sphere component of Auto-Rx
 Unaided VA Estimation Method
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BVS = (Sphere Rx) + (Astigmatic Rx ÷ 2)
Best Vision Sphere (BVS)

24. VISUAL ACUITY
Snellen 6/VA Decimal MAR (Minutes of Arc) logMAR
3 2.00 0.50 -0.30
4 1.50 0.67 -0.18
5 1.20 0.83 -0.08
6 1.00 1.00 0.00
7.5 0.80 1.25 0.10
9 0.67 1.50 0.18
9.5 0.63 1.58 0.20
12 0.50 2.00 0.30
15 0.40 2.50 0.40
18 0.33 3.00 0.48
19 0.32 3.17 0.50
24 0.25 4.00 0.60
30 0.20 5.00 0.70
36 0.17 6.00 0.78
38 0.16 6.33 0.80
48 0.13 8.00 0.90
60 0.10 10.00 1.00
120 0.05 20.00 1.30
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25. RELATIONSHIP BETWEEN REFRACTIVE ERROR
AND VA
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Vision
6/6 (20/20)
6/9 (20/30)
6/12 (20/40)
6/18 (20/60)
6/24 (20/80)
6/36 (20/120)
6/60 (20/200)
Spherical*
small
0.50
0.75
1.00
1.50
2.00
2.00 to 3.00
Astigmatic
small
1.00
1.50
2.00
3.00
4.00
high
Refractive Error (D)
Bennett and Rabbetts, 1984
* Myopia or absolute hypermetropia

26. RELATIONSHIP BETWEEN REFRACTIVE ERROR
AND VA
26
Vision
6/6 (1.00)
6/9 (0.67)
6/12 (0.50)
6/18 (0.33)
6/24 (0.25)
6/36 (0.13)
6/60 (0.10)
Spherical *
< 0.50
0.50
0.75
1.00
1.50
2.00
2.00 to 3.00
Astigmatic
< 0.75
1.00
1.50
2.00
3.00
4.00
> 4.00
Refractive Error (D)
Bennett and Rabbetts, 1984 * Myopia or absolute hypermetropia

27. ESTIMATE RESIDUAL SPHERICAL ERROR:
DISTANCE RX
27
• Note the Best Snellen VA obtained
• Estimate the Amount of Spherical
Error
Procedure
Residual Spherical Error =
Snellen (metric) VA Denominator ÷16

28. ESTIMATE RESIDUAL SPHERICAL ERROR:
DISTANCE RX
Unaided Visual
Acuity
RE LE
Patient A
Spherical Rx
Snellen 6/12 Snellen 6/9
Patient B
Spherical Rx
Snellen 20/30 Snellen 20/60
Patient C
Spherical Rx
Decimal VA 0.1 Decimal VA 0.17
Patient D
Spherical Rx
MAR 4 logMAR 0.7 28
0.75D 0.56D
0.56D 1.12D
2.25D3.75D
1.50D 1.75D

29. MONOCULAR SUBJECTIVE RX
• Use the ‘highest plus’ sphere as a starting
point
• Add plus lenses in 0.50 steps until VA
begins to decrease
• Then add negative lenses in 0.25D steps
until there is no further VA improvement:
“Does this lens make the letters clearer
or just smaller and darker?”
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Refinement: Sphere (BVS)
Letter Chart

30. SPHERICAL CORRECTION
Points to note:
 Accommodation
 if the letters get darker and smaller only,
then too much minus has been
prescribed
 When adding plus lenses,
assure the patient you know it is
getting worse
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Letter Chart

31. SPHERICAL CORRECTION
Duochrome
(starting point)
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Combination Tests
Letter chart
(refinement)
Duochrome
(end point)
Letter chart
(BVS)
OR