The Anti-Spin Doctor

Every cataract and refractive surgeon hears the same thing from patients: that they want to be spectacle-free after cataract surgery. The introduction of (what’s now a wide range of) premium intraocular lenses (IOLs) has made surgeons able to achieve that in most patients. But astigmatism still poses problems. Traditional monofocal IOLs correct the spherical equivalent of refractive error, but not pre-existing corneal astigmatism – and as 20–30 percent of patients have astigmatism of 1.25 D or greater (and one in 10 patients have 2.00 D or greater) (1). That’s a significant proportion of patients. There are essentially two options in such cases: limbal relaxing incisions (LRIs) – a tried and tested method of correcting corneal astigmatism during cataract surgery, but one that also carries a risk of infection and can cause damage to the cornea (2,3). The other option is toric IOLs, which are often more costly relative to monofocal IOL implantation plus LRIs, but have a better safety profile and offer more predictable results (4,5).

The evolution of IOL design

IOL design continues to evolve and every manufacturer is trying to improve upon their existing designs. For example, square edges on the posterior edge of the IOL’s posterior face help reduce posterior capsule opacification (PCO); aspheric optic designs should eliminate spherical aberration; better haptics help with IOL centration and rotational stability; and there’s always a push to minimize the incisions made to the cornea during surgery below 2 mm, as this minimizes surgically induced astigmatism. The Miniflex Toric IOL (Mediphacos) claims to tick all of these boxes – and so we decided to evaluate it. But in terms of ensuring patients are satisfied and remain spectacle-free after surgery, it’s important to ensure that the IOL is aligned along the correct axis to correct the astigmatism, and that it stays correctly aligned after surgery. There are a number of  factors in an IOL’s design that can promote rotational stability – principally, the total diameter of the IOL and the design of the haptics (6–8). To minimize optical torsion and tilting, the Miniflex Toric has a large overall diameter (12.5 mm), self-centering double haptics, and step-vaulted haptic angulation to keep the haptics in parallel alignment with the optic at all times. Data published to date indicate that no patient who has received one has experienced rotation greater than 7° (1).

Our experience

In cooperation with the International Vision Correction Research network, I and my colleagues at the University of Heidelberg are currently conducting our own clinical analysis of the IOL. To date, 19 eyes (14 patients; mean age 69±9.6 years) have received the IOL as part of cataract surgery. Preoperatively, our patients’ UDVAs ranged from 1.3 to 0.24 LogMAR, and corrected distance visual acuities (CDVAs) ranged from 1.10 to 0.20 LogMAR, with preoperative cylinder ranging from –3.48 D to –0.16 D. All patients were implanted with the Miniflex Toric lens with a sphere ranging from 15.0 to 29.0 D and a cylinder of 1.5 to 6.0 D. Target refraction was emmetropia in all but one patient (in whom the target refraction was -2.5 D). At postoperative day one, patients’ UDVAs ranged from 0.5 to 0.20 LogMAR and their CDVAs from 0.40 to 0.06 LogMAR. Of course, the study is still underway – but longer-term follow-up data from our first three patients (see Case Studies) further support the idea that this IOL significantly reduces refractive error and has good rotational stability.

Case Studies

Case #1
A 76-year-old male patient’s right eye was implanted with the Miniflex Toric IOL (sphere 21.0 D; cylinder 1.5 D) during cataract surgery. Preoperatively, the patient’s CDVA was 1.1 LogMAR, his cylinder was 1.61 D/67°, and his refraction was +0.5/–1.25/76°. Two months postoperatively, his UDVA was 0.2 LogMAR, his CDVA 0.0 LogMAR, and his refraction –0.5/–0.5/150°. The patient had a residual astigmatism of only 0.08 D. The IOL showed good rotational stability; the axis of placement was 167° and the actual axis at the two-month follow-up was 170°.

Case #2
A 68-year old female patient’s left eye was implanted with the Miniflex Toric IOL (sphere 19.5 D; cylinder 1.5 D) as part of routine cataract surgery. Preoperatively, the patient’s CDVA was 0.44 LogMAR, her cylinder was –1.37 D/172°, and her refraction was –0.75/–1.0/175°. Rotational stability of the lens was good at the two-month follow-up (axis placement 78°; actual placement 74°).

Case #3
A 77-year old female patient underwent bilateral cataract surgery, and both eyes received the Miniflex Toric IOL (OD: 21.5 D sphere, 3.0 D cylinder; OS:
22.5 D sphere, 2.25 D cylinder). Preoperatively, the patient’s CDVA was 0.3 LogMAR in both eyes, her cylinder was –1.38 D/78 OD and –0.86 D/108° OS, and her refraction was +1.5/–2.75/100° OD and +1.75/–1.5/110° OS. One month postoperatively, her UDVA in her left eye was 0.0 LogMAR and her refraction was plano. Two months postoperatively, UDVA in her right eye was 0.1 LogMAR – also with a refractive error of zero. No rotation of the IOL was observed.

Cyclorotation and IOL power calculations

These early successes are a good sign, but we can’t rely on the IOL alone to appropriately address astigmatism. To avoid lens misalignment and achieve accurate results, we need to consider cyclorotation (rotation of the eye around the line of sight), axis marking, intraoperative alignment and accurate toric IOL power calculation. Key considerations with regard to cyclorotation include head posture, change in fixation distance, monocular versus binocular viewing, and sitting versus supine position. In my practice, I always mark the axis of alignment with the patient awake and sitting upright. I make sure that the head and upper body are straight, and then I mark the cylinder axis using a pendulum marker. Toric IOL power calculation requires a little more data – not only biometry, but also an assessment of corneal topography. I always make sure I get three comparable keratometry results before proceeding, and to improve accuracy, I ask patients to refrain from wearing contact lens for at least two weeks beforehand. Because there have been reports of different K readings with different keratometers (9), I also recommend that ophthalmologists measure the corneal radius, rather than relying solely on D-values.

Thus far, my findings indicate that patients with corneal astigmatism of at least 0.75 D benefit from toric IOLs. Although we still need data from longer follow-up, early results in my patients suggest that the Miniflex Toric IOL prevents rotational instability, affords excellent visual outcomes, and may help to increase post-surgical spectacle independence in patients with both cataract and astigmatism.

Florian Kretz is a consultant ophthalmologist and research fellow at the IVCRC and the David J Apple International Laboratory for Ocular Pathology at the Department of Ophthalmology, University Hospital Heidelberg, Germany, research coordinator for the International Vision Correction Research Centre Network (IVCRC.net), Heidelberg, Germany and one of the lead surgeons at the Eyeclinic Ahaus-Raesfeld-Rheine (Gerl Group), Ahaus, Germany.