·Review Article·
The
correlation between keratoconus and eye rubbing: a review
Hatim Najmi1, Yara Mobarki2, Khalid
Mania2, Bashaer Altowairqi3, Mohammed Basehi4,
Mohammed Salih Mahfouz5, Mona Elmahdy5
1Department of Ophthalmology, King
Fahad Hospital of the University, Al Khobar 34445, Saudi Arabia
2King Abdulaziz University Hospital,
Jeddah 21589, Saudi Arabia
3King Fahad Central Hospital, Jazan
45142, Saudi Arabia
4Department of Emergency, King Fahad
Hospital of the University, Al Khobar 34445, Saudi Arabia
5Department of Family and Community
Medicine, Faculty of Medicine, Jazan University, Jazan 45142, Saudi Arabia
Correspondence to: Hatim Najmi. Department of
Ophthalmology, King Fahad Hospital of the University, Al Khobar 34445, Saudi
Arabia. hatim_najmi@hotmail.com
Received:
Abstract
Keratoconus is a
non-inflammatory disorder which is gradual in development; corneal thinning and
ectatic protrusion characterizes it. Keratoconus prevalence varies between
different regions depending on several factors that affecting its prevalence.
There are risk factors for developing keratoconus such as demographic and
environmental factors. It was suggested that eye rubbing was associated with
the development of keratoconus. The main aim of this review was to summarize
the literature data about keratoconus and to identify the role of eye-rubbing
in the aetiology of the disease. A number of 24 articles was reviewed through
the PubMed, Google Scholar and Research Gates. There are many keywords used
such as keratoconus, aetiology of keratoconus, eye rubbing, keratoconus
prevalence, keratoconus and eye rubbing correlation. We concluded that eye
rubbing causes the thinning of keratocyte, and the degree of effect of eye
rubbing depends on the period and force of performing eye rubbing. It is
recommended to avoid eye rubbing to prevent keratoconus, this can be achieved
by avoiding itching and treating dryness of the eye and avoiding wearing eye
lenses.
KEYWORDS: keratoconus; eye rubbing;
keratoconus risk factors
DOI:10.18240/ijo.2019.11.17
Citation:
Najmi H, Mobarki Y, Mania K, Altowairqi B, Basehi M, Mahfouz MS, Elmahdy M. The
correlation between keratoconus and eye rubbing: a review. Int J Ophthalmol 2019;12(11):1775-1781
INTRODUCTION
Eye diseases are considered a
critical health problem in the Middle East, especially in Saudi Arabia[1]. Keratoconus is an eye disease causes curvature of
cornea gradually, transforming it from a symmetrical dome shape into an
asymmetric cone shape. This results in reduced visual acuity and a change in
eyeglasses[1]. It was described by Nottingham
firstly in 1854[2], this disease is accompanied by
blurred vision secondary to irregular astigmatism[2].
It affects all ethnic groups.
However, it is more prevalent in Caucasians and Asians[3].
The prevalence of keratoconus varies between different studies due to the
differences in diagnostic tests as well as the definition of keratoconus; the
prevalence was reported to be 1 case in every 2000 individuals globally[4]. In Saudi Arabia, it was found that keratoconus in the
previous 20y was the primary reason for corneal transplantation[5]. Several factors increase the development of
keratoconus including demographic factors and environmental factors, the
demographic factors including ethnic differences and genetic factors, while
ecological factors including eye rubbing, atopy and ultraviolet (UV) exposure[6]. Postulation of keratoconus development by eye rubbing
discussed multiple published case reports such as[7]
that suggest the association between keratoconus and eye rubbing. Eye
rubbing is a common activity of the individuals that occurs in response to
emotional stress, fatigue or ocular irritation, it happens also before sleep
and when waking[8]. Eye rubbing can be evoked by
symptoms of allergy and dryness of eye[9-10].
The current review aims to find out the association between keratoconus and eye
rubbing by reviewing the previous studies and to summarize the literature data
about keratoconus.
In this review, we have used the
internet as a method to review articles discussing the current subject. The
PubMed, Google Scholar and Research Gates are visited to have access to the
selected articles. There are many keywords used such as keratoconus, aetiology
of keratoconus, eye rubbing, keratoconus prevalence, keratoconus and eye
rubbing correlation; we obtained 24 articles, we excluded 13 articles as they
did not meet the study criteria. Eleven articles only are included as they meet
the study criteria; 3 of them were review articles, and 8 were originals
articles. The articles included in this review were published in the English
language between 2003 and 2017. The information extracted from the selected
articles included a definition of keratoconus, its pathology, prevalence,
classification, symptoms, diagnosis, risk factors, and management.
KERATOCONUS
Keratoconus Definition Keratoconus is a term derived from
the Greek word keras (horn) and konos (cone)[6]
which means cone-like protrusion of the cornea[11].
Keratoconus is an eye disease causes curvature of cornea gradually,
transforming it from a symmetrical dome shape into an asymmetric cone shape.
This results in reduced visual acuity and a change in eyeglasses[1]. This disorder has been known in the middle of the 19th
century[6]. Keratoconus is a non-inflammatory
disorder that leads to thinning of the cornea, it usually occurs bilaterally[12], in 96% of cases[13],
but it can develop asymmetrically[14]. The vast
majority of cases have bilateral keratoconus, but they are asymmetric in
severity and progression[6].
Keratoconus Pathology The disease may begin as unilateral,
but finally, the other eye becomes involved[15].
All cornea layers are affected by keratoconus, but corneal stroma is the most
notable[16]. Thinning of corneal stroma occurs at
the inferior or central portion of the cornea, and it becomes thinner and
causes distortion of the cornea resulting in a cone shape of the cornea[17-18], this in turn results in
changes in refractive powers[11].
The thinning of the superior part of
the cornea is very rare[19]. Keratoconus is an
acquired ectasia which causes irregular, progressive, myopic astigmatism[15]. Myopia and irregular astigmatism are induced by the
thinning of the cornea which leads to mild or even marked visual impairment[19]. Corneal oedema and decompensation result in corneal
scarring which further decreases the visual acuity in the advanced cases[20].
Keratoconus appears between 10 and
20 years of age[13]. At puberty, keratoconus has
its usual onset, and it develops in many cases until the third or fourth decade
of life then it usually stops[13].
Keratoconus Prevalence Keratoconus prevalence differs
between different studies, the prevalence ranges from 1/500 to 1/2000 cases
globally[21]. Corneal topography devices were
used in recent studies and prevalence was found to be higher[22-23].
It was reported that in the general
population the prevalence rates ranged from 8.8 to 229 cases/105 per
year[24-25]. The prevalence in
Russia was estimated to be 0.3/105 while prevalence in the US and
central India was reported to be 1 per 2000 and 2300/105
respectively[25-26].
In Tehran study from Iran, the
keratoconus prevalence was 3.3%[27]. A review
from Saudi Arabia mentioned the prevalence in several countries; it was stated
that the prevalence in Columbia was 3900/105, in Yemen was 15 500/105
and 9400/105[11]. Keratoconus prevalence in
Macedonia was estimated to be 6.8 cases/105[13]
and in Israel was 2340/105[28]. A study from King
Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia, showed that the
prevalence of keratoconus represented 0.81/105 citizens. However,
the authors suggested that these results may not represent the prevalence in
Saudi Arabia assuming that patients may be referred to other ophthalmic
facilities or hospitals[1].
The prevalence of keratoconus in
Asir Province, Saudi Arabia by using a clinic-based protocol was found as 20
cases/105[29]. Another study from King Khalid
Hospital in Hail city, Saudi Arabia, showed that the prevalence between general
population was 4/105[30] which was lower than the
prevalence reported from Asir[29]. The variation
in prevalence rates between different regions in the world returns to change in
different factors between various studies such as methods of assessment and
diagnostic criteria[11].
Classification of Keratoconus Keratoconus is categorized into
three broad categories. The first involves keratoconus associated with rare
genetic disorders (such as neurofibromatosis, Down syndrome and nail-patella
syndrome). The second involves keratoconus associated with some factors such as
eye rubbing, atopy, contact lens wear, Leber congenital amaurosis, mitral valve
prolapse and positive family history, the third and last category involves
keratoconus with no association and of unknown aetiology[21].
Signs and Symptoms of
Keratoconus Signs and symptoms of keratoconus
differ according to the severity of the disease[1].
In the early stages of the disease, the patients may experience no symptoms[6], however they may experience some symptoms which
involve increased sensitivity to light, seeing lights or haloes around objects,
eye strain, irritation, allergy, pain, desire for rubbing, decreased resolution
at all distances and blurred vision[11,31].
The symptoms range from mild to severe visual impairment as a result of myopia,
irregular astigmatism, and frequently, corneal scarring[6].
There are three signs of keratoconus
including thinning of the stromal cornea with subsequent ectasia, Fleischer’s
ring which reflects the deposition of iron (hemosiderin pigment) in the basal
layer of the corneal epithelium and the breaks in Descemet’s and Bowman’s
layers[4,18].
Vogt’s striae and Fleischer’s ring
are vertical lines produced by compression of Descemet’s membrane which may be
observed near the apex of the cone. The ectatic cornea becomes visible at the
advanced stage of keratoconus; the protrusion pushes the lower lid out in a
V-shaped dent by looking downward, this called Munson’s sign. In the most
severe and advanced cases, breaks in Descemet’s membrane takes place, and it referred
to as hydrops have been observed. Stromal oedema and vision loss with
associated pain results from these breaks[32-33].
Diagnosis of Keratoconus Diagnosis of keratoconus regarding
symptoms in early and mild stages is difficult as the first symptoms of
keratoconus similar to that of other ocular conditions[11].
The classic way to assess keratoconus involves external examination of the eye
using both anterior segment expert opinion and utilization of same widely used
scales[11]. Keratoconus diagnosis became easier
as a result of advances in corneal imaging[12].
Electronic and molecular methods including elevation-based slit scanning and
topographic are available now and increased dramatically as an essential tool
for differential diagnosis and categorization of keratoconus[11].
Retinoscopy can show irregular
astigmatism as the disease progress. However corneal topography is the
most sensitive strategy to detect early keratoconus[6].
Corneal topography and tomography assessment instruments can efficiently use to
diagnose keratoconus and to determine its level of severity; these strategies
enabled performing of fine screening of the central corneal steeping, asymmetry
of the interior corneal steeping and asymmetry of optical power[11]. Ultrasonic pachymetry can show the difference
between the superior and inferior thickness of the cornea, hence keratoconus
grading can be done[34].
The corneal topography has become a
routine ophthalmic practice, it is considered now as the standard gold test in
both monitoring and diagnosing of keratoconus[4,18]. The pattern of the cornea on the topographic differs
between keratoconus and normal cornea qualitatively and quantitatively[6], the cornea appears as an asymmetric bow-tie with a
skewed radial axis in case of keratoconus when diagnosing it qualitatively[4]. In the quantitative evaluation of keratoconus, the
area of corneal power increased, and inferior-superior (IS) power appears
asymmetry[35-36]. There were
several video-keratography derived indices have been developed to assess the
topographic pattern of keratoconus quantitatively[6].
Posterior corneal surface elevation has an important role as a non-invasive
method of diagnosis. It helps in measuring the extent of the injury, as well as
it represents a very sensitive method of diagnosis[37].
Causes and Factors of Keratoconus
Risk The risk factors of keratoconus
include demographic factors, ethnic differences, genetic factors and
environmental factors. The ecological factors involve eye rubbing, atopy and UV
exposure[6].
Environmental and genetic factors
are considered one of the possible causes, some genetic defects that cause
keratoconus[6], but there may still be many flaws
to be discovered. In some cases, conical cornea appears in a number of family
members, especially in families where kinship occurs[21].
Where scientists were able to identify a chromosome link has a role in this
case. Keratoconus may be associated with other allergic diseases such as hay,
eczema, asthma, this condition may be clearly related to the problem of eye
rubbing, which may cause a rapid exacerbation. It may also affect people who
use contact lenses[11].
In the current review, we will
highlight on eye rubbing as a risk factor for keratoconus.
EYE RUBBING
Definition and Causes of Eye
Rubbing Eye rubbing is a common habit that
occurs spontaneously before sleep when awakening and throughout the day as a
response to ocular irritation fatigue and emotional stress[8].
It was stated that abnormal eye rubbing could be secondary to bothersome
symptoms such as dryness and itching, and it can be psychogenic with compulsive
or unprovoked rubbing[12]. Atopy and allergy were
the most dominant risk factors for the chronic habit of abnormal eye rubbing[38]. Also, compulsive behaviour, mental stress or
emotional tension and psychogenesis are associated with abnormal eye rubbing[39].
Eye Rubbing as a Risk Factor for
Keratoconus Chronic abnormal eye rubbing is
associated with keratoconus development[6].
Repetitive gentle and vigorous knuckle-grinding rubbing are associated with progression
of keratoconus[40]. There are many reasons for
eye rubbing habit. However, the reason will not affect the role of persistent
eye rubbing in the development of keratoconous[12].
Bilateral keratoconuswas reported in a girl with four years old who practised
persistent eye rubbing for long-term[41].
In a survey that included 240
keratoconus patients, it was found that 65.6% of them had a history of eye
rubbing[42]. McGhee et al[43] found that 48% of keratoconus patients rubbed their
eyes. In the Saudi study, it was found that 44.8% of patients had eye rubbing[30]. Rabinowitz[44] in his
case-control study reported that in 218 keratoconus patients and 183 healthy
age-matched controls, eye rubbing was present in 83% of keratoconus subjects
compared to 58% in healthy controls. A study from Iran showed that there was a
healthy relationship between the positive history of eye rubbing and prevalence
of keratoconus[31].
In Saudi study[30]
it was reported that the most common risk factors between keratoconus patients
were eye-rubbing representing 100%. Positive history of eye rubbing represented
a higher frequency of keratoconus patients[45].
Corneal curvature becomes worse by the asymmetric eye rubbing[46]. Asymmetric keratoconus was found to be related to
the eye that severely affected by abnormal eye rubbing[47].
Monocular keratoconus in a patient with bilateral eye-rubbing was found to be
related to hand dominance[48]. Keratoconus
develops after 14mo in case of chronic compulsive eye rubbing and psychogenic
eye rubbing[12]. Also, it was found that eye
rubbing was a significant risk factor in the development of keratoconus in
patients with a history of parental consanguinity[10].
Eye rubbing represented 91.8% of 49
children patients, where eye rubbing was secondary to induced ametropia or
atopy[49]. Other several studies failed to find
an association between eye rubbing and keratoconus, as tudy from Lebanon
reported no association between eye rubbing and keratoconus, where it showed
that 12% of keratoconus patients had a family history of keratoconus, while eye
rubbing was not a significant factor[50]. In the
other two studies by Owens and Gamble[51] and
Millodot et al[52], it was found no
significant association between keratoconus and eye rubbing (Table 1).
Table 1 Some articles outcomes in details
|
Authors |
Type of
study |
Year of
publication |
No. of
patients |
Conclusion |
|
Hashemi H, et al[27] |
Cross-sectional |
2013 |
263 |
This study provides the first population-based estimate
of the prevalence of keratoconus in Iran. The prevalence of topographic
keratoconus was high among citizens of Tehran districts 1 to 4. To confirm
the hypothesis of a high rate of keratoconus in Iran, more extensive studies
are needed which would examine the role of genetics and the environment. |
|
Assiri AA, et al[29] |
Clinical
study |
2005 |
125 |
44.8% of patients had eye rubbing. |
|
Rabinowitz Y[44] |
Case-control |
2003 |
401 |
Eye rubbing was present in 83% of keratoconus subjects
compared to 58% in standard controls. A study from Iran showed that there was
a strong relationship between the positive history of eye rubbing and
prevalence of keratoconus. |
|
Gordon-Shaag A, et al[10] |
Cross-sectional |
2013 |
210 |
This study supports the hypothesis that consanguinity
is a significant risk factor for keratoconus and provides strong support for
a genetic contribution to the disease. Wearing sunglasses in this environment
is beneficial, and the study confirmed that eye rubbing, allergy, and
education are also significantly associated with keratoconus after adjusting
for other predictors. |
|
Alabdelmoneam M[1] |
Retrospective |
2012 |
1638 |
In total, 1638 patients were referred to King Khaled
Eye Specialist Hospital for treatment of keratoconus from one of the five
regions of Saudi Arabia at an average annual rate of referral of 136.5
patients per year. The overall distribution of keratoconus patients was
almost equal between men and women, with a higher incidence in younger
patients aged 16-26y. |
|
Hassan H, et al[31] |
Cross-sectional |
2014 |
1280 |
Keratoconus may have a higher prevalence in the Middle
East and Asia than in Western countries. |
|
AlShammari Z, et al[30] |
Retrospective |
2016 |
About
12000 patients for each year |
In this study, a significant relationship was found
between increases in the age and the severity of the presenting features of
keratoconus. |
Mechanism of Keratoconus due to Eye
Rubbing Several mechanisms have been suggested
for the keratoconus development secondary to eye rubbing[53].
The cornea is elastic and, therefore, susceptible to changes in shape. The
frequency and force of rubbing are the factors that influence corneal eye rubbing
related changes; these changes occur as the cornea is elastic, which made it
susceptible to changes in shape[12]. It was found
that the keratocyte density in human corneas was reduced significantly by
slight eye rubbing for 10s repeated 30 times over 30min[54].
Also, changes in intraocular pressure (IOP) due to eye rubbing can lead to the
development of keratoconus, where indirect traumatization to keratocytes
results from the significant fluctuations in IOP, this traumatization to
keratocytes in turn results in keratoconus[55].
Several studies[56-58]
reported that the level of IOP was found to increase by increasing the compressive
rubbing forces that exerted in eye rubbing at the corneal surface.
Ocular Complication Result from Eye
Rubbing Acute hydrops can be developed in
patients with keratoconus of 9 years old of age as a result of continues eye
rubbing[59-61]. Hydrops in
keratoconus patients may result from the mechanical stress of rubbing[12]. Several studies showed an association between the
development of acute hydrops and vigorous eye rubbing[61-63]. Effects of eye rubbing on corneal topography were
observed, where eye rubbing increase the irregularity index of the corneal
surface, after 60s of eye rubbing, a 0.5 diopter of astigmatism was found to be
induced[53].
Management of Keratoconus The management of keratoconus
differs according to the severity of the case, so there was no single method is
the best for all patients[64]. Spectacles can be
used to correct mild keratoconus[63]. Rigid
contact lenses can be required then patient becomes unable to obtain good
visual acuity as a result of higher order aberrations and increasing levels of
irregular astigmatism, the rigid contact lens in this case effectively provide
a new anterior surface to the eye[63]. There are
several types of lens designs for keratoconus and it hard to predict which one
is suitable for the patient, in addition, the corneal collagen cross-linking
affects the frequency of keratoplasties in patients with keratoconus[63].
Keratoplasty can be used as a
separate management procedure for keratoconus, as it has different advantages
upon long and short-term such as preserving the health of the host endothelium
and preventing the rejection of the endothelial graft. In addition, as the
graft survival is an important issue, it helps in the promotion of graft survival[65].
CONCLUSION
Keratoconus is an eye disorder; its
prevalence evaluation varies according to several factors. Several factors are
affecting the development of keratoconus; eye-rubbing is the main factor which
is causing a major number of eye injuries especially keratoconus. Eye rubbing
causes the thinning of keratocyte, and the degree of effect of eye rubbing
depends on the period and force of performing eye rubbing. Although few studies
did not find a significant association between keratoconus and eye rubbing, the
vast majority of the studies confirmed the correlation. It is recommended to
avoid eye rubbing to prevent keratoconus; this can be achieved by the treatment
or prevention of itching causes and treatment of dryness of the eye. In
addition, it is recommended to avoid wearing eye lenses if they were
unnecessary, also it is essential to increase awareness of individuals about
the risk of eye rubbing as most of the persons are performing it as a habit.
ACKNOWLEDGEMENTS
The authors would like to thank all
colleges and groups that helped in the production of this work in the
University of Jazan, and specifically in the Faculty of Medicines and its
different specialities.
Conflicts of Interest: Najmi H, None; Mobarki Y, None;
Mania K, None; Altowairqi B, None; Basehi M, None; Mahfouz
MS, None; Elmahdy M, None.
References