000071_12770491_Soboleva_Introduction_to_Practical...

Refractometry
Refractometry
Is the measurement of the refractive
error of an eye
• Objective Refractometry – Retinoscopy,
Autorefractor
CPMC Department of Ophthalmology
• Subjective Refractometry
Marina Soboleva, COMT, ROUB, CDOS
Sir William Bowman (1816-1892)
1892)
The Bowman’s s retinoscope
• Invented the Spot
Retinoscope
• Father of ophthalmic
anatomy
• In 1880 founded
Ophthalmological
Society
• In 1884 knighted by
Queen Victoria
Jack C Copeland (1900 – 1973) Allvar Gullstrand (1862 – 1930)
• Swedish
Ophthalmologist
• Created the Model
Eye
• Invented the Slit
Lamp
• The Nobel Prize
winner 1911 in
Ophthalmology

The Model Eye
Refractive states
Strong Optical System vs Weak
Optical System
• Emmetropia – the Image
is on the Retina
• Hyperopia – the power of
the Eye is weak for its AL
• Myopia – the power of the
Eye is strong for its AL
Ametropia
The further the focal point is from the retina, the
more powerful Myopia and the less powerful
Hyperopia are
• M 3.00D > M 1.00D
• H 1.00 > H 3.00D
• H 4.00 > H 5.00D
Astigmatism
• Stigma in Greek means “mark”
• In the optical context it means the focal
point
• A - stigmatism means the absence of the
focal point
Astigmatism or Stylistic Choice?
Astigmatism
• A person with
astigmatism sees the
blur and elongation
• El Greco
• Modigliani

Corneal Shape is the culprit of
astigmatism
• Sphere – no astigmatism
Cylindrical Lens
• Ellipsoid – astigmatism
• WTR – with the rule ATR – against the
rule
• The Power
• The Sign +/-
• The Ax
The Image ( the focal plane) is parallel to the Ax of
Cyl
Spherocylindrical System
• +3.00 +1.50 x 90
Spherocylindrical System
• The axis of positive cyl goes along the most
powerful meridian to increase the power of
the least powerful meridian
• The axis of negative cyl goes along the least
powerful meridian to decrease the power
the most powerful meridian
Spherocylindrical System
• +3.00 +1.50 X 90
• +4.50 – 1.50 X 180
• + cyl 3.00 X 180 + cyl 4.50 X 90
3D Astigmatic Bundle – conoid of
Sturm
Since the convergence in the horizontal
meridian occurs faster than in the vertical
meridian, the resulting pattern is a vertical
ellipse – a vertical line – a vertical ellipse – a
circle – a horizontal ellipse – a horizontal
line
+1.00
+5.00

“El
Grecos” telescope
Stylistic Choice
Sturm’s conoid is the 3D model of
astigmatism
• Compound Myopic
Astigmatism
• Simple Myopic
Correcting astigmatism you are collapsing the Sturm’sconoid
+3.00 +1.50 X 90
+4.50 – 1.50 X 180
• Mixed
• Simple Hyperopic
Astigmatism
• Against the rule
44.00/43.00 X 90
Astigmatism
• Compound Hyperopic
• With the rule
43.00/44.00 X 90

Phoropter
What the pt. Needs to Know
• The procedure is used to select the lens to provide
the clearest vision
• For each choice, please indicate which is clearer
• Sometimes the choices may look the same . In this
case, just say that you can not tell the difference
• Do not worry about making a mistake. I will test a
lens more than once
• If the lens moves too quickly, ask me to slow down
Set-up
• The Phoropter should be leveled (bubble)
• The pupillary distance is adjusted so that
each eye is centered within the aperture
• If the eyes are not looking trough the center
of the aperture, check to see that pt’s s head
is not tilted
• Please note that some pts have one orbit
that is higher than the other, in this case you
adjust Phoropter for each eye separately
Starting Point
• Retinoscopy
• Autorefractor
• Prescription of the pt’s s habitual spectacles
(from lesometry)
• Refractometry results from a previous visit
• Keratometry (to estimate cyl – best used for
post-op op pts where SE is close to plano and
no lenticular astigmatism is expected)
Your Patient
Spherocylindrical system
• +3.00 +1.50 X 90
• As the resultant

To keep in Mind
• My patient is young – the
control of
accommodation is
important:
1. Proper fogging
2. Binocular balance
Subjective Refractometry
Steps
1. To Fog and to Refine the sph
2. To Refine the Ax of (+) cyl
3. To Refine the power of (+) cyl
4. To Balance
3. To check the Accommodative
Amplitude
• Use one line above the
threshold for the
target
• You are fogging your pt.
(adding (+) to control
accommodation) until the
pt can not longer read the
letters. Once the pt.
reports blur, make sure
the letters remain blurry
• Reduce the plus slowly,
until the pt can read most
of the letters even it blurry
Step #1
Step #1
• When presenting the choices the least plus
choice first. Avoid to over-minusing
your
pt.
• The size of the steps used when presenting the
lens choices depends on the initial ucorrected
V/A and sensitivity of your pt.
1. V/A 20/40 or better – 0.25 step (one click)
2. V/A 20/70 – 0.5 step (two clicks)
3. V/A 20/400 – 0.75 step (three clicks)
• Make it easy to see the difference
Step #1
• Remember your goal is to find the greatest plus
power, or the least minus power, that creates the
sharpest vision
• If the first step into plus direction results in blurry
vision, begin testing in the minus direction
• If pt reports that the lens two is clearer, present
the choice again, asking “is it really sharper and
clearer or just smaller and darker?”
• Remember that pt has “to earn” the minus power
by actually reading the smaller letters
Step #2 Jackson Cross Cyl
Red Dot +0.25
White Dot -0.25
• The Red Dot represents the – cyl axis
• The White Dot represents the + cyl axis

Step #2 Jackson Cross Cyl
• Jackson Cross Cyl can be used to determine
both astigmatism power and axis.
• The wider tolerance is allowable for
astigmatism than for sph
Step #2 Jackson Cross Cyl
• The Target is 2 lines above V/A threshold
• Fogging should be carefully avoided. Use
the best sphere
• Keep in mind that the test sensitivity is very
low when the axis errors are large (90
degrees of the axis)
Step #2 Jackson Cross Cyl, Ax
• The round letters are
the best O or B
• Rotate the cross cyl 45
degrees from your
starting point Ax –
straddle the Ax
• You are working with
(+) cyl , your dot is the
white one, follow it!!!
• Your step is 5 degrees
• The end point is when
both flips make the letter
looks the same
Step #2 Jackson Cross Cyl, Ax
• The location of the cyl Ax becomes more
critical with increasing amount of
astigmatism. For example, if the axis is
moved 10 degrees with 0.50 D of cyl in
place, the vision will not change
dramatically. However, moving the Ax the
same amount when the cyl power is 3.00 D
will sinificantly change the pt. vision
• Place the red or white
mark over the Ax
• Your step is + 0.25 D
• The white dot +0.25
• The red dot – 0.25
• For each + 0.5 D
increase of cyl, you
decrease sph by -
0.25D
Step #3
Step #3
• Continue offering choices and making
appropriate changes in cylinder power until
booth choices appear equally blurry, your
pt responds “the same” or “no difference”

Binocular Refraction
• The main advantage of Binocular
Refraction is more accurate determination
of the cyl ax (eyes sometimes cyclo-rotate
under monocular condition)
Binocular Balance
• The main advantage of Binocular Balance is
better control over accommodation
Binocular Balance
• Von Graefe
1. You have to have equal
BCVA
• Red–Green Von
Graefe
1. The balance can be done
on pts with slightly
different V/A
2. It does not work well
with Hyperops
3. Some pt’s s are not good
with colors
Von Graefe Balance
• Target – three lines above threshold
• Dissociate two eyes: OD – 3.00 PD base up, OS –
3.00 PD base down, the down row for OD and the
upper row for OS
• Fog with + 0.75 D OU
• Add + 0.25 D in front of the eye which appears
clearer
• You are trying to achieve equality
• Remove the prisms. Unfog the pt. Refine the sph
binocularly.
R/G or Bichrome Balance
• The same target with R/G filter in place
• The same prismatic dissociation
• Fog by + 0.75D OU
• Have the pt concentrate on the bottom row of
letters, OD
• Green is clearer – add +0.25D, Red is clearer –
add -0.25D
• You are trying to achieve equality
• Do the same with OS
• Remove the prisms. Unfog. . Refine the sph
binocularly
Accommodative Amplitude
• Set-up: pt is tested behind the Phoropter
• Occlude pt’s s left eye to test the right eye
• Target: near pont acuity card, single number, one
line above threshold near V/A
• Move the target towards the pt in slow and steady
movement and ask pt to report “when the letters
become and remain blurry”
• Measure the distance in cm, divide 100 into this
number =AA; 100/20cm=5.00 D
• Check the right eye
• Check both eyes

References
• “Geometric, Physical and Visual Optics” Michael P.
Keating
• “Optics, Retinoscopy and Refractometry” Al Lens
• “Last Minute Optics” David G. Hunter, Constance E.
West
• “Ophthalmic Technical Personnel” Barbara Cassin
• “Artist’s Eyes” Michael F. Marmor and James G.
Ravin
• “Optometry” Lab Syllabus, U.C. Berkley School of
Optometry
• JCAHPO Learning Systems
Thank You
sobolem@sutterhealth.org