High Myopia with IDS and High Myopia with IDS and VV

Dr. Madhu KarnaDr. Madhu KarnaM.S., Fellow Strabismus (Sankara M.S., Fellow Strabismus (Sankara

Nethralaya)Nethralaya)Consultant Pediatric Consultant Pediatric

Ophthalmologist,Ophthalmologist,

• Plus lenses decrease and minus Plus lenses decrease and minus lenes increase the measured lenes increase the measured deviationdeviation

• If glasses are plusIf glasses are plus Measured deviation = True deviation – 2.5 D%Measured deviation = True deviation – 2.5 D% [D-lens power][D-lens power]• If glasses are minusIf glasses are minus Measured deviation = True deviation + 2.5 D%Measured deviation = True deviation + 2.5 D%

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

Spectacle Spectacle lens powerlens power

True True deviation as deviation as %of %of measured measured deviationdeviation

To find true deviationTo find true deviation

Change Change

measured measured

deviation by Exampledeviation by Example

-20-20 6767 Decrease by Decrease by 33%33%

4/64/6

-10-10 8080 Decrease by Decrease by 20%20%

4/54/5

PLANOPLANO 100100 No changeNo change 4/4 4/4

+10+10 133133 Increase by Increase by 33%33%

4/34/3

+20+20 200200 Increase Increase by100%by100%

4/24/2

DISCUSSIONDISCUSSION

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

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

• This becomes Sx significant with refractive errors of This becomes Sx significant with refractive errors of ++ 5 5 dd

• These analysis dealt with strabismus measurements with These analysis dealt with strabismus measurements with distance fixationdistance fixation

• While fixing for near the visual axes no longer pass thru While fixing for near the visual axes no longer pass thru optical centre of lenses, prismatic effects get importantoptical centre of lenses, prismatic effects get important

• Distance model predicts the near situation if distance Distance model predicts the near situation if distance graph is multiplied by 0.90graph is multiplied by 0.90

PreoperativePreoperative

POSTOP