Page 132 - July-August 2020

ABERRATIONS OF

PLANO-PRISMS

Dr Prof Mo Jalie, SMSA, FBDO (Hons), Hon FCGI Hon FCOptom, MCMI, is a
Visiting Professor of Optometry at the University of Ulster in Coleraine, and
at the post-graduate facility at Varilux University. He served for nine years
as Head of Department of Applied Optics at City & Islington College, where
he taught optics, ophthalmic lenses and dispensing. He is a recognised
international authority on spectacle lens design and has written several books
including Principles of Ophthalmic Lenses. His most recent book, Ophthalmic
Lenses & Dispensing was translated into Russian. He has authored over 200
papers on ophthalmic, contact and intra-ocular lenses, and on dispensing; and
is a consultant editor to The Optician (UK) and technical editor to The Indian
Optician journal. He holds patents for aspheric spectacle and intra-ocular
lenses. Jalie is a past-chairman of the Academic Committee of the Association
of British Dispensing Opticians, and was the first Chairman of the Faculty of
Dispensing Opticians. He is the ABDO representative on the BSI committees on
ophthalmic lenses and spectacle frames and a past member of the Education
Committee of the General Optical Council. In 1998 Jalie was thrice honoured:
he was made Honorary Fellow of the British College of Optometrists, a Life
Fellow of the Association of British Dispensing Opticians, and in December of
that year he was granted the Max Wiseman Memorial Research Medal.
Dr Prof Mo Jalie

hen white light is refracted the window, through points near aberration is manifest in conditions
by a plano-prism (such the periphery of their lenses, or of low contrast. Accompanying the
Was those found in the they may complain of off-axis blur chromatism for the spectacle wearer
refractionist’s trial case) the light is when viewing low contrast objects are magnification effects, even from
dispersed into its monochromatic since this is the way chromatic plano-prisms, which alter the
constituents forming coloured
fringes seen around images viewed
through the prism. Usually, these
coloured fringes are only noticed
when the prism power is 6Δ or
greater. Wearer’s of high-powered
spectacle lenses may also complain
of these effects when they view
through off-axis points on their
lenses especially when the lenses
have been made in a high refractive
index material with a low Abbe
number. Myopes in particular may FIGURE 1. ANGULAR
comment on this effect when DISPERSION OR TRANSVERSE
viewing high contrast objects such as CHROMATIC ABERRATION
window bars with daylight beyond TCA = P - P = P/V
C
F
| JULY-AUG 2020 | 128 LENS TALK