Do Spectacles alter all squints?

Dr. Madhu KarnaStrabismologist

Accomodative esotropia

Infantile esotropia after surgery

Hyperopia & Congenital esotropia

Frequency Degree Management

Habitual Mild Earlier surgery

Occasional Significant(>3.5D) Early surgery contraindicated

Postoperative Eventual increase Secondary Et that improves with

optical Rx

This squint may trap you by seeming simple but

HYPEROPIA WITH EXOTROPIA

Before you operate this patient

Just remove the glasses

Esotropia without glasses !!

What is it?

High hyperopia with Accomodative Esotropia with Consecutive ExotropiaExotropia

High hyperopia with Accomodative Esotropia with Consecutive Exotropia

Reduce hyperopic power by half

If exotropia still manifest or there is a drop in visual acuity then operate on the consecutive Exotropia after measuring over maximum cyclopegic refraction.

What do you do when you see this kind of a patient?

EXOTROPIA

HIGH MYOPIA

ESOTROPIA

HIGH HYPEROPIA

Or one like this

Do you measure with prism over glasses and operate on the measured angle?

A hyperopic patient of +10.00 ref error measured to have 50 pd of esotropia over glasses.

He was operated for 50 pd to achieve ortho

but was undercorrected

with residual eso of 15-20pd

We really don’t learn anything from our experience we only learn from reflecting on our experience.

ARTIFACTS INTRODUCED BY SPECTACLE LENSES IN THE MEASUREMENT OF STRABISMIC DEVIATIONS

KIRK D. SCATTERGOOD , M H BROWN,D L GUYTON

AJO 96:439-448,1983

The peripheral prismatic effect of corrective spectacles introduce an

artifact when measuring strabismus

The peripheral prismatic effect of corrective spectacles introduce an artifact when measuring strabismus

cθt∆t

h

11.5 13.5

25

D

∆m

[ ∆t ][ ∆t ] x 100 = x 100 = 100 100 %%[ ∆m ] 1- 0.025 D[ ∆m ] 1- 0.025 D Simplified model

In clinical practice it is the measured deviation that is found first and true deviation must then be calculated

In clinical practice it is the measured deviation that is found first and true deviation must then be calculated

Calculating the true deviation

If glasses are plus Measured deviation = True deviation – 2.5 D% [D-lens power]

If glasses are minus Measured deviation = True deviation + 2.5 D%

In clinical practice it is the measured deviation that is found first and true deviation must then be calculated .

Using the simplified model the authors obtain an expression for true deviation [∆t]

as a percentage of measured deviation [∆m]

[ ∆t ] x 100 = 100 % [ ∆m ] 1- 0.025 D

Plus lenses decrease and minus lenes increase the measured deviation.

Spectacle lens power

True deviation as %of measured deviation

To find true deviationChange measured deviation by Example

-20 67 Decrease by 33%

4/6

-10 80 Decrease by 20%

4/5

PLANO 100 No change 4/4

+10 133 Increase by 33%

4/3

+20 200 Increase by100%

4/2

High Plus lenses in both exo & eso – M D <T D [undercor]

High Minus lenses in both exo & eso – M D >T D [overcor]

This becomes Sx significant with refractive errors of + 5 d

This formula deals with strabismus measurements with distance fixation

If you have built castles in the air, your work need not be lost, that is where they should be, now put the foundations under them.

If you have not measured with C L, with this formula you can still achieve orthophoria

Myope of 10D with measured deviation-exo of 40 pd was operated for the true deviation 32pd (20% less) which gave good alignment

-10D MYOPE WITH EXOTROPIA

POSTOPERATIVE

MEASURED DEVIATION 40PD PREOP

Take home message

Plus lenses decrease

&

Minus lenses increase

the measured deviation

Fortune favors the prepared mind

THANK YOU