[Acute keratoconus as a complication of keratoconus].
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Acute Disease↗
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[Some considerations on the histopathogenesis of keratoconus: apropos of a possible association of disseminated leukoencephalomyelitis, retrobulbar optic neuritis and keratoconus].
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Adult↗
[Determination of refraction after keratoplasty in keratoconus cases; is a keratoconus recurrence possible?].
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Corneal Transplantation↗
Is there an association between diabetes and keratoconus?
PURPOSE: To examine whether there is an association between diabetes mellitus (DM) and keratoconus. DESIGN: A retrospective comparison of the proportion of keratoconus patients with DM versus the proportion of overall patients with DM, and a retrospective cross-sectional study of a cohort consisting of all diabetic keratoconus patients and randomly selected keratoconus patients without DM at a single center. PARTICIPANTS: Patients seen at the Wilmer Eye Institute from January 1, 1995, through March 18, 2004. METHODS: Review of billing data and clinic charts. Eligibility criteria for the cross-sectional study were 1 or more clinic visits, lack of other eye pathologic features (excluding cataract and diabetic retinopathy), and absence of bilateral penetrating keratoplasty (PK) at presentation. Application of novel keratoconus severity index was based on best-corrected visual acuity (BCVA) in the better eye at last visit and defined as: grade 1 (least severe), spectacle wear with BCVA of 20/40 or better; grade 2 (intermediate), spectacle wear with BCVA worse than 20/40 or rigid gas permeable lens wear; grade 3 (most severe), PK. MAIN OUTCOME MEASURES: Prevalence of DM in keratoconus patients and those without keratoconus, odds ratio of having DM on a diagnosis of more severe keratoconus, and prevalence of DM in keratoconus patients and those without keratoconus who underwent corneal transplantation. RESULTS: There was no difference in the prevalence of DM in keratoconus patients and those without keratoconus, and there was no difference in the prevalence of DM in keratoconus patients and those without keratoconus undergoing PK. However, our results suggest a negative association between DM and severity of keratoconus (P = 0.03, Fisher exact test). The odds of being in the most severe group as opposed to the least severe group were lower in DM patients than in those without DM (P = 0.01; odds ratio [OR] = 0.20; 95% confidence interval [CI], 0.05-0.70). Compared with those without DM, DM patients also had lower odds of being in the intermediate group than in the least severe group (P = 0.02; OR = 0.25; 95% CI, 0.08-0.80). After adjustment for age, gender, and race, these differences remained statistically significant. CONCLUSIONS: We found that DM is not associated with a diagnosis of keratoconus, but having DM decreases the odds of having more severe keratoconus.
Adolescent↗
Unilateral keratoconus. Incidence and quantitative topographic analysis.
OBJECTIVE: This study was designed to determine the incidence of unilaterality in a population of patients with clinical keratoconus and to compare quantitative descriptors of topography between affected corneas from patients with unilateral keratoconus and corneas of patients with bilateral disease. DESIGN: Retrospective clinical study with new evaluation of some patients. PARTICIPANTS: One hundred sixty-four patients from the University of Texas South-western Medical Center and Wills Eye Hospital who were diagnosed to have moderate-to-advanced keratoconus on the basis of characteristic topographic patterns associated with corneal thinning. INTERVENTION: Corneal topography was evaluated in both eyes of each patient. MAIN OUTCOME MEASURES: Quantitative descriptors of corneal topography were compared between 5 affected corneas of patients with unilateral keratoconus (combined cases from University of Texas Southwestern, LSU Eye Center, and Wills Eye Hospital) and 15 corneas of patients with moderate-to-advanced bilateral keratoconus (1 cornea from each patient). Indices selected for statistical analysis were the Keratoconus Predication Index (KPI), Surface Asymmetry Index (SAI), and Surface Regularity Index (SRI). RESULTS: Three (1.83%) of 164 patients with moderate-to-advanced keratoconus had no topographic evidence of keratoconus in the opposite eye. There were no statistically significant differences in KPI, SRI, or SAI values between the affected corneas of patients with unilateral and bilateral keratoconus. Over a period of 4 years of observation, signs of keratoconus in the previously normal eye developed in a patient with unilateral keratoconus. CONCLUSIONS: The authors found no differences in the quantitative descriptors of corneal topography between corneas with keratoconus from unilateral and bilateral cases. The authors' results suggest that the incidence of "unilateral" keratoconus is very low. Patients initially diagnosed with unilateral keratoconus, if observed for a sufficient period, commonly had signs of keratoconus develop in the opposite eye. The possibility that all cases of unilateral keratoconus may eventually become bilateral cannot be excluded. Therefore, refractive surgical procedures should not be performed on apparently normal corneas when keratoconus is detected in the opposite eye.
Cornea↗
Personality in keratoconus in a sample of patients derived from the internet.
PURPOSE: Keratoconus is a corneal disease that manifests itself in young adulthood and decreases vision. Anecdotally, keratoconus patients are commonly described as having unusual personality characteristics; however, previous researchers have not been able to define a unique keratoconus personality profile. We sought to better define the personality of patients with keratoconus. METHODS: The Millon Behavioral Health Inventory (MBHI) is a psychological instrument designed for use with physically ill patients to assess factors relevant to their medical care. The MBHI may aid in the evaluation of keratoconus patients and provide information relevant to the doctor-patient relationship. Patients with keratoconus were recruited through the World Wide Web. Surveys were conducted by mail, with all responses returned anonymously. One hundred fifty-three keratoconus patients were compared with the MBHI age-matched norms, generated from medical and nonmedical samples of adults. Subgroups of keratoconus patients were compared based on their self-reported rating of the daily burden of keratoconus. RESULTS: Keratoconus patients scored significantly lower (chi, P <0.05) compared with the normative population on the respectful coping style scale, and their scores were not significantly associated with a history of penetrating keratoplasty or their rating of the effect of keratoconus on their lives. This suggests that keratoconus patients are less respectful of practitioners, uncooperative, and noncompliant with treatment plans. Practitioners may look unfavorably on patients who exhibit these characteristics. This would also explain why the clinical perception of keratoconus patients persists, but other personality inventories have not defined a distinct keratoconus profile. CONCLUSIONS: These data from the MBHI, showing that keratoconus patients score lower on the respectful coping style scale, may explain eye care practitioners' perceptions about these patients' personality characteristics.
Adolescent↗
Corneal thickness indices discriminate between keratoconus and contact lens-induced corneal thinning.
PURPOSE: To evaluate two indices generated from measurements obtained from the Orbscan Corneal Topography System (CTS; Orbscan, Inc., Salt Lake City, UT) to distinguish contact lens-induced corneal thinning from keratoconus. The corneal thickness index (CTI) was used to compare central and peripheral corneal thicknesses. The discriminant function 1 (DF1) was used to evaluate corneal thickness and central keratometry measurements. DESIGN: Case-control study. PARTICIPANTS: Fifty-four patients with keratoconus or suspected keratoconus, 75 contact lens wearers, and 67 normal controls. METHODS: In the initial model-building study, the central and peripheral corneal thickness and central keratometry (K) readings were evaluated retrospectively in 1 eye each of 23 patients with clinically defined keratoconus, 31 contact lens wearers, and 43 normal patients with the Orbscan CTS. Two methods (corneal thickness index [CTI] and discriminant function 1 [DF1]) were evaluated for their efficacy in classifying these conditions. The CTI was designed as the ratio between mean peripheral corneal thickness and the central corneal thickness, and the formula for the DF1 was as follows: DF1 = 0.044 x central thickness - 0.030 x nasal thickness + 9.210 x CTI - 0.157 x Max K - 8.9. In the subsequent validation study, the results were verified in a separate group of keratoconus patients (n = 23), keratoconus suspects (n = 8), contact lens wearers (n = 44), and normal patients (n = 24). MAIN OUTCOME MEASURES: Corneal thickness index (CTI) and discriminant function 1 (DF1). RESULTS: The corneal thickness in patients with keratoconus and contact lens wearers was significantly thinner than that of normal eyes in the central and eight peripheral measured sites (P < 0.001). The corneal thickness in contact lens wearers was significantly greater than in keratoconus patients in the inferotemporal (P = 0.013), inferior (P = 0.003), and central (P < 0.001) sites and was borderline different in the superior site (P = 0.07). In the model-building study, the CTI in keratoconus patients (1.28 +/- 0.15) was significantly greater than in contact lens-wearing (1.10 +/- 0.03; P < 0.001) and normal eyes (1.09 +/- 0.04; P < 0.001). The CTI was not significantly different between normal and contact lens-wearing eyes (P = 0.68). A CTI value of 1.16 or more showed a sensitivity of 91% and specificity of 99% in differentiating keratoconus from contact lens-wearing and normal eyes. The DF1 value was significantly lower in keratoconic eyes than in contact lens-wearing and normal eyes. A DF1 value of -0.6 showed a 96% sensitivity and 99% specificity in differentiating keratoconus from contact lens-wearing and normal eyes. Similar results were obtained in the validation study. CONCLUSIONS: Corneal thickness indices generated from the Orbscan CTS appear to be sensitive and specific for diagnosing keratoconus. These indices may prove to be clinically useful parameters for distinguishing keratoconus from contact lens-induced corneal thinning.
Adult↗
Contrast and glare testing in keratoconus and after penetrating keratoplasty.
AIM: To compare the performance of keratoconus, penetrating keratoplasty (PK), and control subjects on clinical tests of contrast and glare vision, to determine whether differences in vision were independent of visual acuity (VA), and thereby establish which vision tests are the most useful for outcome studies of PK for keratoconus. METHODS: All PK subjects had keratoconus before grafting and no subjects had any other eye disease. The keratoconus (n = 11, age 35.0 (SD 11.1) years), forme fruste keratoconus (n = 6, 33.0 (13.0)), PK (n = 21, 41.2 (7.9)), and control (n = 24, 33.7 (8.6)) groups were similar in age. Vision testing, conducted with optimal refractive correction in place, included low contrast visual acuity (LCVA) and Pelli-Robson contrast sensitivity (PRCS) both with and without glare, as well as VA. RESULTS: Normal subjects saw better than PK subjects who in turn saw better than keratoconus subjects on all raw measures. However, when adjusted for VA, the normal group only saw significantly better than the keratoconus group on LCVA (low contrast loss 0.05 (0.04) v 0.15 (0.12), F(2,48) = 6.16; p<0.01, post hoc Sheffé p<0.05), and the decrements to glare were no worse than for normals. The forme fruste keratoconus group were indistinguishable from normals on all measures. CONCLUSIONS: PK subjects have superior vision to keratoconus subjects, but not as good as normal subjects. Including mild keratoconus subjects within a keratoconus group could confound these differences in vision. While VA is an excellent test for comparing normal, keratoconus and PK groups, additional information can be provided by LCVA and PRCS, but not by glare testing. Outcomes research into keratoconus management should include a measure in the contrast domain.
Adult↗
Automated topographic screening for keratoconus in refractive surgery candidates.
PURPOSE: We evaluated an automated corneal topography classification system developed as an adjuvant for screening patients prior to keratorefractive surgery. We screened for patterns suspicious for keratoconus by applying the system to the analysis of a series of patients who presented for evaluation for surgical correction of myopia. METHODS: Both eyes of 53 consecutive patients who were included in a previously reported prospective study were evaluated using the Expert System classification algorithm. This quantitative classification system incorporating eight indices was applied to the videokeratoscopic data from each patient to divide the topographic patterns into keratoconus and non-keratoconus groups. The group assignment of the Expert System classifier was compared with the clinical diagnosis of keratoconus versus non-keratoconus based on the topographic pattern and objective biomicroscopy signs. RESULTS: The Expert System classified eight of the videokeratographs as keratoconus. All five corneas that had clinical evidence of keratoconus were classified as such by the Expert System (sensitivity 100%). The other three corneas that were classified as keratoconus were of patients who wore rigid contact lenses and had pseudo-keratoconus topographic patterns, without other clinical signs of keratoconus. The specificity with which the Expert System detected normal corneas was 97% (98/101). CONCLUSIONS: Evaluation of the videokeratographic data with computerized algorithms designed to detect keratoconus may aid preoperative evaluation and facilitate distinction between keratoconus and some keratoconus-like topographic patterns.
Algorithms↗
The effect of vernal keratoconjunctivitis on clinical outcomes of penetrating keratoplasty for keratoconus.
BACKGROUND: Although good visual results and low complication rates are commonly reported following penetrating keratoplasty (PKP) in eyes with keratoconus, the outcome of PKP in eyes with keratoconus and concomitant vernal keratoconjunctivitis (VKC) has not been well documented. We performed a study to compare the outcome and relative risk factors of PKP for keratoconus with and withoutVKC. METHODS: Review of the medical records of all patients who underwent PKP for keratoconus at a university-affiliated hospital in Izmir,Turkey, from Nov. 1, 1991, to Jan. 31, 2002. Only eyes that had been followed for at least 18 months postoperatively were included in the study. Twenty-three eyes of 19 patients (14 males and 5 females) had keratoconus with VKC, and 65 eyes of 57 patients (33 males and 24 females) had keratoconus alone. We compared clinical outcomes and complications between the two groups. RESULTS: The mean length of follow-up was 34.0 months (standard deviation [SD] 16.3 months) (range 18-67 months) in the eyes with comitant VKC and 41.0 (SD 19.8) months (range 18-98 months) in the eyes with keratoconus alone. During the follow-up period, 2.35 (SD 1.90) suture-removal sessions for loosened sutures were performed in the eyes with VKC, compared with 1.34 (SD 1.69) sessions in the eyes with keratoconus alone (p = 0.016). Steroid-induced glaucoma developed in two eyes (8.7%) in theVKC group and in three eyes (4.6%) in the keratoconus-alone group (p = 0.603); the rates of steroid-induced cataract were four (17.4%) and two (3.1%) respectively (p = 0.038). The average final best-corrected visual acuity was 20/22 (range 20/50 to 20/20) in the eyes with VKC and 20/23 (range 20/60 to 20/20) in the eyes with keratoconus alone. INTERPRETATION: The clinical outcome of PKP in eyes with keratoconus and VKC is comparable to that in eyes with keratoconus alone. However, because complications such as prematurely loosened sutures and steroid-induced cataract are more common in the coexistence of VKC, closer monitoring is necessary in these cases.
Adolescent↗
Lectin binding in normal, scarred, and keratoconus corneas.
PURPOSE: Keratoconus is characterized by central thinning and an increased curvature of cornea. Scarring of cornea accompanies the disease as it proceeds, and the ultimate treatment is keratoplasty. The pathogenesis of keratoconus is still unknown, and therefore we studied normal, keratoconus, and scarred corneas by a panel of lectin conjugates. METHODS: The following lectin conjugates were used: concanavalin A (Con A), Dolichos biflorus agglutinin (DBA), peanut agglutinin (PNA), Ulex europaeus agglutinin (UEA-I), wheat-germ agglutinin (WGA), Helix aspersa agglutinin (HAA), Psophocarpus tetragonolobus agglutinin (PTA), soybean agglutinin (SBA), Griffonia simplicifolia agglutinin-I-B4 (GSA-I-B4), Ricinus communis agglutinin (RCA-I), and Lotus tetragonolobus agglutin (LTA) conjugates, differently recognizing saccharide residues in glycoconjugates. RESULTS: One of the keratoconus corneas was badly scarred, whereas no scars were seen on histopathologic examination in other keratoconus corneas. In all keratoconus corneas, discontinuities or breaks (defects) were seen in the Bowman's layer. DBA and HAA conjugates, both blood group A reactive, reacted with corneal and conjunctival epithelium, blood vessels, and endothelium in blood groups A and AB. The blood group B-reactive GSA-I-B4 conjugate reacted with corneal and conjunctival epithelium, blood vessels, and endothelium only in specimens with blood group B. The blood group O-reactive UEA-I conjugate revealed the apical epithelial cells and blood vessels in all blood groups, whereas LTA conjugate, also blood group O reactive, reacted with all structures in cornea and conjunctiva despite blood groups. HAA and DBA conjugates reacted with defects in keratoconus corneas, SBA and RCA-I conjugates with defect area in keratoconus and scar region in scarred corneas, and PNA and WGA conjugates with the scar region of scarred keratoconus and scarred corneas. No other differences in the binding of lectins between normal, scarred, and keratoconus corneas were seen. CONCLUSIONS: The results indicate that the blood group status influences lectin binding in cornea. Furthermore, the difference in lectin binding to defects in keratoconus corneas (HAA and DBA conjugates) and to scar regions in scarred corneas (PNA and WGA conjugates) suggests that the defects in keratoconus are not solely the results of scarring.
Adolescent↗
KISA% index: a quantitative videokeratography algorithm embodying minimal topographic criteria for diagnosing keratoconus.
PURPOSE: To formulate and test an algorithm using minimal topographic criteria for accurately diagnosing clinical keratoconus. SETTING: Subspecialty cornea practice and Keratoconus Genetic Research Project. METHODS: Both eyes of 86 keratoconic patients who had never worn contact lenses and 195 normal participants were studied with the TMS-1 videokeratoscope to evaluate the KISA% index, an algorithm that topographically quantifies the phenotypic features of keratoconus. The diagnostic efficacy of the KISA% index was compared with that of the modified Rabinowitz/McDonnell (K- and I-S values) and the Maeda/Klyce (KCI% and KPI) indices. The same indices were calculated for an additional 8 eyes with keratoconus-suspect topography and 12 eyes with early keratoconus. RESULTS: The mean KISA% was significantly greater in the keratoconus group (10,382%) than in the normal control group (20.44%) with minimal overlap. At a cutoff point for KISA% of 100, 280 of 281 participants (99.6%) were correctly classified. In contrast, the correct classification rate for the other indices were KCI%, 274 of 281 (97.5%); KPI, 249 of 281 (88.6%); K, 272 of 281 (96.8%); I-S, 269 of 281 (95.7%). Six of the 8 eyes with keratoconus-suspect topography had a KISA% between 60% and 100%, and 11 of the 12 eyes with early keratoconus had a KISA% greater than 100%. CONCLUSIONS: The KISA% index set at 100 was highly sensitive and specific for diagnosing keratoconus; a range of 60% to 100% may be useful for designating suspects. This index is more useful than any of the other currently available tools for classifying patients with keratoconus for computerized segregation analysis and for distinguishing eyes with keratoconus from normal eyes in topographic screening of refractive surgical candidates.
Algorithms↗
The immunohistochemical composition of corneal basement membrane in keratoconus.
PURPOSE: Keratoconus is a gradually progressing disease of unknown cause, characterized by central thinning, increased curvature, and finally scarring of the cornea. This causes myopia and astigmatism and the ultimate treatment is keratoplasty. We studied the composition of basement membranes (BMs) in normal, scarred and keratoconus corneas to find out possible changes specific for keratoconus. METHODS: Frozen sections of normal, scarred and keratoconus corneas were immunostained with various antibodies against basement membrane (BM) proteins and integrin beta 4. RESULTS: In the keratoconus corneas, we found discontinuities or defects in Bowman's layer, sometimes distorted stroma beneath the defects, and also thinning of the stroma. The results show that within the defects in keratoconus corneas, there is an expression of proteins that are not normally present in the corneal BM, i.e. collagen alpha 1/2 (IV) chains, and on the contrary, absence of the expression of some proteins, i.e. collagen alpha 5-6 (IV) chains that normally are continuously expressed in the corneal epithelial BM. In addition, either increased or decreased expression of laminin-1 (alpha 1 beta 1 gamma 1), laminin-5 (alpha 3 beta 3 gamma 2) and collagen type VII, depending on the keratoconus defect, was seen and the expression of integrin beta 4 was decreased. These findings seem to be specific for keratoconus, as they were not found in scarred corneas. CONCLUSIONS: The results show that the defects in BM and changes in the BM composition are involved in the pathogenesis of keratoconus. Furthermore, it seems that scarring alone does not explain the breaks in Bowman's layer and immunohistochemical changes seen in keratoconus. Therefore, we suggest that a process similar to wound healing, which is initiated by breaks in Bowman's layer, would largely contribute to the differences seen in keratoconus corneas.
Adult↗
Clinical detection of unilateral keratoconus.
PURPOSE: To determine the incidence of true unilateral keratoconus on the basis of computerised corneal topography in a group with clinically diagnosed unilateral keratoconus. METHODS: Retrospective review of 295 patients with keratoconus identified 51 patients with a provisional diagnosis of unilateral keratoconus. Thirty-one of these patients were re-examined clinically and 21 patients met the criteria for a clinical diagnosis of unilateral keratoconus. Computerised corneal topographic analysis (Tomey TMS) was then performed. RESULTS: In a group of 21 patients with clinically diagnosed unilateral keratoconus, computerised corneal topographic analysis identified 14 (67%) patients with bilateral keratoconus and seven (33%) patients with true unilateral keratoconus. Contact lens wear had no significant influence (P=0.76) on the topographical diagnosis of keratoconus in the clinically unaffected fellow eye. The estimated incidence of true unilateral keratoconus in the cohort of 295 patients was 4%. CONCLUSIONS: Computerised corneal topography improves sensitivity in detection of true unilateral keratoconus.
Adult↗
Keratocyte apoptosis associated with keratoconus.
Keratoconus is an ectatic corneal dystrophy associated with stromal thinning and disruption of Bowman's layer. The purpose of this study was to explore a possible association between keratocyte apoptosis and keratoconus. Keratocyte apoptosis was evaluated in corneas of patients with keratoconus, corneas of patients with stromal dystrophies, and normal donor corneas using the transferase-mediated dUTP-digoxigenin nick and labeling (TUNEL) assay. Keratocyte apoptosis was also studied in keratoconus and normal corneas using transmission electron microscopy. TUNEL-stained keratocytes were detected in 60% of corneas with keratoconus, but only 35% of corneas with stromal dystrophies (P =0.03). The number of TUNEL-positive keratocytes detected in the keratoconus, stromal dystrophy, and normal corneas was 7+/-1 (mean+/-standard error, range 0-20), 2+/-0. 8 (range 0-9), and 0+/-0 (range 0-0) TUNEL-positive cells per section, respectively. The differences between the keratoconus and the stromal dystrophy (P =0.0097) or the normal cornea (P =0.01) groups were statistically significant. The difference between the stromal dystrophy and normal cornea groups was not statistically significant (P =0.45). The stromal dystrophy group was included to account for surgery-associated keratocyte apoptosis. No TUNEL-stained keratocytes were detected in normal corneas. Cell morphologic changes consistent with apoptosis were detected by transmission electron microscopy (TEM) in keratocytes of keratoconus corneas, but not in keratocytes in normal corneas. Chronic keratocyte apoptosis associated with ongoing epithelial injury may link risk factors associated with keratoconus such as chronic eye rubbing, contact lens wear, or atopic eye disease. Similarly, increases that have been detected in several different degradative enzymes in keratoconus corneas could be associated with chronic keratocyte apoptosis and less than perfect control of release of intracellular contents.
Apoptosis↗
The expression of tenascin and fibronectin in keratoconus, scarred and normal human cornea.
BACKGROUND: The etiology and pathogenesis of keratoconus remain unclear, and therefore we decided to study the distribution of different isoforms of tenascin (Tn) and fibronectin (Fn) in normal human corneas and in those obtained from penetrating keratoplasty for keratoconus and corneal scarring. METHODS: Frozen sections of human cornea and conjunctiva were stained by immunohistochemical methods with a panel of monoclonal antibodies (MAbs) against different isoforms of Tn and Fn. RESULTS: In the normal human eye, Tn was found in the limbal and conjunctival basement membrane region, in the conjunctival blood vessels and at the junction of the cornea and sclera, but no immunoreaction was seen in the normal cornea. In the corneas from the keratoconus patients, a clear immunoreaction for Tn was seen in the defects of Bowman's membrane as well as in the distorted stroma beneath the defects. In some of the keratoconus corneas, basement membrane adjacent to the defects also showed reactivity for Tn, and in clinically and histologically scarred keratoconus corneas the scars expressed Tn. In the scarred corneas, only blood vessels in the posterior portion of the cornea showed immunoreactivity for Tn, while no Tn was noted in the scar area or in Bowman's membrane. No major differences were noticed in the reactivity of different MAbs against Tn isoforms. Fn, extradomain A Fn (EDA-Fn) and oncofetal Fn (onc-Fn) were found in the basement membrane of the central cornea of the normal eye. In keratoconus corneas, the defects and clinical and histological scars bound MAbs against Fn, EDA-Fn and onc-Fn, but in the scarred corneas no enhancement in the expression of Fns was noted. Extradomain B cellular Fn (EDB-Fn) was not expressed in any of the eyes studied. CONCLUSIONS: The results suggest that the anterior portion of the cornea is involved in the pathogenesis of keratoconus. Furthermore, it seems that the expression of Tn and Fns in the clinically scarred keratoconus corneas is due to a process in which both repairing and scar-forming mechanisms operate at the same time. However, the origin of the defects in Bowman's membrane seen in keratoconus still remains unclear. They may be minor scars due to the disease or primary defects in the process leading to keratoconus.
Adolescent↗
[Measuring intraocular pressure in keratoconus. Effect of the changed biomechanics].
BACKGROUND: Keratoconus is associated with changes in the corneal structure, such as defects of Bowman's layer, a decrease of corneal thickness etc. They result in alterations of some of the biomechanical parameters of the cornea, namely, rigidity and elasticity. The present study was performed to examine how impression tonometry and applanation tonometry for determination of intraocular pressure (IOP) are affected by the changed biomechanical parameters associated with keratoconus. PATIENTS AND METHODS: We examined 20 normal subjects (40 eyes) and 17 keratoconus patients (25 eyes). The corneal thickness was measured by ultrasound pachymetry in the corneal center. In the keratoconus patients, an additional measurement was made at the conus peak. The corneal curvature was determined using the TMS keratoscope. The IOP measurements were made with the Schiötz tonometer (10 g). For comparison, additional IOP measurements in the corneal center and, in the keratoconus group, on the conus peak were made with the applanation tonometer. RESULTS: The normal subjects had a central corneal thickness of 548 +/- 30 microns, compared to 505 +/- 42 microns in the corneal center and 425 +/- 41 microns on the conus peak in keratoconus patients. The average corneal curvature was 43.3 +/- 1.8 D in the normal subjects and 47.8 +/- 4.1 D in keratoconus patients. Applanation tonometry produced results on 11.33 +/- 1.43 mm Hg in the normal group (corneal center) compared to values of 12.00 +/- 2.55 mm Hg (corneal center) and 7.30 +/- 1.95 mm Hg (conus peak) in the keratoconus cohort. The coefficient of rigidity was 0.0236 +/- 0.0026 microliter-1 in the normal subjects, compared to 0.0173 +/- 0.0050 microliter-1 in the keratoconus patients. CONCLUSION: The morphological changes associated with keratoconus may cause tonometry errors.
Adult↗
Tear function and ocular surface changes in keratoconus.
PURPOSE: To describe the ocular surface disorder in patients with keratoconus. DESIGN: A prospective, case-controlled study. PARTICIPANTS: Seventy-five eyes of 38 patients with keratoconus seen at Uludag University School of Medicine, Department of Ophthalmology, from March 2000 through April 2001, and 80 eyes of 40 normal control subjects were studied. INTERVENTION: The subjects underwent routine ophthalmic examinations, corneal sensitivity measurements, Schirmer test, tear film breakup time (BUT), fluorescein and rose bengal staining of the ocular surface, and conjunctival impression cytology. MAIN OUTCOME MEASURES: Patients and control subjects were compared for corneal sensitivity, tear function, ocular surface staining parameters, goblet cell density, and squamous metaplasia grade. The relation of these parameters to the severity of keratoconus progression was also investigated. RESULTS: The mean corneal sensitivity was significantly lower in keratoconus patients compared with control subjects (P < 0.001). The BUT values were also significantly lower in the keratoconus group. Patients with keratoconus had significantly higher fluorescein and rose bengal staining scores (P < 0.001). Corneal sensitivity and tear function changes seemed to get worse with advanced stages of keratoconus. Impression cytology showed goblet cell loss and conjunctival squamous metaplasia, both of which again related to the extent of progression of keratoconus. CONCLUSIONS: The ocular surface disease in keratoconus is characterized by disorder of tear quality, squamous metaplasia, and goblet cell loss, all of which seem to relate to the extent of keratoconus progression.
Adolescent↗