Transcript PRESCRIPTION WRITING

PRESCRIPTION WRITING
PRESENTED BY
T.Muthuramalingam
Introduction
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The final part of the clinical routine is to give
the patient a prescription for spectacles.
Clinical refraction should be done to provide
best glass prescription.
Mainly it include
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Objective refraction
Subjective refraction
Binocular balancing
Near vision assessment
Objective refraction
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In objective refraction (retinoscopy),
the examiner determines the type and
degree of refractive error without active
participation of patients.
Retinoscopy is performed with the patient gazing at a distant
object.
Observe the movement of reflex (with or against)
Neutralize the reflex using appropriate lens.(plus lens for with
movement and minus lens for against movement)
Lens which neutralize the reflex is the total refractive error of
eye.
Subjective refraction
The findings of retinoscopy should be
checked subjectively.
 The most comfortable lenses should be
prescribed to patients by trial and error
method.
 The corrections of refractive errors
determined by the objective technique are
entered into the lens aperture of trial frame
before eye.
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Contd.
Spherical lens are
altered first.
The lens which gives
best vision is chosen.
 Then cylinder lens are altered to correct the
remaining error.
 Verification of the axis is done by rotating the
cylinder in 5-10deg. In either direction and
asking whether the acuity improves
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Supplementary test
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To verify the subjective refraction and to
achieve best glass prescription supplementary
tests are done.
Some important tests are:
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Cycloplegic refraction
Jackson cross cylinder
Duochrome test
Muscle balance
Worth four dot test
Cycloplegic refraction
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The test is performed when abnormally
accommodation is actively involved.
(especially for children )
Cycloplegic eye drops (atropine, cyclopentolate and
tropicamide) are instilled to achieve cycloplegia
(paralysis) of ciliary muscles, which results in full
relaxation of accommodation.
It is recommended when patient have following
situations:
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Asthenopic symptom
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Hypermetropia
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Convergent strabismus
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Active accommodation
Jackson cross cylinder
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The cross cylinder is a sphero-cylinder lens in which the
power of the cylinder is twice the power of the sphere and
of the opposite sign.
It is used to refine power and axis of cylindrical power
Axis check:
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Position the cross cylinder axis 450 from the principal meridian of
correcting cylinder
Determine preferred flip choice
Rotate the axis towards the corresponding axis of cross cylinder
(plus cylinder axis rotated to + cylinder axis of JCC, minus
cylinder axis rotated to - cylinder axis of JCC)
Repeat until two flip choices are equal.
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Power check:
Align JCC axes with the principal meridians of
correcting cylinder
 Determine preferred flip choice
 Add or subtract cylindrical power according to the
preferred position of cross cylinder
 Compensate for change in position of the circle of least
confusion by adding half as much sphere in opposite
direction.
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Duochrome test
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Each eye is tested separately to find
out if eye is over corrected or under
corrected.
It consist of letters in red and green
color background.
An emmetropic eye sees the letters on
both sides of the chart to be of equal
clarity, darkness and definition
Over corrected of myopia green more
clear.
Over corrected of hypermetropia red
more clear.
Then fog and unfog so that both color
seen equally clear or blurr.
Muscle balance
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Before final prescription is given it is important to test
for the oculomotor balance both for near and distant
vision with and without the correction.
To find out the presence of
 any squint,
 convergence insufficiency
 fusional reserves.
It include:
 Corneal reflex done by torch light.
 Ocular movement in all direction.
 Cover test.
 Accommodation and convergence by RAF ruler.
 Fusion with prism bar with base out.
Cover test
RAF ruler
Prism bar
Worth four dot test
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The test is done using red glass in right
and green glass in left eye to find the
presence of binocular single vision.
It consist of four dots.one white,two
red, one green.
Interpretation:
 If two red is seen then left eye is
suppressed.
 If three green is seen then right eye
is suppressed.
 If five dots are seen then diplopia is
present.
 If four dots with respective color are
seen patients have no diplopia
Near vision assessment
A suitable weakest convex lens addition should
be made over the distant correction with which
an individual can see clearly and binocularly at
normal near distance should be prescribed.
 It should be performed on the basis of
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working distance,
 visual needs and
 age of the patients.
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Binocular balancing test
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It is done
To avoid the asthenopic symptoms due to
unstable accommodation.
 To ensure the subjective finding include an
over or under correction for the two eyes.
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It is carried by prism dissociation method.
Prism dissociation method.
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With the best correcting lens, both eyes are fogged
with+1.0Ds and a vertical prism of 3 or 4 Δ BD OD
and 3 or 4 Δ BU OS and ask the patient to see a
single line.
If the line is seen simultaneously with both eye then
+0.25Ds is placed before one eye.
BD prism will cause image to be higher (top)The
image will be displaced towards the apex (point) of
the prism ΔBU prism will cause image to be lower
(bottom)
Contd.
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If the patient reports the top image clearer,
add +0.25DS to the OD. If the patient
reports the lower image clearer add
+0.25DS to the OS and again asked the
patient which image is clear.
Remove prisms and take down binocularly
to BCVA
Do not add minus to the more blurry image,
instead add plus to the clearer image
Then bring patient down out of the fog by –
0.25 steps until the BCVA is reached
Guide lines for prescribing
the glass
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For myopia:
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Never over correct the myopia.
Choose under correction for indoor profession
Full correction for out door profession
Complete correction of cylinder in low myopia.
Under correction of cylinder in high myopia
If more cylinder and less sphere, then give
spherical equivalent in low myopia, and in
high myopia under correct the cylinder.
Above 3D cylinder check the keratometer.
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For myopic anisometropia:
BE. Low myopia:- less myopic eye full
correction and more myopic eye slight
under correction
 BE.high myopia:- never fully correct.
keeping the near vision comfortable
balance the two eye by slightly over
correcting less myopic eye and under
correction the more myopic eye to
balance the prescription.
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Hypermetropia :
For first time wear initially under correct.
 Do not correct the latent hypermetropia.
 Do not over correct the facultative
hypermetropia.
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Astigmatism: (low < 0.5D, mod < 0.75 to
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1.5D,high > 1.75D)
In low astigmatism:- it can be ignored with
horizontal and vertical axis, with oblique axis it can
be corrected to relieve the symptoms of asthenopia.
In moderate astigmatism:- it should be corrected
optimally. If spherocylinder having high sphere then
spherical equivalent can be used.
In high astigmatism:- under correction of high
cylinder
Format
226878
06/07/2006
Paulsamy
m
+2
-1
90
6/6
add
+ 2.50
Ds
N6
32mm
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+1.50
add
-1.0
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90
+2.50 Ds
31mm
32mm
56yrs
6/6
N6
31mm
Additional points to write in
prescription
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Lens material:
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Lens design: Specially for Presbyopic patient
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Bifocal ( kryptok, executive, univis –D)
PAL
Vocational glasses( trifocal)
Instruction to patients:
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Glass
plastics
Constant use
Near vision only
Vocational use
Interpupillary distance: For near and distance
Interpupillary distance
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The distance between the center of pupil of
one eye to the other eye.
It is important for placement of optical centers
of the eye glasses coincide with it, to prevent
the unwanted prismatic effect produced by
decentration.
Measurement :
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By using ruler or optical ruler
By instrument called pupilometer
Some examples…
1)
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R.E. = +2.0Ds 6/6
Age: 35/M
L.E. = +10Ds 6/18
Occupation:Weaver
 Check diplopia
 Check binocular single vision
 Test binocular balance
Diagnosis: Hypermetropic Anisometropia
Treatment
 Contact lens
 Secondary IOL
 Spectacle correction
Spectacle prescription
R.E. +2.0DS 6/6, L.E. Secondary IOL or contact lens
For near vision separate glass is advice
2)
R.E. = 6/6 ( IOL)
L.E. = - 3.0Ds 6/12 (IMC)
Age: 35/M
Occupation:Agriculture
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Check binocular single vision
 Check diplopia
 Test binocular balance
Alternative vision using
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Diagnosis: Antiometropia
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So need of glass
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3) R.E. = - 2.0Ds 6/6
Age: 35/M
L.E. = - 10Ds 6/12 Occupation:Field Work
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Check diplopia
 Check binocular single vision
 Test binocular balance
Diagnosis: Myopic Anisometropia
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Treatment
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Lasik
Contact lens
Spectacle correction
Spectacle prescription
R.E. -2.0Ds 6/6, L.E.-5.0Ds
under correction in L.E.
6/36
4) R.E. = +2.0Ds 6/6
Age: 35/M
L.E. = +4.0Ds 6/12 Occupation:Accountant
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Check diplopia
Check binocular single vision
Test binocular balance
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Diagnosis: Anisometropic Ambylopia
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Treatment
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Contact lens
Spectacle correction
Spectacle prescription
R.E. +2.0Ds 6/6, L.E. +4.0Ds
6/12
5)R.E. = +1.0Ds 6/6
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L.E. = +1.0Ds 6/6
add +1.0Ds
Diagnosis:Hypermetropic with presbyopia
Treatment
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Age: 40/M
Occupation:Weaver
Spectacle correction
Spectacle prescription
R.E.+1.0Ds
6/6, L.E. +1.0Ds 6/6
Bifocals is not necessary only distance
vision glass is sufficient
6)R.E.= -3.0Ds/-4.0Dcylx90 6/12 Age:25/M
L.E. = -4.0Ds/-6.0Dcylx90 6/12 Student
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Diagnosis:myopic with astigmatism
Treatment
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Check diplopia
Check binocular single vision
Test binocular balance
Keratometer Reading
Lasik
Contact lens
Spectacle correction
Spectacle prescription
R.E. -3.0Ds/-4.0Dcylx90 6/12
L.E. -3.0Ds/-4.0Dcylx90 6/12
Points to remember
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Prefer is given to prescription in minus
cylinder form unless vision is improves
significantly with plus cylinder.
If axis of cylindrical component is not
vertical and horizontal, it is better to under
correct astigmatic power.
Prescription should be written clearly with
correct sign and power.
Prescription should not be over corrected.
All the information given to patient should
be written.