ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Attachment ofAcanthamoebaspecies to hydrogel contact lenses is a possible route of infection inAcanthamoebakeratitis. In this study,Acanthamoebaadsorption was compared with extent of lens deposition in worn lenses of different hydrogel polymers. After wear, lenses (80 lenses of 5 different types) were analyzed for total protein, surface area of deposition, andAcanthamoeba castellanitrophozoite and cyst adsorption. Adsorption ofAcanthamoebatrophozoites to worn lenses was greater than adsorption to unworn lenses for four of the five lens polymers (p < 0.01). Adsorption of cysts was greater for one of the five lens polymers (p < 0.001); all other adsorption assays showed no change with wear (p > 0.05). Adsorption was affected by both the water content and ionicity of the lens polymer. These results show that adsorption ofAcanthamoebato worn hydrogel contact lenses is greater than or equal to adsorption to unworn lenses.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Keratoconus is typically managed by a variety of rigid contact lens fitting techniques and lens designs. The two most fundamental fitting techniques are apical corneal touch (including divided or three-point touch) and apical clearance. In the course of designing a multi-center study of keratoconus patients, a standardized keratoconus fitting protocol was developed. All contact lens parameter options are uniform except for base curve and secondary curve radii, which are determined by interpretation of fluorescein patterns using the CLEK Study trial lens set and protocol. The initial trial lens's base curve is the average keratometric reading; sequentially steeper lenses are applied until definite apical clearance is observed. We have evaluated the feasibility of this standardized fitting protocol on 30 keratoconus patients. Our results suggest that we have developed a standardized contact lens fitting set and fitting protocol to simplify contact lens management in patients with mild to moderate keratoconus.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Validation of surveys is an important step in establishing the usefulness of questionnaires for gathering information in clinical studies. Often in large studies of refractive error, it is not possible to examine and refract all subjects and their relatives. Therefore, we used 3 methods to evaluate 112 consecutive clinic patients' abilities to report myopia through a survey: (1) The Lay Terms Method asks: “are you nearsighted?”; (2) The Direct Method asks: “are you myopic?”; and (3) The Indirect Method uses a series of questions about the use of eyeglasses and age at first dispensing. Patient responses to the survey before examination were compared to subjective refraction findings at the completion of the eye examination. The Lay Terms Method had the highest sensitivity (0.98) but poor specificity (0.48), and the Direct Method yielded the highest specificity (0.83) but poor sensitivity (0.54). The rate of nonresponse (“don't know”) was high (25.9 and 46.4% for the Lay Term and Direct Methods, respectively). The Indirect Method gave both high sensitivity and specificity (0.76 and 0.74, respectively), and only an 8.9% don't know response rate. The survey method that reports the presence or absence of myopia with the best balance of sensitivity and specificity and fewest don't know responses is the Indirect Method, suggesting it is the most suitable of our three approaches for use in clinical studies.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Assessment of the accommodative response (AR) is an essential part of the optometric examination. This study compared a number of clinical procedures for determining the AR with the findings of an objective infrared autorefractor. First, the AR to a 2.5 D binocular stimulus was measured by dynamic retinoscopy (neutralization being obtained both with lenses and by varying the working distance), dynamic cross-cylinder (with and without fogging lenses), and a near red-green duochrome test. Second, the response to a monocular 2.5 D stimulus was examined using dynamic retinoscopy (neutralizing with lenses), dynamic cross-cylinder, and the red-green duochrome. Third, the monocular AR was examined with both red-green and blue-yellow near duochrome tests. Under binocular conditions, the mean ARs for all the tests were clinically equivalent. However, comparison with the findings from the objective autorefractor indicated that dynamic retinoscopy (where neutralization was obtained by varying the working distance) showed the closest agreement, whereas the two dynamic cross-cylinder procedures exhibited the greatest variability. For the monocular condition, the mean lag of accommodation observed with the autorefractor was significantly less than that observed with dynamic retinoscopy, the dynamic cross-cylinder, or the red-green duochrome. However, the blue-yellow near duochrome test did not provide a valid estimation of the AR. It is concluded that the technique of dynamic retinoscopy where the working distance is varied to obtain a neutral reflex should be the method of choice for the clinical assessment of the AR, because this procedure does not require the introduction of supplementary lenses, which may themselves alter the AR.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Many methods of heterophoria measurement are available clinically. This paper reviews several studies which have examined the reliability of phoria measurements, and have compared various tests of phoria measurement. Different methods of data analysis make comparison of studies difficult. Two studies indicated 95% limits of agreement of 2 to 4 Δ for reliability of modified Thorington, von Graefe, and Maddox rod phoria tests. Studies using correlational analysis to compare different measurement methods have found a high degree of association of the results of these methods. Studies using statistical methods assessing the agreement of test results found a high level of agreement among some tests and a low level of agreement among some tests. Some of the various phoria measurement methods differ in the technique used for dissociation, in the ability to control accommodation adequately, in the level of proximal convergence induced, or in the method by which the phoria is quantified. These differences can result in different phoria measurements on the same patient.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

BackgroundRecent evidence suggests that small letter contrast sensitivity (CS) is more sensitive than visual acuity (VA) to defocus, luminance, binocular enhancement, and visual differences among pilot trainees. It would be valuable to make this test available for general use. We developed a hard copy (letter chart) version called the Small Letter Contrast Test (SLCT) and evaluated its sensitivity and reliability in comparison to standard vision tests.MethodsThe SLCT has 14 lines of letters with 10 letters per line. The letters are of constant size (20/25 or 4/5 at 4 m), but vary in contrast by line in 0.1 log steps (0.01 log units per letter). Normal room illumination is used. The SLCT was evaluated in 16 subjects under various conditions (spherical and astigmatic blur, low luminance, 2 eyes vs. 1 eye) to determine test sensitivity and reliability, and in patients with clinical conditions. Scores were compared to those obtained with standard tests of VA (Bailey-Lovie) and CS (Pelli-Robson).ResultsSLCT scores were similar to previous measures, and retest reliability was one line. The SLCT was more sensitive than VA to spherical and astigmatic blur, low luminance, and vision with two eyes vs. one eye. Greater sensitivity of the SLCT endured despite correction for variability. The SLCT was more sensitive than standard tests to visual loss from early cataract, keratoconus, corneal infiltrates, edema, and amblyopia.ConclusionsThe SLCT is a sensitive, adjunctive test, which complements existing measures of VA. It can reveal subtle visual deficits that may be undetected by standard clinical techniques. The SLCT should prove useful for monitoring vision in refractive surgery, corneal and macular edema, optic neuritis, and for selection and evaluation of candidates for occupations requiring unique visual abilities like aviation.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

It is not known if temporal integration for periodic stimuli is affected by changes in scotopic luminance. Contrast thresholds were measured as a function of duration for 0.25 cpd grating patches across a 2.3 log-unit scotopic range. Threshold vs. duration (TVD) functions were identical in shape regardless of mean luminance once scaled by translating along log-log axes. Critical duration decreased 0.09 log-units per log-unit increase in retinal illuminance. This slope is identical to that reported for photopic conditions, suggesting that temporal integration may be determined by the same neural pathway at all light levels.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Most patients with end-stage age-related macular degeneration (ARMD) depend on their eccentric viewing for distance and near vision. The purpose of this study was to evaluate the subjective effects of eccentric viewing spectacles (EVS) in order to achieve the use of perimacular regions in primary gaze position.MethodWe fitted EVS on patients with a central scotoma secondary to end-stage ARMD. After determining the preferred retinal locus, high power prism glasses were adjusted to this area. After a follow-up period of at least 3 months, patients filled in a questionnaire concerning their perception of positive or negative effects.ResultsTwenty-three of 38 patients considered the fitted EVS to be an improvement.ConclusionEVS may be helpful for the rehabilitation of patients with a central scotoma resulting from ARMD.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The application of the concept of ray vector fields to optical systems is reexamined. Paraxial or linear optics defines a four-dimensional ray vector field for any optical system: the vector field maps the incident ray vector into the emergent ray vector. In the case of thin systems, including thin astigmatic lenses, one can define a vector field of reduced dimensionality: the vector field is two-dimensional and maps the ray's incident position into the change in reduced direction. When the index of refraction is the same before and after a thin system, the change in reduced direction is the reduced deflection through the system or the reduced prismatic effect. Contrary to what has recently been claimed, this type of two-dimensional vector field does not apply in general to thick systems. However, a number of different types of two-dimensional vector fields can be defined for various particular classes of optical systems. Thick systems differ qualitatively from thin systems. They do not have equivalent thin lenses and cannot generally be replaced by thin lenses. Equations are derived for the change in reduced direction and deflection for a ray through optical systems in general and through separated two- and three-lens systems in particular.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID