Distribution of ocular biometry in 7- and 14-year-old Chinese children

Purpose: To describe distributions of ocular biometry and their associations with refraction in 7- and 14-year-old children in urban areas of Anyang, central China. Methods: A total of 2271 grade 1 students aged 7.1 ± 0.4 years and 1786 grade 8 students aged 13.7 ± 0.5 years were measured with ocular biometry and cycloplegic refraction. A parental myopia questionnaire was administered to parents. Results: Mean axial length, anterior chamber depth, lens thickness, central corneal thickness, corneal diameter, corneal radius of curvature, axial length/corneal radius of curvature ratio, and spherical equivalent refraction were 22.72 ± 0.76 mm, 2.89 ± 0.24 mm, 3.61 ± 0.19 mm, 540.5 ± 31 μm, 12.06 ± 0.44 mm, 7.80 ± 0.25 mm, 2.91 ± 0.08, and +0.95 ± 1.05 diopters (D), respectively, in 7-year-old children. They were 24.39 ± 1.13 mm, 3.42 ± 0.41 mm, 3.18 ± 0.24 mm, 548.9 ± 33 μm, 12.03 ± 0.43 mm, 7.80 ± 0.26 mm, 3.13 ± 0.14, and −2.06 ± 2.20 D, respectively, in 14-year-old children. Compared with 7-year-old children, the older group had significantly more myopia (−3.0 D), longer axial length (1.7 mm), deeper anterior chamber depth (0.3 mm), thinner lens thickness (−0.2 mm), thicker central corneal thickness (10 μm), and greater axial length/corneal radius of curvature ratio (0.22) (all p < 0.001), as well as smaller corneal diameter (−0.03 mm, p = 0.02) and similar corneal radius of curvature. Sex differences were similar in both age groups, with boys having longer axial length (0.5 mm), deeper anterior chamber depth (0.1 mm), shorter lens thickness (0.03 mm), greater central corneal thickness (5 μm), greater corneal diameter (0.15 mm), and greater corneal radius of curvature (0.14 mm) than girls (all p < 0.01). The most important variables related to spherical equivalent refraction were vitreous length, corneal radius of curvature, and lens thickness. Conclusions: The 14-year-old group had larger parameter dimensions than the 7-year-old group except for corneal radius of curvature (unchanged) and lens thickness and corneal diameter (both smaller). Boys had large parameter dimensions than girls except for lens thickness (smaller). Axial length, corneal radius of curvature, and lens thickness were the most important determinants of refraction.

Paraxial schematic eye models for 7- and 14-year-old Chinese children

Purpose.: To develop three-surface paraxial schematic eyes with different ages and sexes based on data for 7- and 14-year-old Chinese children from the Anyang Childhood Eye Study. Methods.: Six sets of paraxial schematic eyes, including 7-year-old eyes, 7-year-old male eyes, 7-year-old female eyes, 14-year-old eyes, 14-year-old male eyes, and 14-year-old female eyes, were developed. Both refraction-dependent and emmetropic eye models were developed, with the former using linear dependence of ocular parameters on refraction. Results.: A total of 2059 grade 1 children (boys 58%) and 1536 grade 8 children (boys 49%) were included, with mean age of 7.1 ± 0.4 and 13.7 ± 0.5 years, respectively. Changes in these schematic eyes with aging are increased anterior chamber depth, decreased lens thickness, increased vitreous chamber depth, increased axial length, and decreased lens equivalent power. Male schematic eyes have deeper anterior chamber depth, longer vitreous chamber depth, longer axial length, and lower lens equivalent power than female schematic eyes. Changes in the schematic eyes with positive increase in refraction are decreased anterior chamber depth, increased lens thickness, decreased vitreous chamber depth, decreased axial length, increased corneal radius of curvature, and increased lens power. In general, the emmetropic schematic eyes have biometric parameters similar to those arising from regression fits for the refraction-dependent schematic eyes. Conclusions.: The paraxial schematic eyes of Chinese children may be useful for myopia research and for facilitating comparison with other children with the same or different racial backgrounds and living in different places.

Do small-aperture presbyopic corrections influence the visual field?

Purpose To explore the effect of small-aperture optics, designed to aid presbyopes by increasing ocular depth-of-focus, on measurements of the visual field. Methods Simple theoretical and ray-tracing models were used to predict the impact of different designs of small-aperture contact lenses or corneal inlays on the proportion of light passing through natural pupils of various diameters as a function of the direction in the visual field. The left eyes of five healthy volunteers were tested using three afocal, hand-painted opaque soft contact lenses (www.davidthomas.com). Two were opaque over a 10 mm diameter but had central clear circular apertures of 1.5 and 3.0 mm in diameter. The third had an annular opaque zone with inner and outer diameters of 1.5 and 4.0 mm, approximately simulating the geometry of the KAMRA inlay (www.acufocus.com). A fourth, clear lens was used for comparison purposes. Visual fields along the horizontal meridian were evaluated up to 50° eccentricity with static automated perimetry (Medmont M700, stimulus Goldmann-size III; www.medmont.com). Results According to ray-tracing, the two lenses with the circular apertures were expected to reduce the relative transmittance of the pupil to zero at specific field angles (around 60° for the conditions of the experimental measurements). In contrast, the annular stop had no effect on the absolute field but relative transmittance was reduced over the central area of the field, the exact effects depending upon the natural pupil diameter. Experimental results broadly agreed with these theoretical expectations. With the 1.5 and 3.0 mm pupils, only minor losses in sensitivity (around 2 dB) in comparison with the clear-lens case occurred across the central 10° radius of field. Beyond this angle, sensitivity losses increased, to reach about 7 dB at the edge of the measured field (50°). The field results with the annular stop showed at most only a slight loss in sensitivity (≤3 dB) across the measured field. Conclusion The present theoretical and experimental results support earlier clinical findings that KAMRA-type annular stops, unlike circular artificial pupils, have only minor effects on measurements of the visual field.

Mechanical testing of internal fixation devices: A theoretical and practical examination of current methods

Successful healing of long bone fractures is dependent on the mechanical environment created within the fracture, which in turn is dependent on the fixation strategy. Recent literature reports have suggested that locked plating devices are too stiff to reliably promote healing. However, in vitro testing of these devices has been inconsistent in both method of constraint and reported outcomes, making comparisons between studies and the assessment of construct stiffness problematic. Each of the methods previously used in the literature were assessed for their effect on the bending of the sample and concordant stiffness. The choice of outcome measures used in in vitro fracture studies was also assessed. Mechanical testing was conducted on seven hole locked plated constructs in each method for comparison. Based on the assessment of each method the use of spherical bearings, ball joints or similar is suggested at both ends of the sample. The use of near and far cortex movement was found to be more comprehensive and more accurate than traditional centrally calculated inter fragmentary movement values; stiffness was found to be highly susceptible to the accuracy of deformation measurements and constraint method, and should only be used as a within study comparison method. The reported stiffness values of locked plate constructs from in vitro mechanical testing is highly susceptible to testing constraints and output measures, with many standard techniques overestimating the stiffness of the construct. This raises the need for further investigation into the actual mechanical behaviour within the fracture gap of these devices.

Experimental and numerical investigation of strain-rate-dependent behavior of kangaroo shoulder cartilage

This thesis introduces a new animal model, kangaroo, to biomechanical investigations of shoulder cartilage research. It examines the effect of cartilage structure and constituents on tissue behavior and its adaptation to mechanical loading. In doing so, the study explains the relationship of tissue's functional behaviors to its structure and constituents which has important implications for tissue engineering strategies catering joint specific cartilage tissue generation.

Investigation of the effects of extracellular osmotic pressure on morphology and mechanical 1 properties of individual chondrocyte

It has been demonstrated that most cells of the body respond to osmotic pressure in a systematic manner. The disruption of the collagen network in the early stages of osteoarthritis causes an increase in water content of cartilage which leads to a reduction of pericellular osmolality in chondrocytes distributed within the extracellular environment. It is therefore arguable that an insight into the mechanical properties of chondrocytes under varying osmotic pressure would provide a better understanding of chondrocyte mechanotransduction and potentially contribute to knowledge on cartilage degeneration. In this present study, the chondrocyte cells were exposed to solutions with different osmolality. Changes in their dimensions and mechanical properties were measured over time. Atomic Force Microscopy (AFM) was used to apply load at various strain-rates and the force-time curves were logged. The thin-layer elastic model was used to extract the elastic stiffness of chondrocytes at different strain-rates and at different solution osmolality. In addition, the porohyperelastic (PHE) model was used to investigate the strain-rate dependent responses under the loading and osmotic pressure conditions. The results revealed that the hypo-osmotic external environment increased chondrocyte dimensions and reduced Young’s modulus of the cells at all strain-rates tested. In contrast, the hyper-osmotic external environment reduced dimensions and increased Young’s modulus. Moreover, by using the PHE model coupled with inverse FEA simulation, we established that the hydraulic permeability of chondrocytes increased with decreasing extracellular osmolality which is consistent with previous work in the literature. This could be due to a higher intracellular fluid volume fraction with lower osmolality.

Tissue compression following short-term miniscleral contact lens wear

To quantify regional (nasal, superior, temporal and inferior) and location specific (corneal and scleral) tissue compression following short-term miniscleral contact lens wear.

Induced higher-order aberrations after laser in situ keratomileusis (LASIK) performed with wavefront-guided IntraLase femtosecond laser in moderate to high astigmatism

Background Wavefront-guided Laser-assisted in situ keratomileusis (LASIK) is a widespread and effective surgical treatment for myopia and astigmatic correction but whether it induces higher-order aberrations remains controversial. The study was designed to evaluate the changes in higher-order aberrations after wavefront-guided ablation with IntraLase femtosecond laser in moderate to high astigmatism. Methods Twenty-three eyes of 15 patients with moderate to high astigmatism (mean cylinder, −3.22 ± 0.59 dioptres) aged between 19 and 35 years (mean age, 25.6 ± 4.9 years) were included in this prospective study. Subjects with cylinder ≥ 1.5 and ≤2.75 D were classified as moderate astigmatism while high astigmatism was ≥3.00 D. All patients underwent a femtosecond laser–enabled (150-kHz IntraLase iFS; Abbott Medical Optics Inc) wavefront-guided ablation. Uncorrected (UDVA), corrected (CDVA) distance visual acuity in logMAR, keratometry, central corneal thickness (CCT) and higher-order aberrations (HOAs) over a 6 mm pupil, were assessed before and 6 months, postoperatively. The relationship between postoperative change in HOA and preoperative mean spherical equivalent refraction, mean astigmatism, and postoperative CCT were tested. Results At the last follow-up, the mean UDVA was increased (P < 0.0001) but CDVA remained unchanged (P = 0.48) and no eyes lost ≥2 lines of CDVA. Mean spherical equivalent refraction was reduced (P < 0.0001) and was within ±0.50 D range in 61 % of eyes. The average corneal curvature was flatter by 4 D and CCT was reduced by 83 μm (P < 0.0001, for all), postoperatively. Coma aberrations remained unchanged (P = 0.07) while the change in trefoil (P = 0.047) postoperatively, was not clinically significant. The 4th order HOAs (spherical aberration and secondary astigmatism) and the HOA root mean square (RMS) increased from −0.18 ± 0.07 μm, 0.04 ± 0.03 μm and 0.47 ± 0.11 μm, preoperatively, to 0.33 ± 0.19 μm (P = 0.004), 0.21 ± 0.09 μm (P < 0.0001) and 0.77 ± 0.27 μm (P < 0.0001), six months postoperatively. The change in spherical aberration after the procedure increased with an increase in the degree of preoperative myopia. Conclusions Wavefront-guided IntraLASIK offers a safe and effective option for vision and visual function improvement in astigmatism. Although, reduction of HOA is possible in a few eyes, spherical-like aberrations are increased in majority of the treated eyes.

The Use of Mesenchymal Stromal Cells in the Treatment of Diseases of the Cornea

As a key component of the ocular surface required for vision, the cornea has been extensively studied as a site for cell and tissue-based therapies. Historically, these treatments have consisted of donor corneal tissue transplants, but cultivated epithelial autografts have become established over the last 15 years as a routine treatment for ocular surface disease. Ultimately, these treatments are performed with the intention of restoring corneal transparency and a smooth ocular surface. The degree of success, however, is often dependent upon the inherent level of corneal inflammation at time of treatment. In this regard, the anti-inflammatory and immuno-modulatory properties of mesenchymal stromal cells (MSC) have drawn attention to these cells as potential therapeutic agents for corneal repair. The origins for MSC-based therapies are founded in part on observations of the recruitment of endogenous bone marrow-derived cells to injured corneas, however, an increasing quantity of data is emerging for MSC administered following their isolation and ex vivo expansion from a variety of tissues including bone marrow, adipose tissue, umbilical cord and dental pulp. In brief, evidence has emerged of cultured MSC, or their secreted products, having a positive impact on corneal wound healing and retention of corneal allografts in animal models. Optimal dosage, route of administration and timing of treatment, however, all remain active areas of investigation. Intriguingly, amidst these studies, have emerged reports of MSC transdifferentiation into corneal cells. Clearest evidence has been obtained with respect to expression of markers associated with the phenotype of corneal stromal cells. In contrast, the evidence for MSC conversion to corneal epithelial cell types remains inconclusive. In any case, the conversion of MSC into corneal cells seems unlikely to be an essential requirement for their clinical use. This field of research has recently become more complicated by reports of MSC-like properties for cultures established from the peripheral corneal stroma (limbal stroma). The relationship and relative value of corneal-MSC compared to traditional sources of MSC such as bone marrow are at present unclear. This chapter is divided into four main parts. After providing a concise overview of corneal structure and function, we will highlight the types of corneal diseases that are likely to benefit from the anti-inflammatory and immuno-modulatory properties of MSC. We will subsequently summarize the evidence supporting the case for MSC-based therapies in the treatment of corneal diseases. In the third section we will review the literature concerning the keratogenic potential of MSC. Finally, we will review the more recent literature indicating the presence of MSC-like cells derived from corneal tissue.

Biomaterials and Regenerative Medicine in Ophthalmology [2nd Edition]

"Biomaterials and Regenerative Medicine in Ophthalmology, Second Edition, focuses on an aging population and the increasing instances of eye diseases. Biomaterials continue to be used for numerous medical devices for the restoration of eyesight, improving many patients’ quality of life. Consequently, biomaterials and regenerative medicine are becoming increasingly important to the advances of ophthalmology and optometry. This book provides readers with an updated and expanded look at the present status and future direction of biomaterials and regenerative medicine in this important field."--Publisher website

Reconstruction of the ocular surface using biomaterial templates

This chapter discusses the effect on vision of a large group of pathological conditions, known as ocular surface disorders (OSDs), and presents the therapeutic strategies to reconstruct the abnormal ocular surface. If left untreated, most of the OSDs will lead to partial or total loss of eyesight, especially when limbal stem cell deficiency is involved. An overview of various treatment strategies is presented, with the emphasis on the development of the ex vivo expansion of corneal limbal epithelial cells (presumed to be progenitor or stem cells) and the creation of transplantable epithelial constructs. The use of naturally derived biomaterials (collagen, fibrin, amnion, etc.) or synthetic polymers (polylactides, thermoresponsive polymers, etc.) as substrata in these constructs is critically analyzed. Emphasis is placed on the templates from silk proteins, which are being developed by the authors.

Evaluation of the AlgerBrush II rotating burr as a tool for inducing ocular surface failure in the New Zealand White rabbit

The New Zealand White rabbit has been widely used as a model of limbal stem cell deficiency (LSCD). Current techniques for experimental induction of LSCD utilize caustic chemicals, or organic solvents applied in conjunction with a surgical limbectomy. While generally successful in depleting epithelial progenitors, the depth and severity of injury is difficult to control using chemical-based methods. Moreover, the anterior chamber can be easily perforated while surgically excising the corneal limbus. In the interest of creating a safer and more defined LSCD model, we have therefore evaluated a mechanical debridement technique based upon use of the AlgerBrush II rotating burr. An initial comparison of debridement techniques was conducted in situ using 24 eyes in freshly acquired New Zealand White rabbit cadavers. Techniques for comparison (4 eyes each) included: (1) non-wounded control, (2) surgical limbectomy followed by treatment with 100% (v/v) n-heptanol to remove the corneal epithelium (1-2 minutes), (3) treatment of both limbus and cornea with n-heptanol alone, (4) treatment of both limbus and cornea with 20% (v/v) ethanol (2-3 minutes), (5) a 2.5-mm rounded burr applied to both the limbus and cornea, and (6) a 1-mm pointed burr applied to the limbus, followed by the 2.5-mm rounded burr applied to the cornea. All corneas were excised and processed for histology immediately following debridement. A panel of four assessors subsequently scored the degree of epithelial debridement within the cornea and limbus using masked slides. The 2.5-mm burr most consistently removed the corneal and limbal epithelia. Islands of limbal epithelial cells were occasionally retained following surgical limbectomy/heptanol treatment, or use of the 1-mm burr. Limbal epithelial cells were consistently retained following treatment with either ethanol or n-heptanol alone, with ethanol being the least effective treatment overall. The 2.5-mm burr method was subsequently evaluated in the right eye of 3 live rabbits by weekly clinical assessments (photography and slit lamp examination) for up to 5 weeks, followed by histological analyses (hematoxylin & eosin stain, periodic acid-Schiff stain and immunohistochemistry for keratin 3 and 13). All 3 eyes that had been completely debrided using the 2.5-mm burr displayed symptoms of ocular surface failure as defined by retention of a prominent epithelial defect (~40% of corneal surface at 5 weeks), corneal neovascularization (2 to 3 quadrants), reduced corneal transparency and conjunctivalization of the corneal surface (demonstrated by the presence of goblet cells and/or staining for keratin 13). In conclusion, our findings indicate that the AlgerBrush II rotating burr is an effective method for the establishment of ocular surface failure in New Zealand White rabbits. In particular, we recommend use of the 2.5-mm rotating burr for improved efficiency of epithelial debridement and safety compared to surgical limbectomy.