IOL POWER CALCULATION IN PEDIATRIC PATIENTS

1. IOL POWER
CALCULATION IN
PEDIATRIC PATIENTS
DR ANISHA RATHOD
MS,FPOS
(PEDIATRIC OPHTHALMOLGY AND
STRABISMUS)

2. • THE AUTHOR HAS NO FINANCIAL INTEREST IN THE SUBJECT MATTER BEING
PRESENTED
FINANCIAL DISCLOSURE

3. FACTORS AFFECTING IOL CALCULATION
• Age at Surgery
• Laterality Age at surgery
• Laterality Post operative degree of amblyopia
• Axial length and keratometry
• IOL power
• Myopic shift
• Visual Deprivation
• Amblyopia
• Axial elongation - Fixed IOL power and change
in IOL position in growing eye
•
• Pre op form deprivation
• Stereopsis
• Target refraction
• IOL implantation
• Genetics
• Nutrition
• Heredity Factors
• Myopic shift is directly related to normal eye
growth in eyes in fixed IOL power

4. NORMAL EYE DEVELOPMENT
• At birth ,axial length=16.6-17 mm
• Keratometry=51.2 D
Corneal diameter
At Birth 16-17 mm
At 1 yr 20 – 21 mm
At 6 yr 23 mm
At 10 -15 yr- Stabilizes rapid growth
1st 3 months AL = 18.23 mm
Slow Growthtill 15 yrs ,AL = 23.6 mm
Most AL elongation Ist 2 years of life

5. LENS POWER
• 51 D AT BIRTH WHICH STABILIZES AT 6 MONTHS OF AGE WITH MINOR
CHANGE
• LENS POWER DROPS BY 10 D IN FIRST YEAR OF LIFE ,
• LATER DROPS BY ONLY 4-3D FROM 2 TO 10 YEARS OF AGE
• HENCE LENS POWER DROPS FROM 34.4 D AT BIRTH TO 18.8 AT 10 YEARS
OF AGE

6. MYOPIC SHIFT
• Expected postoperative residual refraction based on patient age at cataract surgery.
• Age at surgery Residual refraction to minimize late myopia
0
1st month + 12 + 8.3 4 – 5 years + 4 + 0.5
2 – 3 months + 9 + 8.5 5 – 6 year + 3 + 0.5
4 – 6 months + 8 + 6.0 6 – 7 year + 2 + 0.1
6 -12 months + 7 + 4.5 7 – 8 year +1.5 + 0.2
1 – 2 years + 6 + 3.0 8 – 10 year + 1 + 0.1
2 – 4 years + 5 + 0.9 10 – 14 years + 0.5
0 >14 years Plano -0.1

7. • EXPECTED COMPLIANCE
• Better to leave less refractive error if the child and/or family is expected to comply poorly with glasses,
contact lenses or occlusion therapy.
• PARENTS REFRACTIVE ERROR
• Important to ask about high refractive error (especially myopia) in the parents.
• Children with myopic parents expected more eye growth, these eyes left with more hyperopic.
• STATUS OF THE FELLOW EYE
• Surgery will be done in both eyes, a larger amount of hyperopia acceptable
• Aniseikonia avoided by equivalent refraction in both eyes

8. AGE & FELLOW EYE STATUS GENERAL RECOMMENDATIONS
• +12 D in first month of life
• +8 to 10 D the second to third month of the life
• +6 D in four to six months of life
• +4 D in six to 12 months of life
• Hoevenaars et al yielded the following equation using multiple regression analysis including prediction
error and myopic shift higher expected myopic shift in younger children and unilateral cataract
• Br J Ophthalmol 2011
Amount of myopisation: -7.97 + 0.05 × age at surgery +0.97 X bilaterality

9. POST OP REFRACTION
• Determine the Target Postoperative Undercorrection
• For children, another factor to consider is the projected growth of the eye.
• The ideal IOL power should give :
• 1)The best help for fighting amblyopia
• 2)Inducing the least refractive error in adulthood.
• Power can be calculated by anticipating the expected myopic shift and undercorrecting.

10. TARGET POST OP REFRACTION
AGE +
TARGET
HYPEROPIA
7
Enyedi LB et al. AJO 1978

11. TARGET POST OP REFRACTION
• OLDER CHILDREN
• •2 - 4 yrs IOL power = Sph equiv (fellow
eye) -1.25D
• •> 4 yrs IOL power = Sph equiv (fellow
eye)
Chen KP. Duane’s Clinical
Ophthalmology
• INFANTS
•< 6m : Moderate hyperopia (≥ 3D to 7D)
•12 m : Mild hyperopia (>0 to < 3D)
• Wilson ME et al. JCRS 2003

12. INFANT APHAKIA TREATMENT STUDY
• Objective—To compare contact lenses and intraocular lenses (IOLs) for the optical correction of
unilateral aphakia during infancy.
• Methods—In a randomized, multicenter clinical trial, 114 infants with a unilateral congenital cataract were
assigned to undergo cataract surgery either with or without IOL implantation.
• Children randomized to IOL treatment had their residual refractive error corrected with spectacles.
• Children randomized to no IOL had their aphakia treated with a contact lens
• 8 dioptres-4-6 weeks
• 6 dioptres-6 weeks-8months
• Fifty patients were 4–6 weeks of age at the time of enrollment, 32 patients were between 49 days and 3
months of age and the remaining 32 children were 3 to 7 months of age.
• Fifty-seven children were randomized to each treatment group with either IOL placement or aphakia.

13. DIFFICULTIES IN EVALUATION
•Difficult in office setting
•EUA
•Error in measurement

14. TECHNIQUE OF A SCAN
• Applanation-Indentation of cornea
• Immersion -Perpendicular to retina
• Important details to be kept in mind include
• Velocity (phakic /aphakic/ pseudophakic)
• A constant
• Ensure good quality reading

15. • Errors in axial length (AL) measurement affect the IOL power calculation , average error(2.5 D per mm of
AL )in adults.
• Error jumps to 3.75 D per mm in short eyes (i.e., AL 20 mm or less).
• The contact method
• The probe touches the cornea
• May result in corneal compression and a shorter AL.
• Immersion A-scan measurement
• Eliminates corneal compression
• Superior to contact biometry in adults.

16. • Axial length was measured by both contact and immersion techniques for all eyes
• Measurements using the contact technique-average 0.27 mm shorter than immersion technique
• Difference was the result of the anterior chamber depth than the lens thickness value
• AL measured by contact technique-will result in average 1-D stronger IOL power.
• This can lead to induced myopia in the postoperative refraction
Trivedi et al Ophthalmology 2011;118:498–502

17. • Axial length was measured by both contact and immersion techniques for all eyes
• Measurements using the contact technique-average 0.27 mm shorter than immersion technique
• Difference was the result of the anterior chamber depth than the lens thickness value
• AL measured by contact technique-will result in average 1-D stronger IOL power.
• This can lead to induced myopia in the postoperative refraction
Trivedi et al Ophthalmology 2011;118:498–502

18. • Striking difference in axial length measurements comparing the contact and immersion A-scan
techniques, immersion group (average of 1.06mm longer. )
• All measurements were performed using the handheld contact A-scan probe, with the patient supine
under general anesthesia.
• Leads to more indentation of the cornea compared with performing the contact technique with a table-
mounted unit on a seated adult patient
Ben-Zion et al ,J AAPOS 2008;12:440-444

19. ULTRASOUND BIOMICROSCOPY
• Depends on US velocity setting
• AL of >25 mm best measured with 1550m/sec
• AL of <20 mm best measured with 1560m/sec
• Accurate measurement by setting average velocity of 1532m/sec and correcting for AL Corrected AL
Factor (CALF) 0.32 added to AL
• Errors in axial length measurement are regarded as the most significant factor leading to incorrect
selection of IOL power after cataract extraction.
• Can account for an error of 2.5 D/mm in IOL power, increasing to 3.75 D/mm, or even higher in short
eyes
HofferKJ. JCRS 1994

20. • Horizontal corneal diameter measurement (mm) using calipers
• The average corneal diameter of a full-term infant is 9.9 mm at birth and 11.1 mm at 12 months of
postnatal age.
• Age Group (months) Mean K (D) 0 - 3 47.9
• 3 - 6 - 45.9
• 6 – 12- 45.1
• 12 – 18- 44.9
• 18 – 30- 43.6
• 30 – 42- 44.0

21. KERATOMETRY
• For the K measurement, handheld keratometer is frequently used
• The measurements should be taken without the use of an eye-lid speculum. -
• Measurements taken soon to avoid the problems associated with corneal dryness
• BSS instilled to maintain a smooth corneal surface.
• At least two keratometry measurements should be taken
• Average K reading should be within 1 D of each other.
• If the two average K readings are more than 1 D different, then make a third measurement and find
the average of the two closest K reading.

22. FORMULA
• SRK II,
• SRK-T,
• Hoffer-Q
• Holladay-I.
• The Hoffer-Q may be slightly more accurate in the shorter eyes of children
• •Unpredictable outcome with Hoffer Q, Holladay, SRK, SRK II and SRK T
• •Little difference between above formulae
Mezer E et al. JCRS 2004

23. OPTICAL BIOMETRY
• Has gained popularity because of its non-contact feature
• Increased accuracy, and provides more information on ocular biometry.
• Uses light instead of sound for the measurement;
• The shorter the wavelength the more precise the measurement.

24. IOL TYPES
• If a decision regarding the site of fixation needs to be changed after opening an eye and before IOL
implantation – an appropriate adjustment may need to be made.
• A plus-power IOL that is more anterior in the eye will have a greater refractive effect than i posterior.
• Sulcus fixation produces a relative myopic shift from the estimated refraction.
• IOL be decreased by 0.75 D to 1.00 D when placed in the ciliary sulcus

25. IOL TYPES
• •PMMA : inflammation, PCO formation
• •Square edge IOL comparable to acrylic
• Brar GS et al. CEO 2008
• Rowe NA et al. BJO 2001
• •Hydrophobic acrylic single piece : in-the-bag
• •Hydrophobic acrylic 3 piece : in-the-sulcus
• •Safe to use
• Wilson ME et al. JAAPOS 2001
• Trivedi RH et al. JCRS 2003

26. THANK YOU