real RET

Question 1

What are the reasons why real retinoscopic reflex rarely spherical or elliptical ?

Answer 1

• Lots of reflections- as patients may not sit still , pupils may be small or large etc
• media opacties- non uniform reflex
• can get a scissors reflex caused by spherical aberration.- part of reflex is moving a different direction to another part of reflex- where centre of reflex giving a with movement but periphery giving against - moving against eachother due to the spherical aberration
• corneal irregularities e.g. after refractive surgery- affect appearance of reflex-
• coloured bands - chromatic aberration- means light from different wavelength are focused at different points in the eye- esp when close to reversal
• unwanted reflexes- can reduce number of lenses in trial frame to stop this from happening.

Question 2

What are the errors in retinoscopy ?

Answer 2

• Accommodation- if dont control will be inaccurate
• Error in working distance- if working at 1/2m rather than 2/3m as 0/50D difference
• Finite size of reflex and sighthole
• False reversal
• Oblique astigmatism if examiner off-axis- can be generated in eyes that have no refractive error -so straighten yourself up and sit closer will be fine-
• Aberrations - coloured bands and “scissors” reflex
• Non-uniform illumination due to source
• Sighthole shadow- if you take a long narrow pipe you see a shadow across the reflex
• Interpretation of results by retinoscopist
• Imperfections of eye giving unusual reflex appearance

Question 3

What is the summary ?

Answer 3

Results of retinoscopy can be explained by an optical analysis
An understanding of the theory behind the reflex movements can make you a better practitioner.