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Effect of cylinder power and axis changes on vision in astigmatic participants: A comment [letter]

Abstract

Dear editor We read with interest the article by Sha et al1 in the March 2019 issue. This study evaluated the effects of misalignment axis and undercorrecting cylinder powers on the visual performance of astigmatic people. The aim of this work was mainly to assist eye-care practitioners in reducing the number of toric contact lenses stock-keeping units. The authors analyze the effect of astigmatic undercorrection by 0.25, 0.50 and 0.75 DC, at different amounts of misalignments up to 30°. In this analysis, the effects of cylinder power, cylinder axis and their mutual interaction are analyzed separately. However, it is well known that cylinder power and axis are not independent variables; in fact, astigmatism is a vector magnitude. Several studies2, 4 use vector formalism to quantify the blur strength produced by astigmatism. Even in previous literature, 1 the authors show the power vector components (M, J0, J45) in Table 1, for the different groups in which the sample is divided. ... Remón, L.; Furlan, W.D.

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Effect of cylinder power and axis changes on vision in astigmatic participants: A comment [letter]

Author: Remón, L.; Furlan, W.D.
Year: 2019
DOI: 10.2147/OPTO.S212510
Source: https://zaguan.unizar.es/record/99349/files/texto_completo.pdf
LETTER
E ec o cylinde powe and axis changes on
ision in as igma ic pa icipan s: a commen
[Le e ]
This a icle was published in he ollowing Do e P ess jou nal:
Clinical Op ome y
Lau a Remón
1
Wal e D Fu lan
2
1
Depa amen o de Física Aplicada,
Uni e sidad de Za agoza, 50009
Za agoza, Spain;
2
Depa amen o de
Óp ica y Op ome ía y Ciencias de la
Visión, Uni e si a de València, 46100
Bu jasso , Spain
Dea edi o
We ead wi h in e es he a icle by Sha e al
1
in he Ma ch 2019 issue. This
s udy e alua ed he e ec s o misalignmen axis and unde co ec ing cylinde
powe s on he isual pe o mance o as igma ic people. The aim o his wo k
was mainly o assis eye-ca e p ac i ione s in educing he numbe o o ic
con ac lenses s ock-keeping uni s. The au ho s analyze he e ec o as ig-
ma ic unde co ec ion by 0.25, 0.50 and 0.75 DC, a di e en amoun s o
misalignmen s up o 30°. In his analysis, he e ec s o cylinde powe ,
cylinde axis and hei mu ual in e ac ion a e analyzed sepa a ely. Howe e ,
i is well known ha cylinde powe and axis a e no independen a iables; in
ac , as igma ism is a ec o magni ude. Se e al s udies
2,4
use ec o o mal-
ism o quan i y he blu s eng h p oduced by as igma ism. E en in p e ious
li e a u e,
1
he au ho s show he powe ec o componen s (M, J
0
,J
45
)in
Table 1, o he di e en g oups in which he sample is di ided. Howe e ,
unexpec edly, hey do no use he same o malism o analyze he da a (see
Tables 2, 3 and Figu es 2–6). In his sense, in ou opinion, i would ha e been
much use ul o show he esul s o he e alua ed isual pa ame e s in e ms
o a single scala a iable such as he blu s eng h (B¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ðM2þJ2
0þJ2
45Þ
q).
This could ha e been done by compu ing he modulus o he ec o di e ence
be ween he ull co ec ion and he di e en simula ed misco ec ions, and
hen ep esen ing he di e en pa ame e s o in e es (HCVA, LCVA, e c.) s
he blu s eng h. In his way, he a e o change o each pa ame e pe uni
blu s eng h could ha e been compu ed.
2
F om he da a in e e ence [1]
(Figu e 2 and Table 1), co esponding o high cylinde g oup HCVA, we
ound ha he fi e y well wi h he exp ession: logMAR =0.37 B−0.1
which is he empi ical equa ion ha we ound p e iously,
3
which is also
men ioned in e e ence [2].
Finally, i is impo an o no e ha , like happens o he HCVA,
4
he a e o
change o he o he isual pa ame e s wi h he blu s eng h may depend on he ype
o esidual as igma ism, and also on he ampli ude o accommoda ion o he
pa icipan s. This may be one o he easons o he di e en slopes in he da a
co esponding o unde co ec ion by 0.75 DC in he abo e-men ioned Figu e 2
(do ed line).
Co espondence: Lau a Remón
Depa amen o de Física Aplicada,
Facul ad de Ciencias, Uni e sidad de
Za agoza, C/ Ped o Ce buna, 12,
Za agoza 50009, Spain
Email lau ema @uniza .es
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In conclusion, by using he ec o powe o malism,
p ac i ione s could ob ain he answe o he ollowing
ques ion: Which is he maximum ole able di e ence in
he amoun o blu s eng h (B) be ween 2 lenses in my
s ock? This esul would ce ainly be use ul o “assis in
de e mining oppo uni ies o educing s ock-keeping uni s
o o ic con ac lens”.
Disclosu e
The au ho s epo no conflic s o in e es in his
communica ion.
Re e ences
1. Sha J, Fed ke C, Tilia D, e al. E ec o cylinde powe and axis
changes on ision in as igma ic pa icipan s. Clin Op om.
2019;11:27–38. doi:10.2147/OPTO.S190120
2. A chison DA, Ma hu A. Visual acui y wi h as igma ic blu . Op om
Vis Sci.2011;88(7):E798–E805. doi:10.1097/OPX.0b013e31821
98792
3. Remón L, To nel M, Fu lan WD. Visual acui y in simple myopic
as igma ism: influence o cylinde axis. Op om Vis Sci.2006;83
(5):311–315. doi:10.1097/01.opx.0000197958.83213.b1
4. Remón L, Monso iu JA, Fu lan WD. Influence o di e en ypes o
as igma ism on isual acui y. J Op om.2017;10(3):141–148.
doi:10.1016/j.op om.2016.07.003
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