摘要:

Results of refractive component measurements have shown that eyes of Melanesian schoolchildren living in Vanuatu, almost all of whom are emmetropic, have relatively short axial lengths and relatively flat corneas in comparison to emmetropic eyes of children examined in England. Evidence is presented to suggest that the relation between the axial length of the eye and corneal radius—the axial length/corneal radius (AL/CR) ratio—may be a useful predictor of future refractive state. Mean axial length/corneal radius ratios for 6-to 19-year-old Melanesian school children were found to be 2.88 for boys and 2.86 for girls, as compared to mean AL/CR ratios for 6− to 19-year-old British schoolchildren of 3.05 for boys and 3.04 for girls. It is proposed that an eye having a high AL/CR ratio is at risk for the development of myopia, and that such an eye has maintained its state of emmetropia by virtue of a compensatory flattening of the crystalline lens.ln order to test the proposition that an increase in axial length occurs as a precursor to the development of myopia, a prospective longitudinal study of a group of 6− to 7-year-old schoolchildren is proposed.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Short wavelength absorbing filters (SWAF's) have become very popular in the prescription and commercial sunglass markets. Like other chromatic filters SWAF's have the potential to alter color vision. Performance on the Farn-sworth Panel D-15 (D-15) test was measured to determine whether any of 4 popular SWAF's, in the form of sunglasses, produced color vision changes in 22 color normal adults. Using standard illuminant C, observers were tested under the following conditions: wearing no filter, a 1.0 log unit neutral density filter (NDF), or one of the following SWAF's: Corning CPF 550; NoIR Amber 40%; Blu Blocker; and Vuarnet 4006. In addition, the Vuarnets were tested outdoors in shaded daylight to determine the effects of increased illumination. The NDF served as the control and had no effect on D-15 performance. Compared to it, only the Blu Blockers and Vuarnets affected D-15 cap arrangements for these SWAF's significantly. Blu Blocker error patterns had no predominant axis, whereas the predominant axis of errors in both Vuarnet conditions was tritan. Results of quantitative analysis performed on three factors confirmed these findings and indicated the Blu Blockers and Vuarnet SWAF's caused moderate and moderate-to-severe levels of color confusion, respectively. Increasing the illumination level improved performance with the Vuarnets, but it remained significantly outside the normal range.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

The purpose of this investigation was to determine the influence of noncongruent stimuli on tonic accommodation and tonic vergence. Eight visually normal subjects were tested in a within-subjects design. Tonic states were measured using a haploscope-optometer immediately before and after viewing a reduced Snellen chart binocularly with suppression control in a synoptophore for 8 min. One stimulus was set at either 4 D or 4 MA, with the other set at either the maximally high (e.g., >4 D or 4 MA) or low setting (e.g.,

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

On site swimming pool studies have indicated that soft contact lenses adhere to the cornea when exposed to swimming pool water. It was the aim of this investigation to study, under controlled laboratory conditions, both the adherence of hydrophilic extended wear lenses and any changes in lens movement with exposure to swimming pool water. Normal saline and a hypotonic solution having a pH and osmolality identical to the pool water served as controls. Exposure to both swimming pool water and the hypotonic solution promptly caused both lenses to stop moving and adhere to the cornea. Notably, the instillation of normal saline also caused a dramatic decrease in lens movement for some subjects.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

The present investigation was designed to determine the effect of lens parameters and lens environment on measurements of contact angle. The sessile drop contact angle of saline on four rigid [polymethyl methacrylate (PMMA) and silicone/acrylate] contact lens materials was examined with a Ramé-Hart goniometer to determine how front surface radius, drop size, time after drop placement, humidity, and desiccation affect measurements of lens wett-abilityin vitro. Contact angles of Silafocon A and PMMA were relatively uninfluenced by front surface radii between 7.7 and 8.85 and 7.3 to 8.8 mm, respectively. Contact angles of Pasifocon C and modified PMMA were slightly but significantly influenced by front surface radii between 6.4 and 7.5 mm. For drop volumes from 2 to 20 μl, all materials yielded contact angles, which were unaffected by drop size. The contact angle of lenses stored in the hydrated or dehydrated state was not affected by chamber humidity between 31 and 76%. In the ranges tested, drop size, humidity, and hydration had no significant effect on the contact angle within 1 to 6 min after drop placement. In addition, surface scratches had no effect on lens wettability. The results suggest that goniometry on contact lens surfaces, for the most part, is uninfluenced by lens parameters and environmental conditions.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

A laser beam, aimed at the solid-liquid-air interface of a sessile drop on a contact lens, produces two lines of diffraction which are theoretically normal to the profile of the fluid and solid surfaces at the point of contact. In the present experiments, the beam and the diffraction patterns were projected on a flat screen perpendicular to the beam, and the angle was measured as a contact angle. The angle was measured on curved surfaces (contact lenses) of 6.5 to 8.9 mm radius and for each material studied, the angle: (1) was independent of the front surface radius, (2) was independent of droplet volume at 2 and 10 μl, and (3) decreased with time after drop placement. The laser-derived measurements correlated well with contact angles measured by goniometry on contact lenses and a variety of other materials (r = 0.86; p < 0.0001). Because the diffraction lines are straight and are generated at the point of contact, the angle formed by them is measured easily with a protractor, yielding a convenient and reproducible contact angle measurement. An application of the method was demonstrated by measuring contact angles for saline-containing 0 to 2% bovine serum albumin or bovine submaxillary mucin on Silafocon-A (Polycon II), Pasifocon C (Paragon EW), and polymethyl methacrylate (generic PMMA and Paragon 18) lenses. On each material, physiological concentrations of mucin, but not of albumin, significantly (p < 0.01) decreased contact angles by 8 to 15°. It is suggested that the laser-assisted method is superior to goniometry because it is less subjective and is based on diffraction lines generated at the point of contact, rather than based on hand-placed tangents to curved surfaces.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Recognizing the need for an effective test for screening color vision in young children, we have developed a new pseudoisochromatic (PIC) plate test which is useful for a wide variety of observers at different ages. The test consists of four plates and responses can be used to categorize color vision as normal or as either red-green or blue-yellow defective. Results of this validation study with adults, both color normal and red-green defective, show a high degree of correlation between the new test and the Nagel anomaloscope: there were no false positives and only a few false negatives, which occurred with mild deuter-anomalous observers. The validity of the test compares favorably to the Ishihara, F-2, and the AO-HRR screening plates. Results with toddlers (3 to 6 years) indicate that the task demands of the test are well suited for testing young children. The percentage of color defectives identified in the toddler sample using the new test is closer to the adult prevalence than results obtained with the F-2 and AO-HRR screening plates, which gave dramatically higher failure rates. The new test is culture-free and can be administered rapidly to both verbal and nonverbal observers using pointing or preferential looking.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Intraocular pressure (IOP) and several other parameters were measured on 560 subjects as part of a vision and health screening program. The sample included a large proportion of American Indians with diabetes (15.2%) and obesity. Multiple regression analysis showed that the percentage of ideal body weight index and average blood pressure both had independent effects on IOP, whereas age, blood sugar, sex, degree of Indian blood, and diabetes did not, although the latter three variables narrowly missed having a statistically significant effect in at least one eye. The analysis of variance showed that diabetes was associated with elevated IOP. This association was independent of random blood sugar, blood pressure, obesity index, and age.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Though the Hirschberg test has been used for Over a 100 years, several different formulas are still being recommended and used clinically to determine the amount of a given ocular deviation. The purpose of this study was to obtain a double-masked clinical evaluation of the Hirschberg test. Several strabismic patients were evaluated by one investigator using the alternate cover test and by another investigator using a photographic Hirschberg procedure in a double-masked procedure. It was determined that the Hirschberg test can be used for strabismic patients of all ages and that the most appropriate formula to use is 1 mm = 22 δ.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

The purpose of this investigation was to test the reliability of the American Optical Non-Contact Tonometer Mark II (NCT II) using the Goldmann Applanation Tonometer (GAT) as the validating instrument. The sample contained 102 consecutive patients from our University Eye Clinic, of whom one-half had 4 NCT II measurements first, followed by 4 GAT measurements; the other one-half had 4 GAT measurements first, followed by 4 NCT II measurements. No significant change in intraocular pressure (IOP) was noted over the measurement sequence with either instrument. There was no significant difference between paired NCT II and GAT readings when the NCT II was used first; however, a highly significant difference between paired readings was obtained when the GAT was used first, indicating that the GAT measurement produced a delayed reduction in the IOP. This effect did not occur with the NCT II. Although the NCT II is shown to have a good overall reliability when compared to the GAT in both protocols, the agreement between any two tonometers may be influenced greatly by the very process of taking a measurement and by the dynamic nature of the IOP.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID