1. UNIVERSITY OF GONDAR
COLLEGE OF MEDICINE AND HEALTH SCIENCES
DEPARTMENT OF OPTOMETRY
Refraction and optical management of strabismus patients
Prepared by : Biruk Lelisa
4/5/2022 1

2. Objective
 At the end of this seminar you are expected to:
• List important techniques of refraction for squint pts
• Identify forms of spectacle as a squint management
• Identify indications, aims and principles of prism as a squint
management
• Discuss optical management for specific squint types
• Consider optical management for squint pts
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3. Outline
• Introduction
• Refraction techniques
• Options of optical squint management
• Optical management for specific squint types
• Case
• Articles
• Reference
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4. Introduction
• Squint can be accurately measured using prism and cover tests
• Initially a cover test is performed to determine the fixating eye
and estimate the deviation
• Followed by the prism and alternating cover test, with
adjustment of prism strength until refixation movement of the
eyes is neutralized
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5. Introduction
 Aims of management of Strabismus
• To exclude serious underlying cause
• To maintain or restore optimal visual acuity in each eye
• To maintain or restore normal (subnormal) BSV
• To restore appropriate ocular alignment
• To eliminate diplopia or other induced symptoms (asthenopia)
• To correct significant abnormal (compensatory) head posture
• To improve binocular VF (in the case of esotropia correction)
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6. Introduction
 Basis for Treatment
• Age of the patient at the onset of strabismus
• Current age of the patient
• Overall health status of the patient
• Compliance with therapy
• Concerns of the patient and/or parents
• Symptoms and signs of visual discomfort
• Visual demands of the patient
• Comitancy of the deviation
• Size and frequency of the strabismus
• Presence or absence of fusion
• Presence or absence of amblyopia
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7. Introduction
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8. Refraction for squint pts
• Cycloplegic refraction
• Dry refraction
• Techniques for performing retinoscopy
o Occluding rather than fogging
o Being on the deviating eye position
o Giving target on the deviating eyes position
• Routine subjective refraction
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9. Optical management of squint
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• spectacle
• contact lens
• Prism
• Combination
o Of those optical options
o With non optical options

10. spectacle for squint
• Full Rx
• Modified Rx
• Bifocal/ executive type
• PAL
• Contact lens
o Accommodative esotropia with a normal AC/A
o Any small deviation with RE
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11. prism
 Goals of Prismatic Correction
• Restore binocularity and/or fusion
• Relieve or eliminate diplopia
• Alleviate abnormal head position
• Relieve asthenopic symptoms
• Achieve pleasant Cosmesis
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12. Ways of incorporating prism in spec.
1. Ground In Prism
2. Fresnel Prism (Press-on Prisms)
3. slab-off (Bi-centric grinding)
4. By displacing OC
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13. Slab-off
• Used to correct vertical diplopia in the reading position
• Expensive and should only be considered for stable deviations
 Three grinding techniques for slab-off prism effects
1. Conventional slab-off: Produce base-up prism in the lower
section of the Most Minus or Least Plus lens
2. Reverse slab-off: Produces base-down prism in the inferior
portion of the Least Minus or Most Plus
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14. By displacing OC
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15. Facts
• Larger prism cause image distortions, and poor appearance of
lens and pt, Due to its effect on thickness and weight
• 1Δ adds 1 mm of lens thickness
• Fresnel prism is available up to 40Δ
• But, prisms larger than 8–10Δ start having a poorer optical
quality and will cause ↑sed reflections and a ↓se in VA and CS
• Smaller eye size lens, high index lens material, ARC, and lens
edge Txs can all improve prism lens appearance
• Use on the non-dominant eye, Fresnel lenses change color
over time
• If high prism power required, the total power can be divided
between two eyes (splitting)
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16. Types of prism
1. Relieving Prism:
o Goal: To stabilize sensorimotor fusion controlling
o Action: Reduces the demand for controlling fusional vergence
• In order to move the image to where the eye is looking, thus
restoring fixation and binocular vision: For diplopia
• Base of the prism is placed over the weak (or paralyzed
muscles)
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17. Types of prism con’t
2. Inverse Prism for Cosmesis:
o Goal: To enhance cosmesis of a squint for pt with poor Tx prognosis
o Action: Displaces z image of the eyes in a direction opposite to squint
•Expect ≈1 mm of apparent eye shift for every 8∆ of power
Indication
o For pts with poor VA in 1 eye/poor surgical candidates ≈15∆
prescribed
3. Inverse Prism for Training or Disruptive Prism Therapy:
o Goal: To increase fusional vergence ability
o Action: Increases the demand for fusional vergence
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18. Types of prism con’t
4. Yoked Prism:
o Goal: To stabilize BV
o Action: Directs the eyes into a specific gaze direction
Indications
•Homonymous hemianopia
•Hemispatial neglect
•Nystagmus with head turn
•Head/neck position problems
5. Sector / Regional Prism:
o Goal: To stabilize binocular vision in ≥1 gaze positions
o Action: Reduces the demand for controlling vergence in ≥1 gaze
•Can be applied to a portion of the lens...“A”/“V” pattern
deviations, noncomitant squint, hemianopic VF loss
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19. Principles of Prescribing Prism
 Always correct RE first
– Perform a Cycloplegic refraction with subjective manifest whenever
possible
1. Prism is best tolerated with smaller angle & Comitant squint
2. Perform a prism adaptation trial for 20–30 min
3. Demonstrate effectiveness first with Fresnel prism prior to
grinding into the lens.
4. Identify weather there is both a Vx and Hx deviation 1st
• address the primary deviation first
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20. Way of Prescribing ∆ for Combined Vx & Hx
(oblique ∆)
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21. Way of Prescribing ∆ for Combined Vx & Hx
(oblique ∆)
3. Prescribing the prism
•Draw a line directly on the outside of the spectacles, using the
base of the handheld ∆ as a guide
•Rx includes the ∆ power and a statement regarding the
orientation of prism
•Rx: 25-PD Fresnel prism base out and down as marked
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22. Way of Prescribing ∆ for Combined Vx & Hx
(oblique ∆)
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23. 4/5/2022 23

24. prism
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25. prism
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26. Prism indication
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27. Infantile Esotropia
 Management
1. RE correction:
• Amblyopia and any degree of significant (> +2.50 D) hyperopia
should be treated first
• Cycloplegic refraction to rule out an accommodative component
2. Prism: rarely effective due to lack of sensory motor fusion
3. Surgery: most common Tx option
• Earlier surgery advocated, as the critical period of BV is 3/4 mnth
4. Occlusion & Orthoptic Ex:
• Amblyopia is treated with the end goal of demonstrating
alternate maintained fixation
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28. Infantile Exotropia
• Same ase infantile esotropia
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29. Accomodative Esotropia
 Unifocal Rx
• Accommodative esotropia with a normal AC/A
 Bifocal Rx
• The goal is to encourage relaxation of Accommodative
system
• The most difficult task @ the onset of Dx is minimizing Angle of
deviation & simultaneously maximizing VA….this Allows for An
eventual increase of the hyperopic correction in single vision
form As plus Acceptance increases…follow with 3 mnth interval
to check lens power changes
• Successful in pts with moderate to high AC/A ratio
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30. Accomodative Esotropia
 The time to consider bifocal
1. If the residual deviation exist with the full Amount of Hyperopia
• Determination of bifocal power for An Accom. Eso pt should be
based on AC:A ratio
eg. If pts AC:A ratio is 4:1 with 10 prism D intermittent eso @near
with full cycloplegic Rx , then +2DAdd would Aim to reduce the
deviation to a 2prism D esophoria
2. If the pt can not tolerate full Cycloplegic Rx
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31. Accomodative Esotropia
 Issues to be considered in prescribing bifocal segment
in pediatrics
• In younger preschool population, consider in a manner that
will inforce the ease of use of bifocal
o Recommended segment height is @ lower pupil margin
• As child matures
o height can be lowered to lower lid margin
• Proper frame selection is Also vital to make bifocal functional
• Flat top executive type Add have been practiced better so
far….if cosmesis is An issue ,PAL is An option for young
children
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32. Accomodative Esotropia
 PAL to control esotropia
1. Widest segment Available
2. raise the segment height to the lower pupil
3. increase the desired Add power by At least +0.25D
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33. Accomodative Esotropia
 Relieving prism
• Prescribing BO ∆ for the pt that ↓se or eliminate z deviation
• In Accom. Eso. Pt with central fusion, prism is An option to
decrease motor demand
• Prism will be grounded for pts with mild- moderate residual
deviation with their full Cycloplegic/ maximal tolerated Rx
• Some magnitude of eso deviation must be determined both @
distance and near to be prescribed
• If the residual eso is only @ near, the ∆ Rx is likely to induce
diplopia @distance. bifocal is better Tx option in this case
• Prism with bifocal is better to control the residual deviation
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34. Accomodative Esotropia
 Follow up
• Accommodative Eso pediatrics should be followed 3-4wks After
the initiation of full time spec. correction
• It may need some time for an esotropia to respond to the
hyperopia(Attendants should be awared)
• Appropriate follow up is every 9-12 months
• For esotropia not fully controlled with hyperopic correction,
more frequent follow up will be needed
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35. Intermittent Exotropia
 Management options
1. RE correction
o pts are sensitive to small degree of RE especially astigmatism
2. Prism
o excellent option to decrease frequency &magnitude of deviation
3. Over crxting minus lens therapy
o (stimulating convergence with minus lens to decrease frequency
&magnitude of deviation)
4. Orthoptic training & Occlusion
o Improve vergence control tackle suppression respectively
5. Surgery
o for cosmetically bad and can not control with other options
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36. Intermittent Exotropia
 RE correction
• The clear, single retinal images produced with proper RE
correction can improve fusion and reduce or eliminate exotropic
deviation
• Any effective degree of each type of RE can be prescribed for
intermittent exotropia to elicit a higher frequency of fusion
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37. Intermittent Exotropia
 Relieving prism
• The goal is to give the pt sufficient aid in convergence to
place the exotropic deviation @ the magnitude that can be
compensated by pts convergence skill
• Prescribing BI prism that will decrease /eliminate the deviation
• In pediatric pts, the practitioner may not be able to elicit
Accurate diagnostic values regarding divergence
&convergence Amplitude…simply prescribe ∆ that will leave
the pt with the desired 10-15∆ of Convergence demand
• Can be used as demand decreasing type of therapy
• Can be used in conjunction with other options
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38. Vertical Squint
 Management options
1. RE correction
o As appropriate for vision and visual function
2. Prism
o effective for smaller vertical deviations(<10prism)
3. Occlusion
o not Applicable in most cases; Amblyopia is rare
4. Surgery
o common Tx option for larger deviations
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39. Vertical Squint con’t
 RE correction
• Any effective degree of each type of RE have to be corrected
1st
 Relieving prism
• goal is to eliminate diplopia & Any Anomalous head posture to
improve fusional Ability
• Prescribing Vx prism for pt that will decrease /eliminate the
deviation
• In pediatric pts, we may not be Able to elicit Accurate values
regarding Vx vergence ranges…simply prescribe prism that will
leave the pt with the desired 2-4 ∆ of Vx vergence
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40. Vertical Squint con’t
• B-Down for hyper….B-Up for hypo-eye
• Deviations ≤ 10 prism can be grounded into spectacles
• Splitting for the two eyes can be considered
• Deviations >10prism can be prescribed As Fresnel membrane
prisms…to improve optics, cosmesis and comfort
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41. Consecutive & Residual squint
• If the patient complains of diplopia, the least amount of prism is
given to allow fusion
• The prisms are reduced until the esotropia subsides or are
continued until surgery is performed
• Frequent follow up needed
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42. Case
• Age: 5yrs old
• Sex: Male
• UVA: OD: 6/18 OS: 6/12
• PD: 50mm
• AC/A: 10/1
• Sensory evaluation:
• W4DT: Left dominant
• Motor evaluation
• OM: full & normal with H pattern
• Prism cover test: 35∆ esoT @ 33cm
20∆ esoT @ distance
• Cycloplegic refraction
• OD: +4.00Ds
• OS: +3.00Ds
• Prism cover test with Cyclo-Rx:
• Distance: orthoT
• Near: 15∆ esoT
• W4DT with Rx
• Distance: no diplopia & suppression
• Near: Left dominant
• Near add of 1.50D relieves it
• Ass’t: Accommodative esotropia
• Plan: to give full cycloplegic Rx
with +1.50D add (bifocal
spectacle) for full time wear
• ff up: after 1 month
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43. Articles
1. 2012 Board of Regents of the University of Wisconsin System,
American Orthoptic Journal, Volume 62, 2012, ISSN 0065- 955X, E-
ISSN 1553- 4448
2. Curr Opin Ophthalmol 2012, 23:400–404,
DOI:10.1097/ICU.0b013e3283567276
3. Gill Roper-Hall (2005) Optical Management in Strabismus: Simple,
Advanced, and Unconventional Techniques, American Orthoptic
Journal, 55:1, 144-157, DOI: 10.3368/ aoj.55.1.144
4. N Engl J Med 2007;356:1040-7.
5. Am J Ophthalmol 2007;143:1063–1065. © 2007 by Elsevier Inc. All
rights reserved
6. Sung Hee (Kelly) Lee, et’al (2015) Optical Management Using
Monovision and Yoked Prism for Acquired Strabismus and
Nystagmus Secondary to a Neurodegenerative Disease, Neuro-
Ophthalmology, 39:3, 147-151, DOI: 10.3109/01658107.2015.1035450
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44. Reference
• AOA guideline, Care of the Patient with Strabismus: Esotropia and
Exotropia, 2017
• Binocular Vision and Ocular Motility, THEORY AND MANAGEMENT OF
STRABISMUS, 6th edition
• Guidelines for the Management of Strabismus in Childhood March 2012
• Harley’s Pediatric Ophthalmology, 6th Edition, 2015
• Practical Management of Pediatric Ocular Disorders and Strabismus, A
Case-Based Approach
• Visual Development, Diagnosis, and Treatment of the Pediatric Patient,
May 2006
• CLINICAL STRABISMUS MANAGEMENT Principles and Surgical
Techniques, 2nd edition
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Thank you!!!!!!