Physics Ray Optics and Optical Instruments

Optical instruments can have some of the following defects that may impact their performance, which have arisen due to design limitations, manufacturing and physical properties of light:

• Chromatic Aberration: This defect occurs because of the different wavelengths of light that refract at slightly different angles when they pass through the lens. It causes them to focus on different points.
• Spherical Aberration: This happens because light rays pass through the edges of spherical lens or reflect off spherical mirror focus at different point than rays that pass through the center.
• Astigmatism: This type of defect occurs due to the uneven curvature of lenses or mirrors, which causes light to focus differently in horizontal and vertical planes.
• Field Curvature: One of the defects in optical instruments is field curvature, which occurs due to flat image sensors and film that cannot perfectly match the curved focal plane of a lens.

Yes, optical instruments are used in modern medicine for many purposes including surgery, monitoring, research and diagnosis. Let us take a look at each one by one:

• Many optical instruments are used for visualizing internal structures for diagnosis of a disease and its monitoring. These include Ophthalmoscope, Endoscope, Colposcope and Dermatoscope. 
• Optical instruments are also used for precision and minimally invasive surgeries, including Laparoscope, Arthroscope and Surgical Microscopes.
• Lasers are used for cutting, therapy and coagulation since they have precision and minimal invasiveness. CO? Laser, Excimer Laser and Fiber Optic Lasers are some of the optical instruments.
• Optical instruments also help in monitoring vital signs in the body as well as for analysing biological samples. Pulse Oximeter, Spectrophotometer and Optical Coherence Tomography (OCT) are some of the optical instruments. 
• For cellular-level analysis and medical research, optical instruments like the Confocal Microscope and Fluorescence Microscope are used. 

You can identify whether a medium has higher or lower refractive index through the three ways. The first step is to observe the direction of bending. In this case, if the light is bending towards the normal, the second medium has higher refractive index. If the light bends away from normal, first medium has higher index of refraction. 

In the second method, you can use Snell's law. If the second angle is smaller than the first one, second medium has higher refractive index. In case the first angle is smaller than second one, first medium has higher index of refraction. The third method is critical angle method where, if the light undergoes total internal reflection at boundary, the first medium has higher refractive index.