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At least 145 records · Page 8Linked to original sources
PubMed1993

Videokeratography of the fellow eye in unilateral keratoconus.

PURPOSE: To identify a population of keratoconus patients with unilateral disease based on clinical findings and slit-lamp biomicroscopy and examination with a nine-ring photokeratoscope (Corneascope) and to study the topography of the clinically normal fellow eye with videokeratography. METHODS: Clinical charts and Polaroid Corneascope photographs of both eyes of 200 patients with a diagnosis of keratoconus from three large cornea referral practices in the Los Angeles area were retrospectively reviewed. Patients whose clinical findings were within normal limits and whose Corneascope Polaroid photographs had concentric rings with no detectable abnormalities, consistent with a diagnosis of keratoconus in one eye, were considered unilateral. These patients were recalled to our clinic, and the topography of the apparently normal eye was studied using a Corneascope and a computer-assisted videokeratoscope, the Topographic Modeling System, on the same day. RESULTS: Based on examination with a slit-lamp biomicroscope and the Corneascope, eight patients had unilateral disease. Videokeratography in seven of the eight fellow eyes displayed a pattern of inferior steepening suggesting "early keratoconus." All seven eyes had a positive "I - S value," a quantitative measure, indicating increased dioptric power below the corneal apex. CONCLUSION: Our findings suggest that keratoconus is almost always bilateral. These data support genetic influences in the pathogenesis of this disorder. Additionally, videokeratography data presented might prove useful in the detection of early keratoconus and refining patient selection for myopic keratorefractive procedures.

Adolescent↗
PubMed1998

Accuracy of ultrasonic pachymetry and videokeratography in detecting keratoconus.

PURPOSE: To compare the accuracy of ultrasonic pachymetry measurements and videokeratography-derived indices in distinguishing keratoconus patients from those with normal eyes. SETTING: A subspecialty cornea practice (Los Angeles, California, USA) and the Keratoconus Genetics Research Project. METHODS: Corneal thickness was measured by ultrasonic pachymetry at the center and inferior margins of the pupil of 142 normal and 99 keratoconus patients The corneal surface topography of patients was studied with the Topographic Modeling System (TMS-1). The videokeratographs obtained were analyzed with a computer program that automatically calculates two indices derived from data points in the central and paracentral cornea: central K and I-S values. Linear discriminant analysis was used to determine the correct classification percentages using pachymetry measurements and indices derived from videokeratography as the independent variables. RESULTS: The range of corneal thickness in normal and keratoconic eyes overlapped considerably. In the discriminant analysis, videokeratography indices provided a 97.5% correct classification rate and pachymetry data, an 86.0% rate (P < .01, McNemar's test). CONCLUSION: Keratoconus is more accurately distinguished from the normal population by videokeratography-derived indices than by ultrasonic pachymetry measurements. This may be due to the large variation in corneal thickness in the normal population or the inability of ultrasonic pachymetry to accurately detect the location of corneal thinning in keratoconus by measuring standard points on the cornea. Pachymetry should not be relied on to exclude or diagnose keratoconus because the false-negative and false-positive rates are unacceptably higher than those obtained by videokeratography.

Cornea↗
PubMed2000

Keratoconus evaluation using the Orbscan Topography System.

PURPOSE: To evaluate corneal topography in a series of keratoconus patients using the Orbscan Topography System. SETTING: Department of Ophthalmology, Ruprecht-Karls-University of Heidelberg, Heidelberg, Germany. METHODS: Seventy-one eyes of 38 patients with keratoconus were evaluated. Quantitative topographic parameters were analyzed with special reference to the central point of the cornea, the apex (the point with maximum reading on the anterior elevation best-fit sphere map), and the thinnest point. Evaluation included location, elevation (compared to a best-fit sphere), pachymetry, tangential curvature, and composite curvature. The mirror-image symmetry between the right and left eyes of a patient was also investigated. RESULTS: Mean patient age was 31.2 years +/- 12.2 (SD). Thirty-three patients (86.8%) had bilateral keratoconus and 5 (13.2%), unilateral keratoconus. Most cones (68/71) were located in the inferior temporal quadrant; 3 were above the horizontal meridian. Mean distance between the apex and the thinnest point was 0.917 +/- 0.729 mm (P < .001). The correlations between apex elevation and apex composite curvature and apex tangential curvature were high (r = 0.94 and r = 0.91, respectively; P < .001). In right and left eyes, there was a correlation between the apex and the thinnest point semi-meridians (r = 0.47 and r = 0.65, respectively; P < .05) but not between the radii of the apex and the thinnest point (r = 0.21 and r = 0.24, respectively). CONCLUSIONS: The Orbscan system can provide useful and accurate information in defining the morphology of keratoconus and detecting subtle topographic changes present in early keratoconus. It may also improve the results of contact lens fitting and surgical management.

Adolescent↗
PubMed2004

Influence of ethnic origin on the incidence of keratoconus and associated atopic disease in Asians and white patients.

PURPOSE: To investigate the influence of ethnic origin on the incidence of keratoconus and the association of atopic diseases in patients with keratoconus. METHODS: Retrospective study of new patients referred to Dewsbury District General Hospital and diagnosed with keratoconus in a 6-year period between 1994 and 2000. The ethnic origin of the patient was defined as white, Asian, or other. Incidence was calculated from the catchment population of 176 774 (82% white people, 17% Asians, 1% others). t-Test, confidence intervals and chi2 tests were used to show statistical significance. RESULTS: A total of 74 cases of keratoconus were diagnosed over this period. Of these patients 29 (39%) were white and 45 (61%) were Asian. This equated to an incidence of keratoconus of 25 per 100 000 (1 in 4000) per year for Asians, compared with 3.3 per 100 000 (1 in 30 000) per year for white people (P<0.001). Asians presented significantly younger than white patients. The incidence of atopic disease was found to be significantly higher in white compared to Asian keratoconic patients. CONCLUSIONS: Asians were significantly more likely to present with keratoconus. The Asian patients were mostly of Northern Pakistani origin. This community has a tradition of consanguineous, especially first-cousin marriages. The higher incidence in this population was highly suggestive of a genetic factor being significant in the aetiology. The incidence was higher than revealed by previous studies. Atopic disease was significantly less common in Asians compared to white people, supporting the theory of a different aetiology in these patients.

Adult↗
PubMed2001

The genetics of keratoconus.

Keratoconus is a relatively common, bilateral, non-inflammatory corneal ectasia. The aetiology of this condition is probably multifactorial, or it represents the final common pathway for a variety of different pathological processes. Although a familial history is present only in a minority of cases, one of the major aetiological factors is certainly genetic. This is evidenced by: the condition's familial inheritance; its discordance between monozygotic and dizygotic twins; and its association with other known genetic disorders such as Down's and Marfan's syndromes. In the keratoconic cornea, a possible genetic predisposition to increased sensitivity to apoptotic mediators by keratocytes has also been hypothesized. Differences in prevalence between ethnic groups have been identified. Recent advances in computerized topographic diagnostic techniques for keratoconus, including forme fruste keratoconus, enables higher accuracy in delineating abnormal from normal, and helps define study populations for genetic linkage studies. However, genetic heterogeneity and the phenotypic diversity of keratoconus means that genetic analysis continues to be a complex process. None the less, it is foreseeable that over the next decade, improved diagnostic techniques, in combination with molecular genetics, may reveal conclusive data on the precise nature of the genetic inheritance of keratoconus in specific populations. This review considers the evidence that suggests keratoconus is primarily an inherited condition, and examines research strategies aimed at unveiling the genetic predisposition, and the enigma of environmental influences on its phenotypic expression.

Cornea↗
PubMed1992

Corneal topography of posterior keratoconus.

Posterior keratoconus is an unusual abnormality of the cornea generally classified as one of the anterior chamber cleavage anomalies. It is characterized clinically by the presence of a circumscribed or generalized corneal thinning with posterior depression of the cornea and is considered distinct from keratoconus. Although patients with posterior keratoconus may have visual complaints clearly related to their abnormal corneas, the surface topography of these corneas has not been studied in detail. Keratometry and photokeratoscopy provide an incomplete picture of the surface geometry of posterior keratoconus. We utilized computer assisted topographic analysis to study the cornea of a patient with posterior keratoconus. The Topographic Modeling System demonstrated that the patient's cornea showed a central steepened "cone" coincident with the area of circumscribed posterior keratoconus as well as paracentral flattening. This report documents the topographic abnormality in this rare disorder.

Anterior Chamber↗
PubMed1996

Normal lysosomal enzyme staining in skin tissues of patients with keratoconus.

Keratoconus is a disease characterized by thinning and scarring of the central portion of the cornea. We have shown, in corneas and conjunctival tissues obtained from patients with keratoconus, that lysosomal enzyme staining is enhanced in the epithelial layer. In this study, we examined the lysosomal enzyme staining in skin-biopsy specimens of patients with keratoconus. Tissues collected from four patients with keratoconus and six normal subjects were fixed and processed for histochemical staining. Results showed that the epidermal and dermal layers of all skin specimens stained positively for two lysosomal hydrolases, acid esterase and acid phosphatase. The enzyme staining in the skin epidermal and dermal cells of the keratoconus patients was within the normal range. The staining in the corneal and conjunctival epithelia of the same patients was more prominent than that of normal controls. It appears that the biochemical abnormality identified in keratoconus is not manifested in the skin.

Acetylesterase↗
PubMed2000

Keratoconus associated with continual eye rubbing due to punctal agenesis.

PURPOSE: To highlight a possible causal effect of eye rubbing in the etiology of keratoconus. METHODS: A 43-year-old man presented to the practice of one of the authors (I.F.G.) with the complaint of gradual onset reading difficulty. History revealed the patient to have experienced constant epiphora in the right eye throughout his life as a result of punctal agenesis, which necessitated frequent wiping of this eye. Vision in the patient's right eye had been reduced for approximately 20 years. RESULTS: Based on ocular examination, the patient was diagnosed as having unilateral keratoconus in the right eye. CONCLUSION: It is thought by some that keratoconus is associated with, or indeed caused by, persistent rubbing of the anterior eye. While a number of studies support a genetic basis for keratoconus in some patients, it is possible that mechanical factors play a role in the development of this condition in other patients. This paper presents a case of unilateral keratoconus, where there is a confirmed history of habitual eye rubbing and wiping of excess tears as a result of punctal agenesis in the ipsilateral eye, thereby suggesting a possible causal relationship of eye rubbing in the etiology of keratoconus.

Adult↗
PubMed2001

Anterior keratoconus associated with unilateral cornea guttata.

PURPOSE: To describe a 30-year-old man with bilateral but asymmetric anterior keratoconus and unilateral cornea guttata in the eye with more advanced keratoconus. METHOD: Case report. RESULTS: The patient's keratoconus was diagnosed three or four years earlier. The keratoconus was confirmed by slit-lamp examination, keratometry, and computer-assisted topographic analysis. Cornea guttata were confirmed by clinical examination and specular microscopy. CONCLUSION: This is a rare case of unilateral cornea guttata associated with asymmetric keratoconus, showing severe guttate change only in the eye with more advanced keratoconus.

Adult↗
PubMed2003

A profile of keratoconus in New Zealand.

PURPOSE: To examine the characteristics and risk factors for keratoconus in a New Zealand population. METHODS: A one-page questionnaire was designed and sent to optometrists and ophthalmologists in New Zealand. Eye care practitioners then issued questionnaires to their keratoconic patients over a 6-month period. RESULTS: A total of 673 completed questionnaires were received from patients with keratoconus. A male bias (59%) was apparent in the sample. In line with previous work, a high proportion of the keratoconic cohort rubbed their eyes and suffered from atopy. A familial rate of 23.5% was evident, with several families reporting multiple keratoconus cases. Eleven pairs of twins were identified with at least one keratoconic sibling. Multivariate statistical analysis revealed significant independent correlations between the early development of keratoconus and gender, allergy, asthma, and latitude of childhood domicile. CONCLUSION: Results from the survey concur with a previous local report that keratoconus affects males more frequently and earlier in life than females in New Zealand. The concurrence of atopic disease and eye rubbing with keratoconus was as expected, and an association between the early development of the disease and latitude of the childhood domicile emerged. A strong familial component, exceeding previously reported figures, was evident in the cohort.

Adult↗
PubMed1997

Keratoconus: diagnosis and treatment.

At a minimum, the refractive surgeon should use the patient's history, refraction, keratometry, and slit-lamp examination to determine the status of a patient's cornea. A diagnosis of keratoconus easily can explain a patient's symptoms or greatly alter a plan of action for refractive surgery. If the surgeon finds automated topography useful as a screening device for keratoconus, for patient education, and for the documentation of corneal status, it also should be included in the patient's examination. Indeed, most cases of keratoconus will be demonstrated by automated topography. However, the surgeon must resist the notion that automated topography replaces manual keratometry. The two modalities should be additive to provide increased information about the patient's cornea and should not be considered in competition with each other, as implied by some. The most important information obtained from automated topography is the determination of the optical quality of the cornea. This information greatly affects the choice of refractive surgery and explains postoperative problems. Far too much attention has been paid to the exact dioptric power at different corneal sites indicated by automated topography. Indeed, current automated topography techniques can only estimate the dioptric values of an aspherical cornea several millimeters from the center of the cornea. Refraction is the most accurate means for determining the refractive status of the eye. Refractive surgery is designed to correct a refractive error; it is not a topographical map. Those topography units that afford the observer the most accurate information about corneal irregular astigmatism will become very valuable. Because irregular astigmatism is linked directly to keratoconus, the more sensitive an automated topography system is in detecting irregular astigmatism, the better will it detect the subtle levels of keratoconus. Above all, the astute corneal diagnostician must learn to appreciate irregular astigmatism and should train extensively with a manual keratometer to detect subtle yet very meaningful levels of preoperative keratoconus and irregular astigmatism following refractive surgery.

Cornea↗
PubMed1996

Keratoconus detection based on videokeratoscopic height data.

PURPOSE: To develop a videokeratoscopic-based keratoconus detection scheme that avoids the ambiguity of dioptric power definitions and videokeratoscope design. METHODS: Corneal height data obtained with a commercial videokeratoscope are decomposed into the set of orthogonal Zernike polynomials. Expansion coefficients of a "normal" group and a keratoconus group are compared to find significant differences. Elevated Zernike terms are used to detect the disease in these populations. The performance of this detection scheme is compared to other videokeratoscopic keratoconus Indices. RESULTS: Two low-order Zernike polynomial terms are identified as being elevated in keratoconus patients and combined to form a new detection index. This index performed at least as well as keratoconus detection schemes based on the inferior-superior (I-S) value, the steepest radial axes (SRAX), and the Surface Asymmetry Index (SAI) for the samples studied. CONCLUSION: The proposed Zernike scheme offers a potentially viable algorithm for detecting keratoconus that avoids the ambiguities of dioptric power definitions and is independent of videokeratoscope design.

Cornea↗
PubMed2004

Keratoconus fittings: apical clearance or apical support?

PURPOSE: To examine the relative merits of apical support and apical clearance fitting of rigid gas-permeable contact lenses for keratoconus. METHODS: After an historic review of fitting approaches for keratoconus, a case report is described in which an adventitious apical clearance fitting for early keratoconus might have been associated with accelerated progress of the ectasia. DISCUSSION: The hypothesis that apical clearance fittings increase the risk of accelerating ectasia progression in early keratoconus is examined in counterpoint to the hypothesis that apical support fittings increase the risk of apical scarring. Reference is made to the responses of normal corneas to apical clearance fitting and to apical contact fittings used in orthokeratology fittings. The tendency for corneas to mold to contact lens curvature is reviewed. The possibility that reduced corneal thickness or tissue softening and associated changes to the biomechanical properties of the cornea in keratoconus may facilitate molding with apical clearance fitting is examined. CONCLUSIONS: Known and putative risk factors for fitting complications that are associated with apical clearance and apical touch contact lens fitting are given as a basis for the reader to draw conclusions about the management of contact lens fitting for keratoconus. The possibility of symptomless adverse responses is a strong indication for frequent routine aftercare reviews.

Child↗
PubMed2006

In vivo confocal microscopy findings in keratoconus.

PURPOSE: : To evaluate corneal structure in eyes with keratoconus by using in vivo confocal microscopy. METHODS: : In a prospective institutional study, 48 eyes of 24 consecutive patients with keratoconus were examined by in vivo confocal microscopy. Forty-four eyes of 22 healthy subjects served as the control. The main outcome measures were qualitative and quantitative changes encountered at confocal microscopy examination. RESULTS: : In the keratoconus group, in vivo confocal microscopy findings included elongated, exfoliating superficial epithelial cells; brightly reflective material deposition within the basal epithelial cells; prominent, thickened subbasal nerves; structural changes in subbasal nerve fibers; pronounced reflectivity and irregular arrangement of stromal keratocytes; structurally abnormal anterior stromal keratocyte nuclei; folds in the anterior, mid, and posterior stroma; folds in Descemet's membrane; pleomorphism and enlargement of endothelial cells; and endothelial guttata. No such abnormal findings were present in the control group. There were significant differences between the two groups in terms of the mean basal epithelial, anterior and posterior stromal keratocyte densities, the mean basal epithelial cell area, and the mean endothelial cell hexagonality percentages. CONCLUSIONS: : Quantitative and qualitative structural changes were observed in all corneal layers in eyes with keratoconus by using slit-scanning confocal microscopy. The changes at all levels were more prominent in eyes with severe keratoconus. This noninvasive in vivo technique may prove to be useful in the diagnosis and follow-up of keratoconus and in the understanding of its pathophysiology.

Adolescent↗
PubMed2006

EMMPRIN and MMP-1 in keratoconus.

PURPOSE: This study was conducted to determine the eventual presence and activity of EMMPRIN (extracellular matrix metalloproteinase inducer CD147) and interstitial collagenase MMP-1 in the cornea of keratoconus patients and their eventual interrelationship. MMP-1 was chosen because it is able to degrade fibrillar corneal collagens type I and III and might therefore play a role in stromal thinning in keratoconus. METHODS: Immunohistochemical labeling of EMMPRIN and MMP-1 in relation to histopathological changes in 5 keratoconus patients and 5 matched healthy controls was investigated. RESULTS: Relatively strong EMMPRIN expression was found in normal corneal epithelial cells, but moderate expression was also found in stroma. In keratoconus, EMMPRIN was found in all layers of cornea, especially in histopathologically altered areas. In normal cornea, MMP-1 staining was weak and restricted to epithelial cells. In keratoconus, MMP-1 expression was slightly augmented in epithelial cells and also appeared locally in a scattered manner in the stroma. The distribution of MMP-1 did not totally overlap with that of histologically apparent corneal damage and EMMPRIN expression. CONCLUSIONS: Both EMMPRIN and MMP-1 are upregulated in keratoconus, but MMP-1 may not be the only tissue destructive MMP upregulated by EMMPRIN as only EMMPRIN expression correlated topologically very well with corneal damage.

Basigin↗
PubMed2006

Crosslinking treatment of progressive keratoconus: new hope.

PURPOSE OF REVIEW: A new method has been introduced for the treatment of progressive keratoconus using collagen crosslinking by the photosensitzer riboflavin and ultraviolet A-light. Biomechanical measurements have shown an impressive increase in corneal rigidity of 328.9% in human corneas after crosslinking. RECENT FINDINGS: The 3 and 5-year results of the Dresden clinical study have shown that in all treated 60 eyes the progression of keratoconus was at least stopped ('freezing'). In 31 eyes there also was a slight reversal and flattening of the keratoconus by up to 2.87 diopters. Best corrected visual acuity improved slightly by 1.4 lines. So far, over 150 keratoconus patients have received crosslinking treatment in Dresden. Laboratory studies have revealed that the maximum effect of the treatment is in the anterior 300 mum of the cornea. As for the corneal endothelium, a cytotoxic level for endothelium was found to be 0.36 mW/cm which would be reached in human corneas with a stromal thickness of less than 400 mum. SUMMARY: Collagen crosslinking by the photosensitzer riboflavin and ultraviolet A-light is an effective means for stabilizing the cornea in keratoconus. Collagen crosslinking might become the standard therapy for progressive keratoconus in the future diminishing significantly the need for corneal transplantation. Preoperative pachymetry and individual control of the ultraviolet A-irradiance before each treatment are mandatory. The treatment parameters must not be varied.

Animals↗
PubMed1986

Increase in type I and type IV collagenolytic activity in primary cultures of keratoconus cornea.

The collagenolytic activities were assayed in fibroblast cultures established from ten keratoconus and six control corneal explants. The assays included those for both type I and type IV collagenase. The amount of free, directly assayable type I collagenase was highly increased in the media of keratoconus primary cell cultures. Also the activity of type IV collagenase was increased significantly in these cultures but was detectable only after proteolytic activation. The total hydroxyproline content of keratoconus corneas was decreased when compared to controls. However the activity of the prolyl-4-hydroxylase, reflecting the biosynthesis of collagen, was higher in the keratoconus corneal tissue, either expressed per DNA, soluble protein or hydroxyproline content of corneas. The enhancement in collagenolytic processes could explain the pathological tissue destruction in keratoconus corneas and this enhancement is maintained still in primary cultures of keratoconus corneal fibroblasts.

Adolescent↗
PubMed2005

Incidence and severity of keratoconus in Asir province, Saudi Arabia.

AIM: To assess the incidence and associated signs and symptoms of patients with keratoconus in Asir Province, Saudi Arabia. METHODS: 125 new keratoconus patients (51 male, 74 female; mean age 18.5 (SD 3.8) years; range 8--28 years) were recruited from referrals to the department of ophthalmology, Asir Central Hospital, over a 1 year period. Age, visual acuity, and keratometry were recorded along with clinical signs and symptoms. RESULTS: The incidence of keratoconus in Asir Province is 20 cases per 100,000 population. Also, the disease severity is high, as indicated by an early mean age (17.7 (3.6) years) with advanced stage keratoconus. Visual acuity, with either spectacles or rigid contact lenses, was 6/12 or better in 98% of eyes measured. Just over half (56%) of patients had atopic ocular disease. 16% of patients had a positive family history of the disease and 16% had atopic dermatitis (eczema and/or vitiligo). CONCLUSION: The incidence and severity of keratoconus in Asir Province, Saudi Arabia, is high with an early onset and more rapid progress to the severe disease stage at a young age. This might reflect the influence of genetic and/or environmental factor(s) in the aetiology of keratoconus.

Adolescent↗