Impaired corneal biomechanical properties and the prevalence of keratoconus in mitral valve prolapse

Evaluation of Retinal Layer Thicknesses in Patients with Keratoconus Using Retinal Layer Segmentation Analysis

OBJECTIVE

To conduct an evaluation of the effects of irregular astigmatism on the retinal nerve fiber layer (RNFL) and the retinal layers observed using spectral-domain optical coherence tomography (SD-OCT) in patients who had keratoconus (KC).

MATERIALS AND METHODS

A total of 255 eyes from 255 individuals, comprising 72 eyes of KC patients, 70 eyes of patients with astigmia, and 113 eyes of healthy controls were included in the analysis. RNFL scan maps (comprising global, temporal, superotemporal, inferotemporal, nasal, inferonasal, and superonasal maps) and macular thickness (MT) maps of a standard from the Early Treatment Diabetic Retinopathy Study (ETDRS) grid were assessed. The measurements were segmented automatically using Spectralis software, and included the RNFL, inner and outer plexiform layers (IPL, OPL), inner and outer nuclear layers (INL, ONL), ganglion cell layer, retinal pigment epithelium (RPE) in the central 6-mm ETDRS subfield.

RESULTS

The RNFL thickness in the KC group was lower when compared with the other two groups; however, statistically significant differences were noted in the global, temporal, superotemporal, and inferotemporal sectors (p < 0.05 for all). All of the central MT parameters showed significant variation among the groups, while a statistically significant decrease was noted in the KC group, except in the inferior outer sector (p = 0.741). In the segmentation analysis, the KC group had the significantly lowest IPL, ONL, RPE, and outer retinal layer (ORL) thickness among the groups (p < 0.05 for each). The astigmatic group was similar to the control group with regard to these parameters (p > 0.05 for each).

CONCLUSION

The eyes in the KC group appeared to have a thinner RNFL and MT when compared to those in the astigmatic and control groups. The ORLs, especially the ONL and RPE, were the most affected component of the macula in the KC group.

New Findings in Early-Stage Keratoconus: Lamina Cribrosa Curvature, Retinal Nerve Fiber Layer Thickness, and Vascular Perfusion

PURPOSE

Our aim was to investigate the involvement of posterior pole structures in eyes affected by keratoconus (KC). Optical coherence tomography (OCT) and OCT angiography (OCTA) were used to determine the status of lamina cribrosa (LC), peripapillary retinal nerve fiber layer (RNFL), macular and peripapillary microvasculature.

DESIGN

Observational, cross-sectional, case-control analysis.

METHODS

Single-center investigation involving patients with KC and healthy control subjects. Enrolled subjects underwent anterior segment OCT combined with Placido-disk topography, macular and optic nerve head swept-source OCT and swept-source OCTA scans, and 3D wide glaucoma module for peripapillary RNFL thickness measurement. The LC curvature index was used to express the degree of LC posterior bowing. We calculated the vessel density and vessel length density at the macular superficial capillary plexus, deep capillary plexus, choriocapillaris, and nerve radial peripapillary capillary plexus.

RESULTS

Overall, 32 eyes with KC and an equal number of age- and axial length-matched control eyes were included in the analysis. Almost all (97%) of eyes with KC were classified as early stage. KC displayed a reduction in peripapillary RNFL thickness (104.8 ± 11.9 µm vs 110.7 ± 10.5 µm; P = .039) and nerve radial peripapillary capillary plexus vessel density (46.31% ± 3% vs 43.82% ± 4%; P = .006) when compared with control subjects; these differences were more evident in the temporal sector and were associated with a higher LC curvature index (9.9% ± 2.6% vs 8.48% ± 1.7%; P = .012). Mean macular superficial capillary plexus vessel density was 3 percentage points lower in eyes with KC than in healthy controls (P < .001).

CONCLUSION

Early-stage KC may be characterized by a posterior bowing of the LC along with a subtle peripapillary RNFL thinning and vascular impairment. These findings support the hypothesis that KC may be a corneal manifestation of a more generalized "eye collagen disease."

Exosomes Released by Corneal Stromal Cells Show Molecular Alterations in Keratoconus Patients and Induce Different Cellular Behavior

Exosomes have been related to various disorders, but their study in relation to ocular pathologies has been limited. In this article, we analyze exosomes produced by corneal stromal cells from healthy individuals and from patients with keratoconus. The proteomic study allowed for the identification of 14 new proteins with altered expression, related to molecules previously associated with the pathology. miRNA analysis detected 16 altered species, including miR-184, responsible for familial severe keratoconus. The prediction of its potential biological targets identified 1121 genes, including some related to this pathology. Exosomes produced by keratoconic cells induced a marked increase in the migration of stromal cells and corneal epithelium, while those produced by healthy cells had no effect on stromal cells. Both types of nanovesicles reduced the proliferation of stromal and corneal cells, but those produced by healthy cells had less effect. Exosomes produced by healthy cells had concentration-dependent effects on the transcription of genes encoding proteoglycans by keratoconus cells, with a relative normalization observed at concentrations of 240 µg/mL. These results show the alteration of stromal exosomes in keratoconus and suggest an influence on the development of the pathology, although the use of healthy exosomes could also have therapeutic potential.

The Underlying Relationship between Keratoconus and Down Syndrome

Keratoconus (KC) is one of the most significant corneal disorders worldwide, characterized by the progressive thinning and cone-shaped protrusion of the cornea, which can lead to severe visual impairment. The prevalence of KC varies greatly by ethnic groups and geographic regions and has been observed to be higher in recent years. Although studies reveal a possible link between KC and genetics, hormonal disturbances, environmental factors, and specific comorbidities such as Down Syndrome (DS), the exact cause of KC remains unknown. The incidence of KC ranges from 0% to 71% in DS patients, implying that as the worldwide population of DS patients grows, the number of KC patients may continue to rise significantly. As a result, this review aims to shed more light on the underlying relationship between KC and DS by examining the genetics relating to the cornea, central corneal thickness (CCT), and mechanical forces on the cornea, such as vigorous eye rubbing. Furthermore, this review discusses KC diagnostic and treatment strategies that may help detect KC in DS patients, as well as the available DS mouse models that could be used in modeling KC in DS patients. In summary, this review will provide improved clinical knowledge of KC in DS patients and promote additional KC-related research in these patients to enhance their eyesight and provide suitable treatment targets.

Real-time ultrasound elastographic features and color doppler imaging of mitral valve prolapse

Background: The aim of this study was to investigate the elasticity of ocular structures in patients with mitral valve prolapse (MVP). Material and Methods: This prospective study included a total of 35 patients with MVP (study group) and 35 healthy volunteers (control group). The elastography value of the ratio of orbital fat- sclera (ROF/S) was measured with real-time US elastography. For each eye, central retinal artery (CRA), posterior ciliary artery (PCA), and ophthalmic artery (OA) were evaluated, respectively. Results: The mean ages of the patients in the study and the control groups were 31.77 ± 11.40 years, and 30.65 ± 7.45 years, respectively (P =0.511). Mean ROF/S were 1.95 ± 0.81 and 1.37 ± 1.06 (P=0.001) in the study groups and control, respectively. The mean RI of the OA was 0.67 ± 0.05 in the control group, 0.67 ±0.05 (0.55; 0.87) in study group. The mean RI of the PCA was 0.66 ± 0.05 in the control group, 0.68 ±0.06 in study group. . The mean RI of the CRA was 0.66 ± 0.05 in the control group, 0.66 ±0.06 in study group. The RI value was not a significant difference between control and study group (p > 0.05). Conclusion: Scleral elasticity was significantly increased in MVP patients. These could be related to ocular pathologies such as glacouma, kerataconus in MVP.

Assessment of the Retinal Vessels in Keratoconus: An OCT Angiography Study

This study investigated vascular density and foveal avascular zone (FAZ) parameters using optical coherence tomography angiography (OCT-A) in patients with keratoconus (KC). Participants with KC and healthy controls were included and underwent best-corrected visual acuity (BCVA), keratometry, anterior segment OCT, and macular OCT-A examinations. Of the 70 subjects (mean age 42.9 ± 15.31 years), 79 KC and 47 healthy eyes were included. Significant reductions in the KC group were recorded for the FAZ area, with a mean (±SD) of 0.19 ± 0.12 vs. 0.25 ± 0.09 mm2 p < 0.001. Central vascular density in KC patients was lower compared with the controls: 6.78 ± 4.74 vs. 8.44 ± 3.33 mm−1 p = 0.049; the inner density was also decreased in the study group (13.64 ± 5.13 vs. 16.54 ± 2.89 mm−1, p = 0.002), along with the outer density (14.71 ± 4.12 vs. 16.88 ± 2.42 mm−1, p = 0.004) and full density (14.25 ± 4.30 vs. 16.57 ± 2.48) p = 0.003. Furthermore, BCVA was positively correlated with central vascular density (R = 0.42 p = 0.004, total R = 0.40, p = 0.006) and inner density (R = 0.44, p = 0.002) in patients with KC but not in controls. Additionally, we found a correlation between K2 and inner vascular density (R = −0.30, p = 0.043) and central epithelium thickness and outer density (R = 0.03, p = 0.046). KC patients had lower macular vascular density and a smaller FAZ than healthy participants. The BCVA in KC patients was correlated with the vascular density.

Anterior pituitary, sex hormones, and keratoconus: Beyond traditional targets

"The Diseases of the Horny-coat of The Eye", known today as keratoconus, is a progressive, multifactorial, non-inflammatory ectatic corneal disorder that is characterized by steepening (bulging) and thinning of the cornea, irregular astigmatism, myopia, and scarring that can cause devastating vision loss. The significant socioeconomic impact of the disease is immeasurable, as patients with keratoconus can have difficulties securing certain jobs or even joining the military. Despite the introduction of corneal crosslinking and improvements in scleral contact lens designs, corneal transplants remain the main surgical intervention for treating keratoconus refractory to medical therapy and visual rehabilitation. To-date, the etiology and pathogenesis of keratoconus remains unclear. Research studies have increased exponentially over the years, highlighting the clinical significance and international interest in this disease. Hormonal imbalances have been linked to keratoconus, both clinically and experimentally, with both sexes affected. However, it is unclear how (molecular/cellular signaling) or when (age/disease stage(s)) those hormones affect the keratoconic cornea. Previous studies have categorized the human cornea as an extragonadal tissue, showing modulation of the gonadotropins, specifically luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Studies herein provide new data (both in vitro and in vivo) to further delineate the role of hormones/gonadotropins in the keratoconus pathobiology, and propose the existence of a new axis named the Hypothalamic-Pituitary-Adrenal-Corneal (HPAC) axis.

The Sociodemographic and Risk Factors for Keratoconus: Nationwide Matched Case-Control Study in Taiwan, 1998-2015

PURPOSE

The aim of this study was to determine the sociodemographic and risk factors for keratoconus (KC) patients with a nationwide Asian database.

DESIGN

Population-based matched case-control study.

METHODS

We performed a secondary data analysis of the Taiwan National Health Insurance Research Database (NHIRD). Cases were patients with newly diagnosed KC in 1998-2015. Controls were patients without KC and matched 4:1 with the KC cases by age, sex, and index date. Comorbidities diagnosed before KC included diabetes mellitus (DM), asthma, allergic rhinitis, mitral valve prolapse, collagen vascular disease, aortic aneurysm, Down syndrome, sleep apnea, depression, hyperlipidemia, astigmatism, and myopia. Conditional logistic regression with forward selection were used to obtain risk factors for KC.

RESULTS

A total of 5,055 patients with KC were matched with 20,220 controls. The average age at KC first diagnosis was 29.76 years. Individuals who lived in suburban and rural area had lower odds ratio of KC (adjusted odds ratio [OR] 0.86, 95% confidence interval [CI] 0.80-0.94; and 0.73, 95% CI 0.67-0.79; respectively) when comparing with those who lived in urban area. Multivariate analysis revealed that Down syndrome, astigmatism, myopia, allergic rhinitis, and asthma were positively associated with KC with adjusted odds ratios (adjusted OR 8.69, 95% CI 3.74-20.19; 6.23, 95% CI 5.35-7.24; 2.99, 95% CI 2.70-3.32; 1.22, 95% CI 1.14-1.32; and 1.18, 95% CI 1.07-1.30, respectively). On the other hand, hyperlipidemia, depression, and DM (uncomplicated and complicated) were negatively associated with KC (adjusted OR 0.67, 95% CI 0.59-0.77; 0.58, 95% CI 0.48-0.71; 0.77, 95% CI 0.64-0.93; and 0.61, 95% CI 0.44-0.86, respectively).

CONCLUSIONS

Our study found that patients with hyperlipidemia, depression, or DM were less likely to have KC, and patients with asthma, allergic rhinitis, astigmatism, myopia, or Down syndrome had higher odds ratio of KC.

Risk of Mitral Valve Prolapse in Patients with Keratoconus in Taiwan: A Population-Based Cohort Study

This retrospective, nationwide, matched-cohort study included 4488 new-onset keratoconus (KCN) patients, ≥12 years old, recruited between 2004 and 2011 from the Taiwan National Health Insurance Research Database. The control group included 26,928 non-KCN patients selected from the Taiwan Longitudinal Health Insurance Database 2000. Information for each patient was collected and tracked from the index date until December 2013. The incidence rate of mitral valve prolapse (MVP) was 1.77 times (95% confidence interval (CI) = 1.09–2.88; p = 0.0206) higher in KCN patients ≥40 years old and 1.49 times (95% CI = 1.12–1.98; p = 0.0060) higher in female KCN patients than in controls. After using the Cox proportional hazard regression analysis to adjust for potential confounders, including hypertension, hyperlipidemia, and congestive heart failure, KCN maintained an independent risk factor, MVP being 1.77 times (adjusted hazard ratio (HR) = 1.77, 95% CI = 1.09–2.88) and 1.48 times (adjusted HR = 1.48, 95% CI = 1.11–1.97) more likely to develop in patients ≥40 years old and female patients in the study cohort, respectively. We found that KCN patients ≥40 years of age and female KCN patients have increased risks of MVP. Therefore, it is recommended that KCN patients should be alerted to MVP.

Posterior pole retinal thickness distribution pattern in keratoconus

PURPOSE

To evaluate the pattern of retinal thickness distribution in patients with keratoconus (KCN) and its correlation with disease severity.

METHODS

For this cross-sectional cohort study, the study subjects with documented keratoconus and normal eyes were prospectively enrolled. All subjects had anterior segment (Pentacam HR) and posterior segment (Spectralis) imaging. Posterior segment imaging by optical coherence tomography included the posterior pole asymmetry analysis map. Data were analyzed with multiple linear regression models and correlation tests to examine the mean and variance of the measured thickness of the retina and its distribution relative to the presence and severity of KCN.

RESULTS

A total of 24 subjects with keratoconus (48 eyes) and 14 normal subjects (28 eyes) enrolled in this study. The posterior pole retinal thickness, both superior and inferior hemifields, as well as the overall retinal thickness in KCN patients was greater than the control group. There was a direct correlation between the overall retinal thickness of the posterior pole and the severity of KCN (R² = 0.422, P < 0.001). However, the variability of the retinal thickness showed no difference between KCN-afflicted and healthy eyes.

CONCLUSION

Although KCN is a disease of the anterior segment of the eye, we found an orderly increase in posterior pole retinal thickness that is correlated with the severity of disease in KCN eyes compared to control. These findings suggest that the retina may maintain some degree of plasticity to respond to the degraded optical system of the eye.

Genetic and Environmental Risk Factors for Keratoconus

Keratoconus, a progressive corneal ectasia, is a complex disease with both genetic and environmental risk factors. The exact etiology is not known and is likely variable between individuals. Conditions such as hay fever and allergy are associated with increased risk, while diabetes may be protective. Behaviors such as eye rubbing are also implicated, but direct causality has not been proven. Genetics plays a major role in risk for some individuals, with many large pedigrees showing autosomal inheritance patterns. Several genes have been implicated using linkage and follow-up sequencing in these families. Genome-wide association studies for keratoconus and for quantitative traits such as central corneal thickness have identified several genetic loci that contribute to a cumulative risk for keratoconus, even in people without a family history of the disease. Identification of risk genes for keratoconus is improving our understanding of the biology of this complex disease.

Incidence of Keratoconus and Its Association with Systemic Comorbid Conditions: A Nationwide Cohort Study from South Korea

Purpose

To determine the incidence of keratoconus and to determine its possible association with common systemic diseases using a nationwide cohort.

Methods

This retrospective nationwide cohort study included 1,025,340 subjects from the Korean National Health Insurance Service-National Sample Cohort database from 2004 to 2013. Estimates for incidence rates of keratoconus were identified. After 1 : 5 matching using propensity scores, associations between keratoconus and certain systemic comorbidities were determined using multivariate logistic regression analysis.

Results

The incidence during the same period was 15.1 cases per 100,000 person-years. Adjusted logistic regression analysis after propensity score matching revealed significant associations between keratoconus and allergic rhinitis (odds ratio (OR): 1.86; 95% confidence interval (CI): 1.63-2.13; p < 0.001), asthma (OR: 1.20; 95% CI: 1.06-1.36; p < 0.001), atopic dermatitis (OR: 1.33; 95% CI: 1.13-1.56; p < 0.001), and diabetes mellitus (DM) (OR: 1.35; 95% CI: 1.15-1.58; p < 0.001).

Conclusion

Estimates of the incidence of keratoconus may help in the planning of eye-care policies, and the results of this study determined the associations between allergic diseases and keratoconus. Conflicting results regarding the association between keratoconus and DM should be further evaluated.

The Association Between Keratoconus and Mitral Valve Prolapse: A Meta-Analysis

Objective

The debate pertaining to the association between Keratoconus (KC) and Mitral Valve Prolapse (MVP) continues to occur among physicians. The results of cross-sectional studies attempting to present the co-existing prevalence of these two diseases remain indeterminate. We compiled the first meta-analysis to determine the pattern of prevalence between the two diseases.

Methods

Two separate literature searches for cross-sectional studies were performed for this meta-analysis. The first search encompassed finding literature comparing the prevalence of KC between patients with MVP and a control group. The second search pertained to finding studies comparing the prevalence of MVP patients with KC and a control group.

Results

Six studies reported the prevalence of MVP in patients with KC and a control group. The prevalence was 41.6% in patients with KC and 11.5% in patients without KC (OR = 7.06 [95% CI = 2.41-20.64]). There was a significant heterogeneity among the studies (I² = 84%). Two studies showed the prevalence of KC in patients with MVP and a control group. The prevalence was 17.0% in patients with KC and 2.9% in the control group (OR = 5.07 [95% CI = 1.08-23.83]). There was no heterogeneity within the analysis (I² = 0%).

Conclusion

There is a statistically significant co-existing prevalence between MVP and KC. Patients with KC are more likely to present with MVP, and patients with MVP are more likely to present with KC.

Interplay between hereditary and environmental factors to establish an in vitro disease model of keratoconus

Keratoconus (KC) is a bilateral corneal dystrophy and a multifactorial, multigenic disorder with an etiology involving a strong environmental component and complex inheritance patterns. The underlying pathophysiology of KC is poorly understood because of potential crosstalk between genetic-epigenetic variants possibly triggered by the environmental factors. Here, we decode the etiopathological basis of KC using genomic, transcriptomic, proteomic and metabolic approaches. The lack of relevant models that accurately imitate this condition has been particularly limiting in terms of the effective management of KC. Tissue-engineered in vitro models of KC could address this need and generate valuable insights into its etiopathology for the establishment of disease models to accelerate drug discovery.

Macular Choroidal Thickening in Keratoconus Patients: Swept-Source Optical Coherence Tomography Study

Purpose

To determine the choroidal thickness (CT) profile in keratoconus (KC) patients using swept-source optical coherence tomography (SS-OCT).

Methods

This was a prospective, cross-sectional study. One hundred two eyes of 52 KC patients were studied using Pentacam and SS-OCT. The macular CT profile was created by manually measuring the distance between the retinal pigment epithelium and the choroid-sclera junction on horizontal b-scans at nine different macular locations. The results were compared to 93 eyes of 93 healthy controls.

Results

Mean age of the KC group was 34.9 ± 13.5 years and mean axial length (AL) was 24.1 ± 1.3 mm. Mean topographic KC classification (TKC) was 2.0; 39 eyes were classified as early KC (TKC <1–2), 34 eyes as moderate (TKC 2, 2–3), and 29 as advanced (TKC 3+). Mean subfoveal CT was 383.2 μm in KC patients and 280.5 μm in control group (P < 0.001). CT in KC patients was statistically thicker in all measure locations (P < 0.001). CT in KC eyes decreased with age, approaching control group at >45 years old, losing statistical significance (P = 0.37).

Conclusions

CT in KC patients is statistically thicker than in healthy population. After age 45, CT decreases approaching control group values.

Translational Relevance

This study describes changes in the CT profile of KC patients, a disease that was considered purely corneal. These choroidal changes argue that KC is a disease that likely involves several ocular structures other than the cornea, and could open new research lines related to the pathophysiology of KC.

Molecular and Histopathological Changes Associated with Keratoconus

Keratoconus (KC) is a corneal thinning disorder that leads to loss of visual acuity through ectasia, opacity, and irregular astigmatism. It is one of the leading indicators for corneal transplantation in the Western countries. KC usually starts at puberty and progresses until the third or fourth decade; however its progression differs among patients. In the keratoconic cornea, all layers except the endothelium have been shown to have histopathological structural changes. Despite numerous studies in the last several decades, the mechanisms of KC development and progression remain unclear. Both genetic and environmental factors may contribute to the pathogenesis of KC. Many previous articles have reviewed the genetic aspects of KC, but in this review we summarize the histopathological features of different layers of cornea and discuss the differentially expressed proteins in the KC-affected cornea. This summary will help emphasize the major molecular defects in KC and identify additional research areas related to KC, potentially opening up possibilities for novel methods of KC prevention and therapeutic intervention.

Corneal Sublayers Thickness in Patients With Mitral Valve Prolapse

OBJECTIVES

The aim of this study was to compare the thickness of each corneal sublayer in patients with mitral valve prolapse (MVP) and healthy individuals.

METHODS

A total of 38 eyes from 38 patients with MVP and 34 eyes from 34 age- and sex-matched healthy individuals were included in this study. The thickness of the corneal epithelium, Bowman layer, stroma, and Descemet membrane-endothelium complex were measured on the central cornea (i.e., corneal apex) and both the inferior and superior halves of the cornea with anterior segment module of spectral domain optical coherence tomography.

RESULTS

No statistically significant differences emerged between the study and control groups in terms of Bowman layer thickness in the central cornea and the cornea's superior half (P=0.092 and P=0.128, respectively). However, in the inferior half of the cornea, Bowman layer thickness among patients with MVP was 11.95±2.34 μm (range 7-16 μm) and in the control group was 13.03±1.62 μm (range 10-16 μm), which made for a statistically significant difference (P=0.025).

CONCLUSIONS

Our study revealed thinning of Bowman layer in the inferior half of the cornea in patients with MVP.

Skin Biophysical Characteristics in Patients with Keratoconus: A Controlled Study

Background. Keratoconus is a relatively common corneal disease causing significant visual disability. Individuals with connective tissue disorders that affect the skin such as Marfan's syndrome and Ehlers-Danlos syndrome or patients with atopic dermatitis show an increased prevalence of keratoconus. It seems that there are some concurrent alterations of skin and cornea in patients with keratoconus. Objective. We plan to compare skin biophysical characteristics in patients with keratoconus and healthy controls. Methods. Forty patients with keratoconus (18 females and 22 males) with mean (SD) age of 33.32 (9.55) years (range 19-56) and 40 healthy controls were recruited to this study. Skin biophysical characteristics including cutaneous resonance running time (CRRT), stratum corneum hydration, and melanin values were measured in patients and controls. Results. The median CRRT, stratum corneum hydration, and melanin measurements were significantly lower in patients with keratoconus in comparison with healthy controls. Conclusion. There are some alterations of skin biophysical properties in patients with keratoconus. Therefore, the assessment of these skin parameters could provide us some clues to the possible common biophysical variations of cornea and skin tissue in diseases such as keratoconus.

The Association Between Sociodemographic Factors, Common Systemic Diseases, and Keratoconus: An Analysis of a Nationwide Heath Care Claims Database

PURPOSE

The purpose of this study was to determine whether an association exists between common systemic diseases, sociodemographic factors, and keratoconus (KCN) among a large, diverse group of insured individuals in the United States.

DESIGN

Retrospective longitudinal cohort study.

PARTICIPANTS

Sixteen thousand fifty-three patients with KCN were matched 1:1 with persons without KCN.

METHODS

Persons with KCN were identified using billing codes and matched by age, gender, and overall health with a control group with no record of KCN. Multivariable logistic regression assessed whether sociodemographic factors and certain systemic diseases affected the odds of KCN.

MAIN OUTCOME MEASURES

Odds ratios (ORs) with 95% confidence intervals (CIs) of receiving a KCN diagnosis.

RESULTS

After adjustment for confounders, black persons had 57% higher odds (adjusted OR, 1.57; 95% CI, 1.38-1.79; P < 0.001) and Latino persons had 43% higher odds (adjusted OR, 1.43; 95% CI, 1.26-1.62; P < 0.001) of being diagnosed with KCN compared with whites. Asians had 39% reduced odds (adjusted OR, 0.61; 95% CI, 0.50-0.75; P < 0.001) of being diagnosed with KCN compared with whites. Patients with uncomplicated diabetes mellitus (DM) had 20% lower odds of KCN (adjusted OR, 0.80; 95% CI, 0.71-0.90; P = 0.002), and patients with DM complicated by end-organ damage had 52% lower odds of having KCN (adjusted OR, 0.48; 95% CI, 0.40-0.58; P < 0.001) compared with those without DM. Persons with collagen vascular disease had 35% lower odds of KCN (adjusted OR, 0.65; 95% CI, 0.47-0.91; P = 0.01). Other conditions found to have increased odds of KCN included sleep apnea (adjusted OR, 1.13; 95% CI, 1.00-1.27; P = 0.05), asthma (adjusted OR, 1.31; 95% CI, 1.17-1.47; P < 0.001), and Down syndrome (adjusted OR, 6.22; 95% CI, 2.08-18.66; P < 0.001). There was no association between KCN and allergic rhinitis, mitral valve disorder, aortic aneurysm, or depression (P > 0.1 for all comparisons).

CONCLUSIONS

Clinicians caring for persons with KCN should inquire about breathing or sleeping and, when appropriate, refer patients for evaluation for sleep apnea or asthma. Patients with DM have lower risk of KCN, potentially because of corneal glycosylation.

Keratoconus: an inflammatory disorder?

Keratoconus has been classically defined as a progressive, non-inflammatory condition, which produces a thinning and steepening of the cornea. Its pathophysiological mechanisms have been investigated for a long time. Both genetic and environmental factors have been associated with the disease. Recent studies have shown a significant role of proteolytic enzymes, cytokines, and free radicals; therefore, although keratoconus does not meet all the classic criteria for an inflammatory disease, the lack of inflammation has been questioned. The majority of studies in the tears of patients with keratoconus have found increased levels of interleukin-6 (IL-6), tumor necrosis factor-α(TNF-α), and matrix metalloproteinase (MMP)-9. Eye rubbing, a proven risk factor for keratoconus, has been also shown recently to increase the tear levels of MMP-13, IL-6, and TNF-α. In the tear fluid of patients with ocular rosacea, IL-1α and MMP-9 have been reported to be significantly elevated, and cases of inferior corneal thinning, resembling keratoconus, have been reported. We performed a literature review of published biochemical changes in keratoconus that would support that this could be, at least in part, an inflammatory condition.

Genetics of keratoconus: where do we stand?

Keratoconus is a progressive thinning and anterior protrusion of the cornea that results in steepening and distortion of the cornea, altered refractive powers, and reduced vision. Keratoconus has a complex multifactorial etiology, with environmental, behavioral, and multiple genetic components contributing to the disease pathophysiology. Using genome-wide and candidate gene approaches several genomic loci and genes have been identified that highlight the complex molecular etiology of this disease. The review focuses on current knowledge of these genetic risk factors associated with keratoconus.