Micro-Computed Tomography (µCT) as a Tool for High-Resolution 3D Imaging and Analysis of Intraocular Lenses: Feasibility and Proof of the Methodology to Evaluate YAG Pits

Abstract

Introduction: Posterior capsule opacification (PCO) is the most frequent late sequelae after successful cataract surgery. Neodymium:yttrium aluminum garnet (Nd:YAG) laser capsulotomy is considered the gold standard and a well-accepted, safe, and effective measure in treating PCO. However, iatrogenic damage of the intraocular lens (IOL) due to inappropriate focusing is a quite common side effect. These permanent defects (YAG pits) can critically affect overall optical quality.

Methods: In this laboratory study, we used the micro-computed tomography (µCT) technique to obtain high-resolution 3D images of the lens and the YAG pits.

Results: To the best of our knowledge, this is the first description of a detailed analysis of IOLs with µCT technology. This non-destructive technique seems to be ideal for comparative studies, measuring dimensions of the damage, and visualizing shooting channels within the material.

Conclusion: µCT is excellently suited to examine an IOL in detail, analyze optics and haptics in three dimensions, and to describe all kinds of changes within the IOL without damaging it.

Keywords: Damage in intraocular lenses; Laboratory study to evaluate IOL quality; Micro-computed tomography (µCT); New technique; YAG pits.

Fig. 1

IOL lenses mounted in front of the X-ray source a directly glued on a carbon holder, b in a 3D printed cylinder, c inserted in polymeric foam

Fig. 2

Reconstruction of a monofocal IOL. Top left: full size of the lens (the arrows highlight large pits), Top right: zoom in on the surface (the arrows mark the same two pits). Note: parts of the material are torn out. Bottom: cross section through the lens (the arrows mark the same two pits. Note: different penetration depth and shot channel within the lens.

Fig. 3

Reconstruction of a multifocal, diffractive IOL with ring segments. Top left: front side surface (the arrow highlights one smaller pit), Top right: back side surface, Bottom: cross section through the lens (the arrows marks the same pit at front side surface). Note: using this technique, one can evaluate whether the YAG pit starts directly at the anterior surface or inside the lens and follow the shot channel and measure the dimensions. It can happen that the smaller, superficial defect is only slightly pronounced, but shows a clear and enormous penetration depth

Fig. 4

Reconstruction of another multifocal IOL. Top left: front side surface (the arrow highlights a large pit with clear defect/crater on the surface). Top right: back side surface, Bottom: cross section through the lens (the arrow marks the same pit of front side surface)

Fig. 5

Reconstruction and representation of the shot channel. The angle of entry can be measured, the volume can be calculated and displayed relative to the total thickness of the lens. Note: There are also changes on the surface of the lens directly next to the entry of the YAG pit. It appears as if parts of the material are blown out of the lens

Fig. 6

Impressive slit lamp images showing clinical cases of IOLs with multiple lens pits after capsulotomy. In these cases, patients still achieved good uncorrected visual acuity but experienced dysphotopsia (glare, halo, starburst) when driving at night. One can imagine that the number, location, and extent of the defects play a decisive role