Effects of eye rubbing on the levels of protease, protease activity and cytokines in tears: relevance in keratoconus

Pediatric keratoconus: a review of the literature

PURPOSE

To describe the epidemiology and prevalence, rates of progression, difference between adult and pediatric populations, and therapeutic approaches to pediatric keratoconus from documented literature.

METHODS

A literature search was done on PubMed using key words including pediatric keratoconus, children with keratoconus, adult keratoconus, penetrating keratoplasty, corneal cross-linking and intracorneal ring segments. The literature was reviewed and reported to explore the key epidemiological differences between the pediatric and adult population with regards to presentation and treatment options.

RESULTS

Pediatric keratoconus is more aggressive than adult keratoconus, which has been explained by structural differences in the cornea between both populations. High rates of progression were documented in pediatric populations. While corneal collagen cross-linking, intracorneal ring segments and penetrating keratoplasties have been used as therapies in the pediatric population, the literature overwhelmingly shows higher rates of failure and progression despite these measures as compared to adults.

CONCLUSION

Pediatric keratoconus is more aggressive than adult keratoconus, and current therapies used in adults may not be sufficient for the pediatric population.

Collagen cross-linking impact on keratoconus extracellular matrix

Background

Keratoconus (KC) is a common multifactorial ectatic corneal disease with unknown onset. KC most commonly appears in adolescence and affects approximately 1:400 people worldwide. Treatment options, for advanced KC cases, are collagen cross-linking (CXL) and corneal transplants. CXL is a new KC treatment that helps arrest the disease. Unfortunately, only a fraction of KC patients will qualify for CXL treatment. Our goal, in this study, was to begin to understand how CXL affects the corneal microenvironment and pave the way towards a more patient-driven CXL treatment.

Methods

Primary human corneal fibroblasts from healthy and KC donors were plated on transwell polycarbonate membranes and stimulated by a stable vitamin C. At 4 weeks, riboflavin was added followed by UVA irradiation. Transmission Electron Microscopy (TEM) and western blots were used to assess the effect of CXL on the extracellular matrix (ECM) and the resident cells, pre- and post CXL.

Results

Data shows CXL improved lamellar organization showing more organized collagen fibrils decorated with proteoglycans (PGs). The distribution of the collagen fibrils and interfibrillar spacing was also visibly improved, post-CXL. Lumican, mimecan, and decorin were the dominant PGs and were significantly upregulated in post-CXL cultures. ECM degradation proteins, matrix metalloproteinases (MMPs), MMP-1, -3, and -9, but not MMP-2, were significantly downregulated post-CXL. TIMP-1 and -2 were not modulated by CXL.

Conclusion

The unknown effects of CXL on the human corneal microenvironment have hampered our ability to make CXL available to all KC patients. Our current study provides a deeper understanding on CXL activity, using our unique 3D in vitro model.

Corneal crosslinking for keratoconus in Japanese populations: one year outcomes and a comparison between conventional and accelerated procedures

PURPOSE

We retrospectively investigated the efficacy of corneal crosslinking (CXL) on progressive keratoconus in a Japanese population and compared the outcomes of conventional and accelerated CXL.

STUDY DESIGN

A retrospective cohort study METHODS: A total of 108 consecutive eyes in 95 patients (75 men; 21.9 ± 6.2 years) with progressive keratoconus were enrolled. The epithelium was ablated in all eyes. After presoaking the corneal stroma in riboflavin, UV-A was irradiated at 3.0 mW/cm² (conventional CXL) for 30 min on 23 eyes and 18.0 mW/cm² for 5 min (accelerated CXL) on 85 eyes. Best spectacle-corrected visual acuity (BSCVA), manifest refraction, keratometric value, corneal thickness, corneal endothelial cell density (ECD), intraocular pressure, and complications were evaluated at 1, 3, 6, and 12 months after the procedure.

RESULTS

BSCVA, manifest refraction, ECD, and corneal thickness did not change significantly after both procedures. The keratometric value was significantly decreased from the preoperative value at 12 months (p < 0.001). Progression to more than 1.0 D after CXL was observed in 10 eyes (9.3%). The ΔKmax was negatively associated with preoperative Kmax (p < 0.001) and positively associated with preoperative thinnest corneal thickness (p < 0.001). Both treatment modules showed no significant difference in all parameters.

CONCLUSION

CXL was as effective in treating keratoconus in Japanese patients as in individuals of other ethnicities. Overall, CXL could be performed using either the conventional or accelerated approach to halt the progression of keratoconus in Japanese populations.

Characteristics of keratoconic patients at two main eye centres in Palestine: a cross-sectional study

BACKGROUND

Keratoconus (KC) is a multifactorial, degenerative ectatic condition of the cornea. It usually manifests during late adolescence or the early twenties. A painless disease, KC may end with severe visual loss. The prevalence of KC in middle-eastern countries is much higher than in other regions of the world. This may be due to genetic and environmental risk factors and consanguinity. The goal of this study is to explore the demographic profile of Palestinian keratoconic patients.

METHODS

A retrospective study was conducted in two ophthalmology centres (Tertiary Ophthalmic Centre of An-Najah National University Hospital and An-Noor Centre at the Specialized Arab Hospital). All medical charts of keratoconic patients attending both centres over the period from 2009 to 2016 were reviewed. These patients were diagnosed by ophthalmologists depending on history, examination and Pentacam. Severity was determined using the k median index from the Pentacam map. Data analysis was carried out using SPSS Version 22.

RESULTS

The medical files of 936 keratoconic eyes of 505 keratoconic patients were reviewed. Their mean age at the time of diagnosis was 23.3 ranging from 8 to 62 years. Approximately 70.1% of them presented after the age of 20 years, and younger age groups were more likely to develop a severe disease stage than older ones (P = 0.001, r = - 0.108). There was a nearly equal distribution of patients between the two sexes (49.5% male, 50.5% female). On initial evaluation, the best-corrected visual acuity (BCVA) was recorded as ≥6/12 in most affected eyes (71.5%). Regarding severity, 62% presented in a mild form, while 9.9% were at a severe stage. About 88.2% presented with bilateralism.

CONCLUSIONS

Most of the patients in their twenties presented with a mild bilateral form of the disease. This result is compatible with published international reports. It is recommended that the results of this study be considered when establishing a screening program in Palestine. Subsequently, patients will be identified at an appropriate time where action can be taken before disease progression take place.

Anti-inflammatory cytokine and angiogenic factors levels in vitreous samples of diabetic retinopathy patients

Evaluation of cytokines in patients with diabetic retinopathy (DR) is important for the identification of future additive or alternative treatment options. Therefore, vitreous samples were obtained from patients with DR and patients with macular hole or macular pucker (control group) during 23-gauge-vitrectomy (n = 17/group). The levels of three pro-inflammatory (IL-1ß, IL-6, IFN-γ) and pleiotropic cytokines (IL-2, IL-4, IL-13) as well as VEGF, VEGF-A, and PGF were measured using an enzyme linked immunosorbent assay (ELISA). IL-1ß (p = 0.02) and IFN-γ (p = 0.04), two of the three tested pro-inflammatory cytokines, were elevated in the DR patients, while IL-6 (p = 0.51) level was comparable in both groups. Moreover, in DR samples, a trend towards an IL-13 down-regulation (p = 0.36) was observable. The IL-2 (p = 0.62) and IL-4 (p = 0.78) levels were comparable in both groups. All analyzed angiogenetic factors were up-regulated in DR patients (VEGF: p<0.001; VEGF-A: p = 0.002; PGF: p<0.001). The up-regulation of angiogenetic factors underline their importance in DR development. However, the interaction of the other cytokines showed an interesting pattern. Pro-inflammatory cytokines were also up-regulated, which could be evidence for inflammation processes in the diabetic retina. Furthermore, it seems that a counter response of immunomodulatory cytokines is in an initial process, but not strong enough to regulate the processes. Therefore, to support these anti-inflammatory mechanisms might be additive treatment option in the future.

Altered tear inflammatory profile in Indian keratoconus patients - The 2015 Col Rangachari Award paper

Purpose:

Conventionally, keratoconus (KC) has been considered a noninflammatory corneal ectatic disorder. Recent evidence suggests a possible role of inflammation in the pathogenesis of KC. Hence, we analyzed the levels of inflammatory factors in the tear fluid of Indian KC patients.

Methods:

Tear fluid samples were collected from age- and sex-matched healthy controls and KC patients (with different grades). The levels of the inflammatory factors in tears were analyzed using cytometric bead array (Human Soluble Protein Flex Set System, BD Biosciences) for levels of interleukin-1α (IL-1α), IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-9, IL-10, IL-12p70, IL-23p40, IL-13, IL-17A, IL-17F, IL-21, interferon-α (IFNα), IFNγ, tumor necrosis factor-α, CCL2/monocyte chemotactic protein-1, CCL4/macrophage inflammatory protein-1β (MIP-1β), MIP-1α, CCL5/RANTES, CXCL10/IP10, ICAM1, CD62E, vascular endothelial growth factor and transforming growth factor β.

Results:

An increase in Kmax and Kmean, and a decrease in central corneal thickness was observed with increasing grades of KC. Tear analysis showed that most of the tear soluble factors, including cytokines, chemokines, growth factors and cell adhesion molecules were significantly elevated in the KC patients compared to the controls.

Conclusion:

Our findings suggest that inflammatory factors associated with KC may play a role in its pathogenesis. This opens the potential to explore anti-inflammatory strategies to either halt or delay the progression of KC.

Pathophysiology of Keratoconus: What Do We Know Today

Keratoconus is a common corneal ectasia that leads to progressive visual impairment. Numerous studies have shown abnormal protein expression patterns in keratoconic corneas. However, the specific mechanisms causing this disease remain ambiguous. This review aims to provide an update on morphological studies of the keratoconic cornea, relate these early studies with current findings from proteomic, biochemical and cell culture studies and to postulate possible pathogenic pathways.

Interleukin-6 participation in pathology of ocular diseases

Interleukin-6 (IL-6) is a multifunctional cytokine that affects a variety of cells in the body such as osteoclasts, hepatocytes, endothelial cells, epithelial cells, white and red blood cells and etc. Elevated levels of IL-6 have been detected in many ocular diseases. Studies show that IL-6 has a major role in the pathology of glaucoma, CRVO, macular edema, ocular neovascularization, posterior capsule opacity formation, keratitis, dry eye disease, allergic eye disease, ocular autoimmune disease, corneal chemical burn, ocular inflammation and so on. IL-6 does its effects through the classic or trans-signal pathways in cells. Blocking of IL-6 signal pathways via Tocilizumab or other chemicals and therapeutics will help to overcome complications related to ocular diseases.

Cross-linking in children with keratoconus: a systematic review and meta-analysis

Keratoconus can behave more aggressively in pediatric than in adult patients. We systematically reviewed the literature to determine the effectiveness of corneal collagen cross-linking (CXL) in children. For this study, MEDLINE^® and Cochrane databases were searched for all studies examining the effects of standard, trans-epithelial or accelerated CXL protocols in patients age 18 years or younger. Primary outcomes were; uncorrected visual acuity (UCVA) and maximum keratometry (Kmax) and secondary outcomes were; best-corrected visual acuity (BCVA), mean refractive spherical equivalent (MRSE), central corneal thickness (CCT) and endothelial cell density (ECD). Standardized mean differences (SMD) and 95% confidence intervals were calculated, comparing baseline values with those at 6, 12 and 24 months. A total of 13 papers, published between May 2011 and December 2014 examining 490 eyes of 401 patients with a mean age of 15.25 (±1.5) years, were included in the qualitative analysis in this review. Nine papers were included in the meta-analysis, showing significant improvement in UCVA and BCVA and stable Kmax at 12 months, and stable UCVA, improved BCVA and improved Kmax at 24 months in the standard protocol group UCVA, BCVA and KMax were stable at 12 months in the trans-epithelial group. Mean refractive spherical equivalent (MRSE), CCT and ECD remained stable in both groups. In conclusion it was found that standard CXL may be effective in halting progression of keratoconus in pediatric patients at 1 year. However, larger, more long-term studies are required to ascertain its effectiveness.

Induction of MMP‑1 and ‑3 by cyclical mechanical stretch is mediated by IL‑6 in cultured fibroblasts of keratoconus

In order to understand the effect of mechanical stretch on corneal extracellular matrix remodeling, human keratoconus fibroblasts (HKCFBs) were subjected to cyclic stretch in vitro and the expression of matrix metalloproteinases (MMPs), tissue inhibitor of metalloproteinases (TIMPs), and inflammatory cytokines were evaluated. HKCFBs were seeded into a flexible membrane base and subjected to a cyclic stretch regimen of 10% equibiaxial stretch at a stretching frequency of 1 Hz for 6 h using a Flexcell tension unit. An antibody directed against interleukin‑6 (IL‑6 Ab) was used to investigate the roles of IL‑6 on mechanical stretch mediated regulation of MMP in HKCFBs. Culture supernatants were assayed using an enzyme‑linked immunosorbent assay for MMP‑1 and ‑3, TIMP‑1 and ‑2, and IL‑6. Total RNA from the cells was extracted, and quantitative polymerase chain reaction was used to determine mRNA for MMP‑1 and ‑3, TIMP‑1 and ‑2, and IL‑6. In stretched cells, levels of MMP‑1 and ‑3 demonstrated an increase compared with unstretched cells, but levels of TIMP‑1, and ‑2 revealed a decrease. Mechanical stretch significantly increased the mRNA expression and protein synthesis of IL‑6 compared with unstretched cells. IL‑6 induced MMP‑1 and ‑3 expression, whereas no significant effects were observed in levels of TIMP‑1 and ‑2 compared with the untreated control groups. Additionally, the IL‑6 Ab markedly inhibited the stretch‑induced increase in MMP‑1 and ‑3 in culture supernatants in a dose‑dependent manner. No significant differences in TIMP‑1 and ‑2 protein levels were detected between stretched cells treated with IL‑6 Ab and stretched cells without IL‑6 Ab treatment. These results indicate that cyclical mechanical stretch augments IL‑6 production and MMP expression, and reduces levels of TIMP in HKCFBs. Thus, it is suggested that IL‑6 mediates the stretch‑induced MMP expression.

Very Low Prevalence of Keratoconus in a Large Series of Vernal Keratoconjunctivitis Patients

PURPOSE

To evaluate the prevalence of keratoconus (KC) and other corneal abnormalities by means of videokeratography and tomography in a large series of patients affected by vernal keratoconjunctivitis (VKC).

DESIGN

Cross-sectional study.

METHODS

Setting: Single-center children's hospital.

STUDY POPULATION

A total of 651 consecutive patients with VKC and a control group of 500 were prospectively recruited between May 1, 2012 and September 30, 2013, with a minimum follow-up of 12 months.

OBSERVATION PROCEDURE

All patients were evaluated by means of a Scheimpflug camera combined with a Placido corneal topographer. Keratoconus, suspected keratoconus, or its absence were determined in each patient. The corneal symmetry index of front (SI_f) and back curvature (SI_b), shape indices, and thicknesses were compared between the 2 groups.

MAIN OUTCOME MEASURES

Prevalence of keratoconus and corneal indices modifications.

RESULTS

Five out of 651 patients (0.77%) demonstrated topographic signs of KC. Two of them were bilateral. All patients were older than 7 years of age, and the mean age was 11.54 years. Four other patients (0.61%) were classified as KC suspects by the screening program. Of 304 patients older than 11 years (mean age 14.4 years), 4 (1.32%) were found to have KCN, and 4 (1.32%) were KC suspects. The corneal indices of patients in the VKC group were extremely similar to those in the control group. (P > .05).

CONCLUSIONS

The prevalence of KC in our patient population, compared with previous reports in the literature, is much lower. The similar corneal indices in both groups suggest the absence of permanent corneal deformation due to VKC.

Post Filtering Surgery Globe Massage-induced Keratoconus in an Eye with Iridocorneal Endothelial Syndrome: A Case Report and Literature Brief Review

PURPOSE

To report a case of unilateral post trabeculectomy globe massage-induced keratoconus (KCN).

CASE REPORT

A 52-year-old lady with a history of trabeculectomy due to iridocorneal endothelial syndrome in her right eye was instructed to massage her globe to control gradual rise of intraocular pressure 1.5 years after surgery. The patient experienced high astigmatism and marked inferior corneal steepening after 3 years of globe massage. The left eye was normal in all aspects. Findings in different visual examinations were compatible with the diagnosis of unilateral KCN in the right eye of our patient.

CONCLUSION

Chronic forceful frequent eye rubbing particularly with fingertips can be assumed to be the most important causative factor for KCN formation in this patient.

Tear biomarkers for keratoconus

Keratoconus is a progressive corneal thinning, ectatic condition, which affects vision. Recent advances in corneal topography measurements has helped advance proper diagnosis of this condition and increased research and clinical interests in the disease etiopathogenesis. Considerable progress has been achieved in understanding the progression of the disease and tear fluid has played a major role in the progress. This review discusses the importance of tear fluid as a source of biomarker for keratoconus and how advances in technology have helped map the complexity of tears and thereby molecular readouts of the disease. Expanding knowledge of the tear proteome, lipidome and metabolome opened up new avenues to study keratoconus and to identify probable prognostic or diagnostic biomarkers for the disease. A multidimensional approach of analyzing tear fluid of patients layering on proteomics, lipidomics and metabolomics is necessary in effectively decoding keratoconus and thereby identifying targets for its treatment.

Inflammatory Biomarkers Profile as Microenvironmental Expression in Keratoconus

Keratoconus is a degenerative disorder with progressive stromal thinning and transformation of the normal corneal architecture towards ectasia that results in decreased vision due to irregular astigmatism and irreversible tissue scarring. The pathogenesis of keratoconus still remains unclear. Hypotheses that this condition has an inflammatory etiopathogenetic component apart from the genetic and environmental factors are beginning to escalate in the research domain. This paper covers the most relevant and recent published papers regarding the biomarkers of inflammation, their signaling pathway, and the potentially new therapeutic options in keratoconus.

Eye rubbing type and prevalence including contact lens 'removal-relief' rubbing

BACKGROUND

Eye rubbing is commonly associated with keratoconus and may contribute to disease onset and progression. Verbal counselling to avoid rubbing may not be successful and adverse consequences of rubbing, which occurs on contact lens removal may be more serious. This study examines the prevalence of 'removal-relief' rubbing and its potential consequences.

METHODS

Rubbing histories were recorded for contact lens wearing normal and keratoconic patients as well as for normal non-contact lens wearers. Analogue scaled responses were used to identify and compare abnormal rubbing habits.

RESULTS

Contact lens wearing patients (both with and without keratoconus) reported significantly more rubbing before contact lens insertion (p < 0.05) compared to non-contact lens wearers. Eye rubbing after contact lens removal ('removal-relief' rubbing) was found to be significantly more prevalent among contact lens-wearing keratoconic patients compared to contact lens-wearing non-keratoconic patients (p < 0.001 in both cases).

CONCLUSIONS

Rubbing-related trauma occurring before contact lens insertion may predispose the cornea to wound healing activities and greater levels of adverse response to contact lens wear. Such adverse responses could predispose the cornea to greater trauma, which occurs in response to rubbing on removal of contact lenses. Strong counselling to avoid eye rubbing is often not an adequate form of management for a significant number of patients with keratoconus. Evidence of relapses indicates the need for better methods of counselling and for them to be repeated regularly. Apart from keratoconus, any other keratectasia, corneal disease or wound healing (including post-surgical) may increase susceptibility to corneal rubbing trauma. Such cases also appear to warrant counselling on avoidance of rubbing.

The influence of rigid gas permeable lens wear on the concentrations of dinucleotides in tears and the effect on dry eye signs and symptoms in keratoconus

PURPOSE

To evaluate the signs and symptoms of dry eye and dinucleotide secretion in tears of keratoconus patients (KC) and the potential effect of rigid gas permeable (RGP) contact lens wear.

METHODS

Twenty-three KC patients and forty control subjects were enrolled in this study. Signs of dry eye including tear volume, tear stability and corneal staining along with symptoms were assessed using the McMonnies questionnaire. Tears were collected using Schirmer strips, and dinucleotide concentrations in collected tears measured using high pressure liquid chromatography. Values obtained in KC and controls were compared. The effect of contact lens wear in KC was also assessed.

RESULTS

KC eyes showed a significantly lower tear volume compared to controls, shorter tear break up time (TBUT), higher corneal staining and higher McMonnies dry eye questionnaire scores (p<0.05). When compared with non-wearers, KC contact lens wearers showed significantly higher symptoms, lower Schirmer and TBUT values (p<0.05). Concentration of Ap4A (0.695±0.304μM vs. 0.185±0.178μM) and Ap5A (0.132±0.128μM vs. 0.045±0.036μM) were higher in KC compared to controls (p<0.001) and only Ap4A was statistically higher in RGP wearers compared to non-wearers (0.794±0.478μM vs. 0.417±0.313μM) (p<0.05).

CONCLUSION

Signs and symptoms of dry eye as well as concentrations of Ap4A and Ap5A were markedly increased in KC patients compared to controls. Moreover, Ap4A and symptoms of dry eye were statistically higher in RGP wearers compared to non-wearers. This seems to indicate that factors such as RGP contact lens wear might exacerbate the clinical condition of dry eye.

Effect of Allergic Diseases on Keratoconus Severity

PURPOSE

To investigate the association between keratoconus (KC) and allergic diseases.

METHODS

In a prospective age- and sex-matched case--control study clinical data of 885 KC patients and 1526 controls were evaluated regarding the presence of various allergic diseases. Severity of KC and ophthalmic parameters of KC patients were compared between KC patients with and without allergic diseases.

RESULTS

The prevalence of allergic diseases was significantly higher in KC patients. KC patients with vernal keratoconjunctivitis (VKC) or allergic conjunctivitis (AC) had significantly thinner and steeper corneas in comparison with non-allergic KC patients. Only VKC and AC were significantly associated with KC severity.

CONCLUSIONS

Patients with VKC or AC were at increased risk of KC. They had more severe KC and should be closely followed up and intensively treated.

Eye Rubbing, a Sine Qua Non for Keratoconus?

Keratoconus, a dystrophy of unknown origin, remains an ophthalmic enigma. The contrast between the presence of marked structural changes and deformation of the corneal wall and the relative absence of specific genetic and biomolecular findings continues to intrigue ophthalmologists. In Marfan syndrome, where genetic and molecular abnormalities are well identified, and similar changes in collagen observed, the cornea tends not to be steeper, irregular or ectatic, but are globally flatter. This suggests that an external mechanical force may be necessary to induce the apparition and progression of the ectatic process in keratoconus. Eye rubbing has long been acknowledged as a risk factor for keratoconus and its progression, but could it in fact be the root cause? Many clinical observations and reports support the hypothesis of eye rubbing as a first and necessary hit for inducing progressive ectatic deformation of the corneal wall. Validating or refuting this hypothesis on the basis of patient admission may be impossible. It is difficult to document the frequency, duration and intensity of eye rubbing in patients with keratoconus, and virtually impossible to prove that every patient who denies the habit truly does not rub his eyes. Both the increase in incidence of atopy and the time spent in front of the computer screen in the general population may account for an increased tendency for eye rubbing, and lead to the perceived increased prevalence of keratoconus in both urban and non-urban areas. This paper explores the possibility that the mechanical stress imposed on the cornea by rubbing may not be as much a second hit evoking the structural changes of a predisposed cornea exhibiting unknown collagen progressive alteration, but rather the necessary trigger and sine qua non of the keratoconic process. Even if this provocative hypothesis is impossible to prove, it is equally difficult to refute, and acknowledging eye rubbing as a possible root cause increases awareness within the general population and if true, could dramatically reduce the incidence of keratoconus, and halt its progression in eyes already affected.

How to cite this article

Gatinel D. Eye Rubbing, a Sine Qua Non for Keratoconus? Int J Kerat Ect Cor Dis 2016;5(1):6-12.

Keratoconus: an inflammatory disorder?

Keratoconus has been classically defined as a progressive, non-inflammatory condition, which produces a thinning and steepening of the cornea. Its pathophysiological mechanisms have been investigated for a long time. Both genetic and environmental factors have been associated with the disease. Recent studies have shown a significant role of proteolytic enzymes, cytokines, and free radicals; therefore, although keratoconus does not meet all the classic criteria for an inflammatory disease, the lack of inflammation has been questioned. The majority of studies in the tears of patients with keratoconus have found increased levels of interleukin-6 (IL-6), tumor necrosis factor-α(TNF-α), and matrix metalloproteinase (MMP)-9. Eye rubbing, a proven risk factor for keratoconus, has been also shown recently to increase the tear levels of MMP-13, IL-6, and TNF-α. In the tear fluid of patients with ocular rosacea, IL-1α and MMP-9 have been reported to be significantly elevated, and cases of inferior corneal thinning, resembling keratoconus, have been reported. We performed a literature review of published biochemical changes in keratoconus that would support that this could be, at least in part, an inflammatory condition.

The genetic and environmental factors for keratoconus

Keratoconus (KC) is the most common cornea ectatic disorder. It is characterized by a cone-shaped thin cornea leading to myopia, irregular astigmatism, and vision impairment. It affects all ethnic groups and both genders. Both environmental and genetic factors may contribute to its pathogenesis. This review is to summarize the current research development in KC epidemiology and genetic etiology. Environmental factors include but are not limited to eye rubbing, atopy, sun exposure, and geography. Genetic discoveries have been reviewed with evidence from family-based linkage analysis and fine mapping in linkage region, genome-wide association studies, and candidate genes analyses. A number of genes have been discovered at a relatively rapid pace. The detailed molecular mechanism underlying KC pathogenesis will significantly advance our understanding of KC and promote the development of potential therapies.

Distribution of ABO and Rh Blood Groups in Patients With Keratoconus: A Case-Control Study

Association of keratoconus (KC) with genetic predisposition and environmental factors has been well documented. However, no single study has investigated the possible relationship between ABO and Rh blood groups and KC.

METHODS

A case-control study was designed in a university hospital enrolling 214 patients with KC in the case group and equal number of age- and sex-matched healthy subjects in the control group. Primary characteristics, ABO blood group, and Rh factors were compared between the two groups. Topographic findings of KC eyes and the severity of the diseases were investigated according to the distribution of the blood groups.

RESULTS

Blood group O and Rh(+) phenotype were most frequent in both groups. There was no significant difference between the two groups in terms of ABO blood groups or Rh factors. Mean keratometery (K), central corneal thickness, thinnest corneal thickness, flat K, steep K, sphere and cylinder, spherical equivalent, and uncorrected visual acuity were all similar between ABO blood groups and Rh(+) and Rh(-) groups. However, the best spectacle-corrected visual acuity (BCVA) had the highest value in AB blood group (0.35 ± 0.22 logMAR, P=0.005). Moreover, the blood group AB revealed the highest frequency for grade 3 KC, followed by grades 1, 2, and 4 (P=0.003).

CONCLUSION

We observed no significant excess of any particular blood group among KC cases compared with healthy subjects. Except BCVA, none of the keratometric or topographic findings was significantly different between blood groups.

Signs and Symptoms of Dry Eye in Keratoconus Patients: A Pilot Study

PURPOSE

To compare signs and symptoms of dry eye in keratoconus (KC) patients versus healthy subjects.

METHODS

A total of 15 KC patients (KC group, n = 15 eyes) and 16 healthy subjects (control group, 16 eyes) were enrolled in this study. The Schirmer I test with no anesthetic, tear break-up time (TBUT), corneal staining characteristics, and ocular surface disease index (OSDI) scores were evaluated for both groups. Impression cytology, combined with/scanning laser confocal microscopy (LCM), was performed to evaluate goblet cell density, mucin cloud height (MCH), and goblet cell layer thickness (CLT). Finally, tear concentrations of di-adenosine tetraphosphate (Ap4A) were assessed. Results were statistically analyzed using Shapiro-Wilk and non-parametric Wilcoxon rank sum tests. Statistical significance was set at p < 0.05.

RESULTS

KC patients had lower tear volumes and greater corneal staining than did healthy subjects (p < 0.05). OSDI scores were 44.96 ± 8.65 and 17.78 ± 6.50 for the KC and control groups, respectively (p < 0.05). We found no statistically significant differences in TBUT between groups. Impression cytology revealed lower goblet cell densities in KC group patients versus control group subjects (84.88 ± 32.98 and 128.88 ± 50.60 cells/mm,(2) respectively, p < 0.05). There was a statistically significant reduction in MCH and CLT in KC group patients compared with control group subjects. Ap4A tear concentrations were higher in KC group patients than in control group subjects (2.56 ± 1.10 and 0.15 ± 0.12 µM, respectively, p < 0.05).

CONCLUSIONS

The parameters evaluated in this study indicate that KC patients suffer greater symptoms of dry eye and greater tear instability, primarily due to the decreased mucin production in their tears, than do healthy patients with no KC.

Tear film inflammatory mediators in patients with keratoconus

To determine the concentration of inflammatory mediators in the tear film of patients with keratoconus. Basal tears from patients with keratoconus and from normal controls were collected using a capillary tube. Patients with keratoconus were examined in a routine fashion, and keratometric readings were also taken from corneal topographic maps .The concentration of cytokines including Interleukin 6,10,1b and Interferon-γ was measured by enzyme-linked immunoadsorbent assay. Seventy-two subjects were enrolled in the study including 42 patients with keratoconus and 30 normals. Patients with keratoconus had significantly higher levels of Interlukin 6,1b and Interferon-γ (17.49 ± 1.92 pg/ml), (8.58 ± 1.15 pg/ml), and (33.33 ± 7.57 pg/ml) compared with control subjects (13.81 ± 1.71 pg/ml), (4.98 ± 0.52 pg/ml), and (22.99 ± 4.68 pg/ml), (P = 0.0001, P = 0.0001, and P = 0.0001). But the level of Interlukin-10 in keratoconus patients was significantly lower (6.07 ± 1.35 pg/ml) than controls (8.99 ± 0.70 pg/ml) (P = 0.0001). We realized that the proinflammatory markers (Interlukin-6,1-b and Interferon-γ) are over expressed, whereas the anti-inflammatory marker (Interlukin-10) is under expressed, indicating that the pathogenesis of keratoconus may involve complex chronic inflammatory events. Additional future studies will reveal the exact molecular and biochemical mechanisms that are required to better manage the disease and halt its progression.

Ocular allergy and keratoconus

Keratoconus is the most common corneal ectatic disorder, the cause of which is largely unknown. Many factors have been implicated, and the ocular allergy is being one of them. The commonly proposed pathogenesis includes the release of inflammatory mediators due to eye rubbing which may alter the corneal collagen and lead to corneal ectasias. The onset of keratoconus is often early in cases associated with allergy and routine corneal topography may detect subtle forms of keratoconus. These cases may require early keratoplasty and are at an increased risk of having acute corneal hydrops. Surgical outcomes are similar to primary keratoconus cases. However, post-operative epithelial breakdown may be a problem in these cases. Control of allergy and eye rubbing is the best measure to prevent corneal ectasias in cases of ocular allergy.

Eye Rubbing and Keratoconus: A Literature Review

Keratoconus is a progressive corneal ectactic condition that can lead to visual loss. Despite being the most common cause for keratoplasty in the developed world the aetiology is unknown. It is thought to be multifactorial, with genetic and environmental factors implicated. The association of eye rubbing and pathogenesis of keratoconus has been well documented. In this review, we collate the existing literature and summarize the current knowledge of the role of eye rubbing in the pathogenesis of keratoconus.

How to cite this article

Hawkes E, Nanavaty MA. Eye Rubbing and Keratoconus: A Literature Review. Int J Kerat Ect Cor Dis 2014;3(3):118-121.

Expression of SFRP Family Proteins in Human Keratoconus Corneas

We investigated the expression of the secreted frizzled-related proteins (SFRPs) in keratoconus (KC) and control corneas. KC buttons (∼8 mm diameter) (n = 15) and whole control corneas (n = 7) were fixed in 10% formalin or 2% paraformaldehyde and subsequently paraffin embedded and sectioned. Sections for histopathology were stained with hematoxylin and eosin, or Periodic Acid Schiff's reagent. A series of sections was also immunolabelled with SFRP 1 to 5 antibodies, visualised using immunofluorescence, and examined with a Zeiss LSM700 scanning laser confocal microscope. Semi-quantitative grading was used to compare SFRP immunostaining in KC and control corneas. Overall, KC corneas showed increased immunostaining for SFRP1 to 5, compared to controls. Corneal epithelium in all KC corneas displayed heterogeneous moderate to strong immunoreactivity for SFRP1 to 4, particularly in the basal epithelium adjacent to cone area. SFRP3 and 5 were localised to epithelial cell membranes in KC and control corneas, with increased SFRP3 cytoplasmic expression observed in KC. Strong stromal expression of SFRP5, including extracellular matrix, was seen in both KC and control corneas. In control corneas we observed differential expression of SFRP family proteins in the limbus compared to more central cornea. Taken together, our results support a role for SFRPs in maintaining a healthy cornea and in the pathogenesis of epithelial and anterior stromal disruption observed in KC.