American journal of optometry and physiological optics最新文献

Hydrogen peroxide disinfection has caused discomfort for some soft contact lens wearers even though the solution was neutralized properly. The discomfort could be due to the endpoint pH of the system used or the residual H2O2 concentration. Using a digital pH meter and H2O2 concentration detection strips, we measured the pH and H2O2 concentration of seven different hydrogen peroxide disinfection systems over their recommended disinfection and neutralization cycles to determine their time courses and endpoint values. The final pH of the seven systems varied from 6.15 to 7.74 pH units. All systems resulted in residual H2O2 concentrations below threshold values. These findings indicated that the final pH may be the cause of patient discomfort after hydrogen peroxide disinfection and neutralization.

Using American Optical Vectographs and a Disparometer, vertical fixation disparities and associated phorias were measured on 19 essential hypertensives and 19 matched normotensives. Subjects were matched on the basis of race, sex, age, use of tobacco, and family history of hypertension. Correlated variance comparisons of the measured associated phorias and fixation disparities, as well as calculated x and y intercepts derived from forced-duction vertical fixation disparity curves were made and a t-test for related measures was used to compare slopes. The x and y intercepts and slope data showed no significant differences between the groups. However, statistically larger measured associated phorias for the hypertensive group were found on all but one test. This suggests a relation between the magnitude of vertical associated phorias and the occurrence of essential hypertension, but the relation found was not of sufficient strength to warrant clinical application.

Usually two factors are not rigidly standardized in the routine tangent screen examination: (1) the stimulus characteristics of the carrier that fixes the spot to the wand, and (2) patient instructions about what aspects of the stimulus they should attend to. Differences in these factors within the range of what is commonly done in the tangent screen test can lead to significant differences in the locations of the isopters. There is also an interesting interaction between these two factors in establishing isopter size.

We conducted a survey to evaluate the incidence of various complications associated with extended wear (EW) contact lenses. Of the 137 surveys sent out, 44 responded, 15 with data. The analysis indicates: (1) EW contact lens patients receive nonuniform care, evident from the fact that the EW follow-up to EW dispensing ratio varied between 1.6 and 16.75; (2) the incidence of epithelial microcysts, striae, and giant papillary conjunctivitis (GPC) was found to be considerably lower than that reported previously; (3) the incidence of "red-eye" response and corneal ulcers was calculated to be within the lower end of the range of previously reported research; and (4) there may be a seasonal variation in the incidence of GPC and red-eye response as indicated by an increase in both conditions during the month of March as compared to February.

The procedure of applying pressure to a lens until fracture occurs and the use of the fracture pressure as a measure of lens strength has been proposed as a quantitative alternative to the drop ball test. The fracture pressure or pressure resistance of untempered, thermally tempered, and chemically tempered glass lenses and CR39 lenses were compared. The results for the glass lenses were consistent with workplace experience and previous studies using the drop ball test. The results for glass and CR39 lenses showed the reverse to what was expected. In order to investigate the basis of this difference, a second procedure was followed in which the annulus supporting the lens and the steel ball applying the pressure to the lens were systematically changed. Glass lenses showed a highly statistically significant change in fracture pressure with decreasing ball size and a small but statistically significant change with annulus size. CR39 lenses showed no statistically significant change in fracture pressure with changing ball size but a highly statistically significant increase in fracture pressure with increasing annulus size. The mechanism of fracture is known to differ in the glass and plastics materials and it is concluded that this method should not be used to compare the performance of different materials.

The Standard pseudoisochromatic Plate (SPP) test was administered to 346 normals, 55 anomalous trichromats, and 46 dichromats. Its ability to detect and classify congenital color defectives was assessed. The performance of each plate was assessed separately and compared with its colorimetric properties. The test as a whole achieves a high level of accuracy in separating normals from color vision defectives [Youden's Index (YI) = 92.4%] and a high reliability (71.3%) in classification of the congenital color vision defectives. The performance of individual plates in separating color normals and color vision defectives of individual plates varies (YI ranges from 69.8 to 86.1%). A set of three plates can be chosen, which achieves a performance similar to that of the whole test. The test is found to be a reliable clinical screening method for congenital red-green color vision defectives.

Accommodative amplitude decreases with age, not with aging. The decrease is largely completed by age 40 years; only minor residual accommodation is present in most subjects after the mid-40s. Dynamical measurements show the accommodative response of subjects over 30 years of age to be significantly slowed (time constants of accommodation increases). Accommodation amplitude is less than 3 D by 30 years of age. Thus prepresbyopia is a sign of continual development, not of deterioration of the accommodative mechanism. Accommodation, or the change of clear vision with change in lens power, has been studied by many distinguished scientists including Descartes and Thomas Young. Helmholtz's "Theory of Accommodation" is a dual, indirect, active theory. There are both lenticular, including lens and capsule, and also extralenticular mechanisms, comprised of the zonule of Zinn or suspensory ciliary ligament and the ciliary muscle itself. The ciliary muscle does not act directly on the lens but indirectly through its action on the zonule of Zinn. Active contraction of the ciliary muscle, a unified muscle, produces accommodation; relaxation of the ciliary muscle permits relaxation of accommodation.