CLINICAL REFRACTION

• Retinoscopy is used with plane mirror settings.

• the patient is asked to look at distant target like largest letter on snellens chart

• light is thrown into patiens pupil and examiner observes the reflex of light in patient pupil. If a with movement is observed then increasing plus lenses are placed in front of patients eyes. 

• if against reflex is seen, increasingly minus lenses placed infront of patients eye. 

• the point where no movement of reflex is observed and light fills the pupil completely is taken as neutral point.

• With 2 spheres. Neutralize 1 axis with a spherical lens; then neutralize the axis 90° away. The difference between these readings is the cylinder power. For example, if the 90° axis is neutralized with a +1.50 sphere and the 180° axis is neutralized with a +2.25 sphere, the gross retinoscopy is +1.50 +0.75 × 180. The examiner’s working distance (ie, +1.50) is subtracted from the sphere to obtain the final refractive correction: plano +0.75 × 180 

• formula is R1/R2-R1 WITH AXIS OF R1

spheres are placed with increasing number untill patient sees clearly

To check the axis of spherocylindrical lenses

1. astigmatic dial is a chart with radially oriented lines 

2. stenopeic slit 

3. Cross cylinder technique