Page 110 - The Indian Optician Digital Edition July-August 2021

ADAPTIVE POWER

SPECTACLE LENSES

̶PART 4

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

VARIABLE POWER LENSES MADE FROM
ELECTRO-ACTIVE MATERIALS
The fourth and
concluding part of Consider an optical material whose refractive index
this series on Adaptive is 1.67, until an electric current is passed through the
Power Spectacle Lenses material, causing the refractive index to fall to 1.53. Then,
enlightens the reader on when the current is switched off, the material instantly
variable power lenses regains its original refractive index of 1.67 (Figure 1). Such
made from electro- a material has been developed in the form of a cholesteric
1
active materials such liquid crystalline material and has been used to produce
as cholesteric liquid electrically adaptive multifocal lenses.
crystalline materials.
This technology was Cholesteric liquid crystalline materials are optically
employed in the uniaxial and, therefore, birefringent, with an ordinary
ophthalmic field by refractive index, n , and an extraordinary refractive index, n .
E
O
Dr. Ronald Blum* of However, in a cholesteric liquid crystal, the director rotates
Pixel Optics in the USA in a helical manner over the thickness of the material. The
under the trade name, helical rotation of the director is characterised by an axis
emPower Read on to of rotation as well as a handedness, dextro-rotatory or
TM
find out more… laevo-rotatory, and a twist pitch. The twist pitch is defined
as the length along the axis of rotation over which the
director rotates through a full 360°. Optical waves having

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