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PubMed1995

Comparison of methods for detecting keratoconus using videokeratography.

BACKGROUND: The detection of keratoconus patterns on videokeratography is important for screening candidates for refractive surgery and for studying the genetic basis of keratoconus. OBJECTIVE: We compared three quantitative approaches to identifying keratoconus from videokeratographic information to examine the limitations and capabilities of each test and to determine their suitability for use in the clinical setting. METHODS: Videokeratographs typical of clinically diagnosed keratoconus (n = 44) and of various non-keratoconus conditions (n = 132, including normal, with-the-rule astigmatism, contact lens-induced corneal warpage, photorefractive keratectomy, keratoplasty, and pellucid marginal degeneration) were selected. Three methods for detecting keratoconus were used: keratometry (average Simulated Keratometry [SimK] readings > 45.7 diopters [D]); the modified Rabinowitz-McDonnell test (central corneal power > 47.2 D and/or Inferosuperior Asymmetry [I-S] value > 1.4 D); and an expert system classifier (classification based on discriminant analysis and classification tree with eight topographic indexes). Sensitivity and specificity were calculated for each test. RESULTS: Sensitivities were 84% for keratometry, 96% for the modified Rabinowitz-McDonnell test, and 98% for the expert system classifier. Specificities for the three methods were 86%, 85%, and 99%, respectively. In terms of sensitivity, the expert system classifier was significantly better than keratometry (P = .04). In terms of specificity, the expert system classifier was significantly better than either of the other methods (P = .001). CONCLUSIONS: For screening candidates for refractive surgery, where high sensitivity is needed, either the modified Rabinowitz-McDonnell test or the expert system classifier is suitable. For diagnosing keratoconus, where high specificity is more useful, the expert system classifier is more appropriate than the other two methods.

Cornea↗
PubMed1996

A study of aqueous humor dynamics in keratoconus.

Clinical observations suggest that patients with keratoconus have lower intraocular pressures, on average, than normal subjects. Our purpose was to determine whether differences in aqueous production and outflow facility could account for differences in intraocular pressure between a group of patients with keratoconus and a group of normal, age-matched control subjects. Aqueous humor dynamics were determined by the use of fluorophotometry in one eye of seven patients with keratoconus and ten age-matched normal subjects. Intraocular pressure was measured by applanation tonometry. Keratoconus patients had a statistically significant lower mean intraocular pressure than normal control subjects (11.3 +/- 1.6 mmHg vs. 16.6 +/- 2.8 mmHg, P = 0.0004). The difference in mean intraocular pressure remained significant even after correcting for possible errors in applanation tonometry due to thin corneal stroma. There was no difference in mean aqueous humor flow rates in the keratoconus patients as compared to controls (2.29 +/- 0.53 microliter min-1, P = 0.73). The mean apparent outflow facility was 0.21 +/- 0.07 microliter min-1 mmHg-1 for keratoconus patients compared to 0.14 +/- 0.03 microliter min-1 for controls (P = 0.02). Lower mean intraocular pressure in keratoconus patients appears to be due to increased outflow facility as compared to normal subjects.

Adult↗
PubMed1999

Enhanced expression of a transmembrane phosphotyrosine phosphatase (LAR) in keratoconus cultures and corneas.

The purpose of the study was to identify genes that are differentially expressed in normal versus keratoconus corneas. Total RNA isolated from corneal stromal cell cultures was reverse-transcribed and then amplified by the polymerase chain reaction (PCR) using defined, arbitrary primers. The products were displayed on polyacrylamide gels and bands that were differentially expressed were excised, re-amplified and subcloned. The resulting clones were sequenced and utilized as probes for Northern blots with cultured cell RNA or Southern blots of corneal cDNA. One of the products that appeared to be more highly expressed in keratoconus cultures and corneas displayed 100% homology with leukocyte common antigen related protein (LAR), a transmembrane phosphotyrosine phosphatase. Western analyses and immunohistochemistry with monoclonal and/or polyclonal antibodies to LAR were used to examine keratocyte cultures and fresh frozen normal, keratoconus and pseudophakic bullous corneas. We identified a gene product with 100% homology to LAR that is expressed at the RNA level in keratoconus corneas and cell cultures but is found only at low or undetectable levels in normal cultures and normal and pseudophakic bullous keratopathy (PBK) corneas. By Western blotting and immunofluorescence with specific LAR antibodies, the protein was identified in keratoconus stromal cell cultures but not in normal cultures. When fresh frozen tissue was examined, LAR protein was localized to numerous stromal cells throughout central keratoconus corneas, while no central staining was seen in normal or bullous keratopathy corneas. LAR, a transmembrane phosphotyrosine phosphatase, is more highly expressed in keratoconus corneas and stromal cell cultures as demonstrated by differential display, Northern analyses, immunohistochemistry and Western blotting.

Adolescent↗
PubMed1998

[Corneal topography of the partner eye in unilateral keratoconus].

PURPOSE: To study the incidence and shape of subclinical keratoconus with corneal topography in the fellow eye in the case of clinically, slit-lamp biomicroscopically and topographically diagnosed unilateral disease. METHODS: Eighty patients with keratoconus were fitted with contact lenses. Twelve of them revealed clinical features of unilateral disease. In these patients we performed a computed topographic analysis in the clinically normal fellow eye. We measured quantitative parameters (central corneal power, I-S value) and qualitative parameters (localization and shape of corneal steepening). RESULTS: In all 12 patients we found in the fellow eye no slit-lamp evidence for keratoconus. Nine patients were emmetropic in the fellow eye, three patients myopic between -1.5 and -4.0 D. The myopia in these patients was corrected with contact lenses and the investigation was performed 5 days after discontinuance of contact lenses. The corneal topography showed the typical keratoconus pattern in 11 patients with a steepening of the inferior cornea and in 1 case a superior steepening of the cornea; range of I-S values -1.0 to +5.0 D. All patients revealed a configuration of oval type cone keratoconus in the corneal topography. CONCLUSION: Keratoconus occurs with a high degree of bilaterality, but with onset of the disease at different times in the two eyes. Corneal topography seems to be a sufficient method to detect early keratoconus.

Adolescent↗
PubMed2005

Inflammatory molecules in the tears of patients with keratoconus.

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 Oftalmoloxia, 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 alpha [TNF-alpha]), 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-alpha (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-alpha, and MMP-9 are overexpressed in the tears of patients with keratoconus, indicating that the pathogenesis of keratoconus may involve chronic inflammatory events.

Adult↗
PubMed2002

Keratocyte density in keratoconus. A confocal microscopy study(a).

PURPOSE: To estimate keratocyte density in human corneas with keratoconus by confocal microscopy. DESIGN: Prospective, observational cohort study. METHODS: Twenty-nine unscarred corneas of 19 patients with keratoconus and 29 corneas of 19 controls matched for age (+/-3 years) and contact lens wear were examined by using confocal microscopy. Images were recorded from the full-thickness central cornea. A masked observer manually counted bright objects (keratocyte nuclei) in images without motion blur. Cell densities in anteroposterior stromal layers of keratoconus corneas were compared with densities in corresponding layers of control corneas. RESULTS: In keratoconus patients, age 40 +/- 15 years (mean +/- standard deviation), keratocyte density was 19% lower in those who wore contact lenses (16,894 +/- 4032 cell/mm(3), n = 12) than in those who did not wear contact lenses (20,827 +/- 4934 cell/mm(3), n = 17, P =.03). In control patients, age 39 +/- 16 years, there was no difference in keratocyte density between those who wore contact lenses (n = 12) and those who did not wear contact lenses (n = 17, P =.80). Among contact lens wearers, keratocyte density was 25% lower in keratoconus corneas (16,894 +/- 4, 032 cell/mm(3), n = 12 [9 = rigid gas-permeable lenses, 3 = soft lenses]) than in control corneas (22,579 +/- 2, 387 cell/mm(3), n = 12 [3 = rigid gas-permeable lenses, 9 = soft lenses], P =.002), the result of cell density being lower in the most anterior keratocyte layer (P =.001) and the layers between 0% to 10% (P <.001), 67% to 90% (P <.001), and 91% to 100% (P <.001) of stromal thickness. Among noncontact lens wearers, there was no difference in cell density between keratoconus and controls (P =.41). CONCLUSION: Keratocyte density is decreased in the anterior and posterior stroma of keratoconus patients who wear contact lenses.

Adult↗
PubMed1978

Hard contact lens wear as an environmental risk in keratoconus.

We studied 162 keratoconus patients in an attempt to clarify the role of hard contact lens wear in the development of keratoconus. Forty-three (26.5%) of these 162 patients developed keratoconus while wearing hard contact lenses. In a group of 1,248 controls who were fitted for soft contact lenses and observed by us from one year to six years, only one patient developed keratoconus. We demonstrated a circumstantial association between hard contact lens wear and the development of keratoconus, but no cause-effect relationship can be drawn from the existing data. However, we concluded that hard contact lenses do not retard or halt progression of the cone. Hard contact lens wear could not be ruled out as the specific environmental risk factor triggering keratoconus in 26.5% of the patients. If we identify the genetic risk present in this subpopulation, eliminating environmental risks would be an effective means of preventing keratoconus in those predisposed individuals.

Contact Lenses↗
PubMed1991

Lack of association between keratoconus, mitral valve prolapse, and joint hypermobility.

The authors enrolled 95 patients with keratoconus and 96 matched controls in a cross-sectional study to determine if mitral valve prolapse and hypermobile joints occur with greater frequency in individuals with keratoconus than in individuals without keratoconus. The hypothesis that keratoconus may not be a distinct eye disease, but a nonspecific sign representing a more generalized systemic disorder, possibly a mild collagen tissue abnormality, was considered. M-mode and two dimensional echocardiography and cardiac auscultation detected no statistically significant difference in the prevalence of mitral valve prolapse in patients with keratoconus compared with controls. Formal, systematic examination of five joints also failed to detect a statistically significant difference in the prevalence of hypermobile joints in keratoconus patients and controls. However, as an ancillary finding, a significantly higher proportion of patients with keratoconus was found to have a history of hay fever than was the case with controls.

Adult↗
PubMed1998

Posterior keratoconus. An expanded classification scheme based on corneal topography.

OBJECTIVE: The purpose of the study was to evaluate corneal changes in posterior keratoconus. DESIGN: A retrospective review. RESULTS: Distinct topographic patterns were identified. Generalized posterior keratoconus showed uniform corneal steepening. Localized central and paracentral posterior keratoconus showed corneal steepening, and localized peripheral posterior keratoconus showed corneal flattening overlying the area of corneal change. The changes in central and paracentral posterior keratoconus appear to progress with an increase in patient age. Unilateral disease may have more amblyogenic potential. CONCLUSIONS: Posterior keratoconus manifests significant corneal surface alterations. The distinct topographic patterns seen probably warrant a further classification of localized posterior keratoconus into central-paracentral and peripheral varieties.

Adult↗
PubMed1999

Photorefractive keratectomy in keratoconus suspects.

PURPOSE: To compare the refractive outcome after photorefractive keratectomy (PRK) in keratoconus-suspect patients with that in patients with normal corneal topography. SETTING: Gimbel Eye Centre, Calgary, Alberta, Canada. METHOD: In a retrospective study, 3 patients (5 eyes) with unusually shaped corneal topography before surgery were selected as keratoconus suspects. Corneal topography (inferior-superior [I-S] value, central corneal power, and central power difference between both eyes), preoperative and 1 year postoperative refraction, and visual acuity in the keratoconus suspects were compared with those in a control group. RESULTS: The mean preoperative I-S value was 1.79 diopters (D) in the keratoconus-suspect eyes and 0.35 D in the control group eyes (P = .0001). The I-S value of individual corneas in the keratoconus suspects was more than 2 standard deviations above the mean in the control group except in 1 eye in which the steepened area was located in the central cornea. The central power difference between the eyes of this patient was 3.60 D, which was significantly higher than that in the control group. The refractive outcomes in the keratoconus suspects were comparable to those in the control group. CONCLUSION: In this study, the refractive outcomes after PRK in the keratoconus suspects and controls were comparable. However, further investigation with a larger sample and longer follow-up is needed.

Adult↗
PubMed2001

Is the corneal degradation in keratoconus caused by matrix-metalloproteinases?

The thinning of the cornea that occurs in keratoconus has been well described; however, the mechanism of tissue degradation remains unknown. Elevated proteinase activity is one possibility and approximately 20 publications over the last 20 years have addressed this hypothesis. Early studies reported increased collagenase and gelatinase activities in the medium of keratoconus corneal cultures. After the characterization of the matrix metalloproteinase (MMP) enzymes, studies focused on the expression of specific MMPs, in particular the gelatinases, MMP-2 and MMP-9. Matrix metalloproteinase-2 was found to be the major MMP of the cornea and was constitutively produced in normal tissue, whereas MMP-9 expression was induced by various stimuli, including phorbol esters and even tissue culturing. These studies suggested that there were no differences in the amounts or states of activation of MMP between normal and keratoconus corneas, although the amounts of some proteinase inhibitors, including tissue inhibitors of metalloproteinases, alpha-1-proteinase inhibitor and alpha-2-macroglobulin, were decreased in keratoconus. Most recently, the lysosomal proteinases, cathepsin B and cathepsin G were reported to be elevated in keratoconus corneas, and it is possible that it was cathepsin activity, not MMP activity, that was measured in some early studies. Nevertheless, there are now about 20 human MMPs identified and it is possible that some of these, other than the well known collagenase (MMP-1) and gelatinases (MMP-2 and MMP-9), could be implicated in the pathology of keratoconus. Studies have begun to address more recently described MMPs and it has been reported that the membrane-bound MT1-MMP (MMP-14), which activates latent MMP-2, was found to have increased expression in keratoconus corneas, whereas the stromelysins, MMP-3 and MMP-10, were not.

Cornea↗
PubMed1997

[Live epikeratophakia and deep lamellar keratoplasty for I-III stage-specific surgical treatment of keratoconus].

BACKGROUND: Perforating keratoplasty (PKP) for the treatment of keratoconus is a temporary procedure that sacrifices the healthy recipient endothelium. As an alternative to PKP we perform live-epikeratophakia (L-EPI) in keratoconus I-II and deep lamellar keratoplasty (DLKP) in keratoconus II-III. PATIENTS AND METHODS: 20 patients with keratoconus were operated on either with L-EPI for keratoconus I-II (n = 10) or DLKP for keratoconus II-III (n = 10) respectively. In all cases, corneal tissue eligible for corneal transplantation was used. L-EPI: The corneal lenticule was prepared by means of the Barraquer-Krumeich-Swinger (BKS) set. The recipient cornea was trephined to a depth of 0.3 mm with the Guided-Trephine-System (GTS). The incision was extended manually (inner diameter 7.0 mm, outer diameter 9.0 mm). No keratectomy was performed. The lenticule was fixed with a 10 x 0 nylon double-running anti-torque suture (DRA). DLKP: The recipient cornea was trephined with the 8.0 mm GTS to a depth of 0.68 mm. A lamellar removal of the upper layers was performed by hand. After mechanical removal of the graft endothelium, the remaining full thickness donor cornea was sutured into the bed with a 10 x 0 nylon DRA suture. RESULTS: L-EPI: Within this series, there was no disturbance of the healing process. Spherical equivalent and corneal astigmatism remained stable from the first month on. Visual acuity of 20/40 or better was obtained in 40% of the cases at 1 month, 53% at 6 months, and 100% at 1 year and 2 years. We did not observe any late decline of VA. Two patients with kerato-conus borderline stage II did not reach useful VA due to insufficiently reduced pre-existing irregular corneal astigmatism. These patients successfully underwent DLKP at 8 and 10 months respectively. DLKP: Except for 1 case (neurodermatitis), all lenticules remained stable with respect to refraction and radii up to the longest follow-up of 2 years. Starting from the first month on, refraction was stable. Visual acuity of 20/40 or better was reached in 33% of the cases at 1 month, in 56% at 6 months, and in 89% at 1 and 2 years. We did not administer systemic cyclosporine-A in either group. In the lamellar techniques presented, we did not observe any graft rejection. According to corneal topography, corneal astigmatism, spherical equivalent, and keratometry we did not observe any late re-onset of a progression of the cone. CONCLUSION: In patients with keratoconus stage I to III, L-EPI or DLKP appeared to be very useful therapies. Both procedures seem to end progression of the disease and allow to preserve the healthy recipient endothelium. If unsuccessful, either procedure may be repeated. Neither procedure precludes possibly later needed PKP.

Astigmatism↗
PubMed1994

Altered gelatinolytic activities in an apparent unilateral keratoconus patient. A case report.

Recent studies have suggested that one possible cause of keratoconus involves increased degradation of the corneal extracellular matrix. Most studies have examined corneas from patients with bilateral, sporadic keratoconus. In this report, both corneas from a 70-year-old man with a history of familial keratoconus and clinical signs of unilateral keratoconus were examined for gelatinase activity. Our results demonstrated a qualitative (three additional activity bands of 88, 92, and 100 kDa molecular weights) and quantitative differences (an apparent increase in overall amounts) in the gelatinolytic enzyme profiles of the affected keratoconus cornea as compared with his unaffected (nonkeratoconus) cornea, normal corneas, bilateral sporadic keratoconus corneas, and cultured keratocytes. In addition, gelatinolytic enzymes were more readily extracted from the affected cornea compared with controls. These data lend support to the hypothesis of a heterogeneous etiology for keratoconus and to previous suggestions that this disorder may be related to an alteration in extracellular matrix degradation.

Adult↗
PubMed1999

Levels of alpha1-proteinase inhibitor and alpha2-macroglobulin in the tear film of patients with keratoconus.

PURPOSE: Levels of alpha1-proteinase inhibitor and alpha2-macroglobulin in the tear film of patients with keratoconus were measured to elucidate their possible roles in the pathogenesis of keratoconus. METHODS: Tear samples were collected from 15 keratoconus patients and 14 age-similar human control subjects. Levels of alpha1-proteinase inhibitor and alpha2-macroglobulin in each tear sample were quantified and compared between the two groups. RESULTS: Mean values for alpha1-proteinase inhibitor were 101.0+/-35.5 and 106.1+/-41.7 ng/microg protein for the keratoconus and control groups, respectively. The corresponding mean values for alpha2-macroglobulin were 13.5+/-6.8 and 14.8+/-7.5 ng/microg protein. Neither inhibitor showed a statistically significant difference between the keratoconus and control specimens. Subset analysis to evaluate the effects of contact lens wear and the presence of a graft in the fellow eye did not reveal a statistically significant difference. CONCLUSION: The tear film of patients with keratoconus contains normal levels of protease inhibitors. Therefore, the tear film may not be a source of the reduced inhibitor levels shown in the corneas of patients with keratoconus.

Adolescent↗
PubMed2002

Keratoconus associated with corneal granular dystrophy in a patient of Italian origin.

PURPOSE: To report a rare case of keratoconus concurrent with granular dystrophy in a patient of Italian origin. It is the seventh case in the literature and the second histopathologically documented case. METHODS: Keratoconus combined with granular dystrophy developed bilaterally in a 15-year-old boy from Italy. The corneal host button of the left eye obtained during penetrating keratoplasty 8 years later was analyzed histologically, immunohistochemically, and ultrastructurally. RESULTS: Histologic evaluation showed characteristic features of keratoconus, such as breaks in Bowman's layer and typical electron-dense trapezoidal deposits ultrastructurally. Other corneal dystrophies, such as Avellino dystrophy, were excluded. CONCLUSIONS: The concurrence of keratoconus and granular dystrophy raises the possibility of a genetic linkage of the diseases, although a chance association cannot be excluded. The diagnosis of keratoconus in patients with granular dystrophy is important because impairment of vision might be the result of keratoconus and could be treated with contact lenses instead of keratoplasty. In the future, the use of computerized corneal topography might help to detect more cases of keratoconus concurrent with granular dystrophy.

Adolescent↗
PubMed2003

Keratoconus-like topographic changes in keratoconjunctivitis sicca.

PURPOSE: To describe a case of inferior corneal steepening with a keratoconus-like pattern in a patient with nocturnal lagophthalmos and aqueous tear deficiency (ATD). METHODS: Axial curvature mapping was performed with the Tomey TMS-2N videokeratoscopy instrument. Keratoconus-like topography patterns were identified with the Klyce Software package of this instrument. RESULTS: Axial videokeratoscopy showed asymmetric inferior corneal steepening in the right eye. The surface regularity index (SRI), surface asymmetry index (SAI), and the simulated keratometric cylinder change (CYL) were 1.05, 5.05, and 0.75, respectively. The keratoconus screening indices were as follows for the right eye: Klyce/Maeda index of 95% similarity (clinical keratoconus interpreted) and Smolek/Klyce index of 23.09% severity (keratoconus suspect interpreted). Ultrasound pachymetric mapping showed a normal central corneal thickness. We found a similar topographic pattern of keratoconus in seven eyes of 74 dry eye patients who were previously evaluated with the Tomey TMS-2N. CONCLUSION: Chronic ocular desiccation and aqueous tear deficiency can produce inferior corneal steepening and high astigmatism resembling keratoconus.

Adult↗
PubMedDate not supplied

Genomewide linkage scan in a multigeneration Caucasian pedigree identifies a novel locus for keratoconus on chromosome 5q14.3-q21.1.

PURPOSE: Keratoconus is a corneal dystrophy with an incidence of 1 in 2000 and a leading cause for cornea transplantation in Western developed countries. Both clinical observations and segregation analyses suggest a major role for genes in its pathogenesis. It is genetically heterogeneous, most commonly sporadic, but inherited patterns with recessive or dominant modes have also been reported. We studied a four-generation autosomal-dominant pedigree to identify disease loci for keratoconus. METHODS: A two-stage genome-wide scan was applied to 27 family members. First linkage analysis was performed with 343 microsatellite markers along the 22 autosomal chromosomes at approximately 10 cM density. This was followed by fine mapping at approximately 2 cM density, in regions suggestive of linkage. Multipoint linkage analysis was performed using GeneHunter2. RESULTS: Evidence of suggestive linkage from the initial scan was observed at the 82 to 112 cM region of chromosome 5q14.1-q21.3 with a maximum lod score (LOD) of 3.48 (penetrance = 0.5). Fine mapping by testing an additional 11 microsatellite markers at 1 to 3 cM intervals revealed a narrower and higher peak (99-119 cM) with LOD 3.53. By analysis of the recombination of haplotypes, the putative locus of keratoconus was further narrowed to a 6 cM region (8.2 Mbp physical distance) between markers D5S2499 and D5S495. CONCLUSION: These results indicate a promising new locus for keratoconus in this pedigree. Because of the heterogeneous nature of keratoconus, this locus may be specific to familial autosomal-dominant keratoconus. Nevertheless, the identification of this locus may provide new insights into the pathogenesis of keratoconus.

Adult↗
PubMed2003

Keratoconus, allergy, itch, eye-rubbing and hand-dominance.

BACKGROUND: One hypothesis for the pathogenesis of keratoconus includes teenage allergy, ocular itch and associated eye-rubbing. METHODS: This study examined the prevalence of these factors for teenage and adult patients. The results for a sample of 53 subjects with bilateral keratoconus were compared with those for a control sample of non-keratoconus subjects, who also routinely wore RGP contact lenses. The strongest dominant hand and the eye with more advanced keratoconus were also determined, to examine for a relationship between them. RESULTS: The keratoconic sample reported significantly higher levels of allergy, itch and rubbing as teenagers and as adults. However, all distributions were bimodal, consistent with the hypothesis that allergy, itch and rubbing are relevant in the pathogenesis of keratoconus only when the highest levels of these factors are present. For example, a significant relationship between the stronger dominant hand and the more advanced eye was evident only in subjects who reported the most severe rubbing. CONCLUSIONS: This finding adds weight to the circumstantial evidence that rubbing contributes to the pathogenesis of keratoconus. Low levels of teenage rubbing by some keratoconic subjects suggest a non-rubbing pathogenesis and that emphasis on rubbing management is not warranted in these cases. However, high levels of adult rubbing reported by many keratoconic subjects indicate that the standard advice to avoid vigorous and prolonged rubbing is often not effective, even when repeated. There appears to be an indication for the need to improve the management of eye-rubbing for some patients with keratoconus or at risk of developing this disease.

Adolescent↗