摘要:

AbstractEquations are presented for the theoretical determination of back vertex power changes in soft contact lenses due to bending. The main assumption is that the volume of the lens remains unchanged. A description of changes in other lens parameters, namely, central thickness, overall diameter, and anterior radii, is presented for both spherical and toric lenses. In general, power changes predicted by the proposed model are less than those suggested by previous workers in this field. Changes however occur in other parameters which have previously been regarded as remaining constant such as the central thickness of the lens. These changes are of small degree but have significant bearing on back vertex power.

ISSN:0093-7002    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

AbstractMathematical formulas are used to infer volumetric tear exchange from power changes of flexible contact lenses in situ. These calculations are developed from changes along the radius, and must be considered approximate due to several underlying assumptions.

ISSN:0093-7002    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

AbstractA group of 10 subjects were optimally fitted with soft lenses by photoelectronic keratoscopic analysis of corneal form. Lenses with diameters of 12.8 and 13.5 mm were worn incorporating prism ballasting varying between 0 and 1.5Δ in 0.25Δ steps and truncation between 0 and 2.0 mm in 0.5-mm steps. The performance of each lens was evaluated according to eight commonly applied clinical criteria: visual stability, lens position, recentering ability, amount and direction of movement, subjective comfort, meridional location of the lens, and amount of blink-initiated rotation. No benefit in performance was obtained from incorporating larger amounts of prism and truncation in the lens design, the best combination being 0.75Δ with 0.5-mm truncation. As a single stabilizing feature, truncation appeared more effective in locating a lens in the correct meridian than prism ballasting. It was found that corneal-fitting soft lenses of differing diameters (between 12.8 and 13.5 mm) performed similarly with the same stabilizing features.

ISSN:0093-7002    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

AbstractOxygen tensions were calculated under two different oxygen-permeable, flexible contact lenses (daily wear and extended wear) both with and without consideration of tear layers (but without tear exchange). Tear layers do not have significant effects on precorneal oxygen tension.

ISSN:0093-7002    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

AbstractA comparison of results obtained by direct and indirect methods of ophthalmodynamometry on nine patients indicates that the indirect method provides dependable results. In some eyes, only the indirect method is possible. As with direct ophthalmodynamometry, a difference of 20% or greater between the two eyes suggests carotid insufficiency on the side of the eye with the lower pressure.

ISSN:0093-7002    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

AbstractEight myopic patients wearing Permalens contact lenses continuously for 18 months were monitored for corneal thickness changes. The averaged results showed maximum corneal swelling after 1 week of wear with the cornea gradually returning to near prefitting thickness levels. However, great individual variation in corneal thickness response was noted with some patients showing chronic corneal thickening and some showing corneal thinning after the 18-month wearing period.

ISSN:0093-7002    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

AbstractDr. W. F. Long pointed out that calculations of decentration in spherocylindrical lenses, as well as calculations of combinations of obliquely crossed spherocylindrical lenses, are considerably simplified by the use of matrix methods. In the obliquely crossed lens problem, Long used eigenvalue techniques to obtain the sphere, cylinder, and axis of the equivalent lens. This paper presents an alternative to the eigenvalue method. This alternative method uses the invariance of the trace and determinant of the dioptric power matrix. This alternative is conceptually easier to understand than the eigenvalue method and perhaps will encourage more people to use the matrix methods.

ISSN:0093-7002    

出版商:OVID    

年代:1980

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1980

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1980

数据来源: OVID