Analysis of YAG Laser-Induced Damage in Intraocular Lenses: Characterization of Optical and Surface Properties of YAG Shots

A Novel 3D High Resolution Imaging Method Using Correlative X-Ray and Electron Microscopy to Study Neodymium-Doped Yttrium Aluminum Garnet Laser-Induced Defects in Intraocular Lenses

INTRODUCTION

Cataract extraction is the most frequently performed ophthalmological procedure worldwide. Posterior capsule opacification remains the most common consequence after cataract surgery and can lead to deterioration of the visual performance with cloudy, blurred vision and halo, glare effects. Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser capsulotomy is the gold standard treatment and a very effective, safe and fast procedure in removing the cloudy posterior capsule. Damaging the intraocular lens (IOL) during the treatment may occur due to wrong focus of the laser beam. These YAG-pits may lead to a permanent impairment of the visual quality.

METHODS

In an experimental study, we intentionally induced YAG pits in hydrophilic and hydrophobic acrylic IOLs using a photodisruption laser with 2.6 mJ. This experimental study established a novel 3D imaging method using correlative X-ray and scanning electron microscopy (SEM) to characterize these damages. By integrating the information obtained from both X-ray microscopy and SEM, a comprehensive picture of the materials structure and performance could be established.

RESULTS

It could be revealed that although the exact same energies were used to all samples, the observed defects in the tested lenses showed severe differences in shape and depth. While YAG pits in hydrophilic samples range from 100 to 180 µm depth with a round shape tip, very sharp tipped defects up to 250 µm in depth were found in hydrophobic samples. In all samples, particles/fragments of the IOL material were found on the surface that were blasted out as a result of the laser shelling.

CONCLUSION

Defects in hydrophilic and hydrophobic acrylic materials differ. Material particles can detach from the IOL and were found on the surface of the samples. The results of the laboratory study illustrate the importance of a precise and careful approach to Nd:YAG capsulotomy in order to avoid permanent damage to the IOL. The use of an appropriate contact glass and posterior offset setting to increase safety should be carried out routinely.

Image Contrast and Spectral Transmission in Intraocular Lenses with Nd:YAG Pits

PURPOSE

Neodymium yttrium aluminum garnet (Nd:YAG) laser capsulotomy is considered as safe and effective method in the treatment of posterior capsule opacification. Nevertheless, side effects are described. The incorrectly adjusted focus of the laser beam during the procedure can lead to so-called YAG-pits or YAG-shots. In this experimental study, we measured spectral transmission to evaluate the image contrast and analyze the impact of YAG-pits in intraocular lenses (IOL).

METHODS

Acrylic, foldable, one-piece IOLs with 6.0 mm optic and different material properties were studied. These included: monofocal IOLs and enhanced monofocal IOLs with water content of 0.3%, 26.0%, and 4.0% and a refractive index of 1.49, 1.46, and 1.54, respectively. All measurements were done with new, unaltered IOLs and IOLs with YAG-pits. Damage was intentionally created, performing YAG-pits (n = 7) in the central zone (3.5 mm) using a photodisruption laser (2.0mJ). All laboratory measurements were repeated: These included surface topography characterization, United States Air Force (USAF) resolution test chart analysis, spectral transmittance measurements and through focus contrast measurement.

RESULTS

Significant differences were found between the unaltered lenses and lenses with defects. The YAG-pits within the optic of the IOLs decreased the image contrast and spectral transmission and changed results of USAF test images at the focal position by 62%, 57% and 54%, respectively. In all IOLs a reduction of the relative intensity of total transmitted light was observed between 450 and 700 nm wavelength.

CONCLUSION

This experimental study confirmed that the IOL image performance deteriorates with YAG-pits. The total intensity of transmitted light or transmittance (without scattering) was reduced in the wavelength between 450 and 700 nm. The contrast was significantly reduced and USAF test targets showed much worse results compared to unmodified counterparts. There was no systematic difference between monofocal and enhanced monofocal lenses. Further experiments should investigate the effect of YAG-pits on diffractive IOLs.

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

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.

Incidence of Retinal Detachment, Macular Edema, and Ocular Hypertension after Neodymium:Yttrium-Aluminum-Garnet Capsulotomy: A Population-Based Nationwide Study-The French YAG 2 Study

PURPOSE

To estimate the incidence and assess the risk factors associated with 3 adverse events (AEs) after neodymium:yttrium-aluminum-garnet posterior capsulotomy (Nd:YAG-caps): ocular hypertension (OHT), macular edema (ME), and retinal detachment (RD).

DESIGN

Observational cohort study using a nationwide claims database.

PARTICIPANTS

Adults who underwent Nd:YAG-caps between 2014 and 2017, with no ocular disease history in the year before.

METHODS

Patients who underwent Nd:YAG-caps were identified using data from the French national representative sample and followed up for 12 months postprocedure. The time to AE was assessed using the Kaplan-Meier method. Factors associated with AE were assessed using Cox models.

MAIN OUTCOME MEASURES

Neodymium:YAG-caps epidemiology, patients' characteristics, proportion of patients with AE, and hazard ratios (HRs) associated with variables identified as factors associated with AEs.

RESULTS

During the study period, 6210 patients received Nd:YAG-caps (7958 procedures). The mean age (± standard deviation) at Nd:YAG-caps was 75.0 (± 10.3) years. The 3-month and 12-month overall AE rates (≥ 1 AE of interest) were 8.6% and 13.3%, respectively. Among patients with ≥ 1 AE of interest, 68.4% of AEs occurred within 3 months post-Nd:YAG-caps. Three-month rates were ≈5% for OHT and ME. Retinal detachment remained ≤ 0.5% over follow-up. Cox models showed that patients with Nd:YAG-caps performed within 1 year after cataract surgery had a higher risk of AEs than those with later Nd:YAG-caps (hazard ratio [HR], 1.314 [1.034-1.669], P = 0.0256), notably ME (HR, 1.500 [1.087-2.070], P = 0.0137). Diabetic patients were more at risk of OHT (HR, 1.233 [1.005-1.513], P = 0.0448) and ME (HR, 1.810 [1.446-2.266], P < 0.0001) than nondiabetic patients. Patients with Nd:YAG-caps performed between 1 and 2 years after cataract surgery were more at risk of OHT than patients with later Nd:YAG-caps (HR, 1.429 [1.185-1.723], P = 0.0002).

CONCLUSIONS

According to a national claims database, OHT and ME were the most frequent AEs of interest post-Nd:YAG-caps, mainly observed within 3 months postprocedure, highlighting the need for a close follow-up during this period or a delayed capsulotomy. Diabetes and an early Nd:YAG-caps after cataract surgery were among the main drivers for AE occurrence.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Evaluating impact of Nd: YAG laser associated defects on optical quality of hydrophilic and hydrophobic intraocular lenses using visualization of light propagation and USAF test targets

BACKGROUND

Neodymium:yttrium aluminum garnet (Nd:YAG) laser capsulotomy is a well-accepted, safe, and effective measure in the treatment of posterior capsule opacification. However, iatrogenic intraocular lens damage is a relatively common side effect that happens due to inappropriate focusing during the procedure. This experimental study analyzes the impact of YAG-pits to obtain qualitative information.

METHODS

Acrylic, monofocal hydrophilic and hydrophobic intraocular lenses (IOLs) with 6.0 mm optic and the with the same power (21D) were studied. First, all measurements were done with unmodified IOLs. Damage was intentionally created, performing YAG-pits (n = 5) in the central area of the lens optic (3.0 mm) using a photodisruption laser with the same energy level of 1.8 mJ. To simulate the cruciate pattern, the 5 defects were created in a cross shape within the 3.0 mm optical zone. Afterwards, all laboratory measurements were repeated: These included the United States Air Force (USAF) resolution test chart to study the imaging performance of the IOL, light field measurements to show the course of the rays behind the IOL and the modulation transfer function (MTF) measurements were analyzed.

RESULTS

Evaluating USAF showed that unmodified lenses produced a sharper image. Damaged lenses led to a more blurred image and to the impression of a lower contrast with a kind of halo/glare effect. The light field measurement showed that YAG-pits led to a kind of dispersion and scattering effect, which was higher in hydrophobic IOLs. MTF showed a deterioration in damaged hydrophilic and hydrophobic IOLs, respectively.

CONCLUSION

Our experimental study confirms that YAG-pits can reduce imaging quality of intraocular lenses. These defects behave as a new Huygens source, distribute a spherical wave that additionally illuminate the background of the USAF target. It can be assumed that material properties of the IOL (water content, refractive index) play an important role and affect results. The impact level is strongly dependent on the number, size and position of YAG-pits within the optic.

LIMITATION

Only monofocal IOLs have been investigated so far, further tests with various IOL optics have to follow. In addition, simulating the circular pattern of YAG capsulotomy is necessary.