,
N'avez-vous jamais senti,
l'envie,
de vous frotter avec violence,
vos pauvres cornées,
après avoir pleuré en grande abondance.
Un peu de sérieux...
Voici un article étudiant la composition des larmes des cornées kératoconiques. Les chercheurs trouvent une forte concentration de molécules inflammatoires (MMP9, TNF-alpha, Interleukine 6) dans nos chaudes larmes, participant ainsi à cette "envie de frottement".
Ne l'avez-vous jamais senti (par exemple, le matin au réveil)?
Une chose est sûre, le KC EST UNE MALADIE INFLAMMATOIRE!
Voici le texte pour les adeptes
:
Inflammatory Molecules in the Tears of Patients with Keratoconus
Presented in part at: Association for Research in Vision and Ophthalmology meeting, May, 2003; Fort Lauderdale, Florida.
Isabel Lema MD, PhD1 and Juan A. Durán MD, PhD2, ,
1Instituto Galego de Oftalmoloxía, Universidad de Santiago de Compostela, Santiago de Compostela, Spain
2Instituto Clínico-Quirúrgico de Oftalmología, Universidad del País Vasco, País Vasco, Spain
Received 25 June 2004; accepted 11 November 2004. Available online 1 April 2005.
Purpose
To determine levels of a panel of inflammatory molecules and matrix metalloproteinases in the tears of patients with keratoconus.
Design
A prospective, case–control study.
Participants
Twenty-eight patients (1 eye from each) diagnosed with keratoconus at the Instituto Galego de Oftalmoloxía, Santiago de Compostela, Spain, during the period from September 2001 to June 2002, and 20 normal control subjects (1 eye each) were studied.
Methods
Patients with keratoconus were examined in a routine fashion, and keratometric readings were taken to monitor the degree of ectasia. Fifteen microliters of tears was collected by capillary flow from each eye.
Main Outcome Measures
The concentrations of cytokines (interleukin-4 [IL-4], IL-6, IL-10, and tumor necrosis factor α [TNF-α]), cell adhesion molecules (intercellular adhesion molecule 1 and vascular cell adhesion molecule 1), and matrix metalloproteinase 9 (MMP-9) were measured by enzyme-linked immunoadsorbent assay.
Results
Patients with keratoconus initially had significantly higher levels of IL-6 (6.7 [4.8–10.8] pg/ml vs. 2.2 [1.0–4.1] pg/ml in control subjects [P<0.0001]), TNF-α (3.8 [2.9–14.4] pg/ml vs. 1.8 [1.5–2.3] pg/ml in control subjects [P<0.0001]), and MMP-9 (66.5 [49.2–139.3]ng/ml vs. 6.1 [3.9–8.3] ng/ml in control subjects. The extent of the increase was found to be associated with the severity of keratoconus.
Conclusions
Interleukin-6, TNF-α, and MMP-9 are overexpressed in the tears of patients with keratoconus, indicating that the pathogenesis of keratoconus may involve chronic inflammatory events.
Article Outline
Materials and Methods
Subjects and Examinations
Tear Analysis
Statistical Analysis
Results
Clinical Features
Inflammatory Mediators
Discussion
References
Keratoconus is a disorder characterized by a conical ectasia of the cornea in the absence of clinical signs of corneal inflammation. Typically, the pathology is characterized by a central or inferior corneal thinning with increased curvature at the apex of the cone.1 The etiology of this disease is unknown, but it has been classically described as being associated with certain systemic diseases, such as atopy and connective tissue disorders.2 and 3 In most cases, keratoconus occurs bilaterally but asymmetrically.4 It generally affects young adults and has an incidence of about 1:2000 of the general population.5 Many cases progress slowly and gradually in severity, but the rate of progression and the length of time that keratoconus remains actively progressive vary considerably. The factors governing the progression and stabilization of keratoconus are currently unknown.
In recent years, extensive studies of the biochemical and pathologic changes that occur at the structural and cellular levels of the cornea have been carried out.6, 7 and 8 Nevertheless, the specific mechanisms underlying the development of keratoconus and its relationship to heredity or environment are still not fully understood. Although there may be a relationship between keratoconus and several conditions of allergic etiology,9 and 10 the influence of these conditions on the pathogenesis and natural history of keratoconus remains unclear. For example, atopy is associated with elevated levels of serum immunoglobulin E. Likewise in keratoconus patients, an increased incidence of elevated serum immunoglobulin E has been reported.11 An association between keratoconus and eye rubbing, particularly in patients with an associated allergic condition, has also been reported. It has been estimated that 66% to 73% of patients with keratoconus rub their eyes frequently.4, 10, 12, 13 and 14 Moreover, Zadnik et al11 found that many patients (53.9 %) who enrolled in the Collaborative Longitudinal Evaluation of Keratoconus Study reported a history of allergy. However, the significance of these observations remains to be clarified.
The cornea is part of an integrated system (the ocular surface) that contains specific and nonspecific immune molecules. Tissue degradation in thinning disorders, such as keratoconus, involves the expression of inflammatory mediators, such as proinflammatory cytokines, cell adhesion molecules, and matrix metalloproteinases.15, 16, 17 and 18 With a view to contributing to our understanding of the factors that govern the etiology and development of keratoconus, we evaluated the levels of proinflammatory cytokines (interleukin-4 [IL-4], IL-6, IL-10, and tumor necrosis factor α [TNF-α]); cell adhesion molecules (intercellular adhesion molecule 1 and vascular adhesion molecule 1); and matrix metalloproteinase 9 (MMP-9) in tears from control subjects and patients with keratoconus.
Materials and Methods
Subjects and Examinations
We have designed a prospective, case-controlled study in which 28 patients with keratoconus and 20 normal subjects were enrolled. Patients with keratoconus had never worn contact lenses or had not worn lenses for a period of more than 1 year (52.3% males; mean age, 22.4±6.5 years). Normal subjects had never worn contact lenses (47.8% males; mean age, 22.6±6.6 years). We studied 1 eye from each patient, generally the right eye. Exclusion criteria included the existence of active inflammatory or infective systemic or ocular disease and current treatment with systemic or local antiinflammatory drugs.
Patients with keratoconus and normal subjects were recruited from the Contact Lens Unit, Instituto Galego de Oftalmoloxía (INGO), Complejo Hospitalario Universitario de Santiago de Compostela (CHUS), Spain, from September 2001 through June 2002. The protocol was approved by the ethics committee, and informed consent was given by all patients. All examinations were performed by the same researcher (IL). Data collected included gender, age, the patient's ocular history, medical history (allergy, eye rubbing), and family history. Careful attention was paid to evaluate the presence of a clinical history of atopy.
Ophthalmic examinations consisted of best-corrected visual acuity measurements, slit-lamp examination, and corneal topography. Slit-lamp biomicroscopy involved examination of the external adnexa and cornea (Vogt's striae, Fleischer's ring, keratoconic scars). An Eyesys unit (Corneal Analysis System CAS, Eyesys Laboratories, Houston TX) was used for corneal topography. Topographic data were evaluated by means of Rabinowitz5 criteria for the diagnosis of keratoconus; central corneal power, inferior-superior dioptric asymmetry, and central corneal power differences between the 2 eyes. The assessment of keratoconus progression was performed by use of steep keratometric reading categories described in the Collaborative Longitudinal Evaluation of Keratoconus Study Baseline.19 The stage of keratoconus was graded as mild when the steepest keratometric reading (K2) was <45 diopters (D), moderate if K2 was between 45 and 52 D, and severe with K2 >52 D. We considered K2 the quantitative clinical variable to assess the severity of keratoconus.
Tear Analysis
Tear samples were obtained by capillary flow, without nasal stimulation (the stimulation of reflex tearing was maintained at a minimum) or previous instillation of drugs or vital dyes. Anesthetic drops were not instilled. The samples were collected atraumatically from the inferior meniscus (near the exterior canthus). Care was taken to avoid touching the corneal and conjunctival surface. We collected 15 μl of tear sample in micropipettes (Disposable Micro Sampling Pipettes, Corning, NY) and placed them in microtubes (Micro Titertube natural 845-TP, TTE Laboratories, Hopkinton MA). A new capillary tube was used for each tear sample. Within 1 hour of obtaining the samples, they were frozen and stored at −70°C.
Samples were diluted 1:20 with sample diluent (reagent provided by enzyme-linked immunosorbent assay kit) to a final volume of 300 μl. The concentrations of cytokines (IL-4, IL-6, IL-10, and TNF-α) and cell adhesion molecules (intercellular adhesion molecule 1, vascular cell adhesion molecule 1) in tear samples were measured with commercially available quantitative sandwich enzyme-linked immunoadsorbent assay kits (Quantikine, R&D Systems, Minneapolis, MN), and the assays were performed in accordance with the supplier instructions. These cytokines were chosen as representative of molecules that are associated with chronic inflammation or regulatory processes; the limited volume of the tear samples precluded including further members in our panel of molecules. Matrix metalloproteinase 9 is the metalloproteinase that is most widely studied in human fluids, and its role in inflammation and in other diseases has been well documented. Its levels were determined by commercially available enzyme-linked immunosorbent assay kits (Biotrack, Amersham Pharmacia Biotech, Buckinghamshire, UK). Enzyme-linked immunosorbent assays were performed according to the manufacturer's instructions. All determinations were carried out without knowledge of the corresponding clinical data (blind test), and the final results were multiplied by the dilution factor (×20).
Statistical Analysis
Descriptive statistical analyses were performed with percentage for categorical variables. Discontinuous variables were expressed as median (quartiles). Graphic expressions were elaborated by box and whisker plots.
Statistical significance for intergroup differences was assessed by the chi-square test for categorical variables. Inflammatory molecular marker values were not normally distributed (Kruskal–Wallis analysis). The Mann–Whitney test was performed for comparison between groups. The Spearman correlation coefficient was used to analyze the statistical significance between keratometric readings (K2) and the concentrations of molecular markers. A multiple linear regression analysis was performed using both dependent (K2) and independent variables (IL-6, TNF-α, MMP-9). Another regression model was applied including the same variables, and 95% confidence intervals were calculated from β coefficients. A value of P<0.05 was considered to be statistically significant.
Results
Clinical Features
No age-related or gender-related statistical differences were detected between patients with keratoconus and control subjects. The duration of patient-reported keratoconus varied from 1 to 16 years (mean, 7.0–6.2 years). Only 1 patient (5%) from the control group was diagnosed as having allergic disease, whereas 16 patients (57.1%) from the keratoconus group had experienced at least 1 allergic episode. Eighteen patients with keratoconus (64.3%) admitted frequent and vigorous eye rubbing; no control subject presented this behavior. Eight patients with keratoconus (28.5%) had a familial history of keratoconus.
Slit-lamp biomicroscopy of the cornea revealed keratoconus characteristics (Vogt's striae, a Fleischer ring of at least 2-mm arc, or corneal scarring characteristic of keratoconus) in 23 keratoconus eyes (82.1%). Six eyes (21.4%) presented mild keratoconus (K2<45 D), 14 eyes (50%) had moderate keratoconus (K2 between 45 D and 52 D), and severe keratoconus (K2>52 D) was diagnosed in 8 eyes (28.6%).
Inflammatory Mediators
Levels of inflammatory molecules in control and keratoconus tears are shown in Table 1. Mean values of IL-4 and IL-10 were similar in control and keratoconus samples. However, patients with keratoconus had significantly higher levels of both IL-6 (6.7 [4.8–10.8] pg/ml vs. 2.2 [1.0–4.1] pg/ml in control subjects [P<0.0001]) and TNF-α (3.8 [2.9–14.4] pg/ml vs. 1.8 [1.5–2.3] pg/ml in control subjects [P<0.0001]).
Table 1.
Levels of Inflammatory Molecules in Tears Molecule Control Keratoconus P
Cytokines
IL-4 (pg/ml) 6.1 (4.7–8.2) 6.5 (4.6–8.3) 0.975
IL-6 (pg/ml) 2.2 (1.0–4.1) 6.7 (4.8–10.
<0.0001
IL-10 (pg/ml) 1.7 (1.1–3.0) 2.0 (1.5–3.1) 0.315
TNF-α (pg/ml) 1.8 (1.5–2.3) 3.8 (2.9–14.4) <0.0001
Adhesion molecules
ICAM-1 (ng/ml) 8.9 (6.5–10.9) 8.8 (5.1–13.3) 0.950
VCAM-1 (ng/ml) 29.6 (25.3–36.0) 30.6 (23.2–38.4) 0.778
Matrix metalloproteinases
MMP-9 (ng/ml) 6.1 (3.9–8.3) 66.5 (49.2–139.3) <0.0001
Values are median (quartiles).
ICAM = intercellular adhesion molecule-1; IL = interleukin; MMP-9 = matrix metalloproteinase-9; TNF-α = tumor necrosis factor α; VCAM-1 = vascular cell adhesion molecule 1.
As illustrated in Table 1, no significant differences were found in the concentrations of intercellular adhesion molecule 1 and vascular cell adhesion molecule 1 in patients with keratoconus and control subjects. In contrast, increased values of MMP-9 were found in patients with keratoconus (66.5 [49.2–139.3] ng/ml) versus control subjects (6.1 [3.9–8.3] ng/ml). This difference was very statistically significant (P<0.0001).
In this study, we did not find a relationship between patients with and without a clinical history of allergy, because mean levels of up-regulated inflammatory markers were found to be similar in both groups (P = 0.732 for IL-6; P = 0.767 for TNF-α; and P = 0.760 for MMP-9). A correlation between eye rubbing and different concentrations of these markers was not found either (IL-6, P = 0.395; TNF-α, P = 0.978; MMP-9, P = 0.371).
The association between increased levels of inflammatory markers and the severity of keratoconus (mild, moderate, or severe) was also analyzed. As indicated in Figure 1, higher concentrations of cytokines (IL-6, TNF-α) and MMP-9 were associated with severe keratoconus rather than with the mild or moderate stages (P<0.001). Differences between the mild and moderate stages were not statistically significant.
(155K)
Figure 1. Concentrations of inflammatory molecules associated with different degrees of keratoconus. K2 refers to the steep keratometric reading. A, Interleukin-6 (IL-6). B, Tumor necrosis factor α (TNF-α). C, Metalloproteinase 9 (MMP-9). D = diopters. *P<0.001 in relation to the other groups.
A significant correlation was found between the concentration of IL-6, TNF-α, and MMP-9 in keratoconus tears and the steep keratometric reading (K2) by simple regression analysis. The Spearman coefficient associated with the concentration of IL-6 and K2 was 0.570 (P = 0.002); that for TNF-α was 0.474 (P = 0.011); and that for MMP-9 was 0.796 (P<0.0001; Fig 2).
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Figure 2. Correlation between the concentration of inflammatory molecules and the steep keratometric reading (K2). A, Interleukin-6 (IL-6). B, Tumor necrosis factor α (TNF-α). C, Metalloproteinase 9 (MMP-9).
As shown in Table 2, when all the inflammatory molecules were included in a multiple regression analysis, MMP-9 was found to be the only single, independent variable associated with the degree of keratoconus.
Table 2.
Multiple Linear Regression Analysis Independent Variables β 95% Confidence Interval P
IL-6 0.25 −0.05–0.56 0.099
TNF-α −0.02 −0.26–0.22 0.848
MMP-9 0.07 0.01–0.13 0.012
β = beta coefficient of linear regression; IL = interleukin; MMP = matrix metalloproteinases; TNF = tumor necrosis factor.
Dependent variable = K2.
Discussion
Despite extensive basic and clinical studies of keratoconus in recent years, the precise mechanisms underlying this pathology still remain largely unknown. Most of these studies used corneas that had been obtained from transplants, and erroneous conclusions have been drawn from a number of these studies.20 Moreover, it has been shown that the reported increased levels of TNF-α and IL-1 are not specific to keratoconus but are present in other pathologies of the cornea as well.8 Nevertheless, despite contradictory reports,21 it is becoming clear that mediators of inflammation are present in the keratoconus cornea.17, 18, 22 and 23 This finding contrasts with the generally accepted idea that keratoconus is a corneal ectasia that does not involve inflammation.5
Studies of tears are limited by methodologic difficulties and by results that can be inconsistent and transitory. Nevertheless, events that take place on the ocular surface are likely to be reflected in the composition of tears. Thus, the presence of collagen degradation products has been reported in the tears of patients with keratoconus.24 In this study, we demonstrate that tears, which are a part of the corneal surface, contain detectable levels of cytokines, adhesion molecules, and MMPs. Moreover, the levels of some studied cytokines (IL-6 and TNF-α) are significantly increased in the tears of patients with keratoconus. To our knowledge, this is the first study supporting an important increase of proinflammatory markers in the tear film of patients with keratoconus who did not have clinical signs of inflammation. Increased levels of MMP-9 in the tears of patients with keratoconus have also been reported by others in studies of keratoconus and atopy.22 Discrepancies between this study and other published reports may be because different data/subjects were analyzed (e.g., keratoconus patients with clinical signs of inflammation) and different methods (tear sample collection) were used.
The lacrimal gland is the principal effector in the secretory immune system of the eye and plays a critical role in protecting the eye against allergic, inflammatory, and infectious diseases.15 The preocular tear film contains numerous specific and nonspecific immune components. These include cytokines and cell adhesion molecules.23 and 25 The increased levels of these molecules observed in this study may be a consequence of increased secretion from the corneal epithelium or from another noncorneal cell type. Clarifying this issue may contribute significantly to determining the origin of the disease. Various cell types, including keratocytes, produce IL-6 in response to stimulation by IL-1 or TNF-α.26 It is, thus, conceivable that the tear may act as a reservoir of cytokines produced by the stroma and corneal or conjunctival epithelium; alternatively, it may act as a vehicle of cytokines produced by the lacrimal gland or other epithelia of the ocular surface.
In recent years, numerous clinical studies of keratoconus support the idea that its pathogenesis involves an inflammatory component. A variety of changes in the ocular surface of patients with keratoconus have been found, including reduced corneal sensitivity, increased fluorescein and rose bengal staining scores, and abnormal impression cytology such as squamous metaplasia and lower goblet cell density.27 In the same way, increased enzymatic activity has been demonstrated in the conjunctiva of patients with keratoconus.28 and 29 Despite the fact that the origin of these changes is not completely understood, Dogru et al27 have suggested recently that keratoconus may have an epithelial origin, which would explain the re-incident cases of keratoconus after keratoplasty. Overall, it cannot be ruled out that keratoconus originates in events that take place outside the cornea but that are ultimately responsible for the induction of its ectasia.
The association between keratoconus and allergy,9, 10, 11, 12 and 13 as well as the role played by eye rubbing in the development of ectasia, is well established.4, 10 and 14 Eye rubbing may well contribute to the development of keratoconus by activating inflammatory mediators,30 more so than by the physical pressure applied to the eyeball. Indeed, IL-1 has been implicated as a mediator of keratoconus in eye patients who rub their eyes.31 This study included numerous patients who reported previous episodes of allergy and frequent eye rubbing. However, we did not find an association between either of these parameters and the increased levels of inflammatory molecules in tears. It is conceivable that the concentration of interleukins increases only during episodes of itching and eye rubbing.
The tear may be a vehicle of some of the pathogenic protagonists of keratoconus, such as IL-6, TNF-α, or MMP-9. Increased levels of these molecules may be sporadic, but sufficient to provoke slowly progressive ectasia.20 Our results indicate that the concentration of inflammatory molecules in tears is associated with the intensity of keratoconus; however, a similar association with the progression of ectasia was not determined. Nevertheless, the presence of different classes of enzymes that play a role in the pathologic process is not necessarily accompanied by an immediate presentation of corresponding clinical manifestations.18 It is likely that keratoconus is a disease with a multivariable origin, in which corneal ectasia results from the degradation of stromal collagen. The results of this study support this hypothesis and indicate that these processes may be accompanied by chronic inflammatory events. This would explain the findings of many studies that have reported the participation of all the layers of the cornea, as well as other structures of the ocular surface, in keratoconus.8, 27, 28, 29 and 32
Thinning and ectasia of the cornea are suggestive of a degraded extracellular matrix. Many studies have described changes in corneas with keratoconus, but only a few have studied the tear fluid of these patients. The small volume of the tear sample, the different methods used, and the possibility of modifying real parameters may explain the different results reported in various studies. However, it has become clear by now that inflammatory events do take place in keratoconus. This study reveals that high levels of some cytokines (IL-6 and TNF-α) and MMP-9 are associated with advanced keratoconus, but the precise role of each of these molecular players still needs to be defined. The pathogenesis of keratoconus seems to be multifactorial and governed by genetic, biologic, and biomechanical bases. It can also be concluded from our current data that keratoconus cannot be defined any more as a noninflammatory disorder.
References
1 J.H. Krachmer, R.S. Feder and M.W. Belin, Keratoconus and related noninflammatory corneal thinning disorders, Surv Ophthalmol 28 (1984), pp. 293–322. Abstract
2 A.R. Gasset, W.A. Hinson and J.L. Frias, Keratoconus and atopic diseases, Ann Ophthalmol 10 (1978), pp. 991–994. Abstract-EMBASE | Abstract-MEDLINE
3 I.H. Maumenee, The cornea in connective tissue disease, Ophthalmology 85 (1978), pp. 1014–1017. Abstract-EMBASE | Abstract-MEDLINE
4 Zadnik K, Steger-May K, Fink BA, et al, CLEK Study Group. Between-eye asymmetry in keratoconus. Cornea 2002;21:671–9.
5 Y.S. Rabinowitz, Keratoconus, Surv Ophthalmol 42 (1998), pp. 297–319. Abstract | PDF (2468 K)
6 D.A. Newsome, J.M. Foidart and J.R. Hassell et al., Detection of specific collagen types in normal and keratoconus corneas, Invest Ophthalmol Vis Sci 20 (1981), pp. 738–750. Abstract-EMBASE | Abstract-MEDLINE
7 B.Y. Yue, J. Sugar and K. Schrode, Histochemical studies in keratoconus, Curr Eye Res 7 (1988), pp. 81–86. Abstract-EMBASE | Abstract-MEDLINE
8 L. Zhou, B.Y. Yue and S.S. Twining et al., Expression of wound healing and stress-related proteins in keratoconus corneas, Curr Eye Res 15 (1996), pp. 1124–1131. Abstract-EMBASE | Abstract-MEDLINE
9 P.L. Jacq, Y. Sale and B. Cochener et al., Keratoconus, changes in corneal topography and allergy: study of 3 groups of patients [in French], J Fr Ophtalmol 20 (1997), pp. 97–102. Abstract-MEDLINE
10 A.M. Bawazeer, W.G. Hodge and B. Lorimer, Atopy and keratoconus: a multivariate analysis, Br J Ophthalmol 84 (2000), pp. 834–836. Abstract-EMBASE | Abstract-Elsevier BIOBASE | Abstract-MEDLINE | Full Text via CrossRef
11 E.G. Kemp and C.J. Lewis, Immunoglobulin patterns in keratoconus with particular reference to total and specific IgE levels, Br J Ophthalmol 66 (1982), pp. 717–720. Abstract-EMBASE | Abstract-MEDLINE
12 A.G. Karseras and M. Ruben, Aetiology of keratoconus, Br J Ophthalmol 60 (1976), pp. 522–525. Abstract-EMBASE | Abstract-MEDLINE
13 J.T. Coyle, Keratoconus and eye rubbing [letter], Am J Ophthalmol 97 (1984), pp. 527–530.
14 D.C. Gritz and P.J. McDonnell, Keratoconus and ocular massage [letter], Am J Ophthalmol 106 (1988), pp. 757–758. Abstract-EMBASE | Abstract-MEDLINE
15 J.W. Chandler, Ocular surface immunology. In: J.S. Pepose, G.N. Holland and K.R. Wilhelmus, Editors, Ocular Infection and Immunity, Mosby, St. Louis (1996), pp. 104–111.
16 S. Bonini, A. Lambiase, T. Juhas and P. Rama, Inflammatory immune-associated diseases of the cornea. In: D. BenEzra, Editor, Ocular Inflammation: Basic and Clinical Concepts, Martin Dunitz, London (1999), pp. 151–168.
17 L. Zhou, S. Sawaguchi and S.S. Twining et al., Expression of degradative enzymes and protease inhibitors in corneas with keratoconus, Invest Ophthalmol Vis Sci 39 (1998), pp. 1117–1124. Abstract-EMBASE | Abstract-Elsevier BIOBASE | Abstract-MEDLINE
18 S.A. Collier, M.C. Madigan and P.L. Penfold, Expression of membrane-type 1 matrix metalloproteinase (MT1-MMP) and MMP-2 in normal and keratoconus corneas, Curr Eye Res 21 (2000), pp. 662–668. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef
19 K. Zadnik, J.T. Barr and T.B. Edrington et al., Baseline findings in the Collaborative Longitudinal Evaluation Of Keratoconus (CLEK) Study, Invest Ophthalmol Vis Sci 39 (1998), pp. 2537–2546. Abstract-EMBASE | Abstract-MEDLINE
20 S.A. Collier, Is the corneal degradation of keratoconus caused by matrix-metalloproteinases?, Clin Experiment Ophthalmol 29 (2001), pp. 340–344. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef
21 M. Saghizadeh, M. Chwa and A. Aoki et al., Altered expression of growth factors and cytokines in keratoconus, bullous keratopathy and diabetic human corneas, Exp Eye Res 73 (2001), pp. 179–189. Abstract | Abstract + References | PDF (388 K)
22 V.A. Smith, H. Rishmawi, H. Hussein and D.L. Easty, Tear film MMP accumulation and corneal disease, Br J Ophthalmol 85 (2001), pp. 147–153. Abstract-EMBASE | Abstract-Elsevier BIOBASE | Abstract-MEDLINE | Full Text via CrossRef
23 A. Solomon, D. Dursun and Z. Liu et al., Pro- and anti-inflammatory forms of interleukin-1 in the tear fluid and conjunctiva of patients with dry-eye disease, Invest Ophthalmol Vis Sci 42 (2001), pp. 2283–2292. Abstract-EMBASE | Abstract-Elsevier BIOBASE | Abstract-MEDLINE
24 J.H. Abalain, H. Dossou, J. Colin and H.H. Floch, Levels of collagen degradation products (telopeptides) in the tear film of patients with keratoconus, Cornea 19 (2000), pp. 474–476. Abstract-MEDLINE | Full Text via CrossRef
25 K. Barton, D.C. Monroy, A. Nava and S.C. Pflugfelder, Inflammatory cytokines in the tears of patients with ocular rosacea, Ophthalmology 104 (1997), pp. 1868–1874. Abstract-EMBASE | Abstract-MEDLINE
26 S.R. Planck, X.N. Huang, J.E. Robertson and J.T. Rosenbaum, Cytokine mRNA levels in rat ocular tissues following systemic endotoxin treatment, Invest Ophthalmol Vis Sci 35 (1994), pp. 924–930. Abstract-EMBASE | Abstract-Elsevier BIOBASE | Abstract-MEDLINE
27 M. Dogru, H. Karakaya and H. Özçetin et al., Tear function and ocular surface changes in keratoconus, Ophthalmology 110 (2003), pp. 1110–1118. SummaryPlus | Full Text + Links | PDF (394 K)
28 T. Fukuchi, B.Y. Yue, J. Sugar and S. Lam, Lysosomal enzyme activities in conjunctival tissues of patients with keratoconus, Arch Ophthalmol 112 (1994), pp. 1368–1374. Abstract-EMBASE | Abstract-MEDLINE
29 Shen JF, McMahon TT, Cheng EL, et al, Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group. Lysosomal hydrolase staining of conjunctival impression cytology specimens in keratoconus. Cornea 2002;21:447–52.
30 W. Edwards, C.N. McGhee and S. Dean, The genetics of keratoconus, Clin Experiment Ophthalmol 29 (2001), pp. 341–351.
31 E.J. Fabre, J. Bureau, Y. Pouliquen and G. Lorans, Binding sites for human interleukin 1α,γ interferon and tissue necrosis factor on cultured human fibroblasts of normal cornea and keratoconus, Curr Eye Res 10 (1991), pp. 585–592. Abstract-EMBASE | Abstract-MEDLINE
32 R.M. Kaldawy, J. Wagner, S. Ching and G.M. Seigel, Evidence of apoptotic cell death in keratoconus, Cornea 21 (2002), pp. 206–209. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef
Manuscript no. 240507.
The authors have no proprietary interest in any of the products mentioned in the article.
Reprint requests to Isabel Lema, MD, PhD, Instituto Galego de Oftalmoloxía, Hospital de Conxo, Santiago de Compostela 15706, Spain
pour la trade! 
. Je vais essayer de le faire pour ce soir...
