how to prescribe prism in orthoptics? formula of prism prescription

1. PRISM THERAPY
- Rachana Kafle
- BOVS, 2ND YEAR
- NAMS, NEH

2. Presentation layout
 Prism introduction and its characteristics
 Types of prism used in ophthalmology
 Clinical use of prisms
 Clinical types of prism
 Criterias for prescribing prism
 Uses of prisms in different disorders
 Diferent methods to prescribe prism

3. Prism
portion of a refracting medium bordered by two plane
surfaces which are inclined at a finite angle.
ray is deviated towards the base obeying the Snell’s
law... forming erect, virtual & apically displaced image.
Net change in direction is the angle of deviation.

4. Characteristics of a prism
a) Its orientation is defined by its apex
b) light is deviated towards the apex
c) light of shorter wavelength is deviated more than
longer
d) angle of the prism apex is called the refracting angle
e) all the ophthalmic prisms are calibrated according
to the Prentice's position

6. The image formed by a prism is
a) Erect
b) Magnified
c) Laterally inverted
d) Virtual
e) Deviated towards the apex

7. Factors determining the angle of deviation in air:
 refractive index
 refracting angle
angle of incidence

8. Primary positions
1. Angle of minimum deviation
2. Prentice position.
3. Frontal plane prisms

9. Angle of minimum deviation
When the angle of incidence equals the angle of
emergence, it is called as Symmetrical refraction
Under these strict condition,
D= (n-1) * A
For glass prisms
D= A/2
Plastic prism

10. Prentice position
 When the incidence angle is zero, so that all the deviation takes
place at the other surface of the prism.
 The “prentice position” power of the prism is greater than the
“angle of minimum deviation” power.
 Glass prism

11. Frontal plane position
Prism is held parallel to frontal plane
Very nearly produces MAD

12. MAD PRENTICE POSITION Frontal plane position

13. Notations of prisms
Prism dioptre ( Δ ) =Linear of apparent displacement
of 1 cm of an object that’s situated at 1 m.

14. TYPES OF PRISM
1. Dispersive prism
2. Reflecting prism
3. Polarizing prism

15. I. DISPERSIVE PRISMS
-Triangular prism
-Abbe Prism
- Pellin-Broca Prism
-Amici Prism
II. Reflecting prism
-Penta
-Porro
-Dove
III. Polarizing prism
-Nicol
- Wallastone

16. In ophthalmic use
The prentice position is specified for glass
ophthalmic prisms and the angle of minimum
deviation power is specified for the plastic prism.
Stacking prisms one on top of another doesn’t bring
cumulative power of both prisms, so it’s not advised...
except if used on different planes (one H & one V)
because of perpendicular planes which result in
independence refraction.

17. How do prisms enhance vision therapy?
 Stimulate accommodation, peripheral awareness, eye movements, convergence,
and other visual skills.
 Prism-based therapy exercises can facilitate changes in all of these visual skills
areas.
 Prism lenses also facilitate changes in posture, balance, coordination, and
cognition.
 While wearing prism lenses during therapy sessions, the patient not only receives
visual information, but also vestibular, proprioceptive, and tactile information.
 All of this new information forces the patient to be aware and actively involved
in the learning process, as their “new” vision is trained.
 Yoked prism lenses are a powerful therapeutic tool that serve to actively train
the brain for improved processing of visual information, and enhance the way
vision therapy exercises are performed.

18. PRISMS USED AS- IN OPHTHALMOLOGY
OPTICAL
DIAGNOSTIC
THERAPEUTIC

19. OPTICAL PRISM
1. Risley prim-?
2. Fresnel prism
3. Prism in keratometer-?
4. Telescope
5. Magnifying aids
6. May prism ?
7. Rodenstock prism ?
8. Slit lamp-?
9. GAT- ?
Ramsdan, Plano- wallastone
Porro
Biprism

20. DIAGNOSTIC PRISM
1. Hirschberg test
2. Krimsky test
a. krimsky
b. modified krimsky
3. Prism cover test
4. Simultaneous cover test
5. Maddox rod
6. Distance and near fusional reserve
7. Microtropia diagnosis
8. Intermittent deviations
9. Convergence
10.Divergence
FOR
MEASUREMENT
OF DEVIATIONS

21. 11.Accommodative convergence
12.AC/A
13.CA/C
14.VA in infants

23. Therapeutic indications
 Treatment of phorias
 Treatment of tropias
 Convergence insufficiency
 Divergence insufficiency
 Nystagmus
 Visual field defects (hemianopia)
 In the management of glaucoma and retinitis pigmentosa (RP)
 Prisms in treatment in bedridden patients
 Prisms in paralytic squint (diplopia)
 Prisms in contact lens (CL) correction.

24. Why do we need prism lenses?
 The following list includes the most common symptoms of vision conditions
that may be alleviated with prism lenses:
 Double vision
 Headaches
 Eye strain and fatigue
 Neck, shoulder and back pain
 Dizziness, vertigo and lightheadedness
 Unsteady gait
 Postural problems
 Feeling anxious in crowds and big open spaces
 Difficulty reading, fatiguing, losing place, words running together, etc.
 Difficulty focusing and maintaining concentration
 Difficulty driving for long periods

25. CLINICAL CLASSIFICATION OF
PRISMS TYPES
RELIEVING PRISM
CORRECTING PRISM
OVERCORRECTIONG PRISM
INVERSE PRISM
YOKED PRISM
ROTATING PRISM
REGIONAL PRISM

26. RELIEVING PRISM
 AIM:
Optically reduces thedemand to the controlling fusional vergence system for bifixation of the
target.
 AMOUNT PRESCRIBED:
Rx is less than the angle of deviation.
 COMMONLY PRESCRIBED FOR:
intermittent strabismics and phorias in certain instances.
 The most commonly prescribed prism.

27. MECHANISM:
The base is prescribed opposite to the direction of the
eyeturn.
Moves light closer to the fovea.
Eg: when BI is prescribed, retinal image moves nasally
towards the base of prism where as the apparent image
moves towards the apex prism i.e temporally
Thus, the amount of convergence needed to obtain foveal
bifixation of the real object of regard is optically reduced
for exodeviations.

29. Criterias for prescribing relieving prisms
1. Minimal criteria
2. Dissociated prism criteria
a. Percentage prisms
b. RVD criteria prisms
3. Associated prism criteria
a. Fusional prisms
b. Vergence-reserve prism
c. FDN prism
d. FDC prism
Sherad’s
criteria
Precival
criteria

30. Minimal criteria for relieving prism Rx
 It includes minimal Rx of prism of 1-2 PD
 In case of unsolved ametropia
 Reduces the vergence demand
 Non specific approach of prescription

31. Dissociated prism criteria
 With this method,the fusion free oculomotor deviation is
measured , and prism that optically reduces thus deviation is
prescribed.
1. PERCENTAGE CRITERION:
 Percentages equalling 1/3rd or ½ of the measured deviation is
prescribed
 Some may use higher like 2/3rd
 For horizontal angke of >10 PD, 1/3rd of deviation is adequate
due to..LRVD
 Clinically may be effective but lacks spacificity for other cases

32. 2. Residual vergence demad criteria(RVDC)
 Considers the deviation size that can be expected to be controlled efficiently and
comfprtably through normal sensorimotor fusion skills.
 Prism is chosen that reduces the dissociated deviation to RVD , needed for predicted
confortable vergence control
 Residual vergnce demand critera guidelines
PATIENTS TYPES DEVIATION RVDC
Esodeviations 6-20 pd 4-6 pd
Hyperdeviations 3- 10 pd 2-4 pd
Exodeviations 20- 30 pd 10-15 pd

33. ASSOCIATED PRISM CRITERIA
 Consider eye positioning or vergence responses when
binocular vision is present
1. FUSION PRISM CRITERION
 The minimum amount of prism that produces either a stable
second-degree fusion response or a normal level of
stereopsis is prescribed for full time wear.
 A typical example would be prescribe prism that changes a
Worth dot response of five dots (diplopia) to four
dots(fusion) for an intermittent strabismus.In this case, the
prism power needed for fusion at different distances or gazes
should be considered before arriving at the final prescription
power

34. 2. VERGENCE RESERVE CRITERIA
A.Sherad’s criterion
 It states that the relative fusional vergence reserve (as
measured by the blur point) should be twice as large as the
fusional demand) i.e the dissociated deviation or the so-
called phoria in heterophoria
 Best for EXO patients
 The fusional reserve must be at least 2 times the demand
 Prism = 2(phoriaa) – compensating vergence finding/3
 Demand = phoria calculated, Reserve = compensating
vergence

35. Can also be expressed as
Prism Needed = 2/3(Demand) – 1/3(Reserve)
ex) @40cm = 10xp || BO: 12/20/10
So Demand = 10 || Reserve = 12
Prism = ?
If the pt has 8 PD exophoria while measuring
at distance of 40 cm and a base-out-to blur is
10 PD then what will be the prism prescription?

36.  1:1 Rule
 Best for ESO patients
 The base in recovery should be at least as great as the amount
of the esophoria
 Base-Out Prism Needed = (Esophoria – BI Recovery) / 2
 ex) @40cm = 12ep || BI: 12/18/8
 12ep – 8 / 2 = 2BO needed
 https://www.aao.org/focalpointssnippetdetail.aspx?id=6aa2f58f-
cacc-4a5a-9b79-cb5dfc2ac1ca

37. B.PERCIVAL CRITERIA
 states that the target demand should fall in the
middle third of the fusional range if comfortable
binocular vision is to be present.
Comfort zone is the middle third of the width of
the Zone of Clear Single Binocular Vision,
Base in Prism Needed = 1/3G– 2/3L
Where G= (Greater of lateral range blur limit BI or
BO)
Where L = (Lesser of lateral range blur limit BI or
BO

38. ex) BI: 26/30/20 || BO: 6/14/8
So G= 26 || L= 6
Prism =?

39. 3.FIXATION DYSPARITY CRITERIA
4.FIXATION DYSPARITY NEUTRALIZATION
CRITERIA
5.FIXATION DYSPARITY CURVE CRITERIA

40. CORRECTING PRISM
 AIM:
Optically eliminates the oculomotor deviation.
 AMOUNT PRESCRIBED:
Rx prism equal to the magnitude of the objective angle.
 The residual vergence demand is zero.
 Ways to prescribe:

41. MECHANISM
Rx the base opposite to the direction of the
deviation.
In certain cases, sensory fusion can occur without the
need for any fusional vergence if there's no ARC or
deep suppression.
EXCEPTIONS:
don't give patients with ARC or deep suppression
corrective prism.

42. NOTE:
Never Rx relieving and correcting prism for ARC patients
because they will "eat it" and it will make the deviation
look worse.
if you give a 20∆ ET with HARC 7∆ BI, the observer will see
the eye shifted out and to maintain the HARC, the patient
will diverge the amount of the prism 7∆ ,so the ET will
look smaller
For a 20-30∆ ET with HARC and a poor prognosis, a
8∆prism is a good first lens.
You put the prism over the strabismic eye.
If you get patient<20∆,you make them a non cosmetic ET.
These patient rarely complain of diplopia.

43. OVER CORRECTING PRISM
 AIM:
optically changes the direction of the deviation.
 AMOUNT PRESCRIBED:
The power of the prism is greater than the magnitude of the deviation.
 Example : 20 ∆ XT = give 25 – 30 ∆ BI
 In such a position on a cover test ,you see the deviation reverse in terms of direction.
AKA disruptive prism
 Ways to prescribe

44.  MECHANISM:
overcorrecting prisms move the image beyond the fovea opp
to hemi retinal area than that was previously stimulated.
 This kind of like when you get reversal on ACT.
 An eso becomes an optical exo.
 Used on certain instances
 To disrupt ARC through a specific technique.
 To change ARC to NRC.
 To eliminate existing suppression zone in retina

46. INVERSE PRISM
 AIM:
optically increase the demand to the controlling vergence system
by putting put the base in the same direction as the deviation
 AMOUNT PRESCRIBED:
2-6 pd initially and gradually increase in strenghth for constant
wear and certaion visual activities
 Eso = give BI
 Exo =give BO

47. MECHANISM:
by increasing the fusional vergence
USES
To eliminate ARC
To eliminate eccentric fixation
As exercising as well as training prism

48. Uses of inverse prism
1. TRAINING
Only used for a phoria patient in the later stages of strab
VT.
Ex) Give BO to an exophoria to increase the convergence
demand for bifixation.
the patient has to use vergence to control his deviation
and also to meet the demand of the prism.
a passive technique.
commonly used for VT (ex: read through prism). -some
people Rx in glasses~ less common

49. 2. DISRUPTIVE:
 To eliminate EF and ARC
3. COSMETIC
 Used when there is poor prognosis for a functional cure and the patient doesn't want
surgery or surgery isn't indicated.
 makes the eye look better.
 ex) ET =give BI
 You'll see a dual effect if the patient has ARC:
 The observe sees the eye moved temporally when looking through the prism.
 The patient will make anomalous motor fusion movements.
 If you were to give a 20∆ET with HARC 5∆BO of relieving prism:
 The image is shifted but the patient wants to maintain the HARC so he makes a convergence
movement of 5∆
 On a CT, you'll measure 25∆ET.
 This is called prism adaptation or eating prism and ARC patient are notorious for this.

50. YOKED PRISM
 AIM:
To synergistically move eyes from primary gaze to different
field of gaze to stabilize binocular vision.
 AMOUNT PRESCRIBED:
Differs from person to person usually 5-m10 PD
 WAYS TO PRESCRIBE:
(BO OD & BI OS ) BASE RIGHT prism
( BI OD & BO OS ) BASE LEFT prism
 BASE DOWN prism ( OU )

51. MECHANISM:
Optically moves the retinal images of a fixed target
a parallel direction toward the base and moves the
light toward the base and shows the target toward
the apex.

53.  USES OF YOKED PRISM
1. HEMIANOPSIA:
 more : in low vision
 Give prism so you shift the patient's world over so that they're never looking where
they're missing vision.
2. PARETIC MUSCLE
 Ex) =A little girl with a Duane's Syndrome OS (13y.o.)
 abduction deficit
 She presented with a small head turn
 If you straighten her head or she looks into L gaze, she sees double.
 We could have given her base L prism if she would have had a significant head turn.
 The prism would shift the world over to the R and move the eyes from L gaze so she
won't have to turn her head

54. 3. NYSTAGMUS
 To move the eyes into the null position.
 Null position = position where the frequency and magnitude of the
is dampened or eliminated.
 when you Rx prism with non concomitant deviations to get fusion ,you put all
or most of the prism in front of the paretic eye.
 Typically we just split prism equally between the two eyes for cosmetic
purposes.
 EXAMPLE:10 ∆ Right ET & has a RLR paresis
 when the prism is before the OS, the light is bent toward the base and the
image is projected toward the apex. Initially, the first movement is going to be
a version inward by the left eye.
 BY Herring's Low , the right eye will move outward and then there will be a
fusional vergence movement.
 since you are forcing the OD to move into the field of gaze of the eye to

55. ROTATING PRISM
 AIM:
change from ARC to NRC.
 AMOUNT PRESCRIBED
varies from person to person but usually 10 pd
 WAY TO PRESCRIBE:
Take a Fresnel prism and cut it round. For one week ,the patient wears it BO and
then you rotate it to BU, then BI, then BD.
 Take prism and change the base.

56. MECHANISM
provides a method of changing sensory input for
consant strabismic patient
Uses:
To break down ARC.
This is a disruptive prism technique.

57. Regional prism
 AIM:
To stabilize BSV in different gaze or at different distance.
 AMOUNT PRESCRIBED:
Different amounts of prism are needed in different fields of gaze or for different
distances.
 WAYS TO PRESCRIBE:
ex) 20∆ET at distance and 10∆ET at near Only put the prism on a portion of the
lens.
 ex)only need prism in R gaze.

58. MECHANISM:
reduces the demand for controlling the fusional
vergence in more than one gaze or distance
AKA sector prism.

59. When to pescibe prism
 Think what type of Prism you are going to give the patient.
 If the patient doesn't have normal sensory fusion or has ARC or suppression
,don't Rx relieving prism or corrective prism right away.
 Prism to break down ARC or suppression:
 Over corrective
 Inverse (disruptive)
 Rotating
 Regional Prism
 describes where you are mounting the Prism.
 you can Rx corrective regional relieving Prism.

60. What are the benefits of prism glasses?
 Prisms can be used as a therapeutic tool to provide the following
benefits:
 Alleviate diplopia (double vision)
 Reduce stress
 Increase comfort
 Increase sustaining ability on near tasks
 Increase efficiency
 Restore postural adaptation
 Provide control and protection against additional adverse
adaptation

61. Types of prism used in VT
Loose prism
Prism bars
Risley prism
Fresnel prism
Prism flipper

62. Vision Training Techniques:
a) Stimulate eye movement toward apex of prism
b) Stimulate convergence
c) Stimulate divergence
d) Decrease suppression
e) Reorganize spatial perception:

63. Prism therapy can be given as
1.Monocularly
2.Binocularly
3.Bi-ocularly
4.Yoked prism

64. Slab-off Prisms
 The slab-off prism is placed on the more minus or less plus lens,,
(adds base-up prism)
 The reverse-slab prism is placed on the more plus or less minus lens,
(adds base-down prism)
 An anisometropic patient may experience–diplopia/asthenopia if
the line of sight doesn’t pass through optical center of spectacle
 This is due to displacement induced by net prismatic effect.
 Eg - +1.00 OS and – 3.00 OD, will have difficulty even at 1cm below
from the optical center
 To correct them, Vertical prisms are used in the lower portion of
one lens

65. Amblyopia
 Can be use in diagnosis and treatment
 Diagnosis
 10 Prism test ( vertical Prism test / induced tropia test )
 Preverbal with straight eyes / small angle deviation – for
accurate diag.
 Test – 10 to 15 BU/BD in front of one eye – induces vert. starb.
And fixating presence can be known Inference
 Spontaneous alteration

66. Solution
slab-off Prisms (or) Bicentric Grinding
Myopes- back ; hypermetropic – front
Other – C.L , separate glasses for Nv and Dv, lowering
optical center to an intermediate
prisms are referred to as slab-off or reverse- slab
prisms

67.  Hold well – Smooth / blink fixation by other eye by movements for
atleast 5 sec.
 Holds briefly – refixation delayed by 3 sec.
 Hold momentarily – fixation maintained for 1 -2 sec.
 Will not hold – refixation as soon as prism is remover
 Treatment–Rarely done when therapy fails
 Most commonly for amblyopia eccentric fixation by passive
stimulation of amblyopic eye with full prism correction +
atropinization + Nv correction with + 3 DS

69. Aphakia and Pseudophakia following
Cataract Surgery
Diplopia post cataract Sx can been seen as a late
complication which
can be treated by prisms
Most commonly seen with traumatic cataract due to
torsion

70. Childhood Cranial Nerve Palsies (Third, Fourth,
and Sixth Cranial Nerves)
early treatment is important to prevent amblyopia.
Prisms may be used for smaller amount in order to
maintain binocular function
Fresnel prisms is recommended prior to grinding
prisms into the child’s lens
if prism therapy fails, surgery should be considered.

71. Homonymous hemianopia
 Prisms may be used in
patients with homonymous
hemianopia to bring images
from an area within the
visual field.
 Very high prism powers are
required, which can create
cosmetic problems/
confusing visual
environment in which
objects may appear and
disappear from view
unexpectedly

72. Nystagmus with head turn
 Patients with a head turn to compensate for
nystagmus can benefit from yoked prisms.
high prism powers which may lead to decrease in
visual acuity.
Prescription of bilateral yoked prisms, with base in
the same direction as the head turn, can keep the
patient’s eyes in an eccentric null position while
lessening the head turn.

74. Malingering
Prism Dissociation test
For malingering in monocular blindness
Subjective correction with a 4∆ vertical prism will
cause diplopia
BO prism for the ill eye and when focused to
eliminate diplopia malingering is ruled out

75. Head/neck position problems
patients with severe ankylosing spondylitis,
may benefit from prisms.
 base-up “yoked” prisms can allow for
improvement in straight-ahead vision.

76. Field Defects
 Prisms can be used in the management of visual field defects -
m.c hemianopia's
 They expands the field of view in the direction of hemianopia's
 Object that falls on the edge of the scotoma of one eye is seen
by the other eye
 15 prism is placed over the effected eye with the base towards
the defect, trimmed to be 2mm away from the mid-pupillary
line, avoiding interference with central vision
 Can be used in stroke,field defects and visual neglect patients

77. convergence insufficiency
 To resolve convergence, base-out prisms are used which force the system to
work harder to converge.
 Base-in prisms can be used to artificially align the eyes for reading; however,
their use, patient will develop stronger convergence on their own.

78. Other uses
Incorporated into C.L. for vertical diplopia
For exercise–it increase fusional convergence
ARMD – to relocate retinal image to an area of
preserved retinal functions

79. Prisms prescribing method
 Basic Esophoria and Exophoria. Prism can be used alone or
in combination with vision therapy to treat basic esophoria
and exophoria.
 https://www.reviewofoptometry.com/article/perfecting-prism

80.  Divergence Insufficiency.
 patients are often symptomatic for diplopia and asthenopia at
distance and may present with a decompensated distance
phoria.
 is associated with systemic and neurological disorders, so we
must rule out any underlying conditions that may be causing it.
 Any patient presenting with divergence insufficiency and
neurological symptoms should undergo a full neurological
evaluation and imaging.

81.  Case #1
 A 25-year-old female presented complaining of double
vision and headaches that worsened with prolonged near
work. Her medical history was unremarkable, and her
history was remarkable only for low myopia, for which she
wore glasses.
 Upon examination, she had a small exophoria and a 3 PD
right hyperphoria at distance and near. Her vertical
associated phoria, which I determined using the Wesson
card, was 2 PD right hyperphoria. I trialed 2 PDs of base-
down prism using a Fresnel prism over the right eye and
dispensed at the initial visit. During a follow-up examination
three months later, the patient noted increased comfort
resolved diplopia and headaches while wearing the Fresnel
prism. A new prescription for prism lenses was dispensed to
the patient at the follow-up examination.

82.  Patients with constant strabismus may need corrective prism, or an amount of prism
that completely neutralizes their strabismus, in order to obtain good levels of fusion.
Relieving prism is often prescribed for patients with intermittent strabismus and
sometimes for those with constant strabismus. This decreases the motor fusion
demand, allowing the patient to fuse more comfortably. Prescribing for some patients
with intermittent strabismus can be done by using Sheard’s or Percival’s criteria or
determining the associated phoria as with heterophoric patients.

83.  Another method used for prescribing for patients with intermittent strabismus, particularly
for those who have difficulty with fusion in free space, is Caloroso’s Residual Vergence
Demand (RVD).7 RVD criteria look at the direction and size of the deviation and determine
how much residual vergence demand the patient should have after prescribing relieving
prism. RVD states that esotropic patients of magnitude 6 to 20 PDs should be left with 4 to
6 PDs of residual vergence demand. Patients with 20 to 30 PDs of exotropia should be left
with 10 to 15 PDs of residual vergence demand, and patients with a vertical strabismus of 3
to 10 PDs should be left with 2 to 4 PDs of residual vergence demand.7 RVD is best used in
patients who have vergence ranges that have been maximally trained through vision
therapy but still need prism to maintain binocular vision in free space.12

84.  Determining how much prism is required for improved fusion, or “fusion prism,” is
another method for prescribing prism for your strabismic patients. Fusion prism is
the minimum amount of prism needed to see a change from diplopia or
suppression to normal binocular vision.12 To determine prism using this method,
use the Worth Dot test to find a preliminary prism amount. While viewing the
Worth Dot test, prism is gradually increased until the patient reports fusion. You
can also use Random Dot Stereo (RDS) testing to determine fusion prism. Prism is
gradually increased until a patient is able to appreciate the forms on the RDS test.
After a preliminary prescription of fusion prism is determined, it is recommended
that you trial frame the patient and have them look around to see if they
experience any diplopia when viewing objects in the room. If your patient is still
experiencing diplopia, additional prism may be needed to help them achieve
fusion.

85.  Case #2
 A 5-year-old female initially presented for a strabismus and amblyopia evaluation. She had been previously diagnosed with esotropia
and amblyopia but was not currently wearing any correction.
 On initial presentation, her best-corrected visual acuities were 20/40 OD and 20/25 OS. Her cover test revealed a 25 PD constant
esotropia with a 2 PD constant right hypotropia. Her cycloplegic retinoscopy was +3.00sph OD and +2.25sph OS. I prescribed glasses
(+3.00 sph OD, +2.25 sph OS) for the patient, and she returned for follow-up care, eventually patching and undergoing vision
for her amblyopia.
 Through her full plus spectacles, she still had a 14 PD constant right esotropia and a 2 PD constant right hypotropia. Beginning
treatment, the patient suppressed on Worth Dot testing and had no RDS stereoacuity, even with corrective prism in place. As her
improved with amblyopia treatment, I continued to monitor her sensory fusion.
 At the follow-up examination after nine weeks of patching and vision therapy for amblyopia, her visual acuities were equal in both
and all testing showed normal correspondence. She was able to fuse on the Worth Dot test with 12 PDs base-out and 3 PDs base-up
OD. With a trial frame, she was not able to appreciate RDS stereoacuity in-office. I prescribed 12 PDs base-out and 3 PDs vertical
split between her eyes.
 At the follow-up examination, she reported no diplopia in her glasses, and, eventually, she was able to see 250 seconds of arc RDS
stereoacuity. This patient continued with vision therapy to help improve her sensory and motor fusion with the hope of eventually
titrating down the amount of prism she wears.

86. Refrences
1. Binocular vision and ocular motility – Von Noorden
2. Primary care optometry
3. Clinical management of strabismus- Elizabeth E Caloroso & Michael
4. Theory and practice of optics and refraction- AK kHURANA
5. AAO
6. http://innovativeeyecare.com.au/patient-
resources/U4LXhwEAAC8ACeZP/Vision%20Training%20With%20Loose%20P risms
7. http://www.oepf.org/sites/default/files/22-5-FOX.pdf
8. https://www.reviewofoptometry.com/article/perfecting-prism
9. Pictures – internet sources