Essilor Instruments VISION-R 700, Руководство пользователя

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1. Vertex distance measurement
The “Vertex Distance” is the distance from the back side of a correcting ophthalmic lens (at the rear
surface) to the patient's eye (at the apex of the cornea). The Vertex distance has always been of
importance in refraction since the refraction value of an eye depends on the distance at which the
corrective lens is located in front of the eye. Indeed, the further away the lens from the eye, the more
minus the corrective power; the closer the lens to the eye, the more plus the power, whatever the
ametropia.
Measuring the Vertex distance could be very important
If the patient is set up and tested at a different distance compared to the Vertex distance of the
spectacles, the power change could have an effect on the performance of the spectacles.
This is even more evident on higher powers
Measurement procedure
Ask the patient to position himself/herself behind the phoropter and rest their head against the forehead
support while looking into the distance at the chart screen.
The practitioner checks that the phoropter is located close enough to the patient eye's, so as to offer a
wide field of vision, but far enough to avoid the patient's eyelashes to be in contact with the back side
window of the optical module.
The distance can easily be adjusted by using the rotating button located in front side of the Vision-R,
turning it clockwise to reduce the Vertex distance and anti-clockwise to increase it.
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77 Vision-R 700 - Essilor automatic phoropter > V1 - 09-2020