Assessment and Management

• The two ocular structures that affect the power of the eye are the cornea, which has a fixed power, and the crystalline lens, whose power can vary depending on accommodation of the eye.
• The cornea is responsible for 2/3 of the eyes total refractive power (+40D), while the lens is responsible for 1/3 of the eyes total refractive power (+20D).
• The eye has a total power of +60D.
• The far point is the distance at which the eye can see without any optical aid.
• Far point can be at infinity, behind the eye, or in front of the eye.
• The focal point is where the parallel light rays meet after they passed the crystalline lens.
• Lindner’s method to refine cyl axis: Move ret approx 45º to cyl axis, to both sides of cyl axis, Movement at each side should be equal, if not, the cylinder axis should be moved towards the meridian that shows the with movement
• At neutral point Px’s far point is at ret mirror so Px can see clearly at working distance (usually wd is 2/3 m)
• • If FP is behind ret, movement is WITH
  • If FP is between ret and Px, movement is AGAINST
  • If FP is behind Px, movement is WITH
  • If FP is at ret, no movement
• F sp (spectacle lens) = F rev (reversal lens) – W (working distance)
• Place working distance lens in the back cells of the trial frame (+2.00 DS for a 50 cm working distance, +1.50 DS for 67 cm). This technique has the advantage that all ‘with’ movements indicate hyperopia and all ‘against’ movements indicate myopia. It also provides a ‘fogging’ lens to both eyes that will relax accommodation in a low hyperopia but you can get extra reflexes
• factors that affect the accuracy of retinoscopy: Intra-individual variation (within the same subject), Inter-individual variation (between people), Not concentrating on the movement in the centre of the pupil in a patient with large pupil, Age of patient, Off-axis errors, Working distance errors, Blocking the patient’s view of the distance chart, thereby likely stimulating accommodation
• • if a patient has keratoconus the reflex will swirl over the cone known as the split or scissor reflex
  • in keratoconus the reflex moves simultaneously in opposite directions from the pupil centre, you have to increase ethe room light to reduce the patients pupil size
• if the eye has opacities the light will be scattered and the reflex will be duller. to overcome this you may have to dilate the pupil or move closer and take into account a different working distance
• with large pupils you may get a spherical aberration May see a WITH movement in centre of pupil and an AGAINST movement in the periphery. Concentrate in the centre of the pupil and ignore the reflex from the edges of the pupil
• Dynamic retinoscopy is use to investigate accommodative state of the eye in near vision