Contact lens

About: Contact lens is a research topic. Over the lifetime, 19941 publications have been published within this topic receiving 365827 citations. The topic is also known as: contact & contact lenses.

A Method of Measuring Eye Movemnent Using a Scieral Search Coil in a Magnetic Field

Abstract: With the subject exposed to an alternating magnetic field, eye position may be accurately recorded from the voltage generated in a coil of wire embedded in a scleral contact lens worn by the subject. Using two magnetic fields in quadrature phase and two coils on the lens, one may measure horizontal, vertical and torsional eye movements simultaneously. The instrument described has an accuracy and linearity of about 2 per cent of full scale, a resolution of 15 seconds of arc and a bandwidth of 1000 cyles per second.

Keratoconus and related noninflammatory corneal thinning disorders

Abstract: Keratoconus and other noninflammatory corneal thinning disorders (keratoglobus, pellucid marginal degeneration and posterior keratoconus) are characterized by progressive corneal thinning, protrusion and scarring; the result is distorted and decreased vision. The etiology and pathogenesis of these disorders are unknown but may be associated with a variety of factors, including contact lens wear, eye rubbing, Down's syndrome, atopic disease, connective tissue disease, tapetoretinal degeneration and inheritance. Recent advances in techniques for biochemical and pathological investigation are now allowing further exploration in these areas. Early diagnosis is aided by the finding of irregular corneal astigmatism with inferior corneal steepening. Treatment ranges from simple spectacle correction to keratoplasty. In this review, the past and present literature on corneal thinning disorders is reviewed and practical approaches to diagnosis and management are outlined.

Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach.

Abstract: We determined the "normal" central corneal thickness (CCT) value in human corneas based on reported literature values for within-study average CCT values, and used this as a reference to assess the reported impact of physiological variables (especially age and diurnal effects), contact lens wear, pharmaceuticals, ocular disease, and ophthalmic surgery on CCT. With the expected CCT and its variance defined, it should be possible to determine the potential impact of differences in CCT in intraocular pressure (IOP) assessments, especially by applanation tonometry, using a meta-analysis approach. Some 600 sets of CCT data were identified from the worldwide literature over the period of 1968 through mid-1999, of which 134 included IOP measures as well. The within-study average CCT values and reported variance (SD) was noted along with the number of eyes and any special characteristics, including probable ethnic origin of the study subjects. Various sets of data were subjected to statistical analyses. From 300 data sets from eyes designated as normal, the group-averaged CCT was 0.534 mm. From 230 data sets where interindividual variance was reported, the group-averaged CCT was 0.536 mm (median 0.536 mm; average SD of 0. 031 mm, average coefficient of variation = 5.8%). Overall, studies using slit-lamp-based pachometry have reported marginally lower CCT values (average 0.530 mm, average SD 0.029 mm) compared to ultrasound-based studies (average 0.544, average SD 0.034 mm), which perhaps reflects the type of individual studied (non-surgical vs. pre-surgical patients) rather than the technique itself. A slight chronological increase in reported average CCT values (approximately 0.006 mm/decade) was evident, but a substantial chronological increase was evident for ultrasound pachometry studies (approximately 0.015 mm/decade). Within the meta-analysis-generated average and variance, age had no obvious impact on CCT measures for *whites, although an age-related decline in CCT is evident for non-whites. Any diurnal effects are likely concealed within the expected variance in CCT. Contact lens wear and pharmaceuticals generally produced changes in CCT that were well within the expected variance in CCT. Of the ocular diseases, only those associated with collagen disorders (including keratoconus) or endothelial-based corneal dystrophies (e.g., Fuchs) were likely to result in decreases or increases, respectively, of CCT beyond the normal variance. Routine contact lens wear and diseases such as diabetes seem unlikely to produce changes in CCT of a magnitude that would justify pachometry as a monitoring method beyond routine slit-lamp evaluation. Increases in CCT beyond the expected variance were reported after a range of intraocular surgeries (cataract operations, penetrating keratoplasty), whereas photorefractive surgery produces a measurable decrease in CCT. A meta-analysis of possible association between CCT and IOP measures of 133 data sets, regardless of the type of eyes assessed, revealed a statistically significant correlation; a 10% difference in CCT would result in a 3. 4 +/- 0.9 mm Hg difference in IOP (P

The video head impulse test Diagnostic accuracy in peripheral vestibulopathy

Abstract: Background: The head impulse test (HIT) is a useful bedside test to identify peripheral vestibular deficits. However, such a deficit of the vestibulo-ocular reflex (VOR) may not be diagnosed because corrective saccades cannot always be detected by simple observation. The scleral search coil technique is the gold standard for HIT measurements, but it is not practical for routine testing or for acute patients, because they are required to wear an uncomfortable contact lens. Objective: To develop an easy-to-use video HIT system (vHIT) as a clinical tool for identifying peripheral vestibular deficits. To validate the diagnostic accuracy of vHIT by simultaneous measures with video and search coil recordings across healthy subjects and patients with a wide range of previously identified peripheral vestibular deficits. Methods: Horizontal HIT was recorded simultaneously with vHIT (250 Hz) and search coils (1,000 Hz) in 8 normal subjects, 6 patients with vestibular neuritis, 1 patient after unilateral intratympanic gentamicin, and 1 patient with bilateral gentamicin vestibulotoxicity. Results: Simultaneous video and search coil recordings of eye movements were closely comparable (average concordance correlation coefficient rc 0.930). Mean VOR gains measured with search coils and video were not significantly different in normal (p 0.107) and patients (p 0.073). With these groups, the sensitivity and specificity of both the reference and index test were 1.0 (95% confidence interval 0.69 –1.0). vHIT measures detected both overt and covert saccades as accurately as coils. Conclusions: The video head impulse test is equivalent to search coils in identifying peripheral vestibular deficits but easier to use in clinics, even in patients with acute vestibular neuritis. Neurology ® 2009;73:1134 –1141

Soft contact lens polymers: an evolution

Abstract: A review of patents and literature reveals an evolution in materials technologies. The evolution has been driven by an increased understanding of the physiological needs of the cornea, beginning with the first hydrogel lenses developed by Wichterle, followed by a variety of high water hydrogels. Oxygen transmission requirements have been addressed through the use of siloxane and fluorosiloxane containing hydrogels. An important development has been the appreciation of the importance of polymer phase morphology on lens movement on the eye. In parallel with these activities have come the advancements in materials suitable to high volume, low cost production necessary for today's daily disposable lenses.