1. 06.07.07 | Optician| 31
Contact lenses
opticianonline.net
Correcting higher-order aberrations
with Definition HD contact lenses
Gordon Hughes looks at a comparative study of reduction of HOA in current
lens designs in 16 eyes utilising wavefront aberrometry
C
urrent contact lens
designs correct lower-
order aberrations,
(myopia, hyperopia and
astigmatism) effectively in
most situations. However,
higher-order aberrations (HOA), such
as irregular astigmatism, coma, trefoil,
and spherical aberration, remain intact
and in some cases degrade the clarity of
an image significantly.
Until recently it was not possible to
measure or correct these imperfections;
for many of these patients, symptoms
manifest when driving at night or while
in reduced light conditions. Typical
experiences are ‘comet tails’, halos, glare
aroundlightsatnightorinreducedlight
conditions and these effects result in
compromised near and distance vision.
Approximately 50 per cent of people
have HOA that compromise subjective
vision, while a further 17 per cent have
seriously compromised vision as a result
of HOA. HOA can make up as much
as 20 per cent of refractive error. Until
recently it was not possible for practi-
tioners to easily test for and correct this
component of refractive error.
Last year Veni Vidi launched a new
type of contact lens asphere technology
on the UK market that utilises individu-
alised wavefront corrected surfaces to
correct both lower and higher-order
aberrations (see Optician, February 3
2006). These lenses are available in
a daily, monthly and now multifocal
format, and require no extra technol-
ogy for the practitioner to prescribe.
Recent technological advances have also
resulted in the company launching the Z
View aberrometer for use in practice in
the UK to measure HOA.
Comparison of Definition HD
Vision lenses with others
ThisstudyutilisedaZViewaberrometer
to test and compare the performance of
seven current contact lens designs in
theirabilitytoreduceHOA.TheZView
aberrometeruses3Dwavefronttechnol-
ogy to measure lower- and higher-order
aberrations by firing an aberration free
beam of light onto the patient’s retina,
measuring the reflection from each eye
in turn. The reflected distortions are
measured and quantified for each eye.
This results in a complete refractive map
of the patient’s error, creating an optical
finger print with lower-order and HOA
measurements (down to sixth order).
These are quantified using Zernicke
polynomials and converted into dioptre
equivalents for each measurement with
an accuracy of ±0.01D. The information
isshowninarefractivemapthatiscolour
coded (green = average, yellow = above
average, red = high) and the shape of the
error is then shown.
It is important to recognise that this
is not topography. Figure 1 shows an
example of a patient’s refractive map,
first uncorrected and then corrected
with a Definition contact lens.
Method
Using a Z View aberrometer the
subject eye was measured without any
correction for HOA. This determined
the power of the soft contact lenses
required.
Each of the study contact lenses
was placed on the patient’s eye and re-
measured with the Z View aberrometer.
Thisdeterminedtheamountof corrected
or induced HOA.
This was a masked study for both
patient and investigator such that the
investigator measured each eye without
knowing which brand was worn at
that time. A refractive map was printed
(Figure 1) showing the amount of HOA
thatexistedoneachpatient’seyewearing
eachlens.TheresultingHOAmapswere
then compared and evaluated.
If total HOA had increased over the
amount present in the unaided eye,
then that lens had induced HOA. If the
amountof HOAhaddecreasedfromthe
amount present in the unaided eye then
that lens design reduced HOA. Figure
3 shows a summary of how the lens
compares with other major lenses on
the market.
A similar evaluation was done just for
spherical aberration (Figure 4). Pupil
size was not controlled during the study
and all testing took place in a darkened
room.
Pupil size (as measured by the Z
View aberrometer at time of testing)
ranged from a minimum of 4mm to a
maximum of 7.2mm. Two pupils were
both measured less than 4.5mm and one
was4.8mm.Thepupilsof theremaining
13 eyes measured greater than 5mm at
time of testing.
The full evaluation HOA maps for
the study are available from Veni Vidi
in CD format. Of the 16 unaided eyes
Figure 1 A patient’s refractive map, first uncorrected (top)
and then corrected with a Definition contact lens

2. Contact lenses
opticianonline.net32 | Optician| 06.07.07
evaluated,onehadbelowaverageHOA,
eighthadaverageamountsof HOA,and
seven eyes demonstrated above average
amounts of HOA. The range of aberra-
tion for the 16 eyes was between 0.17D
of total HOA to 0.45 of total HOA.
All of the lenses evaluated did an
acceptable job of correcting the spheri-
cal requirement on each eye study. The
average amount of HOA per study eye
was 0.281D.
The following is a breakdown of the
spherical requirements of each of the 16
eyes:
-1.00 six eyes
-2.00 three eyes
-3.00 three eyes
-5.00 two eyes
-6.00 two eyes
Results: HOA decrease/
increase
DefinitionAC lowered HOA in 14/16
subject eyes, more than all other designs
tested (Figure 2). Indeed, in this study,
DefinitionAC provided the greatest
decreaseinHOA,fourtimesgreaterthan
the nearest competitor. Table 1 summa-
rises the sample base.
Results of spherical aberration
Reduction
DefinitionAC lowered SA in 11/16
subject eyes – again more than all other
contact lens designs tested (Figure 3).
Conclusion
The Definition product with its individ-
ualised asphere wavefront optics offers
a new and better alternative in aberra-
tioncontrolthancurrentfirstgeneration
aspheres for patients and practitioners
alike.
Uncorrected or induced HOA may
resultinpatientvisualdiscomfort,partic-
Figure 2 Figure 3
Table 1
Lens brand Eyes with lowered HOA
DefinitionAC 14/16
Frequency Aspheric 9/16
Biomedics premier
(Evolution)
8/16
PureVision 7/16
O2Optix 5/16
Night & Day 5/16
Acuvue Advance 5/16
ularly in mesopic or scotopic conditions.
Although many currently available lens
designs incorporate advanced aspheric
optics in an attempt to reduce HOA on
theeye,DefinitionreducedHOAbyfour
times that of its nearest competitor.
Despite being designed to reduce
spherical aberration many of the lenses
in this survey showed a surprising
difference in their ability to achieve that
task. Some of the lens brands evaluated
actually induced HOA while others
induced spherical aberration.
Inattemptingtoofferavisualupgrade,
current asphere technology does not
deliver the vision result achieved with
individualised aspheres at each power
curve utilising wavefront optics that
are incorporated into Definition lenses.
Though many factors need to be consid-
eredwhenprescribingsoftcontactlenses
for any individual, to achieve crisper,
clearer, vision, lens designs that demon-
strate the greatest amount of HOA
correction should be considered. ●
● Gordon Hughes is UK & Eire
professional relations & sales & marketing
manager, Contact Lens Division, Veni Vidi
Figure 4 The Z View aberrometer in use
DefinitionAC Night & Day
22%
Acuvue
Advance
6%
O2
Optix
3%
Biomedics
Premier
1%
Pure
Vision
5%
Frequency
AS
6%
%decreasedHOA%increasedHOA
0.281 Average aberration per eye
25
20
20
10
10
30
25
0
5
5
15
15
Percentage of change of higher order aberrations
among leading contact lenses
27%
DefinitionAC Night & Day
15%
Acuvue
Advance
1%
Biomedics
Premier
7%
Frequency
AS
13%
O2
Optix
16%
Pure
Vision
36%
%decreasedSA%increasedSA
0.125 Average aberration per eye
20
40
10
30
60
50
0
10
20
Percentage of change of spherical aberration
among leading contact lenses
52%