Neodymium:YAG laser damage threshold of foldable intraocular lenses

To determine the energy level of the neodymium:YAG (Nd:YAG) laser that induced a 50% incidence of intraocular lens (IOL) damage in 5 foldable IOL materials.

Department of Ophthalmology, Siriraj Hospital Mahidol University, Bangkok, Thailand.

To simulate the condition within the capsular bag, an IOL was sandwiched between 2 rubber membranes. The front membrane had a central opening mimicking the anterior capsulotomy; the back membrane acted as the posterior capsule. The model was submerged in a water-filled chamber. The Nd:YAG laser with an automatic focus 150 microm beyond the focus of the aiming beam was used to perform a posterior capsulotomy. Three IOLs of each of 5 foldable IOL materials were tested. One type of poly(methyl methacrylate) (PMMA) was studied as a reference. The incidence of IOL damage at various energy levels was recorded. Linear regression analysis was used to determine the 50% incidence damage threshold.

The 6 materials tested included 1 silicone lens (SI-40NB, AMO), 1 hydrophobic acrylic lens (MA60BM, Alcon), 3 hydrophilic acrylic lenses (Haptibag Ang, IOLtech; ACR6D, Corneal; H60M, Bausch & Lomb), and 1 PMMA lens (LX10BD, Alcon). The 50% incidence damage threshold values were 0.37 mJ, 0.54 mJ, 0.58 mJ, 0.52 mJ, 0.66 mJ, and 0.68 mJ, respectively.

The 50% incidence damage threshold in all the IOLs was below the energy level normally used to perform a posterior capsulotomy in clinical practice. However, setting the laser at the lowest possible energy, focusing the laser beam beyond the posterior capsule, and performing the capsulotomy early should minimize the risk of IOL damage.