JCRS This Month: Impact of Pupillary Dilation on IOL Calculations (2/2026)
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Summary of the Study
Effect of Pupillary Dilation on Ocular Biometry and IOL Power Calculation Using Six New-Generation Formulas
Purpose
This prospective study evaluated whether biometric measurements obtained after pharmacologic pupil dilation affect the accuracy of modern IOL power calculation formulas by comparing predicted refractive outcomes with actual postoperative refraction.
Study Design
84 cataract eyes undergoing uncomplicated phacoemulsification.
Biometry measured before and after dilation using the IOLMaster 700.
Six formulas evaluated:
Barrett Universal II
EVO 2.0
Hoffer QST
Kane
LISA
Pearl-DGS
Postoperative refraction assessed at least one month after surgery.
Changes in Biometry After Dilation
The most consistent changes were:
Parameter | Change |
Anterior Chamber Depth (ACD) | ↑ Increased by ~0.09 mm |
Lens Thickness (LT) | ↓ Decreased by ~0.036 mm |
Axial Length (AL) | Slight increase (~0.008 mm) |
White-to-White (WTW) | Slight increase |
Central Corneal Thickness (CCT) | Slight decrease |
Keratometry (overall) | No significant overall change |
In eyes with:
Long axial length (>26 mm)
Flat corneas (K ≤43 D)
there was a small but significant decrease in keratometry after dilation.
Effect on IOL Prediction
Compared with measurements obtained before dilation:
Barrett Universal II
EVO 2.0
Kane
LISA
Pearl-DGS
all demonstrated a small myopic shift in predicted postoperative refraction.
Magnitude:
Approximately −0.03 to −0.05 D
In long eyes and flatter corneas the shift was larger:
Up to approximately −0.12 to −0.15 D.
Did Dilation Reduce Accuracy?
No.
Despite the slight systematic myopic bias:
Mean Absolute Error (MAE) remained unchanged.
Median Absolute Error (MedAE) remained unchanged.
Percentage of eyes within ±0.5 D and ±1.0 D showed no clinically meaningful differences.
Therefore,
Measurements taken after dilation remain clinically acceptable for modern IOL calculations.
Why Does This Happen?
Regression analysis showed the change in refractive prediction is mainly driven by:
Change in Axial Length
Change in Keratometry
Change in ACD
Change in Lens Thickness (particularly for EVO, Kane and LISA)
The deeper ACD and thinner crystalline lens after cycloplegia alter the estimated effective lens position, producing a slight myopic prediction.
Clinical Implications
The authors conclude:
Measuring biometry after dilation is generally safe.
Modern formulas are robust against these biometric changes.
However, eyes with long axial length and flatter corneas may experience a predictable myopic bias.
They suggest that when biometry is obtained after dilation in these extreme eyes, surgeons may consider targeting approximately +0.10 to +0.15 D more hyperopia to compensate for the expected myopic shift.
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This is an important laboratory paper because it addresses a question that has been difficult to answer in cases of refractive surprise: Can we accurately measure the power of an explanted IOL if the lens has been cut in half during explantation?
Study
Gu S, Yan W, Khoramnia R, Auffarth GU, Łabuz G. Accuracy of measuring the diopter power of intraocular lenses after hemidissection. Journal of Cataract & Refractive Surgery. 2026. DOI: 10.1097/J.JCRS.0000000000001895.
Why this study matters
When an IOL has to be explanted because of an unexpected postoperative refractive error, surgeons often cut the lens into two pieces before removing it through a small incision.
Until now there has been uncertainty whether such a damaged lens could still be optically measured to determine whether:
the manufacturer produced the correct power,
the implanted lens was mislabeled,
or the refractive surprise was caused by another factor (ELP, biometry, cornea, etc.).
This paper answers that question.
Method
The investigators examined:
8 monofocal IOLs
2 EDOF IOLs
2 trifocal IOLs
from major manufacturers.
Each lens was measured in three situations:
Intact lens
One half of the lens after hemidissection
Both halves reassembled
using laboratory optical power measurements. They then compared the measured powers statistically.
Results
The findings were remarkably consistent.
There was no statistically significant difference between:
intact lens,
one-half measurement,
and reassembled halves
(p = 0.77).
Average change after cutting:
IOL type | Difference |
Monofocal | 0.15 ± 0.17 D |
EDOF | 0.10 ± 0.07 D |
Trifocal | 0.02 ± 0.01 D |
Nearly all measurements remained within ISO tolerances.
Main conclusion
The authors concluded that:
Measuring only one half of a hemidissected IOL provides essentially the same dioptric power as measuring the intact lens.
In other words,
Cutting an IOL during explantation does not prevent accurate laboratory verification of its power.
Why this is important clinically
For cataract surgeons investigating a refractive surprise, there are several possible causes:
incorrect biometry
wrong formula
ELP prediction error
postoperative lens position
transcription error
wrong lens implanted
manufacturing error
This paper shows that manufacturing error can still be investigated even after the explanted IOL has been cut during surgery, because the optical power remains measurable with excellent accuracy.
