A randomized, fellow eye, comparison of keratometry, aberrometry, tear film, axial length and the anterior chamber depth after eye rubbing in non-keratoconic eyes
Chervenkoff et al. Eye and Vision
A randomized, fellow eye, comparison of keratometry, aberrometry, tear film, axial length and the anterior chamber depth after eye rubbing in non-keratoconic eyes
Jordan V. Chervenkoff 0
Elizabeth Hawkes 0
Gabriela Ortiz 0
Deborah Horney 0
Mayank A. Nanavaty 0
0 The results of this study were presented in parts at the United Kingdom & Ireland Society of Cataract & Refractive Surgery
Background: To investigate the effect of eye rubbing on keratometry (K), aberrometry, tear film break-up-time (TFBUT) and anterior chamber depth (ACD). Methods: Volunteers without any corneal pathology or dry eyes were randomised to rubbing in one eye and the fellow-eye was control. Eye rubbing was performed for 2 min. Primary outcomes studied were anterior and posterior K changes. Secondary outcomes were changes in TFBUT, axial length (AL) & ACD, K changes in various zones, asphericity and aberrometry. Pre and post rubbing K, aberrometry, ACD and TFBUT were assessed in a predetermined sequence. The relationship of the above parameters to axial length (AL) was also assessed. Astigmatism was analysed using vector analysis. Results: Pre versus post rubbing, anterior flatter K further flattened (42.51 ± 1.52 D vs. 42.36 ± 1.53 D, p = 0.003) and the changes to J0 vector in central cornea (−0.16 ± 0.26 D vs. -0.27 ± 0.33 D, p = 0.038) suggested change to against-the-rule (ATR) astigmatism. There was significant change in Z2+2 polynomial following rubbing. We found a positive correlation between axial length and change in posterior K (r = 0.335, p = 0.020). The TFBUT reduced following eye rubbing (15.3 s vs. 13.9 s, p = 0.0001). There was a positive correlation between AL and increase in ACD post rubbing (r = 0.300, p = 0.038). There was a positive correlation between ACD and change in mean posterior K (r = 0.305, p = 0.035). Conclusions: In healthy eyes, following eye rubbing, there is a significant change in TFBUT and central anterior K changes towards ATR astigmatism. Longer eyes had more changes in posterior K and ACD. Whereas, eyes with deeper ACD showed more steepness of posterior K. Trial registration: ClinicalTrials.gov ID: NCT02131740.
Eye rubbing; Ectasia; Tear film break up time; Astigmatism; Aberrations
Several biochemical and biomechanical processes link
eye rubbing to structural corneal changes and ectatic
corneal disorders like keratoconus, keratoglobus and
pellucid marginal degeneration, [
] especially in patients
suffering from dry eyes or atopy [
]. Eye rubbing has
been reported to alter the surface regularity prior to
topography and this was thought to be due to changes in tear
film and/or corneal remodelling . However, the detailed
impact of eye rubbing on the anterior segment of a
healthy eye is uncertain. Understanding how the healthy
eye’s anterior segment property changes following eye
rubbing may provide some insight into the understanding
the impact of eye rubbing on abnormal anterior segment
measurements and its impact on aetiology of corneal
and anterior segment disorders (like keratoconus) in
We conducted a randomised, fellow eye controlled
study, to investigate the changes in keratometry (K),
aberrometry, tear film break-up-time (TFBUT) and
anterior chamber depth (ACD) following eye rubbing in
healthy volunteers. We also aimed to analyse the
relationship between the above parameters with age and
axial length (AL) of the eyeball.
This prospective single-centre, randomised, fellow-eye
controlled study (http://clinicaltrials.gov/show/NCT02131740)
was conducted at the Sussex Eye Hospital, Brighton &
Sussex University Hospitals NHS Trust in Brighton,
United Kingdom in March and April 2014. This study
was approved by the National Ethics Committee and
followed the tenets of the Declaration of Helsinki.
Internal email advertising the recruitment for this study
was sent to 3000 employees of the Brighton and Sussex
University Hospitals NHS trust. The volunteers were
requested to contact via email or internal phone to
arrange an appointment. Prior to the study appointment,
all volunteers were sent an information sheet detailing
The participants were consented for taking part in this
study by signing a form. Volunteers with known history
of corneal ectasia (like keratoconus, etc.) and
preexisting ocular abnormalities or diagnoses, concurrent
use of any topical drops including lubricating eye drops,
contact lens wearers, previous surgery or history of
atopy or eczema were excluded. Any included volunteer
who was noted to have any signs of forme-fruste
keratoconus (steep posterior elevation and/or irregular bow tie
pattern on axial map) on topography were not subjected
to any further tests and were excluded.
An online random number generator was used to
randomise the eyes of the subjects to digital rubbing in one
eye (either left or right eye). Eye rubbing was performed
by the same researcher (EDH) for 1 min followed by 5 s
break and a further 1 min using the index finger of the
right hand in a circular, clockwise motion over a closed
eyelid. Volunteers were instructed to look straight ahead
to maintain the primary position of gaze with the fellow
eye, which was a control. The fellow eye (control) was
undisturbed. A video demonstrating the rubbing
methodology can be found online (Additional file 1: Video
S1). A second masked observer performed all other
The subjects underwent the examinations in the
following sequence for each eye:
1) Partial coherence interferometry for axial length
(AL) and optical anterior chamber depth (ACD)
measurement on the IOLMaster® (Zeiss Meditec,
2) Scheimpflug scan of the eye on the Scheimpflug
tomographer (Pentacam®, Oculus, Germany).
3) The TFBUT assessment through the slit lamp
located next to the Scheimpflug tomographer.
4) Whilst they were on the seat for assessment on the
Scheimpflug tomographer, the eye was rubbed as per
the protocol described above by the masked observer.
5) A repeat Scheimpflug scan was performed
immediately on each eye without moving the
patient from the seat.
6) This was immediately followed by TFBUT
assessment which was performed on the slit lamp.
7) This was followed by a repeat measurement of AL
and ACD on the IOLMaster®.
To minimise the duration between rubbing and
scanning, the intervention was performed on the chair of the
Scheimpflug tomographer (Pentacam, Oculus, Germany).
Observers were masked and made conscious efforts to
hide the identity of the rubbed and non-rubbed eye from
each other. Topical anaesthetic drop was not used prior to
eye rubbing as it may affect the TFBUT. Moreover, as the
TFBUT was assessed, intraocular pressure measurement
was not included as a study outcome measure. Only one
eye was randomised and rubbed but the measurements
were performed for both eyes (other eye as control).
Data on the following outcome measures were
collected pre and post rubbing in experimental and control
eyes (in this sequence):
Keratometric changes in anterior and posterior cornea
pre and post rubbing as compared to a fellow eye as
(1)Tear film break-up time (TFBUT): Tear film break
up time was assessed using one drop of 2%
Fluorescein (Fluorescein minims, Bausch and Lomb,
USA) in each eye using a cobalt blue filter on the slit
(2)Axial length (AL) and anterior chamber depth (ACD)
were measured by partial coherence interferometry
(IOLMaster®, Carl Zeiss, Germany). Correlation of
AL and ACD with age, changes in anterior and
posterior keratometry. AL was measured from the
anterior corneal surface.
(3)Scheimpflug Holladay equivalent keratometry (EKR)
in the central (3 mm), paracentral (4-5 mm) and
peripheral (6-7 mm) zones. The detailed Holladay
Equivalent K report of the Pentacam machine gives
equivalent keratometry at various optical scan
diameters. For the purpose of this study, the
keratometric values for the central (3 mm),
paracentral (4-5 mm) and peripheral (6-7 mm)
zones were collected.
(4)Anterior asphericity (Qant), posterior asphericity
(Qpost), pachymetry apex, minimum pachymetry
and corneal volume.
(5)Changes in corneal Zernike wave-front aberrations
(WFA): Total high-order aberrations and the total
low-order aberrations for the anterior, posterior and
total cornea was collected on the Pentacam. The
mean-root square (RMS) error up to the 4th order
All data was entered onto an Excel Spread sheet
(Microsoft Office 2011, USA) and analysed using StatPlus: Mac
Pro 2016 (AnalystSoft Inc., USA). Normality of the data
was tested using Kolmogorov-Smirnov test. Data was
analysed using paired t-tests of means comparing
quantitative outcomes in experimental (rubbed) and control
eyes, pre and post rubbing. Astigmatism was analysed
using power vectors (J0 and J45) [
]. The method is
described elsewhere [
]. In this vectoral analysis, described
by Thibos and Horner, [
] any refractive or keratometric
error can be expressed as a combination of 3 orthogonal
components; that is, M, J0, and J45. In common clinical
terms, M is the spherical equivalent (SE) and is not relevant
for the purposes of studying astigmatism. The J0
component expresses the power of a Jackson cross-cylinder with
its axes at 180 degrees and 90 degrees. The J45 component
expresses the power of a Jackson cross-cylinder with its
axes at 45 degrees and 135 degrees (oblique astigmatism).
Pearson’s correlation was calculated where a correlation
was assessed. P value of less than 0.05 was considered
The study involved 98 eyes (49 patients). The mean age
was 43.3 ± 12.3 years. There were 47 Caucasians, 1 Asian
and 1 Afro-Caribbean. There were 27 (55%) female and 22
(45%) males. No one was excluded. No immediate
complication or unintended effects were observed in any eye
during the study. No patients were referred to acute
ophthalmology services due to the discovery of any
new pathology (e.g., forme-fruste keratoconus, etc.).
(a) Anterior keratometry
Pre versus post eye rubbing, the flattest anterior
keratometry became significantly flatter in case eyes after
rubbing (p = 0.003) unlike the control eyes (p = 0.087).
However, there was no significant change in the steepest
anterior keratometry in experimental (p = 0.558) and
control (p = 0.459) eyes. There was no significant change
in the maximum anterior K (Kmax) in experimental
(p = 0.223) and control eyes (p = 0.116; Table 1). There
was a significant change in J0 (p = 0.003) post rubbing
in experimental eyes only (Table 1).
Pre versus post rubbing, there was no significant
difference in the mean flattest posterior keratometry in
experimental (p = 0.799) and in control eyes (p = 0.699).
Furthermore, the mean steepest posterior corneal
keratometry was not significantly different in case (p = 0.324)
and in controls (p = 0.281) as well. There was no
significant change in the maximum posterior K (Kmax) in
experimental (p = 0.223) and control eyes (p = 0.116;
Table 1). There was no significant difference in posterior
keratometry J0 and J45 (Table 1).
1) Tear-film break-up time
Pre versus post rubbing, the TFBUT decreased from
15.3 s to 13.9 s in experimental (p = 0.0001) eyes only,
compared to 15.3 vs. 14.8 s (p = 0.096) in controls.
2) Axial length (AL) and anterior chamber depth
There was no significant difference in AL between
experimental and control eyes (p = 0.407). There was
positive correlation between AL and age in experimental
(r = 0.371; p = 0.009) and in control eyes (r = 0.366;
p = 0.011). No correlation was found between the AL vs.
the changes in mean anterior keratometry in
experimental compared to control eyes. However, there was a
positive correlation between the AL vs. the change in mean
posterior keratometry in experimental eyes only (r = 0.335;
p = 0.020) (i.e., if the AL was increased, the change in mean
posterior K was greater).
There was no significant difference in ACD pre and
post rubbing in any groups (Table 1). A positive
correlation was found in experimental eyes only between the
AL and increase in the ACD pre and post eye rubbing
(Pearson’s correlation coefficient = 0.3; p = 0.038).
However, although not statistically significant, the average
ACD increased in experimental eyes (Table 1). No
correlation was found between the ACD vs. the changes in
mean anterior keratometry in experimental and control
eyes. However, there was a positive correlation between
the ACD vs. the changes in mean posterior keratometry
in experimental eyes only (r = 0.305; p = 0.035) (i.e., if
the ACD was increased, the change in mean posterior K
Corneal volume did not change significantly pre and post
rubbing in experimental (62.7 ± 3.4 mm3 vs. 62.8 ± 3.9 mm3,
p = 0.847) and in control eyes (63.0 ± 3.5 mm3 vs.
61.4 ± 9.4 mm3, p = 0.205).
3) Keratometry in central, paracentral and peripheral
Further analysis of keratometric vectors in the central,
paracentral and peripheral cornea (Table 2) revealed
significant changes in J0 in the central zones of
experimental eyes with a change towards against-the-rule
astigmatism (p = 0.038) (Table 2).
4) Asphericity, pachymetry and corneal volume
Pre and post rubbing, anterior Q-value did not change
in the experimental eyes (−0.307 ± 0.13 vs. -0.310 ± 0.12,
p = 0.822) and controls (−0.344 ± 0.13 vs. -0.318 ± 0.16,
p = 0.112). This was similar for posterior Q-value in
experimental eyes (−0.382 ± 0.15 vs. -0.392 ± 0.15,
p = 0.182) and controls (−0.391 ± 0.17 vs. -0.396 ± 0.16,
p = 0.606).
Pre and post rubbing, pachymetry did not change
significantly in experimental (575.4 ± 32.9 μm vs. 575.2 ± 31.4 μm,
p = 0.950) and in control eyes (576.1 ± 30.7 μm vs.
574.8 ± 33.9 μm, p = 0.606).
5) Corneal aberrations
Statistically significant differences before and after
rubbing were found in experimental eyes for the Z2+2
aberration for anterior cornea only. The average anterior
corneal Z2+2 RMS became more negative by 0.159 μm
post-rubbing (−0.753 μm pre vs. -0.912 μm post,
p = 0.001) resulting in an increase in the entire corneal
Z2+2 RMS by 0.16 ± 0.52 μm (p = 0.003). There was no
statistically significant difference in any other Zernike’s
coefficient for the anterior or posterior cornea (Table 3).
While previous research has explored the structural and
histological changes on a microscopic level in the cornea
following eye rubbing, [
] our research focused on
the link between keratometric changes, aberrometry,
TFBUT and ACD occurring because of digital rubbing
in healthy eyes. We found a significant change in the
anterior cornea only. Anterior keratometry showed further
flattening and changes to the J0 vector, suggesting a
trend toward against-the-rule (ATR) astigmatism following
± 7 ± 1
J45 .020 −.(02 .002 −.(04 .00 .746
.02 .5 5
−0 −(0 .0 .9
IRP SE .34 .2 .37 .2 30 49
EP CA J0 −0 −(1 −0 −(1 .0 .4
± 8 ± 1
J45 .040 −.(02 00 .04 .004 .081
3 ) 1 )
S .2 0 .3 5
L 0 .1 0 .6
O 0 0
R ± ; ± ;
T 2 8
N .29 .9 .24 .8 6
CO J0 −0 −(0 −0 −(0 .0 .2
l A E
a R S
eye rubbing. The TFBUT reduced following eye rubbing.
We also found a positive correlation between AL and
change in posterior keratometry. There was a positive
correlation between AL and increase in ACD post rubbing.
A previous study by Mansour & Haddad explored
topographic corneal changes immediately and 5 min
after eye rubbing for 1 min [
]. They measured a
statistically significant increase in the induced astigmatism up
to 0.74 D (p = 0.04) post 1 min rubbing. A significant
increase was noted in the surface regularity and surface
asymmetry indices as well. However, astigmatic vectors
were not assessed in their study and the duration of
assessments were different too. In our study, vector
analysis showed negative changes in the J0 component in
the anterior and, to a lesser extent, the posterior cornea
of rubbed eyes, demonstrating a tendency towards
against-the-rule (ATR) astigmatism after rubbing. The
increase in the ATR astigmatism was statistically
significant in the central zone of the anterior cornea only. This
finding is interesting as there is enough evidence now
that keratoconic patients manifest ATR myopic
astigmatism at presentation, which later becomes irregular
]. We hypothesise this change in astigmatism
was caused by structural changes in the central cornea.
There is some evidence that eye rubbing is likely to lead
to transient keratometric changes in the central zone
first where the cornea is thinnest [
]. It is also known
that the rubbing induces transient thinning of the
central and mid-peripheral epithelium, which returned to
baseline thickness in 15 to 45 min (quicker recovery
centrally) . The thinner cornea is less resistant to
intraocular pressure forces in the anterior chamber, which
explains the increase in the ACD we detected (Table 3).
Keratometric changes in the peripheral cornea might
occur later in the pathological process after prolonged
eye rubbing, likely due to the increased thickness
peripherally compared to the central zone.
We did not find any significant changes in posterior
corneal keratometry. Although posterior elevation is
considered a significant differentiating factor between
normal and keratoconic eyes, its reliability to detect
subclinical ectasia is low [
]. From the findings of our
study, we can postulate that it is possible that the
changes in the anterior corneal curvature precede the
changes in posterior corneal curvature after eye rubbing.
Again, this can be multifactorial, as on further assessment
of relationship of AL and ACD to the study parameters,
we found some correlation between the AL and ACD vs.
mean change in posterior keratometry, suggesting that
longer eye and eyes with deeper ACD may have more
changes in posterior keratometery after eye rubbing. This
needs to be researched in future with controlled studies.
Statistically significant changes in corneal wavefront
aberrations were observed in the anterior corneal
astigmatism (Z2+2) and the total corneal wavefront
aberrations (Table 3). Our results showed that lower order
aberrations changed significantly in the anterior cornea.
However, there was minimal and non-statistically
significant change in lower order aberration in the posterior
cornea. The changes observed in the J0 astigmatism
vector may have some bearing with the above findings in
aberrations. A plausible reason for these changes could
be change in the tear film or due to transient corneal
epithelial remodelling following rubbing. Like Osuagwa
and Alanazi [
], we did not find any difference in
pachymetry of the corneal apex after eye rubbing in
healthy volunteers, so epithelial remodelling seems to be
a less plausible aetiology of our findings. Again, our
study did not include specific tests to look solely at the
epithelial thickness pre and post rubbing.
Previous research suggested no change in TFBUT
following eye rubbing in healthy eyes [
]. However, we
found a statistically significant decrease of 1.4 s in the
TFBUT parameter following rubbing. This could be due
to rubbing-associated irritation of the meibomian glands
or distortion of the ducts leading to a disruption of the
outermost lipid layer allowing for quicker evaporation of
the aqueous component [
]. A similar study on rats by
Greiner et al. [
] using digital eye rubbing with
pressure for 5 min also suggested that the changes start in
the conjunctival epithelium within seconds, which leads
to a rapid inflammatory cascade. Due to this reason, we
agreed and decided on fixing the duration of eye rubbing
to 1 min with a 5-s break followed by an additional
minute of eye rubbing.
The strength of this study is that it was a prospective,
randomised, fellow eye controlled study of healthy
volunteers, the same observer rubbed all the eyes, a masked
observer performed all measurements and the rubbing
was done in primary straight position of the eyeball
under the closed eyelids. Another strength of our study
is that it looked at multiple outcomes giving a wider and
real picture of the immediate changes. Due to many
outcome measures assessed in healthy volunteers in this
study, it was not possible to repeat all these measurements
at frequent time intervals post rubbing and perhaps this
may be the limitation of this study. We did not include
IOP as our outcome measure as applanation tonometry
may lead to surface irregularity, which may affect TFBUT
and Schiempflug scanning. We standardized the rubbing
technique in this study and had a single observer rub the
eyes, but the severity of the eye rubbing may have varying
changes on the study parameters. Moreover, we cannot
rule out the theoretical possibility of fluorescein tear
film disturbance when it is instilled prior to TFBUT
In summary, eye rubbing of healthy eyes induces a
significant change in astigmatism and tear film behaviour. There
were significant changes in ATR astigmatism in the
central cornea following eye rubbing. Axial myopia (increased
AL) was associated with more change in posterior K and
deeper ACD post eye rubbing. Whereas, eyes with deeper
ACD showed more changes in posterior K.
Additional file 1: Video S1. On the method of eye rubbing used in
this study. (MP4 1405 kb)
Sources of support
The material in this article is original research, has not been previously
published and has not been submitted for publication elsewhere while
JVC: Design, data analysis, interpretation, manuscript drafting, final approval.
EH: Data collection, interpretation and final approval. GO: Data collection,
interpretation and final approval. DH: Data management, collection,
interpretation, analysis, manuscript drafting and approval. MN: Concept,
design, data analysis, interpretation, manuscript drafting and final approval.
All authors approved the final submission of this manuscript.
The authors declare that they have no competing interests.
1. Zadnik K , Barr JT , Edrington TB , Everett DF , Jameson M , McMahon TT , et al. Baseline findings in the collaborative longitudinal evaluation of Keratoconus (CLEK) study . Invest Ophthalmol Vis Sci . 1998 ; 39 ( 13 ): 2537 - 46 .
2. Hawkes E , Nanavaty MA . Eye rubbing and Keratoconus: a literature review . Int J Kerat Ect Cor Dis . 2014 ; 3 : 118 - 21 .
3. Bawazeer AM , Hodge WG , Lorimer B . Atopy and keratoconus: a multivariate analysis . Br J Ophthalmol . 2000 ; 84 : 834 - 6 .
4. Galvis V , Sherwin T , Tello A , Merayo J , Barrera R , Acera A . Keratoconus: an inflammatory disorder? Eye (Lond) . 2015 ; 29 : 843 - 59 .
5. McMonnies CW , Boneham GC . Keratoconus, allergy, itch, eye-rubbing and hand-dominance . Clin Exp Optom . 2003 ; 86 ( 6 ): 376 - 84 .
6. Mansour AM , Haddad RS . Corneal topography after ocular rubbing . Cornea . 2002 ; 21 ( 8 ): 756 - 8 .
7. Thibos LN , Horner D. Power vector analysis of the optical outcome of refractive surgery . J Cataract Refract Surg . 2001 ; 27 ( 1 ): 80 - 5 .
8. Kaldawy RM , Wagner J , Ching S , Seigel GM . Evidence of apoptotic cell death in keratoconus . Cornea . 2002 ; 21 ( 2 ): 206 - 9 .
9. Krachmer JH , Feder RS , Belin MW . Keratoconus and related noninflammatory corneal thinning disorders . Surv Ophthalmol . 1984 ; 28 ( 4 ): 293 - 322 .
10. Mansour AM . Epithelial corneal oedema treated with honey . Clin Exp Ophthalmol . 2002 ; 30 ( 2 ): 149 - 50 .
11. McMonnies CW . Mechanisms of rubbing-related corneal trauma in keratoconus . Cornea . 2009 ; 28 ( 6 ): 607 - 15 .
12. McMonnies CW , Alharbi A , Boneham GC . Epithelial responses to rubbing-related mechanical forces . Cornea . 2010 ; 29 ( 11 ): 1223 - 31 .
13. Meek KM , Tuft SJ , Huang Y , Gill PS , Hayes S , Newton RH , et al. Changes in collagen orientation and distribution in keratoconus corneas . Invest Ophthalmol Vis Sci . 2005 ; 46 ( 6 ): 1948 - 56 .
14. Sherwin T , Brookes NH . Morphological changes in keratoconus: pathology or pathogenesis . Clin Exp Ophthalmol . 2004 ; 32 ( 2 ): 211 - 7 .
15. Holladay JT . Keratoconus detection using corneal topography . J Refract Surg . 2009 ; 25 ( 10 Suppl) : S958 - 62 .
16. de Sanctis U , Loiacono C , Richiardi L , Turco D , Mutani B , Grignolo FM . Sensitivity and specificity of posterior corneal elevation measured by Pentacam in discriminating keratoconus/subclinical keratoconus . Ophthalmology . 2008 ; 115 ( 9 ): 1534 - 9 .
17. Osuagwu UL , Alanazi SA . Eye rubbing-induced changes in intraocular pressure and corneal thickness measured at five locations, in subjects with ocular allergy . Int J Ophthalmol . 2015 ; 8 ( 1 ): 81 - 8 .
18. Brown B , Cho P , Yap MK . Mechanical manipulation of the lids and tear break-up time measurements in Hong Kong Chinese . Ophthalmic Physiol Opt . 1993 ; 13 ( 3 ): 233 - 8 .
19. Arita R , Itoh K , Maeda S , Maeda K , Furuta A , Tomidokoro A , et al. Meibomian gland duct distortion in patients with perennial allergic conjunctivitis . Cornea . 2010 ; 29 ( 8 ): 858 - 60 .
20. Greiner JV , Peace DG , Baird RS , Allansmith MR . Effects of eye rubbing on the conjunctiva as a model of ocular inflammation . Am J Ophthalmol . 1985 ; 100 ( 1 ): 45 - 50 .