SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Astigmatism

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OBJECTIVE: Because of the northern location of Denmark, the length of the day over the year varies from 7 to 17.5 hours. Experimental and clinical results suggest that the development of myopia may be related to ambient light exposure. The purpose of current study was to investigate whether axial eye growth, myopia progression, or corneal power change in Danish myopic children varies with the length of the day. DESIGN: Cross-sectional study. PARTICIPANTS: Two hundred thirty-five children 8 to 14 years of age found to have myopia during screening for a clinical trial (ClinicalTrial.gov identifier, NCT00263471; accessed December 6, 2005). All children found to have any value of spherical equivalent that was myopic (<0 diopters [D]) at the first of 2 visits were included. METHODS: Cycloplegic refraction was measured using an autorefractor, axial eye length, and corneal power using an automatic combined noncontact partial coherence interferometer and keratometer. The accumulated number of daylight hours during the measurement period was calculated for each participant using an astronomical table. MAIN OUTCOME MEASURES: Change over 6 months in axial length, refraction, and corneal power. RESULTS: Accumulated hours of daylight ranged from 1660 to 2804 hours. Significant correlations were found between hours of daylight and eye elongation (P = 0.00), myopia progression (P = 0.01), and corneal power change (P = 0.00). In children with an average of 2782±19 hours of daylight, axial eye growth was 0.12±0.09 mm, myopia progression was 0.26±0.27 D, and corneal power change was 0.05±0.10 D per 6 months, whereas in children with an average of 1681±24 hours of daylight, axial eye growth was 0.19±0.10 mm, myopia progression was 0.32±0.27 D, and corneal power change was -0.04±0.08 D per 6 months. CONCLUSIONS: Eye elongation and myopia progression seem to decrease in periods with longer days and to increase in periods with shorter days. Children should be encouraged to spend more time outside during daytime to prevent myopia. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Concepts: Cornea, Myopia, Refractive surgery, Lens, Astigmatism, Orthokeratology, Eyeglass prescription, Contact lens

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To determine the contribution of posterior corneal astigmatism to total corneal astigmatism and the error in estimating total corneal astigmatism from anterior corneal measurements only using a dual-Scheimpflug analyzer.

Concepts: Astigmatism

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To compare the corneal astigmatism (magnitude and axis location) derived by total corneal power (TCP), automated keratometry, and simulated keratometry.

Concepts: Comparison, Cornea, Ophthalmology, Comparisons, Astigmatism

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PURPOSE:: To examine the agreement and relationship between refractive and corneal astigmatism in a population of pseudophakic eyes. METHODS:: Patients of age at least 40 years, visual acuity 20/40 or better, and no ocular disease were included (n = 111). Refractive astigmatism was obtained by subjective refraction. Corneal astigmatism was measured by automated keratometry and Scheimpflug scanning analysis. All refractive values were converted to power vector components J0 and J45 for comparison and regression analysis of refractive versus corneal astigmatism. Main outcome measures were refractive and corneal astigmatism components. RESULTS:: Median single Jackson cylinder (J) was similar in refractive [0.37 diopter (D)], keratometric (0.46 D), and Pentacam astigmatism (0.49 D) (P = 0.157). Median J0 astigmatic component was slightly negative, indicating against-the-rule (ATR) astigmatism, in refractive and Scheimpflug, but not in keratometric astigmatism (refractive J0: -0.10 D; keratometric J0: 0.05 D; Pentacam J0: -0.08 D) (P = 0.049). J45 astigmatic component was nearly zero and similar with the 3 methods (P = 0.416). Refractive and keratometric J0 were significantly correlated (r = 0.7, P < 0.01), as well as the corresponding J45 values (r = 0.65, P < 0.01). Refractive and Pentacam astigmatic components were worse correlated (J0: r = 0.36, P = 0.01; J45: r = 0.45, P < 0.01). Keratometric and Pentacam astigmatic components were also significantly correlated (J0: r = 0.58, P < 0.01; J45: r = 0.51, P < 0.01). CONCLUSIONS:: Mean internal ATR astigmatism, which comes mainly from the posterior corneal surface, adds to anterior corneal astigmatism, resulting in ATR refractive astigmatism. Correlation between refractive and corneal astigmatism components is better when keratometric data are used.

Concepts: Eye, Visual acuity, Cornea, Prediction interval, Lens, Astigmatism, Refractive error

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Myopia is an important public health issue, and high myopia may lead to severe complications if left untreated. Orthokeratology lenses, worn overnight to reshape the cornea, are one of many recent modalities used to slow down the progression of myopia in children. This treatment has been proven successful, as evidenced by decreased spherical refractive error and axial length relative to the control at interval follow-up ranging from 6 months to 5 years. In this systematic review, the authors collected published controlled studies that analyzed the efficacy of orthokeratology lens wear and calculated longitudinal relative changes in axial length, revealing a weighted average of -45.1% change in axial length at the 2-year follow-up. The exact mechanism by which orthokeratology lenses reduce myopia progression is unknown, but research shows that the corneal reshaping decreases peripheral hyperopic defocus and therefore increases peripheral myopic defocus to likely reduce stimuli for axial elongation and subsequent development of myopia. Use of orthokeratology lenses is generally safe, but cases of associated infectious keratitis may have a higher incidence of virulent organisms such as Pseudomonas, Acanthamoeba, and antibacterial-resistant strains of Staphylococcus, partially due to the required overnight use of these lenses. Orthokeratology is regarded as one of the most effective non-pharmacologic measures to slow progression of myopia in children and, with regular follow-up to ensure safety, continues to be one of the most effective treatments for myopia management around the world. [J Pediatr Ophthalmol Strabismus. 201X;XX(X):XX-XX.].

Concepts: Cornea, Myopia, Refractive surgery, Lens, Astigmatism, Orthokeratology, Contact lens, Glasses

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To evaluate the safety and efficacy of corneal collagen crosslinking (CXL) for the treatment of corneal ectasia after laser refractive surgery.

Concepts: Surgery, Laser, Cornea, Refractive surgery, Astigmatism, LASIK, Keratoconus, Multicenter trial

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To examine internal astigmatism (IA) in myopes and non-myopes using a new method to assess compensation of corneal astigmatism (CA) by IA, to look for predictors of high IA in young adult myopes, and to determine if as CA changes IA changes to reduce refractive astigmatism (RA) in an active compensatory process in myopes.

Concepts: Myopia, Refractive surgery, Lens, Astigmatism, Refractive error

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Keratoconus management has significantly changed over the last two decades. The advent of new interventions such as cornea cross-linking, intrastromal corneal ring segments, and combined treatments provide corneal clinicians a variety of treatment options for the visual rehabilitation of keratoconus patients. This review summarizes current evidence for these treatments and highlights their place in keratoconus management while new promising emerging therapies are being investigated.

Concepts: Cornea, Corneal transplantation, Refractive surgery, Astigmatism, Contact lens

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Keratoconus (KC) is a progressive corneal ectasia linked to thinning of the central cornea. Hard contact lenses, rigid gas permeable lenses, and scleral lenses are the primary treatment modalities for early to mid- stages of KC to correct refractive error and astigmatism that develops as a result of an irregular corneal structure. These treatments are associated with significant drawbacks, including reduced availability of the tear film and oxygen to the corneal epithelium and stroma. However, it remains unknown whether hypoxia affects corneal integrity in the KC pathobiology. A number of studies have associated elevated oxidative stress with KC both in vitro and ex vivo. We hypothesized that KC-derived corneal fibroblasts are more susceptible to hypoxia-induced oxidative stress compared to healthy controls leading to exacerbation of corneal thinning in KC. This study investigated the effects of hypoxia on ECM secretion, assembly, and matrix metalloproteinase (MMP) expression in human corneal fibroblasts from healthy controls (HCFs) and KC patients (HKCs) in vitro. HCFs and HKCs were cultured in 3D constructs for 3 weeks and maintained or transferred to normoxic (21% O2) or hypoxic (2% O2) conditions, respectively, for 1 additional week. At the 4 week time-point, constructs were isolated and probed for Collagen I, III, and V, keratocan and MMP-1, -2, -3, -9, and -13, as well as hypoxia markers, hypoxia inducible factor-1α and lactoferrin. Conditioned media was also collected and probed for Collagen I, III, and V by Western blot. Thickness of the ECM assembled by HCFs and HKCs was measured using immunofluorescence microscopy. Results showed that hypoxia significantly reduced Collagen I secretion in HKCs, as well as upregulated the expression of MMP-1 and -2 with no significant effects on MMP-3, -9, or -13. ECM thickness was reduced in both cell types following 1 week in a low oxygen environment. Our study shows that hypoxia influences collagen and MMP expression by HKCs, which may have consequential effects on ECM structure in the context of KC.

Concepts: Cornea, Corneal transplantation, Astigmatism, Contact lens, Contact lenses, Tears, Keratoconus, Scleral lens

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Despite extensive knowledge regarding the diagnosis and management of keratoconus and ectatic corneal diseases, many controversies still exist. For that reason, there is a need for current guidelines for the diagnosis and management of these conditions.

Concepts: Truth, Epistemology, Cornea, Corneal transplantation, Refractive surgery, Astigmatism, Contact lens