Optical technologies use light to investigate or influence biological tissue. Medical lasers produce light with specific characteristics, including wavelength and beam properties, that can be selected for diagnostic or therapeutic purposes. Other optical methods, such as fluorescence imaging, optical coherence tomography (OCT), confocal microscopy, and pulse oximetry, use light to obtain information about tissue structure or physiology. Biomedical engineers must understand both optical principles and the biological response to light. How Light Interacts with Tissue When light reaches tissue, some may be reflected, some scattered, and some absorbed by molecules known as chromophores. The wavelength affects how deeply light penetrates and which molecules absorb it. Absorbed optical energy may become heat or trigger other interactions, depending on wavelength, pulse duration, intensity, and tissue properties. Because biological tissues differ in water, blood, pigment, and structural composition, the same laser setting can produce different effects in different tissues. Diagnostic and Therapeutic Applications In diagnosis, optical techniques can measure oxygen saturation, visualize microstructure, or reveal fluorescent signals from selected molecules. OCT produces cross-sectional images using reflected light and is widely used in ophthalmology and other fields. In therapy, lasers may cut, ablate, coagulate, or selectively target tissue. Dermatology, ophthalmology, dentistry, and surgery use different laser systems according to the desired clinical endpoint. A laser's suitability depends on the application, tissue, wavelength, beam delivery, and evidence supporting the procedure. System Design and Safety Laser safety is an engineering requirement, not an optional accessory. Risk depends on wavelength, output power or energy, exposure duration, beam geometry, and the possibility of direct or reflected exposure. Protective measures may include wavelength-appropriate eyewear, controlled access, warning indicators, beam enclosures, interlocks, training, and maintenance. Optical components and fiber delivery systems must be compatible with the selected wavelength and power. Clinical protocols should follow applicable standards and institutional procedures. Future Directions Emerging optical systems combine compact light sources, advanced detectors, computational imaging, and AI-assisted interpretation. Multimodal platforms may combine optical measurements with ultrasound or other imaging techniques to provide complementary information. Portable and wearable optical sensors could support point-of-care assessment, but their performance can be affected by motion, skin properties, ambient light, and sensor placement. Translation into clinical practice requires analytical validation, clinical studies, usability testing, and a clear plan for quality assurance. Conclusion Medical lasers and optical technologies offer precise ways to measure, image, and treat biological tissues. Selecting a suitable wavelength and exposure setting requires understanding light–tissue interaction and the intended clinical endpoint. A successful system combines optical design, reliable controls, risk management, and evidence-based clinical practice. References for further reading International Electrotechnical Commission. IEC 60825-1: Safety of Laser Products — Equipment Classification and Requirements. World Health Organization. Ultraviolet Radiation and Health: general information and safety resources. American National Standards Institute. ANSI Z136 series: Safe Use of Lasers.