Original Article

The Influence of Near Vision Tasks on Intraocular
Pressure in Normal Subjects and Glaucoma Patients

Mohammad Pakravan1, MD; Azadeh Samaeili2, MD; Hamed Esfandiari3, MD; Kiana Hassanpour2, MD; Sadid
Hooshmandi2, MD; Shahin Yazdani2, MD; Farideh Sharifipour2, MD; Azadeh Doozandeh2, MD; Bahram

Einollahi2, MD; Parastou Pakravan4, MS; Mohammad Hasan Shahriari5, MS; Bahareh Kheiri2, MS

1Glaucoma and Neuro-Ophthalmologist, Jones Eye Institute, University of Arkansas for Medical Sciences, AR, USA
2Ophthalmic Research Center, Research Institute for Ophthalmology and Vision Science, Shahid Beheshti University of Medical

Sciences, Tehran, Iran
3Department of Ophthalmology, Olmsted Medical Center, Rochester, MN, USA

4Miller School of Miami, University of Miami, Miami, Florida
5Department of Health Information Technology and Management, School of Science, Shahid Beheshti University of Medical

Sciences, Tehran, Iran

Abstract

Purpose: To investigate the effect of static accommodative tasks on intraocular
pressure (IOP) of glaucomatous and normal eyes.
Methods: Four groups of subjects categorized as primary open-angle glaucoma
(POAG), primary angle-closure suspects (PACS), normal age-matched controls,
and normal young adults (NYA; age <40 years) were enrolled. The baseline IOPs
were measured after the subjects were looking at a distant target for 15 min.
Static accommodation was obtained by execution of near vision tasks (reading
at 33 cm in daylight [300 lux] for 60 min). IOPs were measured at 15, 30, 45, and
60 min intervals while accommodating and then measured again after 15 min of
relaxing accommodation while looking at a distant target.
Results: One-hundred and eighteen eyes of 98 subjects were recruited. The
study groups consisted of the following categories: 25 POAG (46 eyes), 24
PACS (47 eyes), 25 matched controls (50 eyes), and 24 NYA (48 eyes). Within
all groups, the mean IOP decreased throughout the accommodation period at
all time points. Maximum IOP reduction after accommodation was detected at
the 30-min time among the POAG subjects, at the 45-min time in the PACS and
matched control groups, and at 15 min after the relaxation of accommodation in
the NYA group. IOP reduction levels showed no statistically significant difference
among POAG, PACS, and the normal matched groups in their response to
accommodation. However, NYA had significantly lower IOP and greater IOP
reduction after the resting period (relaxation of accommodation).
Conclusion: Static accommodative tasks can significantly reduce IOP in normal,
POAG, and PACS individuals. Encouraging glaucoma patients to practice
periodical near vision tasks could be viewed as an adjunctive measure for
glaucoma management.

Keywords: Accommodation; Accommodative Tasks; Intraocular Pressure; Primary Open-
angle Glaucoma

J Ophthalmic Vis Res 2022; 17 (4): 497–504

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Near Vision Tasks and IOP; Pakravan et al

INTRODUCTION

Accommodation refers to the ability of the eye to
change focus from a distant object to a near object.
During accommodation, ciliary muscle contraction
leads to zonular fiber relaxation which is then
followed by a change in lens shape where it
becomes more spherical. Meanwhile, longitudinal
fibers in the ciliary muscles that adhere to the
scleral spur (SS) cause posterior movement of
the SS during accommodation. As a result, the
trabecular meshwork (TM) and adjacent Schlemm’s
canal expands and trabecular outflow of aqueous
humor increases.[1]

Investigating the role of accommodation
on intraocular pressure (IOP) has presented
contradictory results. Static accommodation
refers to focusing on a near target without
changing to distance target for almost 3 min
or more. While the patients look at near target
and distance frequently for 3 s in repeated
accommodation.[2] In some reports, both static
and repeated accommodations have been shown
to decrease IOP in healthy individuals.[2, 3] The
plausible mechanism could be the adjustment
of elastic tissue structures of the chamber angle
following numerous accommodation and ciliary
muscle contractions. This modification could
enhance trabecular aqueous humor drainage in
a sinusoidal pattern.[4] However, further studies
showed that repeated accommodation does
not induce a significant reduction in IOP as
compared to static accommodation.[2] Similarly,
Baser et al[5] reported that reading does not
affect IOP in healthy individuals. Indeed, some
studies have reported an increase in IOPs during
accommodation. Ha et al[6] investigated the
effects of working with smartphones on the IOP
in normal patients and reported an increasing
effect, especially in low-light conditions. Similarly,

Correspondence to:

Azadeh Samaeili, MD. Ophthalmology Department of
Labbafinejad Medical Center, Boostan 9 St. Pasdaran
Ave., Tehran 16666, Iran.
Email: as100973@gmail.com
Received: 19-01-2021 Accepted: 10-06-2022

Access this article online

Website: https://knepublishing.com/index.php/JOVR

DOI: 10.18502/jovr.v17i4.12350

Vera et al[7] reported IOP to increase while reading
both in supine and sitting positions which was
greater in the sitting position.

Considering the contradictory results on the
effect of engaging in near vision work on IOP and
also the scarcity of studies about accommodation
effects on the IOP of glaucomatous eyes, we
conducted the present study. This study aims to
investigate the magnitude of IOP changes induced
by continuous or static accommodation during near
vision work in glaucomatous and normal eyes.

METHODS

A total of 191 eyes of 98 patients were enrolled in
the study. The Institutional Review Board of Shahid
Beheshti University of Medical Science approved
the protocol of the study. Our research adhered to
the tenets of the Declaration of Helsinki. Informed
written consent was obtained from each subject.
The study groups consisted of 25 POAG subjects
(46 eyes; group 1), 24 PACS subjects (47 eyes;
group 2), 25 matched controls (50 eyes; group
3), and 24 normal young individuals (48 eyes;
group 4). The first three groups were selected
using the independent simple random sample
selection technique. The fourth group were normal
volunteers, young (not presbyopic and aged <40
years) residents of the center. It was assumed
that residents experienced approximately equal
amounts of weekly physical activities. Diagnosis of
POAG was made by the detection of glaucomatous
optic neuropathy in the presence of open angles on
gonioscopy and also by the lack of any evidence
of secondary causes of glaucoma after baseline
examination. PACS was defined when the posterior
TM was not visible at 180 or more degrees of the
angle during gonioscopic examination.[8]

Exclusion criteria were the existence of
peripheral anterior synechiae (PAS), history of
glaucoma surgery, ocular trauma, use of any
topical or systemic medications that could affect

This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.

How to cite this article: Pakravan M, Samaeili A, Esfandiari
H, Hassanpour K, Hooshmandi S, Yazdani S, Sharifipour F,
Doozandeh P, Einollahi B, Pakravan P, Shahriari MH, Kheiri B.
The Influence of Near Vision Tasks on Intraocular Pressure in
Normal Subjects and Glaucoma Patients. J Ophthalmic Vis Res
2022;17:497–504.

498 JOURNAL OF OPHTHALMIC AND VISION RESEARCH Volume 17, Issue 4, October-December 2022

https://knepublishing.com/index.php/JOVR


Near Vision Tasks and IOP; Pakravan et al

accommodation including pilocarpine, ocular
pathologies that would compromise IOP reading,
high myopia (spherical equivalent refractive
error >−6.00 D), and high hyperopia (defined as
spherical equivalent hyperopia of more than 4.0
D).

At baseline, the ophthalmologic examination
included best-corrected visual acuity (BCVA)
measurement, slit-lamp examination (Haag-Streit,
Bern, Switzerland), and IOP measurement with
rebound tonometry performed by a glaucoma
specialist (iCare Finland Oy, Helsinki, Finland). In
addition, gonioscopy with a Zeiss-style four-mirror
lens (model OPDSG, Ocular Instruments, Inc.,
Bellevue, WA), fundus examination, perimetry
(Humphrey visual field analyzer; model 750; Carl
Zeiss Meditec, Dublin, California, USA), and central
corneal pachymetry (Quantel medical pocket,
Japan) were performed at baseline.

Using the Shaffer gonioscopy classification, a
trained ophthalmologist performed the gonioscopy
at ×16 magnification in a darkroom setting. The
same ophthalmologist measured the IOP twice
between 9 and 11 am. The ophthalmologist was
masked about the patients’ group. An average of
two readings were recorded as the patient’s IOP.
If two IOPs differed by more than 2 mmHg, the
measurement was repeated, and the mean IOP
was recorded. To maintain a static accommodative
state, patients were asked to continue their fixation
on the object used for the near vision task
examination with the opposite eye during IOP
measurements.

After a complete explanation of the study
protocol to the patients, they were seated in an
upright position while the neck was in a neutral
position. Patients were then required to look at
a distance target (6/12 Snellen letters) for 15 min
while wearing their corrective lenses. Baseline IOP
was then measured. Static accommodation was
achieved by close monitoring of the volunteers
while they focused on a near target (reading
the same text from a 19 Samsung monitor with
brightness of 250 cd/m2 at 33 cm at daylight [300
lux]) for 1 hr while wearing their presbyopic glasses.
iCare IOP measurements were then taken every 15
min during the 1 hr of the static accommodative
task, and 15 min after focusing on a distant object
in relaxed accommodative state. Before the start
of the study, all subjects’ IOPs were controlled
either by topical medications or Yttrium Aluminum
Garnet (YAG) laser peripheral iridotomy (PI) in the

glaucoma cases, resulting in all IOPs becoming ≤
23 mmHg.

Statistical Analysis

To present the data, we used mean and standard
deviation analysis. To compare the results among
the groups, and throughout the study whenever
needed, we used GEE (Generalized Estimating
Equations) to consider the possible correlation
of the IOP results in the eyes. The primary
outcome measure was the change in IOP 15
min after the start of accommodation. The IOP
values at other time intervals were considered
as secondary outcome measures. To evaluate
the changes within groups during the follow-up
times we used paired t-test. In all the analyses,
multiple comparison corrections were done using
the Bonferroni method. All statistical analyses were
performed using the SPSS software (IBM Corp.
Released 2017. IBM SPSS Statistics for Windows,
Version 25.0. Armonk, NY: IBM Corp.). A P-value
<0.05 was considered statistically significant.

RESULTS

One hundred and ninety-one eyes of 98
consecutive participants were enrolled in the
study. The mean age of participants in groups 1 to
4 were 55.44 ± 13.96, 56.32 ± 13.79, 51.64 ± 11.1,
and 29.75 ± 3.65 years, respectively.

There were no statistically significant differences
among study groups 1, 2, and 3 in terms of age,
refractive status, and central corneal thickness but
there were statistically significant differences in
group 4 [Table 1].

None of the individuals were using either
pilocarpine or other systemic agents that could
constrict or dilate the pupil. Eighty percent (37
eyes) of the POAG patients were on glaucoma
medications that presumably do not affect
accommodation.

Baseline demographic and clinical
characteristics of all groups are presented in
Table 1.

For all groups, the IOP was measured at
baseline, and at every 15 min throughout the hour
of the accommodation period. IOP was measured
again, 15 min after the release of accommodation
where the patients focused on a distant target.

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Near Vision Tasks and IOP; Pakravan et al

The mean IOP decreased in all of the volunteers
during the accommodating period. The mean
baseline IOP ± SD was 14.43 ± 3.96, 14.11 ± 3.99,
13.62 ± 4.57, and 14.27 ± 3.98 mmHg in groups 1 to
4, respectively (P = 0.807).

Table 2 shows the IOP changes and differences
from baseline within and among the groups. In
group 1, IOP significantly decreased from baseline
with a mean change of 0.98 ± 2.2 mmHg (P =
0.004), –1.17 ± 2.24 mmHg (P = 0.001), and –0.8 ±
2.46 mmHg (P = 0.032) at 15, 30, and 45-min time
points after static accommodation.

In group 2, IOP decreased significantly from
baseline at all time points throughout the
accommodation. The amount of IOP decrease
at each pre-determined 15 min time interval was
–1.19 ± 2.09 (P < 0.001), –1.02 ± 2.93 (P = 0.021),
–1.43 ± 2.89 (P = 0.002), and –1.17 ± 2.64 (P =
0.004), respectively. The IOP reduction for group
2 was also significant after 15 min of relaxation of
accommodation (–1.04 ± 2.41 mmHg; P = 0.005). In
group 3, IOP reduced throughout all examinations,
however, it was significant only at the 30 and
45-min time points with a mean reduction of –1.06
± 2.4 and –1.1± 2.4 mmHg, respectively (P = 0.003).
In group 4, IOP reduction was significant at all time
points within and after accommodation (–1.29 ±
2.24, –1.54 ± 2.35, –2.08 ± 2.55, –1.75 ± 2.27,
and –2.15 ± 2.67, respectively, P < 0.001; Table 2).

Maximum IOP reduction was observed 30
min after the near vision task in group 1 (–
1.17 ± 2.24 mmHg), 45 min after accommodation
in groups 2 and 3 (–1.43 ± 2.89 and –1.1 ±
2.46 mmHg, respectively), and 15 min after the
end of the release of accommodation in group
4 (–2.15 ± 2.67 mmHg). The mean IOPs and
IOP reductions showed no statistically significant
difference among the study groups in time intervals
of 15, 30, 45, and 60 min after the start of the
accommodation [Table 2, Figure 1].

However, normal young adults showed
significantly lower mean IOP (12.13 ± 3.59, P =
0.04) and greater IOP reduction (–2.15 ± 2.67, P
< 0.001) after the release of the accommodation.
Utilizing multivariate analysis, only the factor of
age was associated with greater IOP reduction (P
= 0.02).

DISCUSSION

This study found a consistent reduction in the mean
IOP during static accommodation in all groups.

Our results were in line with previous studies
which showed that IOP decreased during
accommodation.[9, 10]

IOP is predominantly controlled by aqueous
outflow through the TM, which is augmented by
traction on the SS. Increased traction on the SS
enlarges the pores of the TM. There is histological,
pharmacological, and electrophysiological
evidence explaining the association between
accommodation and IOP; there is a connection
between elastin fibers in the tendons of the
longitudinal fibers of ciliary muscles and elastin
fibers of the TM lamellae. Ciliary muscle tendon
density is highest in the juxtacanalicular tissue
near the TM adjacent to the Schlemm canal (SC).[11]
Therefore, the presence of pilocarpine or any
factors that may trigger accommodation results in
ciliary muscle contractions followed by a stretch
of the TM and an increase in the area of the SC,
and subsequent increase in aqueous outflow and
IOP reduction.[12, 13] However, human studies have
not yet demonstrated the changes in SC and TM
morphology on physiological accommodation.
The mean IOP reduction during accommodating
occurs between the ranges of 1.8–4.5 mmHg as
shown in the previous reports.[2, 14–16] The period
of IOP measurement was between 8 and 10 min
immediately after accommodation in these studies
which can justify a slightly higher IOP reduction as
compared to our results.[2, 14–16]

We found that age was significantly associated
with IOP reduction in all groups. The magnitude
of IOP reduction was greater in older participants
during accommodation. This observation may be
explained by the pore sizes in TM. It is possible
that changes in normal pore sizes have a limited
effect on IOP corresponding to a small age-related
increase in IOP seen between 20 and 60 years of
age.[17] However, even a 0.25-micron change in the
size of the small pore increasing with age can result
in a 10 mmHg change in the IOP.[18]

We observed that the accommodation-induced
reduction in the IOP was seen in open-angle
as well as angle-closure eyes. We argue that
while accommodation pushes the iridolenticular
diaphragm forward and shallows the angle, its
beneficial effects on TM outweigh these changes
and result in IOP reduction. However, the lower IOP
reduction in POAG individuals at the 60 min time
point could be attributed to the stiffness of TM in
this group of patients.[19]

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Near Vision Tasks and IOP; Pakravan et al

Table 1. The baseline demographic and clinical characteristics of the study participants.

Study Groups

Total POAG PACS Control NYA P-value

Sex M 48 (49.0%) 13 (52.0%) 12 (50.0%) 12 (48.0%) 11 (45.8%) 0.992*

F 50 (51.0%) 12 (48.0%) 12 (50.0%) 13 (52.0%) 13 (54.2%)

Age Ref 48.47 ± 15.62 55.44 ± 13.96 56.32 ± 13.79 51.64 ± 11.1 29.75 ± 3.65 <0.001*
0.34 ± 1.25 0.53 ± 1.36 0.66 ± 1.15 0.72 ± 1.12 -0.45 ± 0.99 <0.001*

CCT 536.56 ± 73.84 549.55 ± 36.35 547.49 ± 23.97 538.71 ± 44.62 522.8 ± 13.01 <0.001*
Baseline IOP 14.1 ± 4.12 14.43 ± 3.96 14.11 ± 3.99 13.62 ± 4.57 14.27 ± 3.98 0.807**

*Based on Fisher’s exact test; **Based on Generalized estimating equations; Ref, refraction; CCT, central corneal thickness;
POAG, primary open-angle glaucoma; PACS, primary angle-closure glaucoma; NYA, normal young adults; IOP, intraocular
pressure

Table 2. Changes in IOP between and within study groups throughout the study.

Study groups P-value** Overall effect
size (Cohen’s

d)

POAG PACS Control NYA

Baseline IOP 14.43 ± 3.96 14.11 ± 3.99 13.62 ± 4.57 14.27 ± 3.98 0.807
IOP at 15min 13.46 ± 3.87 12.91 ± 3.73 13.32 ± 4.47 12.98 ± 3.93 0.884
IOP change at 15 min –0.98 ± 2.2 –1.19 ± 2.09 –0.3 ± 1.93 –1.29 ± 2.24 0.06 0.11
P-within* 0.004 <0.001 0.277 <0.001
IOP at 30 min 13.26 ± 3.62 13.09 ± 4.19 12.56 ± 4.2 12.73 ± 3.78 0.804
IOP change from baseline
at 30 min

–1.17 ± 2.24 –1.02 ± 2.93 –1.06 ± 2.4 –1.54 ± 2.35 0.709 0.14

P-within* 0.001 0.021 0.003 <0.001
IOP at 45 min 13.63 ± 3.3 12.68 ± 4.12 12.52 ± 4.07 12.19 ± 3.62 0.198
IOP Change from baseline
at 45 min

–0.8 ± 2.46 –1.43 ± 2.89 –1.1 ± 2.46 –2.08 ± 2.55 0.075 0.27

P-within* 0.032 0.002 0.003 <0.001
IOP at 60 min 13.8 ± 3.51 12.94 ± 3.65 12.96 ± 4.03 12.52 ± 3.33 0.323
IOP change from baseline
at 60 min

–0.63 ± 2.4 –1.17 ± 2.64 –0.66 ± 2.76 –1.75 ± 2.27 0.068 0.24

P-within* 0.081 0.004 0.097 <0.001
IOP after 15 min rest 14.37 ± 4.28 13.06 ± 3.67 12.8 ± 4.25 12.13 ± 3.59 0.049
IOP Change from baseline
after 15 min rest

–0.07 ± 2.56 –1.04 ± 2.41 –0.82 ± 2.4 –2.15 ± 2.67 0.001 0.41

P-within* 0.864 0.005 0.019 <0.001

*P-within based on Paired t-test; **Based on generalized estimating equation (multiple comparison correction has been done
with Bonferroni method); NYA, normal young adults; POAG, primary open-angle glaucoma; PACS, primary angle-closure
suspect; IOP, intraocular pressure

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Near Vision Tasks and IOP; Pakravan et al

 

Figure 1. Changes in IOP between and within study groups throughout the study. Maximum IOP reduction was observed 30 min
after a near task in POAG, 45 min after accommodation in PACS and control groups, and 15 min after the end of accommodation
in NYA. POAG, primary open-angle glaucoma; PACS, primary angle-closure suspect; NYA, normal young adults.

In contrast to our findings, some studies
demonstrated that IOP was elevated during
accommodation while reading[7] or while using a
smartphone[6] or in myopic eyes.[20, 21] However,
this result is not consistently repeated in other
studies.[22] The divergent reaction of IOP to
accommodation in myopic eyes could be the
result of the differences in structure and function
of the eyes between emmetropic and myopic
subjects.[22] Ahnul et al studied normal-tension
glaucoma cases that were controlled by medication
or filtering surgery. They found an elevation of
IOP after 25 min of working on a smartphone in
low-light conditions.[23] However, their study varied
in the type of glaucoma, the low-light conditions,
the duration of the near vision task, and the
use of smartphones versus computer screens as
was done in the current study. Another concern
that may influence outcomes is that bending the
head when reading on a smartphone may be
comparable to prone positioning[24, 25] which is
different from the upright position normally applied
during computer work.

Although the IOP reduction persisted
throughout the accommodation and at least
15 min after accommodation in our study, it was
hard to predict how long the hypotensive effect
of accommodation would last especially when
compared with alternative studies where IOP was
mainly measured during and immediately after
accommodation.[20–22] Of note, the effect sizes of

IOP estimated by Cohen’s d demonstrated small to
moderate differences among groups [Table 2].

One limitation of the current study is that
we did not include a control group with no
accommodation. Sitting upright could potentially
have some hypotension effects, however, the
literature review for this effect is inconclusive.[26–28]

We also did not evaluate the biometric
changes of the anterior chamber to determine
the interaction between IOP and changes in lens
thickness and positioning, depth of the anterior
chamber as well as angle parameters. In an
anterior segment study, Yan et al demonstrated
that the anterior chamber became shallow, the
lens thickened, and the angle narrowed during
accommodation.[20]

Another limitation of the study is that only
including PACS’ eyes makes it hard to estimate
the reaction of eyes with complete angle-closure
to accommodation. The effect of ciliary muscle
contraction in the presence of PAS could be
opposite to that of the open-angle or PACS; it
is shown that accommodation inhibits uveoscleral
outflow resulting in paradoxical IOP elevation in
synechial angle closure.[4] Further studies with
a longer period of resting after accommodation
along with analyses among different ethnicities are
warranted to elucidate the duration of the effect of
accommodation on IOP as well as correlations as it
pertains to other ethnicities.

In summary, in this present study, IOP was
shown to be significantly reduced after static

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Near Vision Tasks and IOP; Pakravan et al

accommodation for 1 hr in normal, POAG, and
PACS eyes. The hypotensive effect lasted at least
15 min after the relaxation of accommodation.
Encouraging glaucoma patients to perform
periodic near vision tasks such as studying
would not only improve knowledge on the topic
but also be helpful as an adjunctive measure in
glaucoma management.

Acknowledgment

Authors acknowledge the memory of our beloved
coauthor Dr. Mohammad Zare who passed away
during his fight in frontline of COVID-19.

Financial Support and Sponsorship

None.

Conflicts of Interest

Authors have no proprietary or commercial interest
in any materials discussed in this article.

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504 JOURNAL OF OPHTHALMIC AND VISION RESEARCH Volume 17, Issue 4, October-December 2022