HIGH MYOPES

Contrary to previous reports, a new study from Moorfields Eye Hospital concludes cataract patients with high myopia might do just as well as average eyes.

“Our goal in performing cataract surgery is to improve vision, but we would like patients to have a rapid postoperative rehabilitation and achieve accurate refractive outcomes to limit spectacle dependence. As we know, the rate of capsule complications and percentage of eyes within 1 D of target refraction are important criteria in assessing the quality of cataract surgery,” Gianluca Carifi MD, consultant ophthalmic surgeon at Moorfields Eye Hospital in London, said at the XXXI ESCRS Congress in Amsterdam.

“We know that these goals are more difficult to achieve in high myopes, and although they represent less than 10 per cent of cataract surgery patients, hundreds of high myopes may be operated on at large institutions each year, given the size of the cataract surgery population.”

The study included 407 eyes (284 patients) with an axial length of at least 26mm. Based on measurements obtained with optical biometry, the group had a mean axial length of 27.81mm with a range up to 34.86mm, and the axial length was greater than 28.50mm in 25 per cent of eyes. Anterior chamber depth ranged from 2.29 to 4.29mm with a mean of 3.49mm.

Dr Carifi reported on peri-operative complications with a focus on posterior capsule rupture. The safety analyses included data for all 407 eyes, of which nine per cent were operated on by trainees, 54 per cent by fellows and 37 per cent by consultants.

Posterior capsule rupture with or without vitreous loss or zonular dehiscence with vitreous loss occurred in seven (1.7 per cent) eyes. Overall, an intraoperative complication occurred in 19 (4.7 per cent) eyes, including anterior capsule tear, corneal wound burn, iris trauma/prolapse and endothelial touch/trauma.

As a benchmark for comparison, Dr Carifi cited data from the Cataract National Dataset audit of 55,567 cataract surgery operations performed at 12 National Health Service Trusts in the UK [Narendran N, et al. Eye (London). 2009;23(1):31-7]. In the latter paper, the rate of posterior capsule rupture or vitreous loss or both was 1.92 per cent; axial length ≥26.0mm and trainee surgeons performing the operation were among the risk factors identified for these events.

“In our study of eyes with long axial length, the capsule complication rate was not higher than average. However, we feel the operation for these long eyes should be allocated to experienced surgeons whenever possible: despite the fact that 91 per cent of the procedures were performed by a fellow or a consultant, a complication occurred in nearly one of every 20 cases,” Dr Carifi said.

Vasiliki Zygoura MD, FEBO, his colleague at Moorfields Eye Hospital, presented the findings from an analysis of refractive outcomes in a cohort of highly myopic eyes (AL ≥26.0mm). Eyes included had IOL power calculation done using the SRK-T formula and in-the-bag implantation with a one-piece or three-piece hydrophobic acrylic foldable IOL. The analysis excluded eyes that had secondary IOL implantation, previous corneal or refractive surgery, corneal disease affecting keratometry measurement, or any intraoperative or chronic postoperative complication. A total of 315 eyes met all of the eligibility criteria.

At the one-month postoperaritve assessment, the achieved spherical equivalent was within 0.5 D of the predicted target in 63.5 per cent of eyes; the refractive outcomes were within 0.75 D and 1.00 D in 79.5 per cent and 89.5 per cent of studied eyes, respectively.

Dr Zygoura compared the results with those published by Dr Thomas Olsen who analysed the refractive outcomes in an unselected series of 461 consecutive eyes [Olsen T. Acta Ophthalmol Scand. 2007;85(1):84-7]. Using optical biometry data and modern IOL power calculation formulas incorporating anterior chamber depth algorithms, Dr Olsen reported the refractive outcome was within 0.5 D of that expected in 62.5 per cent while 92.5 per cent of eyes were ±1.00 D of target.

“Therefore, the refractive outcomes following modern cataract surgery in our population of high myopes seem to be in line with those achieved in a general population of patients. Our results were also similarly good when comparing eyes implanted with a single-piece or a multi-piece IOL. However, with the use of the SRK-T formula, there was a tendency toward a hyperopic outcome,” Dr Zygoura said.

Gianluca Carifi: gianluca.carifi@moorfields.nhs.uk
Vasiliki Zygoura: vasiliki.zygoura@moorfields.nhs.uk