A recent study published in Acta Ophthalmologica evaluated a new technique for calculating the intraocular lens (IOL) power in pediatric cataracts with the goal of reaching emmetropia by age 15.
Give me some background first.
Selecting the optimal IOL power tends to be more difficult in children, as biometry measurements and IOL power calculations are less accurate and the choice of the target refraction must consider ocular elongation following surgery.
Prior to 1986, surgeons aimed for emmetropia at the time of surgery to aid in the treatment of amblyopia; however, this resulted in large myopic shifts and frequently needed IOL exchanges.
What about existing formulas to calculate IOL power in children?
Consequently, in 1997, Dahan et al. suggested the first guidelines of IOL power undercorrection for pediatric patients.
In 1998, Enyedi et al. built on this guideline and defined more precise parameters with different target refractions according to the age of implantation.
Finally, in 2019, Trivedi et al. suggested the first model that predicted the adult axial length (AL) of children with bilateral congenital cataracts—but their model was based on a linear equation, while ocular elongation is closer to a logarithmic equation, especially before 18 months.
Now, talk about the study.
A research team from the University Hospital Center of Marseille retrospectively collected the data of children younger than 15 years who underwent cataract surgery with IOL implantation between 2005 and 2020 in the ophthalmology department.
They developed a method using a logarithmic model that calculated IOL power based on age and AL at implantation while targeting emmetropia at 15 years.
Exactly how was IOL power calculated?
Investigators utilized a logarithmic regression model to predict the AL growth of the included eyes between implantation and 15 years.
Then, the predicted myopic shift acted as a target refraction to calculate a theoretical IOL power, aiming for emmetropia at 15 years.
And after that?
Subsequently, refractive error with the theoretical lens power was estimated as the spherical equivalent at the last follow-up minus the difference of target refractions between the implanted IOL and the theoretical one.
Lastly, refractive errors were estimated using the Dahan, Enyedi, and Trivedi formulas, and then compared to the new logarithmic model.
Findings?
In total, 35 eyes of 26 children were analyzed. At the final follow-up, the median age of children was 10 years, and the median spherical equivalent was -1.88 D (interquartile range [IQR] -3.81 to -0.75).
Based on the various refractive error guidelines, the estimated median refractive errors were:
- New logarithmic formula: 0.18 D (IQR -1.11 to 1.42)
- Dahan formula: -1.47 D (IQR -3.84 to -0.65)
- Enyedi formula: -0.63 D (IQR -2.15 to 0.32)
- Trivedi formula: 0.38 D (IQR -1.58 to 1.07)
Limitations?
The key limitations of the study included:
- The retrospective monocentric design
- Small sample size
- The median age at the last follow-up was 10 years, while the aim of the formula was to reach emmetropia at 15 years
- Corneal curvature changes are not considered in the new formula
- Unknown impact of factors such as lens position on AL growth or if effective lens position changes with age
Take home.
These findings indicate that, compared to existing refractive error models, this new logarithmic formula is the closest to emmetropia at the last follow-up for pediatric cataracts.
While longer studies are warranted to validate these results, this new method could potentially help reduce myopia in children with IOL implantation for congenital cataracts.