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IOL power selection

Soosan Jacob

Posted: Sunday, April 1, 2018

Selecting the right IOL power for children undergoing cataract surgery poses significant challenges. Careful planning is required to produce good long-term results, according to Rupal Trivedi MD, Medical University of South Carolina, USA, who spoke at the World Congress of Paediatric Ophthalmology and Strabismus 2017 in Hyderabad, India.
She shared results from the Delphi consensus study of a target refraction of about 6-10 dioptres for infants younger than 6 months of age, 4-6D at 6-12 months of age, steadily decreasing down to about 0-1D at more than 8 years of age. She also explained that these target refractions need to be customised based on amblyopia, anticipated compliance to residual refraction, state of the fellow eye, family history and other factors. Eyes with postoperative glaucoma during infancy grow fast, resulting in myopic shift. However, it is not possible to predict preoperatively which eye will develop postoperative glaucoma.
An immediate post-surgical emmetropic target refraction, while making the battle against amblyopia easier, does result in a significant myopic adult refraction. Conversely, an immediate post-surgical high hypermetropic refraction does bring the adult refraction closer to zero, but makes the more pressing need of amblyopia management difficult. A customised approach of moderate hypermetropia avoids very high refractive error during adulthood, yet helps to fight against amblyopia, so is therefore important.
While answering questions from the audience about optimal timing of surgery, she mentioned that available literature suggests that in unilateral congenital, dense cataract should be operated at six weeks of life, as by this age, the eye is more mature and the risk of general anaesthesia is also reduced. In bilateral congenital dense cataract, the window for surgery is up to two months. However, the gap between the two eye surgeries preferably should be shorter than seven days.
She explained that difficulties are to be expected with axial length measurement, with a magnified impact of measurement error in short eyes. Considering the significant differences commonly seen between contact and immersion methods, immersion biometry is preferred. Challenges with keratometry included lack of fixation, supine position of measurement, a quicker tear break-up time and use of eyelid speculum. She recommended that automated keratometer readings should be taken as soon as possible after induction of anaesthesia, immediately after intraocular pressure, and should be measured without an eyelid speculum in place.
Dr Trivedi also shared Professor Warren Hill’s correction table for IOL power adjustment in cases of unplanned sulcus implantation.
She concluded by stating that the aims of paediatric cataract surgery should include having a manageable course of refraction between the period of IOL implantation and adulthood, having good vision as an adult and having the least refractive error in adulthood.

Rupal Trivedi: trivedi@musc.edu