A slit lamp is a microscope with a bright light used during an eye exam. It gives your ophthalmologist a closer look at the different structures at the front of the eye and inside the eye. It’s a key tool in determining the health of your eyes and detecting eye disease. A slit lamp is the most common ophthalmic equipment used by ophthalmologists in daily clinical practice. It is an essential instrument in the ophthalmologist armamentarium. Slit lamp not only provides a magnified view of intraocular structures (anterior and posterior segment) but also help in qualitative and quantitative analysis of various parameters such as corneal endothelial cell count, corneal thickness, anterior chamber cells, and flare assessment, depth of anterior chamber, pupil size, grading of cataract, slit lamp photography, etc. The term slit lamp is a misnomer since the slit is just one component of the instruments which provide slit apertures. A slit lamp consists of an observation system, an illumination system, and a mechanical support system. This activity covers the various methods of slit lamp illumination used to diagnose various ocular conditions.