Flexing Four-Flanged Scleral Fixation

Using a four-flanged intrascleral intraocular fixation approach can produce good refractive outcomes, but there is room for improvement, a new prospective, longitudinal single-site study suggests.

The study of 28 eyes of 28 patients aimed to evaluate the four-flanged technique, first described by Sergio Canabrava¹, using a 6.0 Prolene suture and the PhysIOL Micropure IOL with an A-constant of 119.4. Led by Markus Schranz MD, the study included patients requiring a scleral fixation IOL, with strict selection criteria. Patients with corneal ectasia or dystrophy, surgery, scleral buckling, and macular diseases were excluded.

One of the most important steps of the surgery is marking the spots where to externalise the sutures, placing two spots 3.5 millimetres apart from each other and 2.5 millimetres posterior to the limbus. Dr Schranz stressed the importance of symmetry and its great influence on tilt decentration.

Axial length, TK mean, and white-to-white (WTW) distance were all in normal range. Absolute surgically induced astigmatism was 1.0 D at three months. Considering the mean refractive prediction error, the majority of patients ended up more hyperopic than intended. However, the prediction error appears to correlate with several factors, he said.

Axial length was associated with prediction error. The surgery was associated with more hyperopic outcomes in short eyes and more myopic outcomes in longer eyes, probably due to effective lens position (ELP) instability.

“Considering the absolute error, 80% of patients ended up within the 1.0 D range of intended, which is quite good for scleral IOL fixation,” Dr Schranz observed.

The researchers evaluated correlations between the prediction error and biometry parameters to find a reason for that outcome, revealing how the axial length played an important role. With increasing axial length, the refractive prediction error becomes more negative.

“So, shorter eyes are more hyperopic, and longer eyes tend to be more myopic than intended. No significant correlation was found considering True K or WTW,” Dr Schranz said. “On the other hand, aqueous anterior chamber depth (ELP minus CCT) did show a positive correlation with the prediction error, which is not surprising.”

Improving the refractive outcomes is important for patients’ quality of vision. As Dr Schranz suggested, a possible step could be the search for landmarks visible in the anterior segment optical coherence tomography (AS-OCT) as well as under the microscope in the OR to improve ELP consistency. He cited the scleral spur as one of these landmarks, as it is visible in AS-OCT and as a blue line during surgery. Finding correlations between the ELP and this landmark could create a more precise lens calculation.

“Patients are nowadays getting more and more demanding, asking for the same and previous refraction outcomes,” Dr Schranz noted. “A better understanding of the correlation between AS-OCT and anatomical landmarks should be key to improving IOL calculations in the future.”

Dr Schranz presented at the 2024 ESCRS Winter Meeting in Frankfurt.

Markus Schranz MD is a researcher at the Department of Ophthalmology and Optometry, Medical University of Vienna, Austria. markus.schranz@meduniwien.ac.at

1. Cornea, 2020 Apr; 39(4): 527–528.