1,029 research outputs found
Children's author and poet Carole Boston Weatherford
No full textIncludes descriptive metadata provided by producer in MP3 file: "Arts and Culture - Podcasts - Children's author and poet Carole Boston Weatherford.
Observation of solution-induced corneal staining with fluorescein, rose bengal and lissamine green
No full textEver since sodium fluorescein (‘fluorescein’ [FL]) was first used to investigate the ocular surface over a century ago, the term ‘staining’ has been taken to mean the presence of ocular surface fluorescence [1]. This term has not been necessarily taken to infer any particular mechanism of causation, and indeed, can be attributed to a variety of possible aetiologies [2].\ud
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In recent times, there has been considerable interest in a form of ocular surface fluorescence seen in association with the use of certain combinations of soft contact lenses and multipurpose solutions. The first clinical account of this phenomenon was reported by Jones et al. [3], which was followed by a more formal investigation by the same author in 2002 [4]. Jones et al described this appearance as a ‘classic solution-based toxicity reaction’. Subsequently, this appearance has come to be known as ‘solution-induced corneal staining’ or more recently by the acronym ‘SICS’ [5].\ud
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The term SICS is potentially problematic in that from a cell biology point of view, there is an inference that ‘staining’ means the entry of a dye into corneal epithelial cells. Morgan and Maldonado-Codina [2] noted there was no foundation of solid scientific literature underpinning our understanding of the true basic causative mechanisms of this phenomenon; since that time, further work has been published in this field [6] and [7] but questions still remain about the precise aetiology of this phenomenon..
Impact of manufacturing method on pre-lens tear film of soft pHEMA contact lenses (poster abstract)
No full textImpact of manufacturing method on the mechanical characteristics of pHEMA hydrogel lenses (poster abstract)
No full textImpact of manufacturing technology and material\ud composition on the surface characteristics\ud of hydrogel contact lenses
No full textBackground: Our aim was to investigate the impact of manufacturing method and\ud
material composition on the surface characteristics of hydrogel contact lenses.\ud
Methods: Five lens types were examined; three polyhydroxyethyl methacrylate (pHEMA)\ud
lenses, each manufactured by a different technique, namely, lathing, spin-casting and\ud
cast-moulding, a HEMA/methacrylic acid cast-moulded lens and a HEMA/glycerol\ud
methacrylate cast-moulded lens. Six lenses of each type were examined (front and back)\ud
using scanning electron microscopy (SEM). Additionally, both surfaces of three lenses\ud
from each of the pHEMA lens groups were examined, partially hydrated, using an atomic\ud
force microscope (AFM). Qualitative data were gathered for both SEM and AFM studies\ud
in addition to root-mean-square (RMS) roughness values for the lenses investigated\ud
with AFM.\ud
Results: The surfaces of the lathed lenses were covered in lathing/polishing marks. RMS\ud
roughness values for the anterior surface (10.9 ± 4.3 nm) were significantly greater\ud
(p = 0.02) than those of the posterior surface (9.3 ± 0.8 nm). The two surfaces of the\ud
spun-cast lens appeared similar by SEM but AFM RMS roughness values were greater\ud
(p = 0.02) for the anterior (12.3 ± 1.8 nm) than the posterior (5.8 ± 1.9 nm) surface. Both\ud
SEM and AFM showed similar topographic appearances for the surfaces of the cast-moulded\ud
pHEMA lens, although RMS roughness values were greater (p = 0.02) for the anterior\ud
(5.8 ± 0.9 nm) than the posterior (3.9 ± 0.3 nm) surface. All three cast-moulded lenses\ud
had more processing debris than the lathed and spun-cast pHEMA lenses. Overall, the\ud
surfaces of the lathed lens were 'rougher' than those of the cast-moulded lens (p = 0.01).\ud
Conclusion: The surface topographies of the hydrogel contact lenses are dependent on\ud
the method of manufacture. Cast-moulded lenses are associated with apparently 'stickier'\ud
surfaces, which may be indicative of surface degradation during the manufacturing\ud
process
Dynamic wettability of pHEMA-based hydrogel contact lenses
No full textStandard methods of contact angle analysis include sessile drop, captive bubble and Wilhelmy plate techniques; however, these methodologies are not particularly well suited for assessing the wettability of the surfaces of formed hydrogel contact lenses. This paper describes two methodologies that are adaptations of previously described techniques. The maximum adherent force method is an adaptation of the dynamic Wilhelmy plate technique that allows the assessment of whole, finished contact lenses. The dynamic photographic method allows the simultaneous assessment of the front and back surfaces of strip samples for the assessment of advancing and receding contact angles. Lenses investigated were made from polyhydroxyethyl methacrylate, hydroxyethyl methacrylate/methacrylic acid and hydroxyethyl methacrylate/glycerol methacrylate. The lenses were manufactured by lathing, spin-casting or cast-moulding techniques. Overall, both techniques demonstrated few differences between the wettability of different lens materials and no differences between materials of the 'same' lens type but manufactured by different methods. These findings are consistent with the results of clinical studies, which have shown little difference between contact lens surface wettability in vivo, which may be due to the apparent natural surface wettability-enhancing properties of the pre-lens tear film. © 2006 The College of Optometrists
Impact of manufacturing technology and material composition on the clinical performance of hydrogel lenses
No full textPurpose. To establish the clinical impact of three different methods of manufacture used to produce soft contact lenses. Methods. Clinical performance of five lens types was investigated by undertaking a prospective, double-masked, randomized, crossover study. Three of the lenses were made from poly(hydroxyethyl methacrylate) (pHEMA) by three different manufacturing processes (lathing, spin casting, and cast molding), and the remaining two lenses were cast molded from different materials-hydroxyethyl methacrylate/methacrylic acid and hydroxyethyl methacrylate/glycerol methacrylate (HEMA/GMA). All lenses were specially fabricated for this work at the same manufacturing plant. Thirty-four soft contact lens wearers wore each lens for 1 month on a daily-wear basis. Several clinical variables, such as ocular response, visual acuity, lens fitting, prelens tear film, lens surface dehydration, subjective response, and protein deposition, were measured. Results. In general, the spun-cast pHEMA lens performed inferiorly compared with the other pHEMA lenses. This lens induced significantly more limbal and conjunctival hyperemia than the cast-molded lens and provided poorer low contrast visual acuity (LCVA) than the other two lenses. It dehydrated more and had the least on-eye movement. However, the spun-cast lens deposited the least protein of the pHEMA lenses. In general, the HEMA/GMA lens performed inferiorly compared with the other cast-molded lenses. LCVA was worse with this lens, and subjective responses showed that this lens was thought to give the worst visual performance of the cast-molded lenses. It was also thought to be the most difficult lens to handle. Significantly more breakages occurred with this lens than any other. Conclusions. Overall, this work has shown that manufacturing method and material composition have a fundamental effect on many clinical properties of a lens. Therefore, method of manufacture is also an important consideration in the overall production of a soft lens
Development of Contact Lenses from a Biomaterial Point of View – Materials, Manufacture, and Clinical Application
No full textRigid lenses, which were originally made from glass (between 1888 and 1940) and later from polymethyl methacrylate or silicone acrylate materials, are uncomfortable to wear and are now seldom fitted to new patients. Contact lenses became a popular mode of ophthalmic refractive error correction following the discovery of the first hydrogel material – hydroxyethyl methacrylate – by Czech chemist Otto Wichterle in 1960. To satisfy the requirements for ocular biocompatibility, contact lenses must be transparent and optically stable (for clear vision), have a low elastic modulus (for good comfort), have a hydrophilic surface (for good wettability), and be permeable to certain metabolites, especially oxygen, to allow for normal corneal metabolism and respiration during lens wear. A major breakthrough in respect of the last of these requirements was the development of silicone hydrogel soft lenses in 1999 and techniques for making the surface hydrophilic. The vast majority of contact lenses distributed worldwide are mass-produced using cast molding, although spin casting is also used. These advanced mass-production techniques have facilitated the frequent disposal of contact lenses, leading to improvements in ocular health and fewer complications. More than one-third of all soft contact lenses sold today are designed to be discarded daily (i.e., ‘daily disposable’ lenses)
Impact of manufacturing technology and material composition on the mechanical properties of hydrogel contact lenses
No full textHydrogel materials are not only different as a result of different co-monomer compositions but also as a result of the manufacturing method used to produce them. Hydrogel contact lenses fabricated by different methods are subjected to markedly different processing steps, which are likely to affect the resultant material network structure of a lens. The mechanical performance of five soft contact lens types was investigated using one conventional technique (tensile test) and three novel techniques (probe, tear and ball milling tests). The five lens groups consisted of three polyhydroxyethyl methacrylate (pHEMA) lenses which were each manufactured by a different technique: lathing, spincasting and cast-moulding, a HEMA/methacrylic acid (HEMA/MAA) cast-moulded lens and a HEMA/glycerol methacrylate (HEMA/GMA) cast-moulded lens. Overall, the results show that the best mechanical performance is obtained for the pHEMA lenses, with some differences occurring between the lenses. The HEMA/GMA lens showed the worst performance. © 2004 The College of Optometrists
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