MONGOLISM (DOWN'S SYNDROME) AND KERATOCONUS

Association of 2 Lysyl Oxidase Gene Single Nucleotide Polymorphisms with Keratoconus: A Nationwide Registration Study

Purpose

Keratoconus (KC) is the most common primary ectatic corneal disease, characterized by progressive thinning of the cornea, affecting its shape and structure and leading to visual loss. Lysyl oxidase is an important component of the extracellular matrix and contributes to the homeostasis of corneal stromal extracellular matrix via enzymatic reaction. This nationwide registration study aims to examine the association of KC with 2 known single nucleotide polymorphisms, rs2956540 and rs10519694, in a population of Iranian descent.

Design

Case-control.

Participants

One hundred seventy-eight subjects with KC and 180 clinically healthy subjects participated in the study.

Methods

Genomic DNA was extracted from peripheral blood samples, and their genotypes were determined using tetra-primer amplification refractory mutation system-polymerase chain reaction.

Main Outcome Measures

Allele frequency for rs2956540 and rs10519694.

Results

Genotype frequency was significantly different between cases and controls for rs2956540 (P value = 0.019). The rs2956540 C allele carriers were significantly more frequent among KC cases than healthy controls (P value_chi-square = 0.015, P value_{Fisher exact} = 0.017). There was a significant difference in genotype frequency between groups for rs10519694 (P value = 0.001). T allele carriers were significantly more frequent among KC patients (P value_chi-square = 0.002, P value_{Fisher exact} = 0.001). Sex stratification revealed no significant differences in genotype frequency between males and females in cases and controls. Fitting the general linear model showed that rs10519694 could be considered a predictor for the development of KC (P value = 0.001); however, this was not observed for rs2956540 (P value = 0.323).

Conclusions

rs2956540 and rs10519694 are associated with KC in a population of Iranian descent. rs10519694 could potentially be used for KC risk prediction.

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.

Down syndrome: a review of ocular manifestations

Down syndrome is the most common genetically mediated intellectual disability. Although many physiologic and pathologic features of Down syndrome are discussed at length in the literature, the ocular manifestations of Down syndrome have seldom been discussed in a comprehensive fashion. Given that Down syndrome has ocular manifestations from the front to the back of the eye, it is important for physicians to become familiar with these manifestations, especially given the prevalence of Down syndrome. This review aims to discuss the varied ophthalmologic manifestations of Down syndrome – including strabismus, amblyopia, nystagmus, accommodation deficits, nasolacrimal duct obstruction, keratoconus, optic nerve pathology, neoplastic disease, and retinal pathology – to facilitate better care and visual outcomes in this important patient population.

Inferior Spear-like Lens Opacity as a Sign of Keratoconus

Purpose

To report 21 cases of typical inferior feather-shape lens opacity associated with keratoconus.

Methods

In this cross-sectional study, we evaluated the association of keratoconus with inferior feather-shape lens opacity in refractive surgery candidates. Visual acuity, demographic, refractive, and topographic characteristics of 26 eyes of 21 patients with inferior feather-shape lens opacity were evaluated in detail. Pedigree analysis was also performed to assess possible inheritance.

Results

Overall, 2122 out of 33,368 cases (6.4%) without lens opacity had keratoconus, while 20 out of 21 patients (95.2%) with peculiar lens opacity had definite keratoconus (P < 0.001). Lens opacity was bilateral in 5 cases (24%), and keratoconus was bilateral in all 20 patients with lens opacity. Nine eyes out of thirty-six with a complete data record (25%) had a severe keratoconus and underwent deep lamellar keratoplasty, while 11 (31%) had forme fruste keratoconus. Pedigrees were drawn for eight patients, most families of whom suggested an X-linked recessive inheritance.

Conclusion

The present study was the first to investigate patients with a peculiar inferior feather-shape lens opacity accompanied by bilateral keratoconus, which was observed in 95% of the patients. This finding should raise awareness as to the possibility of diagnosing keratoconus in the eyes of the patients with these characteristics.

Detektion des subklinischen Keratokonus

Das Frühstadium eines Keratokonus, ohne klassische und kennzeichnende klinische Befunde, stellt eine Kontraindikation für refraktive Chirurgie dar. Dieser Beitrag zeigt deshalb gemäß dem aktuellen Stand der Technik Möglichkeiten auf, Risikofaktoren für einen subklinischen Keratokonus zu erkennen.

[Detection of Subclinical Keratoconus]

The early stage of a keratoconus (KC), without classic and characteristic clinical findings, is a contraindication for refractive surgery. This article therefore shows, in accordance with the current state of the art, ways of identifying risk factors for subclinical keratoconus.After delimitation, this publication contains a current summary of epidemiology, etiology and pathophysiology of subclinical and clinical KC. Furthermore, an overview of different grading scales is given. A detailed description of several practical possibilities for detection of subclinical KC is the focus of this publication: typical abnormalities with subclinical KC in ocular aberrometry, corneal topography, Zernike analysis, Fourier analysis, indices of the corneal anterior surface; especially tomography of the anterior segment of the eye respecting addition of the corneal posterior surface and the pachymetry, and also innovative techniques counting in the rigidity or biomechanical properties, as well as traditional techniques giving hints for subclinical KC as retinoscopy, ophthalmoscopy and subjective refraction.In preparation for refractive surgical interventions and to avoid possible consequences of subclinical KC, a suitable analysis with different methods should always be carried out in addition to a specific anamnesis. An exclusive consideration of the available indices is not sufficient, as this does not reveal early stages. Ideally, the biomechanics of the cornea is included in the diagnosis. The combination of tomography and biomechanics with methods of artificial intelligence are trendsetting in detection of subclinical KC.

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.

Descemet Membrane Endothelial Keratoplasty and Bowman Layer Transplantation: An Anatomic Review and Historical Survey

For nearly a century, the definitive treatment of many corneal dystrophies and ectactic disorders was limited to penetrating keratoplasty, but over the past 2 decades, a surge of surgical innovation has propelled the treatment of many corneal diseases to more targeted approaches with significantly better visual outcomes. Anterior stromal diseases were first changed through endothelial-sparing techniques, such as deep anterior lamellar keratoplasty, but have more recently transitioned to stromal-sparing approaches. Ultraviolet corneal crosslinking strengthens the cornea and halts progression of keratoconus in >90% of cases. Intracorneal ring segment and corneal allogenic ring segment implantation offer methods to flatten ectatic corneas. However, Bowman layer transplantation - inlay and more recently onlay techniques - has shown promise for treating advanced keratoconus and preventing keratoplasty. The advent of endothelial keratoplasty radically changed the treatment of corneal endothelial dysfunction, and Descemet membrane endothelial keratoplasty specifically offers an average postoperative visual acuity of 20/25 (0.8) with only 8.8% of grafts requiring retransplantation in the first 5 years. Here, we review the rapid innovations for surgical treatment of corneal diseases, spanning from endothelial keratoplasty and endothelial regeneration to anterior lamellar keratoplasty and stromal augmentation, highlighting key steps which may be moving us closer to a "postkeratoplasty" world.

A Randomized Trial of Objective Spectacle Prescriptions for Adults with Down Syndrome: Baseline Data and Methods

SIGNIFICANCE

It is difficult to determine the most efficacious refractive correction for individuals with Down syndrome using routine clinical techniques. New objective methods that optimize spectacle corrections for this population may reduce limitations on daily living by improving visual quality.

PURPOSE

This article describes the methods and baseline characteristics of study participants in a National Eye Institute-sponsored clinical trial to evaluate objectively derived spectacle corrections in adults with Down syndrome. Intersession repeatability of the primary outcome measure (distance visual acuity) is also reported.

METHODS

Adults with Down syndrome were enrolled into a nine-visit study to compare clinically derived spectacle corrections and two different objective spectacle corrections derived from wavefront aberration data. Spectacle corrections were randomized and dispensed for 2 months each. Distance visual acuity was measured with a Bailey-Lovie-style chart. Intersession repeatability of acuity was established by performing difference versus mean analysis from binocular acuity measures obtained through habitual corrections at visits 1 and 2.

RESULTS

Thirty adults (mean ± standard deviation age, 29 ± 10 years) with a large range of refractive errors were enrolled. Presenting visual acuity at visit 1 was reduced (right eye, 0.47 ± 0.20 logMAR; left eye, 0.42 ± 0.17 logMAR). The mean difference between visits 1 and 2 was 0.02 ± 0.06 logMAR, with a coefficient of repeatability (1.96 × within-subject standard deviation) of 0.12 logMAR.

CONCLUSIONS

This study seeks to investigate new strategies to determine optical corrections that may reduce commonly observed visual deficits in individuals with Down syndrome. The good intersession repeatability of acuity found in this study (six letters) indicates that, despite the presence of reduced acuity, adults with Down syndrome performed the outcome measure for this clinical trial reliably.

Hypothyroidism is Not Associated with Keratoconus Disease: Analysis of 626 Subjects

Purpose

To analyze the association between hypothyroidism and keratoconus, we examined blood thyroid hormone levels and corneal tomographic parameters in healthy subjects and patients with keratoconus.

Methods

We included 626 subjects (304 left eyes, 49%; 431 males, 69%; age 38.4 ± 14.3 y). Patients with keratoconus were from our Homburg Keratoconus Center (HKC) (n = 463); patients with hypothyroidism were from the Department of Internal Medicine of Saarland Medical University, Homburg/Saar, Germany (n = 75); and healthy subjects were from the Department of Ophthalmology of Saarland University Medical Center (n = 88). We included only one randomly selected eye of each subject and the first examination data.

Exclusion criteria

Previous thyroid medication, previous ocular surgery, and patients with suspected keratoconus (topographic keratoconus classification, [TKC]: 0 < 1). Patient eyes were classified (TKC) with dedicated, instrument-based, keratoconus detection software provided with the Pentacam. TKC = 0 was considered “normal,” and TKCs ≥ 1 were considered keratoconus. Subjects were also classified as euthyroid or hypothyroid, based on blood thyroid hormone status (i.e., TSH, FT3, and FT4). A multiple logistic linear regression model was constructed to determine the effects of age (covariate), gender, and hypothyroidism (effect sizes) on “TKC-positive” disease.

Results

The significance levels for a constant parameter, sex, thyroid condition, and age were p < 0.0001, p < 0.0001, p < 0.0001, and p=0.003, respectively. The odds ratios for age, sex, and hypothyroidism were 0.98, 3.05, and 3.34, respectively. Male sex and a euthyroid condition had significantly positive, clinically relevant effects, and age had a significantly negative, but clinically irrelevant effect on the estimated TKC index.

Conclusions

Keratoconus appeared to occur more often in patients classified as euthyroid than in patients with hypothyroidism. Thus, hypothyroidism alone could not support the development of keratoconus. Based on these results, it should not be mandatory to screen patients with hypothyroidism for keratoconus or patients with keratoconus for hypothyroidism.

Genetic Aspects of Keratoconus: A Literature Review Exploring Potential Genetic Contributions and Possible Genetic Relationships with Comorbidities

Introduction

Keratoconus (KC) is a complex, genetically heterogeneous, multifactorial degenerative disorder that is accompanied by corneal ectasia which usually progresses asymmetrically. With an incidence of approximately 1 per 2000 and 2 cases per 100,000 population presenting annually, KC follows an autosomal recessive or dominant pattern of inheritance and is, apparently, associated with genes that interact with environmental, genetic, and/or other factors. This is an important consideration in refractive surgery in the case of familial KC, given the association of KC with other genetic disorders and the imbalance between dizygotic twins. The present review attempts to identify the genetic loci contributing to the different KC clinical presentations and relate them to the common genetically determined comorbidities associated with KC.

Methods

The PubMed, MEDLINE, Google Scholar, and GeneCards databases were screened for KC-related articles published in English between January 2006 and November 2017. Keyword combinations of “keratoconus,” “risk factor(s),” “genetics,” “genes,” “genetic association(s),” and “cornea” were used. In total, 217 articles were retrieved and analyzed, with greater weight placed on the more recent literature. Further bibliographic research based on the 217 articles revealed another 124 relevant articles that were included in this review. Using the reviewed literature, an attempt was made to correlate genes and genetic risk factors with KC characteristics and genetically related comorbidities associated with KC based on genome-wide association studies, family-based linkage analysis, and candidate-gene approaches.

Results

An association matrix between known KC-related genes and KC symptoms and/or clinical signs together with an association matrix between identified KC genes and genetically related KC comorbidities/syndromes were constructed.

Conclusion

Twenty-four genes were identified as potential contributors to KC and 49 KC-related comorbidities/syndromes were found. More than 85% of the known KC-related genes are involved in glaucoma, Down syndrome, connective tissue disorders, endothelial dystrophy, posterior polymorphous corneal dystrophy, and cataract.

Corneal Cross-Linking for Pediatric Keratcoconus Review

PURPOSE

To comprehensively review the available published literature for cross-linking in the pediatric population.

METHODS

Review of the literature published in English in PubMed.

RESULTS

Two hundred ten publications were considered. One hundred fifteen were considered relevant to this review.

CONCLUSIONS

Studies of cross-linking in pediatric patients are sparse, with relatively short follow-up times, and mostly on small groups of patients. Treatment with cross-linking halts progression of keratoconus in the pediatric population, and early treatment seems to be cost-effective compared with later penetrating keratoplasty. Long-term effects and regression rates remain unclear, and further studies are needed in this population.

Genetic associations for keratoconus: a systematic review and meta-analysis

Genetic associations for keratoconus could be useful for understanding disease pathogenesis and discovering biomarkers for early detection of the disease. We conducted a systematic review and meta-analysis to summarize all reported genetic associations for the disease. We searched in the MEDLINE, Embase, Web of Science, and HuGENET databases for genetic studies of keratoconus published from 1950 to June 2016. The summary odds ratio and 95% confidence intervals of all polymorphisms were estimated using the random-effect model. Among 639 reports that were retrieved, 24 fulfilled required criteria as eligible studies for meta-analysis, involving a total of 53 polymorphisms in 28 genes/loci. Results of our meta-analysis lead to the prioritization of 8 single-nucleotide polymorphisms (SNPs) in 6 genes/loci for keratoconus in Whites. Of them 5 genes/loci were originally detected in genome-wide association studies, including FOXO1 (rs2721051, P = 5.6 × 10^-11), RXRA-COL5A1 (rs1536482, P = 2.5 × 10^-9), FNDC3B (rs4894535, P = 1.4 × 10^-8), IMMP2L (rs757219, P = 6.1 × 10^-7; rs214884, P = 2.3 × 10^-5), and BANP-ZNF469 (rs9938149, P = 1.3 × 10^-5). The gene COL4A4 (rs2229813, P = 1.3 × 10^-12; rs2228557, P = 4.5 × 10^-7) was identified in previous candidate gene studies. We also found SNPs in 10 genes/loci that had a summary P value < 0.05. Sensitivity analysis indicated that the results were robust. Replication studies and understanding the roles of these genes in keratoconus are warranted.

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.

Primary health care provision for people with learning disabilities: a survey of general practitioners

The delivery of primary health care to people with learning disabilities living in the community has come under increasing scrutiny. Concerns have been raised over both the current quality of this care and its future organization. A postal questionnaire was sent to 153 general practitioners (GPs) to elicit their views and opinions concerning the delivery of primary health care to people with learning disabilities; the response rate was 57% (88 responses). The majority of respondents appeared to have no idea of the number of patients they had with learning disabilities. There was no consensus as to the workload generated by this population group. Most GPs claimed to undertake health promotion activities for their patients with learning disabilities. Many GPs' knowledge of health needs affecting people with learning disabilities appeared inadequate, and this was reflected in their degree of confidence in meeting medical needs. Many GPs felt that the lead responsibility for dealing with the general medical needs of people with learning disabilities did not belong with them. These findings support difficulties identified elsewhere in the literature: less frequent surgery attendance of people with learning disabilities, people with learning disabilities do not mention their symptoms to carers/GPs, lack of interest/knowledge of GPs, and a difficulty for GPs in reaching a diagnosis. There was a broad acknowledgement of a problem within primary care, but little consensus as to a solution.

Simulated Keratometry Repeatability in Subjects with and without Down Syndrome

PURPOSE

To assess the repeatability of simulated keratometry measures obtained with Zeiss Atlas topography for subjects with and without Down syndrome (DS).

METHODS

Corneal topography was attempted on 140 subjects with DS and 138 controls (aged 7-59 years). Subjects who had at least three measures in each eye were included in analysis (DS: n = 140 eyes (70 subjects) and controls: n = 264 eyes (132 subjects)). For each measurement, the steep corneal power (K), corneal astigmatism, flat K orientation, power vector representation of astigmatism (J0, J45), and astigmatic dioptric difference were determined for each measurement (collectively termed keratometry values here). For flat K orientation comparisons, only eyes with >0.50 DC of astigmatism were included (DS: n = 131 eyes (68 subjects) and control: n = 217 eyes (119 subjects)). Repeatability was assessed using (1) group mean variability (average standard deviation (SD) across subjects), (2) coefficient of repeatability (COR), (3) coefficient of variation (COV), and (4) intraclass correlation coefficient (ICC).

RESULTS

The keratometry values showed good repeatability as evidenced by low group mean variability for DS versus control eyes (≤0.26D vs. ≤0.09D for all dioptric values; 4.51° vs. 3.16° for flat K orientation); however, the group mean variability was significantly higher in DS eyes than control eyes for all parameters (p ≤ 0.03). On average, group mean variability was 2.5 times greater in the DS eyes compared to control eyes across the keratometry values. Other metrics of repeatability also indicated good repeatability for both populations for each keratometry value, although repeatability was always better in the control eyes.

CONCLUSIONS

DS eyes showed more variability (on average: 2.5×) compared to controls for all keratometry values. Although differences were statistically significant, on average 91% of DS eyes had variability ≤0.50D for steep K and astigmatism, and 75% of DS eyes had variability ≤5 degrees for flat K orientation.

Variants in SKP1, PROB1, and IL17B genes at keratoconus 5q31.1-q35.3 susceptibility locus identified by whole-exome sequencing

Keratoconus (KTCN) is a protrusion and thinning of the cornea, resulting in impairment of visual function. The extreme genetic heterogeneity makes it difficult to discover factors unambiguously influencing the KTCN phenotype. In this study, we used whole-exome sequencing (WES) and Sanger sequencing to reduce the number of candidate genes at the 5q31.1-q35.3 locus and to prioritize other potentially relevant variants in an Ecuadorian family with KTCN. We applied WES in two affected KTCN individuals from the Ecuadorian family that showed a suggestive linkage between the KTCN phenotype and the 5q31.1-q35.3 locus. Putative variants identified by WES were further evaluated in this family using Sanger sequencing. Exome capture discovered a total of 173 rare (minor allele frequency <0.001 in control population) nonsynonymous variants in both affected individuals. Among them, 16 SNVs were selected for further evaluation. Segregation analysis revealed that variants c.475T>G in SKP1, c.671G>A in PROB1, and c.527G>A in IL17B in the 5q31.1-q35.3 linkage region, and c.850G>A in HKDC1 in the 10q22 locus completely segregated with the phenotype in the studied KTCN family. We demonstrate that a combination of various techniques significantly narrowed the studied genomic region and reduced the list of the putative exonic variants. Moreover, since this locus overlapped two other chromosomal regions previously recognized in distinct KTCN studies, our findings suggest that this 5q31.1-q35.3 locus might be linked with KTCN.

Predictors for treatment outcomes after corneal crosslinking for keratoconus: a validation study

Previous research suggested that baseline corrected distance visual acuity (CDVA) and maximum keratometry (Kmax) are the predictors for effectiveness of corneal crosslinking (CXL) for keratoconus. The aim of this study was to validate the previously determined predictors in a new treatment cohort. A prospective cohort of 112 eyes in 90 consecutive patients was used to validate the results of 102 eyes in 79 patients from our previous prospective cohort. All patients were treated using epithelium-off corneal CXL in a tertiary hospital setting. Primary outcomes were changes in CDVA (LogMAR) and Kmax between baseline and 1-year post-treatment. Predictive factors for both outcomes were determined using univariable and multivariable analyses. Lower pretreatment CDVA was found to be the sole independent factor predicting an improvement in CDVA 1 year after CXL (β coefficient: −0.476, P < 0.01). Kmax flattening is more likely to take place in eyes with preoperative central cones (β coefficient: 0.655, P < 0.01). These results are consistent with our initial research and indicate high reproducibility in the new cohort. The previously postulated prediction model for postoperative CDVA showed limited predictive value in the validation cohort (R² = 0.15). The clinical implication of these results is that patients with lower pretreatment visual acuity are more likely to benefit from CXL (with respect to visual acuity), and patients with more central cones will benefit more in terms of cone flattening. Furthermore, those results can be used to guide customization of the crosslinking treatment.

Demodex species in human ocular disease: new clinicopathological aspects

Demodex brevis and Demodex folliculorum are likely ubiquitous organisms associated with human eyelashes. However, they have also been implicated in the pathogenesis of external ocular diseases. This article reviews the current literature in regards to life cycle, morphology, pathogenesis and treatment of underlying Demodex spp. infestation and outlines the previously undescribed in vivo behaviour of the mites. Images were obtained from the epilation of lashes from 404 patients seen in clinical practice. Epilated lashes were placed on a microscope slide which had been coated with optically clear hypromellose/carbomer gel (Genteal gel, Novartis pharmaceuticals corporation, East Hanover, New Jersey). Adults were identified with either dark field or standard transmission microscopy at 40-100×. Eggs and other life-cycle stages were examined at 250× magnification, with transmission microscopy giving the best image resolution. The life cycle of the mite has been reviewed and simplified according to clinical observations. Clinical signs suggestive of underlying Demodex spp. infestation have been described, and their pathogenesis was explained based on the micrographic digital images obtained. The problem of symptomatic Demodex spp. disease likely reflects an imbalance in the external ocular ecology; however, the role of Demodex spp. as a commensal should not be overlooked. Treatment should not be aimed at total eradication of the mite but rather restoring the ocular ecology to a balanced state. By revisiting the life cycle of the mite, we can identify areas where possible intervention may be effective.

Polymorphism Analysis of VSX1 and SOD1 Genes in Greek Patients with Keratoconus

BACKGROUND

A number of mutations in the VSX1 and SOD1 genes have been reported to be associated with keratoconus (KC), however the results from different studies are controversial. In this study, we conducted the genotyping of common polymorphisms [VSX1: D144E, H244R, R166W, G160D; SOD1: intronic 7-base deletion (c.169 + 50 delTAAACAG)], in a case-control sample panel of the Greek population.

MATERIALS AND METHODS

A case-control panel, with 33 KC patients and 78 healthy controls, were surveyed. DNA from each individual was tested for the VSX1: D144E, H244R, R166W, G160D and SOD1: intronic 7-base deletion (c.169 + 50 delTAAACAG) polymorphisms by direct sequencing.

RESULTS

We observed no polymorphisms of the VSX1 gene in the case-control panel. Concerning the SOD1 intronic 7-base deletion (c.169 + 50 delTAAACAG), our findings suggest that heterozygous carriers are over-represented among KC cases compared to healthy controls (p = 0.002).

CONCLUSIONS

We cannot confirm the previously reported association of the polymorphism in the VSX1 gene with KC. Our results suggest a possible causative role of SOD1 in the pathogenesis of KC. Further studies are required to identify other important genetic factors involved in the pathogenesis and progression of KC.

Down syndrome: An overview

Optometrists as primary eye care providers examine patients from diverse populations, including those with special needs such as Down syndrome. Down syndrome is a chromosomal abnormality associated with several health conditions including vision anomalies such as refractive, accommodative and vergence anomalies, as well as ocular pathology. In this article, a narrative review of Down syndrome including the background, historical perspective, aetiology and genetic mechanisms, types, epidemiology, as well as the physical and medical profile of Down syndrome is presented.Keywords: Down syndrome review; Trisomy 21; historical perspective; etiology; types and epidemiology; features; Optometrist

Comparison of Whole Eye versus First-Surface Astigmatism in Down Syndrome

PURPOSE

Subjects with Down syndrome have structural differences in the cornea and lens, as compared with the general population. This study investigates objectively measured refractive and corneal astigmatism, as well as calculated internal astigmatism in subjects with and without Down syndrome.

METHODS

Refractive (Grand Seiko autorefraction) and anterior corneal astigmatism (difference between steep and flat keratometry obtained with Zeiss Atlas corneal topography) were measured in 128 subjects with Down syndrome (mean [±SD] age, 24.8 [±8.7] years) and 137 control subjects without Down syndrome (mean [±SD] age, 24.9 [±9.9] years), with one eye randomly selected for analysis per subject. Refractive astigmatism and corneal astigmatism were converted to vector notation (J0, J45) to calculate internal astigmatism (Refractive - Corneal) and then converted back to minus cylinder form.

RESULTS

Mean [±SD] refractive astigmatism was significantly greater in subjects with Down syndrome than in control subjects (-1.94 [±1.30] DC vs. -0.66 [±0.60] DC, t = -10.16, p < 0.001), as were mean corneal astigmatism (1.70 [±1.04] DC vs. 1.02 [±0.63] DC, t = 6.38, p < 0.001) and mean internal astigmatism (-1.07 [±0.68] DC vs. -0.77 [±0.41] DC, t = -4.21, p < 0.001). A positive linear correlation between corneal and refractive astigmatism was observed for both study populations for both the J0 and J45 vectors (p < 0.001 for all comparisons; R(2) range, 0.31 to 0.74). The distributions of astigmatism orientation differed significantly between the two study populations for comparisons of corneal and calculated internal astigmatism (χ(2), p < 0.007), but not refractive astigmatism (p = 0.46).

CONCLUSIONS

This study demonstrates that corneal astigmatism is predictive of overall refractive astigmatism in subjects with Down syndrome, as it is in the general population. The greater magnitudes of astigmatism and wider variation of astigmatism orientation in subjects with Down syndrome for refractive, corneal, and calculated internal astigmatism are likely attributable to previously reported differences in the structure of the cornea and internal optical components of the eye from that of the general population.

Mitochondrial Profile and Responses to TGF-β Ligands in Keratoconus

PURPOSE

Keratoconus (KC) is a complex corneal dystrophy with multifactorial etiology. Previous studies have shown evidence of mitochondrial abnormalities in KC; however, the exact cause of these abnormalities remains unknown. The aim of this study was to identify if transforming growth factor-β (TGF-β) isoforms play a role in the regulation of mitochondrial proteins in human KC cells (HKC).

MATERIALS AND METHODS

Human corneal fibroblasts (HCF) and HKC were isolated and cultured for 4 weeks in three different conditions: (a)

CONTROL

MEM + 10%FBS, (b) MEM + 10%FBS + TGF-β1 and (c) MEM + 10%FBS + TGF-β3. All samples were processed for mitochondrial damage analysis using real-time PCR.

RESULTS

We quantified and analyzed 84 mitochondrial and five housekeeping genes in HCFs and HKCs. Our data showed that when TGF-β1 and/or TGF-β3 were compared with control in HCFs, nine genes were significantly different; however, no genes were significantly regulated by the TGF-β isoforms in HKCs. Significant differences were also seen in seven genes when HFCs were compared with HKCs, in all three conditions.

CONCLUSIONS

Overall, our data support the growing consensus that mitochondrial dysfunction is a key player in KC disease. These in vitro data show clear links between mitochondrial function and TGF-β isoforms, with TGF-β1 severely disrupting KC-mitochondrial function, while TGF-β3 maintained it, thus suggesting that TGF-β may play a role in KC-disease treatment.

Treatment options for advanced keratoconus: A review

Traditionally, the mainstay of treatment for advanced keratoconus (KC) has been either penetrating or deep anterior lamellar keratoplasty (PK or DALK, respectively). The success of both operations, however, has been somewhat tempered by potential difficulties and complications, both intraoperatively and postoperatively. These include suture and wound-healing problems, progression of disease in the recipient rim, allograft reaction, and persistent irregular astigmatism. Taken together, these have been the inspiration for an ongoing search for less troublesome therapeutic alternatives. These include ultraviolet crosslinking and intracorneal ring segments, both of which were originally constrained in their indication exclusively to eyes with mild to moderate disease. More recently, Bowman layer transplantation has been introduced for reversing corneal ectasia in eyes with advanced KC, re-enabling comfortable contact lens wear and permitting PK and DALK to be postponed or avoided entirely. We offer a summary of the current and emerging treatment options for advanced KC, aiming to provide the corneal specialist useful information in selecting the optimal therapy for individual patients.

Gene therapy in keratoconus

Keratoconus (KC) is the most common ectasia of the cornea and is a common reason for corneal transplant. Therapeutic strategies that can arrest the progression of this disease and modify the underlying pathogenesis are getting more and more popularity among scientists. Cumulating data represent strong evidence of a genetic role in the pathogenesis of KC. Different loci have been identified, and certain mutations have also been mapped for this disease. Moreover, Biophysical properties of the cornea create an appropriate candidate of this tissue for gene therapy. Immune privilege, transparency and ex vivo stability are among these properties. Recent advantage in vectors, besides the ability to modulate the corneal milieu for accepting the target gene for a longer period and fruitful translation, make a big hope for stupendous results reasonable.

Corneal Hydrops in Keratoconus

Purpose

The purpose of this review is to outline the etiology, clinical features, and management of acute corneal hydrops (CH) in cases of keratoconus (KC).

Recent findings

The advent of newer investigative modalities like ultra biomicroscopy, anterior segment optical coherence tomography and confocal microscopy has contributed toward the diagnosis, treatment planning and following the course of therapy in cases of acute hydrops.

Summary

Corneal hydrops is an acute complication of keratoconus which in most instances resolves spontaneously. However, prolonged corneal edema can lead to complications, such as corneal neovascularization which can jeopardise a future corneal graft. Hence, timely intervention is required in most cases to prevent such complications as well as for early visual rehabilitation. Intracameral gas injection is the most commonly performed surgical procedure for hydrops. Modifications in surgical technique can help to tackle difficult situations.

How to cite this article

Maharana PK, Nagpal R, Sharma N. Corneal Hydrops in Keratoconus. Int J Kerat Ect Cor Dis 2015;4(2):52-55.

Keratoconus: tissue engineering and biomaterials

Keratoconus (KC) is a bilateral, asymmetric, corneal disorder that is characterized by progressive thinning, steepening, and potential scarring. The prevalence of KC is stated to be 1 in 2000 persons worldwide; however, numbers vary depending on size of the study and regions. KC appears more often in South Asian, Eastern Mediterranean, and North African populations. The cause remains unknown, although a variety of factors have been considered. Genetics, cellular, and mechanical changes have all been reported; however, most of these studies have proven inconclusive. Clearly, the major problem here, like with any other ocular disease, is quality of life and the threat of vision loss. While most KC cases progress until the third or fourth decade, it varies between individuals. Patients may experience periods of several months with significant changes followed by months or years of no change, followed by another period of rapid changes. Despite the major advancements, it is still uncertain how to treat KC at early stages and prevent vision impairment. There are currently limited tissue engineering techniques and/or "smart" biomaterials that can help arrest the progression of KC. This review will focus on current treatments and how biomaterials may hold promise for the future.

Obesity and obstructive sleep apnea in patients with keratoconus in a Turkish population

PURPOSE

The aim of this study was to compare the frequency of occurrence of obesity and high risk of developing obstructive sleep apnea (OSA) in a keratoconus population with that of a control group.

METHODS

This prospective, case-controlled multicenter study was performed on patients with keratoconus and age- and gender-matched control subjects. One hundred forty-six patients were included in each group, and the Berlin Questionnaire was used for classifying patients as having a high risk or low risk of developing OSA. The patients' demographic and clinical characteristics were compared with the Mann-Whitney U test for continuous variables and with the χ test for categorical variables.

RESULTS

The keratoconus (85 male/61 female) and control (79 male/67 female) groups' median ages were 25 (8-65) and 24 (9-60) years, respectively. Of the 146 patients in each group, 11 (7.5%) patients were determined to be at a high risk of developing OSA in the keratoconus group, and 8 (5.5%) patients were determined to be at a high risk of developing OSA in the control group. There was no significant difference between the groups (P = 0.477). The keratoconus and control groups' median body mass index values were found to be within normal ranges of 23.2 and 23.4, respectively.

CONCLUSIONS

In this study, the mean body mass index value of the keratoconus group was determined to be within normal limits. In a Turkish population, the ratio of a high risk of developing OSA was not found to be significantly different between the keratoconus and control groups.

Molecular Screening of Keratoconus Susceptibility Sequence Variants in VSX1, TGFBI, DOCK9, STK24, and IPO5 Genes in Polish Patients and Novel TGFBI Variant Identification

PURPOSE

Keratoconus (KTCN) is a degenerative disorder of the eye that results in the conical shape and thinning of the cornea and is a leading cause for corneal transplantations. A number of studies suggest that genetic factors play a role in KTCN etiology. Some candidate gene variants have recently been shown to be associated with KTCN. The purpose of our study was to verify the role of VSX1, TGFBI, DOCK9, IPO5, and STK24 sequence variants in Polish KTCN patients.

METHODS

Forty-two Polish patients with sporadic KTCN and 50 control individuals were enrolled into this study. Both affected and unaffected individuals underwent detailed ophthalmic examination. The mutations screening in the candidate genes was performed by the direct sequencing method.

RESULTS

Analysis of VSX1, TGFBI, DOCK9, IPO5, and STK24 genes identified numerous sequence variants. Variants c.-264_-255delGGGGTGGGGT, c.627 + 23G > A, c.809-6_809-5insT, and c.*200G > T in the VSX1 gene, and heterozygous c.1598G > A mutation (Arg533Gln) in exon 12 of TGFBI were detected for the first time in KTCN patients. Two known sequence variants of TGFBI c.1620T > C (Phe540Phe) and c.1678 + 23G > A were observed in KTCN patients and control individuals. The newly reported c.717 + 43A > G substitution in intron 7 of DOCK9 was identified in both KTCN patients and healthy individuals.

CONCLUSIONS

Our investigation showed that KTCN-related sequence variants of analyzed genes were found in a very small proportion of the studied patients indicating that genes other than VSX1, TGFBI, DOCK9, IPO5, and STK24 are involved in the development and progression of KTCN in Polish patients. Our results support the hypothesis about the genetic heterogeneity of KTCN.

Genetic and genomic perspective to understand the molecular pathogenesis of keratoconus

Keratoconus (KC; Mendelian Inheritance in Man (OMIM) 14830) is a bilateral, progressive corneal defect affecting all ethnic groups around the world. It is the leading cause of corneal transplantation. The age of onset is at puberty, and the disorder is progressive until the 3^rd–4^th decade of life when it usually arrests. It is one of the major ocular problems with significant social and economic impacts as the disease affects young generation. Although genetic and environmental factors are associated with KC, but the precise etiology is still elusive. Results from complex segregation analysis suggests that genetic abnormalities may play an essential role in the susceptibility to KC. Due to genetic heterogeneity, a recent study revealed 17 different genomic loci identified in KC families by linkage mapping in various populations. The focus of this review is to provide a concise update on the current knowledge of the genetic basis of KC and genomic approaches to understand the disease pathogenesis.

The genetics of keratoconus

Keratoconus is a bilateral, non-inflammatory corneal ectasia characterized by progressive conical thinning and protrusion of the cornea. Its etiology has long been believed to be multifactorial, with environmental, behavioral, and genetic factors all contributing to the disease process. This review focuses specifically on examining the evidence that supports a genetic basis for keratoconus.

In vitro model suggests oxidative stress involved in keratoconus disease

Keratoconus (KC) affects 1:2000 people and is a disorder where cornea thins and assumes a conical shape. Advanced KC requires surgery to maintain vision. The role of oxidative stress in KC remains unclear. We aimed to identify oxidative stress levels between human corneal keratocytes (HCKs), fibroblasts (HCFs) and keratoconus cells (HKCs). Cells were cultured in 2D and 3D systems. Vitamin C (VitC) and TGF-β3 (T3) were used for 4 weeks to stimulate self-assembled extracellular matrix (ECM). No T3 used as controls. Samples were analyzed using qRT-PCR and metabolomics. qRT-PCR data showed low levels of collagen I and V, as well as keratocan for HKCs, indicating differentiation to a myofibroblast phenotype. Collagen type III, a marker for fibrosis, was up regulated in HKCs. We robustly detected more than 150 metabolites of the targeted 250 by LC-MS/MS per condition and among those metabolites several were related to oxidative stress. Lactate levels, lactate/malate and lactate/pyruvate ratios were elevated in HKCs, while arginine and glutathione/oxidized glutathione ratio were reduced. Similar patterns found in both 2D and 3D. Our data shows that fibroblasts exhibit enhanced oxidative stress compared to keratocytes. Furthermore the HKC cells exhibit the greatest level suggesting they may have a myofibroblast phenotype.

A multivariate analysis and statistical model for predicting visual acuity and keratometry one year after cross-linking for keratoconus

PURPOSE

To investigate putative prognostic factors for predicting visual acuity and keratometry 1 year following corneal cross-linking (CXL) for treating keratoconus.

DESIGN

Prospective cohort study.

METHODS

This study included all consecutively treated keratoconus patients (102 eyes) in 1 academic treatment center, with minimal 1-year follow-up following CXL. Primary treatment outcomes were corrected distance visual acuity (logMAR CDVA) and maximum keratometry (K(max)). Univariable analyses were performed to determine correlations between baseline parameters and follow-up measurements. Correlating factors (P ≤ .20) were then entered into a multivariable linear regression analysis, and a model for predicting CDVA and K(max) was created.

RESULTS

Atopic constitution, positive family history, and smoking were not independent factors affecting CXL outcomes. Multivariable analysis identified cone eccentricity as a major factor for predicting K(max) outcome (ß coefficient = 0.709, P = .02), whereas age, sex, and baseline keratometry were not independent contributors. Posttreatment visual acuity could be predicted based on pretreatment visual acuity (ß coefficient = -0.621, P < .01, R(2) = 0.45). Specifically, a low visual acuity predicts visual improvement. A prediction model for K(max) did not accurately estimate treatment outcomes (R(2) = 0.15).

CONCLUSIONS

Our results confirm the role of cone eccentricity with respect to the improvement of corneal curvature following CXL. Visual acuity outcome can be predicted accurately based on pretreatment visual acuity. Age, sex, and K(max) are debated as independent factors for predicting the outcome of treating keratoconus with CXL.

The pathogenesis of keratoconus

Keratoconus (KC) is a common degenerative condition that frequently results in visual loss with an onset typically in early adulthood. It is the single most common reason for keratoplasty in the developed world. The cause and underlying pathological mechanism are unknown, but both environmental and genetic factors are thought to contribute to the development of the disease. Various strategies have been employed to address the gap in our understanding of this complex disease, with the expectation that over time more sophisticated therapies will be developed. In this review we summarise our current knowledge of the aetiology and risk factors associated with KC.

Keratoconus: current perspectives

Keratoconus is characterized by progressive corneal protrusion and thinning, leading to irregular astigmatism and impairment in visual function. The etiology and pathogenesis of the condition are not fully understood. However, significant strides have been made in early clinical detection of the disease, as well as towards providing optimal optical and surgical correction for improving the quality of vision in affected patients. The past two decades, in particular, have seen exciting new developments promising to alter the natural history of keratoconus in a favorable way for the first time. This comprehensive review focuses on analyzing the role of advanced imaging techniques in the diagnosis and treatment of keratoconus and evaluating the evidence supporting or refuting the efficacy of therapeutic advances for keratoconus, such as newer contact lens designs, collagen crosslinking, deep anterior lamellar keratoplasty, intracorneal ring segments, photorefractive keratectomy, and phakic intraocular lenses.

The impairment of lysyl oxidase in keratoconus and in keratoconus-associated disorders

Keratoconus (KC) is an eye disease characterized by the progressive thinning and protrusion of the cornea, which results in the loss of visual acuity. This disorder remains poorly understood, although recent studies indicate the involvement of genetic and environmental factors. Recently, we have found that the distribution of the cross-linking enzyme lysyl oxidase (LOX) is markedly decreased in about 63 % of keratoconic specimens. Similarly, LOX activity is significantly reduced by 38 % compared to control tissue. Nearly 70 systemic disorders have been reported in association with KC, most of them affecting the extracellular matrix. In this review we attempted to ascertain whether any KC-associated diseases exhibit signs that may reflect LOX impairment. We hypothesized that very similar changes in the extracellular matrix, particularly at the level of collagen metabolism, including LOX impairment in mitral leaflets, may reflect an association between KC and mitral valve prolapse. Moreover, this putative association is supported by the high frequency of Down syndrome in both diseases. Among other disorders that have been found to coincide with KC, we did not find any in which the LOX enzyme may be directly or indirectly impaired. On the other hand, in cases where KC is present along with other connective tissue disorders (Marfan syndrome, Ehlers-Danlos syndrome and others), KC may not arise as a localized manifestation, but rather may be induced as the result of a more complex connective tissue disorder.