Strabismus is misalignment of the visual axes of the two eyes. The inability of the two eyes to simultaneously direct their foveae at a common object of regard, occasionally or always. May be accompanied by abnormal motility, double vision, decreased vision, ocular discomfort, headaches, or abnormal head posture. The best optical correction is the starting point. i. Helps to provide a sharp well focussed retinal image which helps fusional control and proper development of binocular vision. ii. Corrects and maintains the relationship between accommodation and convergence mechanisms.

1. University of Gondar
College of Medicine and health sciences
Department of Optometry
Optical managment of strabismus
Getachew Kassahun ( B optom)
October, 2023
11/16/2023

2. Contents
• Introduction
• Goals of strabismus managment
• Principles of strabismus managment
• Considertions for managment
• Managment options
• Optical correction
• Bifocal
• Prism
11/16/2023 2

3. Introduction
• Strabismus is misalignment of the visual axes of the two eyes.
• The inability of the two eyes to simultaneously direct their foveae at a common object
of regard, occasionally or always.
• May be accompanied by abnormal motility, double vision, decreased vision, ocular
discomfort, headaches, or abnormal head posture.
11/16/2023 3

4. The goals of strabismus management
To detect /exclude serious underlying ocular or neurological diseases
To maintain or restore optimal visual acuity in each eye
To maintain or restore normal ( or subnormal) binocular single vision
To restore appropriate ocular alignment
To eliminate double vision or other induced symptoms like asthenopic symptoms
To correct significant abnormal head posture
11/16/2023 4

5. Principles of strabismus management
11/16/2023 5
1. Correct refractive Error
2. Treat amblyopia
3. Restore BSV if possible
4. Improve “cosmesis” if necessary

6. Considertions for treatment of strabismus
• Age of the patient at the onset of strabismus
• Current age of the patient
• Overall health status of the patient
• Patient's developmental level and anticipated
compliance with therapy
• Symptoms and signs of visual discomfort
• Visual demands of the patient
• Comitancy of the deviation
• Size and frequency of the strabismus
• Status of fusion
• Presence or absence of amblyopia.
11/16/2023 6

7. Management of strabismus
• Can be broadly classified as
Surgical and
Non- surgical
1. optical
2. vision therapy
3. medical treatment
Optical management options
Correction of RE (spec or CL)
Bifocals
 Prism
11/16/2023 7

8. Optical Correction( spec or CL)
• The best optical correction is the starting point.
i. Helps to provide a sharp well focussed retinal image which helps fusional control
and proper development of binocular vision.
ii. Corrects and maintains the relationship between accommodation and
convergence mechanisms.
11/16/2023 8

9. General principles to optical correction
1. Full cycloplegic correction should be prescribed specially in younger
children from infancy to preschool age
2. In school going children, the refractive correction should provide an optimal
distance vision.
11/16/2023 9

10. Spectacles
• Spectacle prescription after cycloplegic refraction, can correct strabismus
partially or completely( e.g fully accomodative ET)
• Spectacles can be used for prism incorporation by decentration.
11/16/2023 10

11. Optical corrections in Esotropia
11/16/2023
1. Fully Accommodative ET: full cycloplegic correction should be made to correct
the ET. the deviation gets neutralized with RE correction
11

12. Optical corrections in Esotropia...
2. Partially accommodative ET
 Full cycloplegic Rx
 Show reduction in the angle of esotropia when wearing glasses
 Surgery is reccommended for the residual ET.
11/16/2023 12

13. 3. Accommodative ET with high AC/A ratio
Need to be treated with bifocal glass
Full hyperopic correction in the distance segment and add off upto +3.00 in
the near segment.
• Plus lenses for uncorrected hyperopia reduce accommodation and therefore
accommodative convergence.
• Bifocal glasses further reduce or eliminate the need to accommodate for near
fixation
11/16/2023 13
Optical corrections in Esotropia

14. Optical corrections in Esotropia...
Considerations for bifocals
• Flat- top style bifocals are prescribed initially
• The clinician should use lowest plus power needed (up to +3.00 D) to achieve ocular
alignment at near fixation.
• The bifocal segment should be set high enough that the top of the bifocal segment
bisects the pupil.
11/16/2023 14

15. 11/16/2023

16. Optical corrections in Esotropia
4. Residual ET of small amount( <15PD) should be prescribed the maximum
hyperopic correction. additional plus may be considered
5. Small consecutive ET persisting after 3 weeks of surgery can be treated by
prescribing full hyperopic correction.
11/16/2023 16

17. Optical corrections in Exotropia
1. Full cycloplegic Rx for myopia and undercorrection of hyperopic error is
recommended to reduce the degree of consecutive exotropia. However should not be
at the cost of astenopic symptoms
2. Inverse bifocal with a minus add for near can be used for a convergence insufficiency
type of exotropia.
11/16/2023 17

18. Optical corrections in Exotropia
3. Intermittent XT
• Correct significant refractive error
• Consider over minus to stimulate accommodation
• Patching
• Observation if low frequency of deviation and no associated refractive error
• Patients who have well- controlled, asymptomatic intermittent exotropia
and good binocular fusion can be observed
11/16/2023 18

19. Prisms
Goals of prism corrections
 Restore binocularity and/or fusion
 Relieve or eliminate diplopia
 Alleviate abnormal head position
 Relieve asthenopic symptoms
11/16/2023 19

20. Clinical uses of prism
Prisms may be used in one of two ways
1. Relieving prism
• The principle is to deviate the image of the fixation object onto or close to the
fovea ,so that the patient can fuse diplopia or control the residual deviation
2. Exercising prism
• The principle is to deviate the image of the fixation object away to the fovea ,so
that the patient has to exert motor fuse to maintain BSV
11/16/2023 20

21. Indications of Prism therapy
• Vertical deviation (small degree)
• Divergence insufficiency
• Paralytic strabismus with diplopia in the primary position
• Anomalous head posture
• Blow-out fractures
• Diplopia from convergence paralysis, muscle restriction or palsy
• Prior to surgery in some cases
• Over or under surgical correction
11/16/2023 21

22. Ways of incorporating prism in spectacle
1. Fresnel prism (Press-on Prisms)
( up to 40pd)
2. By displacing OC
3. Ground in prism
4. Slab-off (Bi-centric grinding)
5. Clip on prisms( 10-12 pd)
11/16/2023 22

23. Fresnel prisms
• A series of very narrow adjacent prisms on a thin sheet of plastic.
• The prism is flexible, enabling it to conform to the base curve of the spectacle lens.
• Advantage : Light weight, cosmetically acceptable, easy to apply on the back
surface of spectacle availability in power
• Ixs: large deviations, patients with diplopia and poor candidate for surgery, as trial
prior to surgery or grinding to spectacle,dynamic strabismus conditions( thyroid)
11/16/2023 23

24. Prism by decentration
• A larger uncut lens can be used to move the optical center from the pupil and
hence create a prismatic effect at the centre point.
• The amount of prism can be calculated from prentice’s rule
Δ= cF
where Δ is prism diopters, F is the dioptric power of the lens, and c is the distance
from the OC in centimeters.
11/16/2023 24

25. 11/16/2023 25

26. Base out prismatic effect
11/16/2023 26
Induced by
 Concave lense decenterd nasally
 Convex lense decenterd temporally
OCD
OCD
PD
PD

27. Power of prism
• The patient should be given smallest powered prism which makes him/her
comfortable.
• The power of prism is the total deviation in most cases.
• Prisms are usually prescribed for patients with strabismic deviations of less than 20
PD who are capable of fusion.
11/16/2023 27

28. Splitting or deviding prism
When prism is prescribed, it is usually divided equally between the two eyes to:
• Distribute the weight more evenly.
• Reduce thickness of the intended lens.
• Minimise chromatic aberration
11/16/2023 28

29. Prism for horizontal deviations
Compounding effect (prismatic effects of each eye are additive)
 The prism bases must be in the same direction OU.
Canceling Effect (prismatic effects are subtractive)
 The prism bases must be in opposite directions OU. For example, BI and BO
E.g a patient with 10 ET : 5 BO for each eye
11/16/2023 29

30. Prism for vertical deviations
For small amount of deviations (less than 12)
Compounding effect
• The prism bases must be in opposite directions OU.
Canceling effect
• The prism bases must be in the same direction OU. For example, BU OU.
Eg 4PD right hypertropia can be prescribed with 2PD BD(OD) and 2PD BU(OS)
11/16/2023 30

31. Oblique prism
• When horizontal and vertical deviation ( V and H prism)
• Equivalent single prism at oblique position can be used
• The resultant power can be calculated from resultant vector or pythagoras
11/16/2023 31

32. • Unavailability and expensiveness of Fresnel and plastic prisms
• Only applicable for small deviations (8-15 pd)
• Larger amounts of prism add to lens thickness and weight, cause image distortions,
and give the lens a poor appearance.
• 1Δ adds 1 mm of lens thickness
• Solution
• smaller eye size,
• High index lens material,
• ARC and lens edge treatments can all improve prism lens appearance
11/16/2023 32
Limitations of prism

33. Principles for prsim prescriptions
• Always correct refractive error first, after cycloplegic refraction
• Best tolerated with smaller angle and comitant strabismus.
• A prism adaptation trial for 20–30 min.
• Demonstrate effectiveness first with Fresnel prism prior to grinding into the lens.
• If there is both a vertical and a horizontal deviation, determine first if the vertical
deviation is the primary or secondary deviation.
11/16/2023 33

34. 11/16/2023 34

35. References
• AAO-BCSC 2022-2023, section 6; pediatric ophthalmology and strabismus
• Von Noorden GK, Campos EC. Binocular vision and ocular Motility: Theory and
management of strabismus. 6th ed.
• Modern system of ophthalmology: theory and practice of squint and orthoptics, 3rd
edition
• Michel sheiman & Bruce wick .clinical managements of binocular vision,4th edition
• Leonard B. Nelson and Scott E. Olitsky : Harley’s pediatric ophthalmology, sixth edition.
11/16/2023 35