Open Journal of Ophthalmology, 2012, 2, 60-63
http://dx.doi.org/10.4236/ojoph.2012.23013 Published Online August 2012 (http://www.SciRP.org/journal/ojoph)
Contrast Sensitivity and Eye Drops
Theodosios Chatzibalis1, Konstantinos Stamoulas1, Athanasios Karamitsos1, Diamantis Almaliotis1,
Vasiliki Mirtsou-Fidani2, Nikolaos Georgiadis3, Vasileios Karampatakis1
1Laboratory of Experimental Ophthalmology, Medical School, Aristotle University of Thessaloniki, Thessaloniki, Greece; 2Laboratory
of Pharmacology, Medical School, Aristotle University of Thessaloniki, Thessaloniki, Greece; 31st Eye Clinic, Medical School, Aris-
totle University of Thessaloniki, Thessaloniki, Greece.
Received March 13th, 2012; revised April 16th, 2012; accepted May 10th, 2012
ABSTRACT
Purpose: To evaluate the influence of commonly used eye drops on contrast sensitivity (CS). Design: Prospective study.
Participants: One hundred twenty volunteers were enrolled. Methods: The CS of ophthalmologically healthy indi-
viduals was evaluated at baseline examination before the instillation, 20 and 40 minutes after the instillation of di-
clofenac sodium and commonly used anti-glaucoma eye drops (latanoprost, brimonidine tartrate, combination of dor-
zolamide hydrochloride and timolol maleate). CS was assessed at 7 spatial frequencies varying from 1.5 c/d to 20 c/d by
the use of Mentor B-VAT II-SG video acuity tester. Results: Diclofenac sodium induced a mild, however statistically
significant decrease on the CS in 4 out of 30 subjects 20 minutes after instillation at the spatial frequency of 1.5 c/d and 3
c/d (p < 0.05 for both frequencies). Latanoprost induced a decrease in CS in 1 out of 30 subjects and combination of
dorzolamide hydrochloride and timolol maleate in 2 out of 30 at low spatial frequencies (1.5 c/d and 3 c/d) 20 minutes
after the instillation and this decrease was not statistically significant for any of these drugs (p > 0.05). Brimonidine
tartrate decreased CS in 4 out of 30 subjects 20 minutes after the instillation at a high spatial frequency (20 c/d) yet this
decrease was marginally statistically significant (p = 0.057). CS returned to baseline scores 40 minutes after the instilla-
tion for all drugs. Conclusions: Diclofenac sodium eye drops had a mild temporal effect on the low spatial frequencies
of 1.5 c/d and 3 c/d in some individuals. Latanoprost and dorzolamide/timolol had a non-statistically significant effect
on the same spatial frequencies. Brimonidine eye drops had a temporal effect on the high spatial frequency of 20 c/d
with marginal statistical significance. The CS scores returned to normal, in all cases, within the next 40 minutes after
the instillation. Ophthalmologists should be aware of the fact that some eye drops may have an influence on CS.
Keywords: Cornea; Ocular Surface; External Disease
1. Introduction
Despite the growing number of drugs used as anti-in-
flammatory agents in ophthalmology, diclofenac remains
a reasonable choice when treating a variety of ocular con-
ditions. Owing its anti-inflammatory activity to cycloxy-
genase inhibition which in turn leads to reduction in pros-
taglandin synthesis, this non-steroidal anti-inflammatory
drug (NSAID) is commonly used for prophylaxis and
treatment of postoperative inflammation. Yet diclofenac
exhibits certain adverse effects after topical instillation,
burning and stinging being the most frequent [1]. Blurred
vision has also been reported.
Topical beta-blockers, carbonic anhydrase inhibitors
such as dorzolamide, latanoprost, usually in combination
with beta-blockers, and brimonidine, may have various
side effects, among them blurring of vision.
CS is a parameter used to assess the visual function at
different levels of contrast, usually altered before any
severe change in visual acuity is noticed [2]. There are
various studies correlating the ability of individuals to
fulfill complex tasks, such as driving performance [3] or
computer task accuracy [4], or even accomplish everyday
activities with their CS function. A decrease in the qual-
ity of life has also been shown in relation to the deterio-
ration of visual function [5], including CS.
Because all of the aforementioned drugs included in
our study are widely used in every day practice and some
patients report vision blurring after their instillation, the
purpose of the present study was to evaluate the effect
that these drugs have on CS and consequently on the
quality of vision.
2. Materials and Methods
The aim of this study was to evaluate the blurring of vi-
sion, which is related to the instillation of commonly
used eye drops.

Contrast Sensitivity and Eye Drops 61
Healthy volunteers without any ocular disease were
recruited for this study. Personal medical history was
recorded and all subjects were free of medication. Indi-
viduals reporting symptoms of dry eye or using any other
ophthalmic eye drops (natural tears included) and contact
lenses were excluded from the study. Written informed
consent was obtained from each participant. After a short
explanation of the procedure about to be followed sub-
jects were examined by an ophthalmologist under a slit
lamp. Individuals with abnormal findings from the ante-
rior segment or the fundus were also excluded. All indi-
viduals had Snellen visual acuity of 10/10.
A total of one hundred and twenty volunteers were el-
igible for inclusion and were finally enrolled in the study.
All participants had best-corrected visual acuity of 10/10
or better. The study adhered to the tenets of the Declara-
tion of Helsinki and the procedure followed a standard
protocol that was consistent across the examination.
The participants were randomly divided in four groups.
Each group consisted of 30 subjects, 15 males and 15
females. The CS function of each subject was assessed
with the Mentor B-VAT II-SG video acuity tester (Men-
tor O & O, Norwell, Mass). This monitor has been used
for the evaluation of visual function in several conditions
[6,7]. Apart from its other features, the monitor uses si-
nusoidal gratings of different spatial frequencies and
contrast levels for CS function measurements. In specific,
sixteen spatial frequencies are available from 1.5 c/d to
40 c/d yet we examined the CS function of our subjects
at 1.5 c/d, 3.0 c/d, 4.6 c/d, 6.0 c/d, 8.5 c/d, 12 c/d and 20
c/d. For every spatial frequency there are available thirty
two contrast levels varying from 98% to 0.1% of contrast.
From 98% to 16% contrast levels can be changed in steps
of 0.1 log CS units whilst from 10% to 0.1% contrast
level the log CS units are allocated at regular intervals of
0.2 log units.
The psychophysical method used was the three alter-
native forced choice. Subjects were left to adapt to me-
sopic conditions wearing their best-spectacle correction.
The test luminance was automatically calibrated to 85
cd/m2 and the sinusoidal gratings were presented by the
examiner for approximately 5 seconds using a hand held
controller. Grating’s orientation could be vertical, –14˚ to
the left or +14˚ to the right from vertical. The orientation
varied randomly between the trials. The measurements
advanced gradually from a higher to a lower contrast
level. At each level the subject was asked to identify the
grating’s orientation at four different trials. When three
out of four responses were correct (at random sequence)
the contrast level was considered to be passed and the
examiner advanced to a lower one. The last contrast level
they passed was defined as the contrast threshold of the
eye and was recorded. The measurements obtained were
converted to log CS for the statistical analysis. The test
was performed at a 3-meter distance.
CS was recorded for both eyes at baseline examination
before the instillation of the drugs.
After an initial assessment of CS in the 1st group of
patients (mean age 30.83 ± 10.13 years) diclofenac so-
dium eye drops were instilled, in the 2nd group (mean
age 31.73 ± 10.95 years) latanoprost eye drops, in the 3rd
group (mean age 32.60 ± 10.08 years) dorzolamide hy-
drochloride/timolol maleate and in the 4th group (mean
age 32.43 ± 8.86 years) brimonidine tartrate.
After the baseline CS examination the test was re-
peated 20 and 40 minutes after the instillation.
The data obtained were analyzed using paired-samples
t-test to assess the CS changes 20 minutes after the in-
stillation, given that the scores returned to baseline levels
40 minutes after the drug instillation for all groups and at
any spatial frequency. All statistical analyses were per-
formed using SPSS version 18.0 software (SPSS Inc.,
Chicago, IL); p < 0.05 was judged as statistically signifi-
cant.
3. Results
The log CS was recorded for all groups 20 and 40 min-
utes after the eye drop instillation.
As regards the first group (diclofenac sodium), a mild
CS decrease by 0.2 log units was observed in 4 out of 30
subjects (13.33%) 20 minutes after the instillation at spa-
tial frequencies of 1.5 c/d and 3 c/d (p < 0.05, p = 0.043,
paired samples t-test).
Concerning the second group (latanoprost), log CS
was decreased by 0.2 log units in only 1 out of 30 sub-
jects (3.33%) 20 minutes after the instillation at spatial
frequencies of 1.5 c/d and 3 c/d. This change was not
statistically significant (p = 0.326, paired samples t-test).
In the third group (dorzolamide/timolol) 2 out of 30
subjects (6.66%) showed also a decrease in CS by 0.2 log
units at spatial frequencies of 1.5 c/d and 3 c/d 20 min-
utes after the instillation. Though this change was not
found to be statistically significant (p = 0.161, paired
samples t-test) in the group of the examined subjects.
In the fourth group (brimonidine) 4 out of 30 subjects
(13.33%) showed a decrease in CS by 0.2 log units (in
one subject 0.4 log units) 20 minutes after the eye drop
instillation at the spatial frequency of 20 c/d. The re-
corded scores were approaching a statistically significant
difference at this time point (p = 0.057, paired samples
t-test).
No change was observed at the other spatial frequencies
examined for any of the eye drops instilled. Concerning
the spatial frequencies in which a change was recorded,
all scores returned to baseline examination levels 40 mi-
utes after the instillation for all of the drugs used. n

Current Distortion Evaluation in Traction 4Q Constant Switching Frequency Converters 62
Table 1. Summary of contrast sensitivity (CS) changes.
Regimen Number of subjects
with CS impairment
Percentage (%)
of affected
Altered spatial
frequencies
Paired samples
t-test
Diclofenac sodium 4 out of 30 13.33 1.5 c/d and 3 c/d (0.2 log units) p = 0.043
Latanoprost 1 out of 30 3.33 1.5 c/d and 3 c/d (0.2 log units) p = 0.326
Dorzolamide/Timolol 2 out of 30 6.66 1.5 c/d and 3 c/d (0.2 log units) p = 0.161
Brimonidine 4 out of 30 13.33 20 c/d (0.2 log units, in one subject 0.4 log units) p = 0.057
c/d= cycles/degree.
All results are summarized in Table 1.
4. Discussion
CS function has been used to evaluate the quality of vi-
sion in several conditions including various forms of
retinopathy [8], cataract surgery/IOL implantation [9]
and glaucoma [10]. The effect of a variety of drugs on
visual function has also been studied [11-13]. As regards
glaucoma, most studies have focused on the long term
effect of anti-glaucoma eye drops on visual function.
Their results remain controversial although there is a
great number of reports outlining an improvement in CS
four or more weeks after the drug administration, espe-
cially in intermediate spatial frequencies (6 c/d and 12
c/d) [12]. This improvement can be attributed to a recov-
ery of the damaged ganglion cells and their microenvi-
ronment due to the lowering of the IOP and an increase
in the ocular perfusion and haemodynamics [14]. In the
pre- sent study we investigated the effect of commonly
used anti-glaucoma drugs on CS immediately after the
drug instillation. To the best of our knowledge there is
only one report concerning the influence of anti-glau-
coma drugs on visual quality immediately after the drug
ad- ministration [15]. In this report the investigators
found a substantial reduction in CS function for at least 5
minutes after the instillation of either timolol gel-forming
solution or brinzolamide. This temporary decrease was
fully re- stored 15 minutes after the drug instillation. In
our study the effect of the drugs was examined 20 and 40
minutes after the drug instillation and we used timolol
only in combination with dorzolamide. As concerns di-
clofenac sodium, there are reports underlining an im-
provement on CS after cataract surgery one month after
the drug ad- ministration [16]. In the present study the
decrease of CS function was detected only immediately
after the instilla- tion.
Furthermore, West et al. [17] have showed that a CS
level of ≤1.40 log units and ≤1.30 log units are associated
to disability in reading and recognition of faces respec-
tively in people older than 65 years of age. In our study a
mild decrease was recorded only in 2 low spatial fre-
quencies (1.5 c/d and 3 c/d) after the instillation of di-
clofenac sodium. This reduction was 0.20 log units in
every of the four subjects that manifested the decrease on
their visual function. As regards the anti-glaucoma drops
(latanoprost, dorzolamide/timolol) used in our study,
although no statistically significant decrease was ob-
served at any of the spatial frequencies tested, in some
individuals a mild reduction by 0.2 log units was re-
corded also in the low spatial frequencies of 1.5 c/d and
3.0 c/d. Consequently some patients may experience a
mild visual disturbance under low luminance conditions.
Only brimonidine had an influence on the high spatial
frequency of 20 c/d, (p = 0.057, marginal statistical sig-
nificance) and consequently some patients may have a
mild and temporal effect on the quality of vision.
Though the number of subjects recruited in the present
study is not very large, the results are indicative of the
visual disturbance that some individuals may experience
after the instillation of the above eye drops.
In conclusion, the CS was temporarily influenced in
some individuals. The impaired CS scores returned to the
pre-instillation status within the next 40 minutes. Oph-
thalmologist should be aware that CS impairment may be
a potential cause of visual disturbances, under various
luminance conditions, after the instillation of the above
eye drops.
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