Lasers for gamete micromanipulation: basic concepts.

Journal of Assisted Reproduction and Genetics, Vol. I0, No. 2, 1993 LASER Lasers for Gamete Micromanipulation: Basic Concepts for the preferred approach: (i) heat deposition, (ii) DNA absorption, (iii) ablation threshold, and (iv) simplicity in equipment and training. One may sug- gest adding a few more prerequisites such as (v) absorption in water and proteins, (vi) a spot size smaller then the thickness of the zona pellucida (ZP), and (vii) precision of the entire unit. !n a previous study (12) we have discussed the influence of various physical parameters on the ex- pected effects during gamete manipulations (i.e., cutting geometry, ablation beam size, pulse repe- tition rate and duration, and laser fluence, i.e., en- ergy per unit area). It is the intent of this column to discuss some aspects related to the above- mentioned prerequisites in order to take full advan- tage of the laser as light scalpels. Lasers, (an acronym for Light Amplification by Stimulated Emission of Radiation) are electromag- netic waves with unique properties. The beam is collimated, monochromatic, and coherent. Prog- ress in physics and laser technology in recent years has resulted in the introduction of many lasers for biomedical studies. Although lasers differ from each other by the wavelengths, which are in the visible range (red, green, or blue), ultraviolet (UV), or in the infrared (IR) range (Fig. l a), effects may also vary as a result of different application modes as will be discussed later. INTRODUCTION A brief literature search on the key words micro- manipulation (MM) and male factor infertility may highlight the controversy regarding this issue. It has recently been suggested (1) that so inconsistent are the reported results that at present it is pertinent to ask does microsurgical assisted fertilization (MAF) work at all ? The controversies are related mainly to patient selection needed for establishing prognostic criteria and the method of choice (2,3). Gamete manipulations require special equipment and expertise, while the preparation of disposable microneedles for MAF is time-consuming and, thus, expensive (4). In an attempt to increase accuracy and simplic- ity, it has been suggested that the laser might offer several advantages. Since its first introduction for gamete manipulation in 1989 (5) several studies addressed basic questions on its potential role and discussed various methods (6-10). It is beyond the scope of this article to assess the important issues of effectiveness and safety of the laser for gamete manipulations. Several studies and clinical obser- vations are being performed throughout the world and it will take some time until the controversies regarding the future role of MAF will be answered. However, in view of the increasing interest in lasers for gamete MM, some guidelines are needed. Strohmer and Feichtinger have recently presented in abstract form some biophysical criteria for laser MM (11). They suggested four basic requirements HEAT DEPOSITION IN THE OOCYTE OR THE EMBRYO The opinions presented in this column are those of its author(s) and do not necessarily reflect those of the journal and its editors, publisher, and advertisers, Some heat will always be generated in the micro- manipulated oocyte or embryo if the ablation WL is © 1993 Plenum Publishing Corporation