SEARCH · PubMed Health

Results for “Keratoconus”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed1975

Keratoconus and the Ehlers-Danlos syndrome: a new aspect of keratoconus.

Hypermobility of the joints is a frequent finding in patients who have keratoconus. Twenty-two of 44 patients (50%) presenting in 1973 were found to have hypermobility of joints (mainly Ehlers-Danlos syndrome II or mitis type). The significance of this finding is discussed in relation to biochemical defects recently found in corneas with keratoconus. The hypothesis is presented that keratoconus is often a part of a generalized heritable disorder of connective tissue due to a biochemical defect causing a weakness in its structure.

Adolescent↗

PubMed1992

Synchrotron x-ray diffraction studies of keratoconus corneal stroma.

The aim of this study was to determine any differences in the collagen molecular and fibrillar packing, or the arrangement of the proteoglycans along the fibril axis, in the stroma of keratoconus and control corneas. High and low-angle x-ray diffraction patterns from the fibrillar and molecular packing of collagen in keratoconus and control corneas were obtained using a synchrotron radiation source. The results indicate no difference in interfibrillar spacing between keratoconus and control corneas at normal physiological hydration, or over a range of hydrations (H = 1-11). This unambiguously demonstrates that the thinning of the stroma that occurs in keratoconus is not a result of closer packing of the collagen fibrils in the stroma. Intermolecular spacings were shown to be significantly (P less than 0.001) lower in keratoconus corneas at normal physiological hydration and over a range of hydrations (H = 1-11). Meridional patterns from the axial distribution of electron density along the collagen fibrils were obtained from untreated control and keratoconus corneas and from the corneas after their proteoglycans were stained with cupromeronic blue. Analysis of the integrated intensities of the first nine orders of these reflections show there is a difference in the staining behavior of collagen-associated proteoglycans in control and keratoconus corneas. Determination of the electron density vectors along the collagen fibrils of cupromeronic blue-stained corneas by the use of Patterson functions indicates that the keratoconus corneal stroma has a specific, ordered proteoglycan that is present in lower numbers along the collagen fibrils, and that it stains less with cupromeronic blue or is in a more disordered arrangement than in the controls.

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↗

PubMed1979

The synthesis of glycosaminoglycans by cultures of corneal stromal cells from patients with keratoconus.

Keratoconus is a disease that results in thinning and ectasia of the central cornea. Cultures of corneal stromal cells from patients with keratoconus were established and the synthesis of glycosaminoglycans compared with the synthesis of glycosaminoglycans by normal human corneal stromal cells in culture. Keratoconus and normal control cell cultures were incubated with sodium [(35)S]sulfate and [(3)H]glucosamine for 4 h. After incubation, the labeled glycosaminoglycans were isolated from the medium fractions and cells. Keratoconus and normal control cultures synthesized similar amounts of sulfated glycosaminoglycans independent of the age of donors and(or) the number of subcultures. In contrast to normal control cultures, most of the newly synthesized glycosaminoglycans produced by keratoconus cells were found in the growth medium and much less were in the cell layer. Treatment with glycosaminoglycan-degrading enzymes followed by paper chromatography showed that keratoconus cells, as normal control cells, produced hyaluronic acid and various sulfated glycosaminoglycans. The production of cell layer-related heparan sulfate was markedly reduced in keratoconus cultures. Because heparan sulfate has been shown to be associated with cell surfaces, the decreased heparan sulfate content could reflect changes at this location.

Adolescent↗

PubMed1978

Keratoconus and atopic diseases.

In a survey of 162 keratoconus patients, we set out to investigate individual conditions, such as asthma, hay fever, connective tissue syndromes, and eye rubbing, and to determine their relationship of keratoconus. It was found that the prevalence of asthma rises from 0.4% to 1% in the control group to 17.9% in the keratoconus group, or an eighteenfold increase. In addition, the incidence of hay fever in keratoconus patients was found to be 35.7%. As multifactorial disorders, keratoconus and asthma may share some of the multiple genes necessary for the expression of the disorder. Previous findings of excessive eye rubbing in keratoconus patients were confirmed in this study. Finally, we found that the incidence of connective tissue disorders associated with keratoconus was negligible.

Asthma↗

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↗

PubMed1992

Altered lectin binding sites in keratoconus corneas.

We investigated the glycoconjugates in frozen sections of keratoconus corneas, using a panel of 12 biotin- or fluorescein isothiocyanate-labeled lectins. No differences between the lectin binding sites of the epithelium, endothelium and Descemet's membrane of normal and keratoconus corneas could be observed. However, in contrast to normal corneas, intense staining with peanut agglutinin (PNA) could be detected at breaks in Bowman's layer, in scar tissue and in the adjacent stroma. Furthermore, in the majority of cases binding sites for Phaseolus vulgaris erythroagglutinin (PHA-E) and increased staining with Ricinus communis agglutinin I (RCA-I) and Lens culinaris agglutinin (LCA) could also be detected in ruptures in Bowman's layer and in scar tissue. These data suggest that the scarred regions of the anterior stroma in keratoconus corneas may contain oligosaccharides with terminal D-galactose (beta 1-3)-D-N-acetylgalactosamine disaccharides (recognized by PNA), increased amounts of glycoconjugates with terminal beta-galactose residues (recognized by RCA-I), increased amounts of glycoconjugates with glucose/mannose residues (recognized by LCA), and finally, biantennary complex-type glycopeptides containing two outer galactose residues and a residue of N-acetylglucosamine (recognized by PHA-E). Since corneal scars due to causes other than keratoconus revealed lectin binding sites (particularly for PNA and to a lesser extent also for PHA-E, LCA and RCA-I) similar to those seen in scar tissue of keratoconus corneas, we conclude that it is mainly scar formation that may be responsible for the altered lectin binding sites in keratoconus.

Adolescent↗

PubMed1992

Axial length in keratoconus.

Axial length is a major determinant of ocular refractive power that has not been well established for keratoconus eyes. The purpose of this study was to establish the mean and range of axial length among both keratoconus eyes with no previous surgery and postkeratoplasty keratoconus eyes, and to determine if there is a significant reduction of axial length following variations in surgical techniques in penetrating keratoplasty. The axial length of 157 keratoconus eyes with no previous surgery was measured using applanation ultrasonography. The mean axial length measurement was 24.39 (+/- 1.13 mm), with a range of 21.82-28.69 mm. The axial length of 66 postkeratoplasty keratoconus eyes was similarly measured. The mean axial length measurement was 24.10 (+/- 1.22 mm), with a range of 21.83-26.87 mm. These values are not significantly different from the axial length mean and range found among emmetropic eyes. A significant shortening of the axial length (F = 5.2, p = 0.04) was obtained in the postoperative penetrating keratoplasty eye if the donor trephine was 0.3 mm smaller in diameter than the recipient trephine. The axial length of individual keratoconus eyes is a major factor in determining postoperative refractive error. It therefore becomes important when considering variations in surgical procedures to reduce postoperative myopia.

Analysis of Variance↗

PubMed1976

[Keratoconus and contact lenses (author's transl)].

This work is a survey of 82 cases of keratoconus which have been followed up for 1 to 12 years. Among them only 66 were fitted with contact lenses. The contra-indications for them are: 1. a better visual acuity with spectacles than with contact lenses, 2. advanced cases (4th degree of Amsler) whose fitting is impossible, 3. unilateral keratoconus, 4. associated diseases such as trachomatous pannus, allergic kerato-conjunctivitis. Hard corneal lenses are now in use in most of the cases. Scleral lenses are much less used than they were 10 years ago, owing probably to the great improvement of the corneal lenses during this time. These hard corneal lenses have a short Ro (4 to 7 mm), an overall diameter between 8 and 11 mm, and an optic diameter of 5 mm. They are fitted under fluorescein control. The mobility must be good too. One case was fitted with soft lenses. The visual acuity is good and so is the tolerance: 80% of the patients wear their lenses 10 hours a day or more. Contact lenses do not affect the progression of keratoconus thus finally a keratoplasty must be performed in many cases. After the operation a contact lens is very often necessary, but its daily wearing time must be divided by two, to avoid corneal neo-vascularisation. Soft corneal lenses may be used in some cases of keratoconus. They are indicated when the hard lenses are no longer tolerated and before a keratoplasty. The base curves of these soft lenses are not related to the radii of the conic cornea. In most of the cases they are between 7.50 and 8.60 mm. The diameter is large: 14 or 15 mm. The lenses must not move too much: 1 mm up or down when the patient blinks. The edge of the lens must not depress the bulbar conjunctiva and there must be no air bubble under the lens. In many cases a cylindrical spectacle lens is necessary to obtain a good visual acuity. Some authors prefer to fit a hard corneal lens over the soft one: this is the "piggy back" method. Sometimes keratoconus has appeared in patients already fitted during several years to correct a myopic astigmatism. It is not clear whether these keratoconus have been produced or not be the contact lenses.

Adolescent↗

PubMed1992

Computer-assisted corneal topography in parents of patients with keratoconus.

Recently developed computer-assisted devices allow detection of early topographic abnormalities of the cornea, including mild or abortive forms of keratoconus. To address the possibility that keratoconus is an inherited condition, we examined both parents of 12 randomly selected patients with keratoconus whom we were following up. Of the 12 sets of parents, at least one parent in each of seven sets had abnormal corneal characteristics. Using previously determined quantitative criteria (eg, central corneal steepening, greater steepening inferiorly than superiorly, and asymmetry between the two eyes) to distinguish normal from keratoconic corneas we found evidence of keratoconus in at least one of the 14 parents. The remaining five patients had parents with normal corneal characteristics. These data support the hypothesis that keratoconus is sometimes an inherited condition, exhibiting, at least in some families, autosomal dominant inheritance with incomplete penetrance.

Adult↗

PubMed1976

Aetiology of keratoconus.

Keratoconus has a common association with atopic conditions. Most keratoconus patients rub their eyes excessively. Eye-rubbing is considered the dominant aetiological factor in two-thirds of patients with keratoconus who progress to contact lens wear. A classification of keratoconus based on the dominant aetiological factors is proposed. No significant psychoneurotic factor was found in the keratoconus patients compared with patients in the control group.

Adult↗

PubMed1977

Keratoconus and coexisting atopic disease.

The association of keratoconus and atopic disease has been reported on several occasions but the only controlled clinical study that has so far been published found no evidence to support this view. Since it is now known that atopy is often associated with changes in various immunoglobulins, particularly IgE, it was considered desirable to determine the immunological profiles of a large series of keratoconus cases in order to seek evidence for coexistence of the two conditions in one individual. In this study of 182 cases of keratoconus a definite history of atopy was found in 35% compared with 12% in the matched control group. The serum IgE was significantly raised (P less than 0.001) in keratoconus and markedly so in those cases with associated atopic disease. Serum levels of IgG and IgM were also raised, but contrary to the findings of other observers IgA levels were normal. These findings suggest that atopic traits are more common in patients with keratoconus than in general ophthalmic patients.

Female↗

PubMed1992

Life expectancy in keratoconus.

It is observed that few patients over the age of 60 regularly attend the keratoconus clinic at Moorfields Eye Hospital. The hypothesis that patients with keratoconus have a shorter life expectancy owing to underlying connective tissue related disease was tested. From patient records a sample of 337 keratoconus patients aged at least 40 years by 1991 were identified, of which 279 were living, 13 were deceased, and 45 were untraceable. The mortality rate for keratoconus patients was compared with that of the general population using actuarial English life tables. Results show no significant difference between the general population mortality rate and that of the keratoconus sample even with adjustment for social class. Possible explanations for the non-attendance of older patients are discussed.

Adult↗

PubMed1992

Collagenolytic/gelatinolytic metalloproteinases in normal and keratoconus corneas.

Cells of keratoconus corneas have been reported to produce higher levels of collagenolytic/gelatinolytic enzymatic activities than do cells of normal corneas. The current study investigates the contribution of 1) specific enzyme gene products, and 2) the degree to which these proteins are present in the activated forms, to the increased enzymatic activities. We demonstrate that two neutral gelatinolytic enzymes, a 66/59 kD form and a 92 kD form, can be directly extracted from both normal and keratoconus corneas. These enzymes are identified as the pro- and activated forms of MMP-2 and as the pro-form of MMP-9, specific members of the matrix metalloproteinase family. Normal and keratoconus corneas show no significant differences in amounts or types of extractable neutral gelatinases, nor in the amounts or types that they synthesize in culture. Furthermore, in both the normal and keratoconus corneas, gelatinases are found primarily in the inactive form. These studies suggest the possible importance of changes in proteinase inhibitor levels to the characteristic biochemical features of keratoconus corneas.

Adolescent↗

PubMed1992

Myopia following penetrating keratoplasty for keratoconus.

The frequent occurrence of spherical myopia after penetrating keratoplasty for keratoconus is partly the result of the excessive dioptric power of the grafted cornea which occurs when the diameter selected for the donor button is greater than the diameter of the host incision. This excessive power could be reduced by eliminating disparity between the diameters of the graft and host. To determine what proportion of the myopia in these eyes would persist as a result of axial myopia the axial lengths of 60 patients grafted for keratoconus and 25 emmetropic controls were compared. A keratometry, objective refraction, and contact probe ultrasonic biometry were performed on all eyes. A comparison of the results with a representational schematic eye indicated that the mean spherical refractive error of the grafted keratoconic eyes (-4.83 dioptres) was the combined effect of steepness of the corneal graft (mean radius of curvature 7.46 mm) and an abnormally great axial length (mean 24.84 mm). The increased axial length was mainly the result of elongation of the posterior segment of the globe with a small contribution from an increased anterior chamber depth. Though axial myopia is common in keratoconus, a further study of 70 keratoconic eyes that had not been grafted showed no statistically significant correlation between the posterior segment length and the severity of corneal ectasia. These data suggest that even if excessive corneal power is eliminated after penetrating keratoplasty for keratoconus the associated axial myopia would still produce a mean spherical refractive error of at least -2.8 dioptres.

Adult↗

PubMed1979

Lamellar keratoplasty in the treatment of keratoconus: conectomy.

The first 52 eyes of 48 keratoconus patients treated with conectomy and followed for a period of time ranging from 6 to 48 months are included in this study. An average change in the refractive power of the cornea of 10.3 diopters was found after conectomy. The mode for the best corrected visual acuity was 20/30, and the average corneal astigmatism was 3.00 diopters. Photodiagnosis evaluation, microsurgical techniques and instrumentation monofilament nylon, use of the donor cornea minus the endothelium and improved postoperative refractive techniques have combined to make conectomy a reliable and successful form of treatment in keratoconus patients. Both penetrating keratoplasty and conectomy techniques have proven to be successful in the surgical management of keratoconus, and it is the surgeon's responsibility to determine the appropriate approach for the keratoconus patient. Both of these procedures will continue to be refined as ophthalmic technology and surgical skills improve.

Astigmatism↗

PubMed1977

[Genetic aspects of keratoconus (author's transl)].

The diverging views expressed in the literature on the inheritance of keratoconus gave us cause to examine the genetic relationships in 304 cases of keratoconus from our own clinic material. In the 22 cases (19 families) where two or more family members were affected, the genetic relationships generally indicated a multifactorial mode of inheritance, although isolated dominant or recessive variants could not be excluded. The assumption of a multifactorial inheritance is further supported by the occurrence of keratoconus in connection with various syndromes, as well as the fact that keratoconus does not only express itself in sharply defined stages, but also occurs in all possible degrees, from almost normal to the extreme.

Chromosome Aberrations↗

PubMed1992

Radial keratotomy in a patient with keratoconus.

A 30-year-old white male with keratoconus had uneventful radial keratotomy in his right eye. Although a good initial response was obtained with total correction of myopia and astigmatism, by 18 months postoperatively the entire result had regressed and the patient demonstrated reformation of the cone and regression to high myopia. Scarring occurred in the three inferior cuts overlying the cone. Cuts on the horizontal axis, and superiorly (above the cone), had a normal appearance with normal wound healing. Because of the nature of the wound healing overlying the portion of the cornea affected by the keratoconus and because of the total regression of effect, radial keratotomy in patients with keratoconus does not appear to be an effective modality.

Adult↗