subjective refraction methods

1. SUBJECTIVE
REFRACTION
TESTING
DR RAKHI P DCRUZ

2. ADVANTAGES
– even in absence of
special equipments
and good pupillary
reflex
– for verifying
objective refraction
values
– Glasses can be
prescribed at first
visit
DISADVANTAGES
– Variable results due
to accommodation
– require patient
corporation
– Not possible in small
children
– Senile and mentally
retarded

3. STEPS OF SUBJECTIVE
REFRACTION
– 1.MONOCULAR SUBJECTIVE REFRACTION
– 2.BINOCULAR BALANCING
– 3.CORRECTION FOR NEAR VISION
– MONOCULAR SUBJECTIVE REFRACTION STEPS
– Selection and verification of baseline starting point
– Refinement and finalization ofcylinder axis and power
– Refinement and finalization of spherical lens

4. Subjective refraction
primary aim-to attain a standard of
6/5VA
– Pin hole testing will give us a clue to refractive error and the
best vision attainable.
– But even in absence of definitive pathology in media or
fundus subjects with high hypermetropia and marKed
astigmatism often do not reach 6/6 VA
– Baseline staring point for objective refraction can be
obtained from either retinoscopy, autorefractometry, or
patients old glasses
– VA is usual tested for each eye separately with appropriate
lenses inserted into the trail frame. The patient is asked to
read test types the effect of slight modifications in lenses are
then tried.

5. Clue to approximate
degree of ametropia
vision spherical astigmatic
6/9 0.5 1.00
6/12 0.75 1.5
6/18 1.0 2.0
6/24 1.5 3.0
6/36 2.0 4.0
6/60 2-3 > 4.0

6. – Alteration with sphere is tried first. rapid changing of
spherical lenses to one slightly stronger or weaker is a
common method.
– The BEST VISION SPHERE=the strongest convex lens and
weakest concave lens providing best vision should be chosen
in patients with hypermetropia and myopia respectively
– The verification of cylinder power is not so starightforward
.here both strength and axis haS to be taken into account.its
usually best to check axis first.this can be done by rotating
the cylinder in steps 5 or 10 degrees in either direction and
asking whether the acuity improves
– Once axis has settled the correct strength of cylinder can be
more definitely determined.in low degrees of stigmatism its
well to change cylinder in trial frame, but in high degrees its
better to hold a weak cylinder in front of trial frame tesing
first with axis parallel to that in trail frame and then at right
angles to it.if either of these produces an improvement ,the
spherocylindrical combination in trail frame is adjusted
appropriately.

7. REFINEMENT AND FINALIZATION OF
CYLINDER LENS AXIS & POWER
Jackson cross cylinder
– Helps to ascertain the strength and axis of cylinder.
– It’s a mixed cylinder combination of various strengths In
which the spherical components one half the (opposite)
power of cylindrical with axis at right angles.
– The most convenient form is a combination of -0.25D with
a + 0.5 D CYLINDER.
– To check strength of cylinder in the lenses one of the two
marked cylindrical axis of cross cylinder if first placed in
same direction as the axis of cylinder in frame and then
perpendicular to it. if VA IS unimproved in either of
directions the cylinder in trial frame is correct

8. – if its improving in either of direction,the change should be
made in corresponding direction.and the verification
repeated with new combination by running through cycle
again
– To check the axis of cylinder the principles of obliquely cross
cylinders are applied.A moderately strong cylinder (0.5 or
1.00D) is held before the the eyes so thet each eyes lies
alternatively 45 degrees to either side of axis of trial cylinder.
For this the cross cylinder is held in front of eye with its
handle parallel to axis of cylinder in trial frame and then flip
it.patient is asked to tell about any change in VA
– If improvement is attained by one or other alternative the
correcting cylinder is turned slightly in direction of axis of
cylinder of same denomination in cross cylinder
– the test is then repeated several times until position of trial
cylinder is found at which rotation of cross cylinder gives no
alterations in distinctness

9. Astigmatic fan
– On looking through astigmatic fan if the vertical lines are
more clear ,the diffusion ellipses on retina must be vertical
that is horizontal meridian is more nearly emmetropic than
vertical.
– a cylinder placed in front of eye with its axis horizontal will
therefore correct the vertical meridian and when the correct
glass is found all lines will appear equally distinct.
– The cylinder which thus renders the outline of whole fan
equally clear is a measure of amount of astigmatism & Axis of
cylinder is at right angles to The line which was initially more
clearly defined .

10. Maddox V test
– CONSIST OF SERIES OF RADIATING LINES SPACED AT 10
DEGREE INTERVAL ARRANGED AFTER MANNER OF RAYS OF
RISING SUN over which V AND 2 SETS OF MUTUALLY
PERPENDICULAR LINES(BLOCKS) can be rotated through 180
degree . After removing the cylinder correction and looking
through maddox V few lines appear sharply defined and
distinctly black .V is then rotated to the neighborhood of this
line the exact point of maximum definition is more accurately
determined by comparing relative intensity of oblique lines
forming limbs of V
– The point of maximum definition and a maximum blurring m
may be more easily appreciated by observing the two discs
represented below fan on the figure the one with lines
arranged at right angles to each other which is also rotated
simultaneously with the V .

12. REFINEMENT &FINALIZATION OF
SPHERICAL LENS
Fogging Techinque Using snellen
– Fog the eye ie to make it artificially myopic to about 20/50 by adding
plus sphere to focus all meridia anterior to the retina ,with eye
fogged accommodation can only blur the lines more, and patient
tends to relax accommodation thus stabilizing refractive error of the
eye
– this is kept for some time and strength of lens in one is gradually
lessened by small fractions 0.5D) until maximum acuity is just
reached, the first lens is not removed until next is in position in order
to prevent accommodation from being active.then completely
fogging lens +4D is then placed in front of other eye and second eye
tested.
– The patient must be given strongest hypermetropic correction with
which he can attain normal vision

13. Duochrome test
– GREEN rays are refracted more acutely and brought to
focus early than the red rays .if the eye is corrected so
that it is emmetropic ,a focus is formed between these
two extremes,if its myopic the red is seen more distinctly
,if hypermetropic green is more sharply defined
– Patient should be slightly fogged before test to prevent
accomodation .the letter on red side should appear clearer
and minus sphere should be added till letters with red and
green background are equally clear.

14. BINOCULAR BALANCING
– This allows both eyes to have retinal image simultaneously
in focus,an imbalanced correction can lead to asthenopia
– 1.FOGGING WITH ALTERNATE OCCLUSION METHOD
– Both eyes are fogged with around 1DSPHERE.then a rapid
alternative cover test is done,tell which eye has better
clear image. If balanced equal blur,if not add +0.25D
SPHERE to better seeing eye until balance is achieved
,now slowly defog till both eye read 6/6
– 2.DUOCHROME TEST WITH FOGGING

15. – PRISM DISSOSCIATION METHOD
– Fog both eye with 1 Dsphere and then a vertical prism of
3 or 4 prism dioptre is placed with base down 1 eye base
up other,single line 6/12 is projected
– If patient reports diff in clarity bwn upper and lower lines
then +0.25 sphere is placed before eye with better
vision.this is done till two eyes are equally distinct.the
prism are removed and defogged

16. NEAR VISION
CORRECTION
– USUALLY AFTER AGE 40
– NEAR VISION TESTING WITH JAEGERS CHART.
– In case near vision is defective further tesing as follows
– 1.Determine near point of accommodation and
amplitude of accommodation
– 2.Determine near point of convergence
– 3.Dynamic retinoscopy
– 4.Determination of near ADD

17. DETERMINATION OF
MUSCLE BALANCE
– 1. CORNEAL REFLECTION TEST
– COVER TEST
– /ALTERNATE COVER TEST
– OCULAR MOVEMENTS IN ALL POSTION OF GAZE and
asked for any diplopia
– test for convergence