摘要:

In a previous paper I have derived spectral response curves for the foveal cones of the CIE normal observer. These are based on the 1931 mixture data, the Judd 1951 V(λ) curve, and the absorbance data of the pigments in the human cones. In the present paper I have found that the spectral response curves of congenital dichromats may be assumed to be similar to those of the CIE normal observer.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

After many years of successful contact lens wear, 3 long-term wearers of polymethyl methacrylate (PMMA) lenses (14, 15, and 18 years) and 1 long-term wearer of thick hydrogel lenses (11 years) suddenly developed intolerance to their lenses. Symptoms included ocular discomfort, reduced vision, and photophobia. All patients exhibited an excessive open-eye edema response with low to moderate Dk lenses. Posterior corneal changes included distortion of the endothelial mosaic and moderate to severe endothelial polymegethism. Patients were successfully refitted with lenses having higher oxygen transmissibility. It is proposed that long-term hypoxia and acidosis accompanying PMMA and thick hydrogel contact lens wear may be responsible for a syndrome characterized by endothelial dysfunction which results in inadequate regulation of corneal hydration and subsequent intolerance to contact lens wear. This condition has been termed Corneal Exhaustion Syndrome (CES).

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We measured vision and task performance on 26 presbyopes, ages 46 to 65 years, fitted with diffractive bifocal contact lenses (BFCL) and monovision contact lenses (MVCL). Distance contact lenses combined with reading spectacles (DCL) served as the control condition. Twenty subjects completed the 6-week study. All subjects wore BFCL and MVCL daily for a period of 3 weeks each. Performance times for three near tasks were 6 to 8% longer with BFCL compared with DCL and 2 to 6% longer for MVCL compared with DCL. There were significant reductions in distance visual acuity with BFCL (0.4 to 1.5 Snellen lines) and MVCL (0.5 to 0.8 Snellen lines) compared to DCL. At the conclusion of the study, given a choice between BFCL and MVCL, 2 of the 20 subjects chose to continue wearing BFCL, whereas 18 of the 20 subjects chose MVCL. Our results show greater visual compromise and decreased task performance with BFCL and MVCL compared to DCL and greater patient preference for MVCL

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We investigated the validity of replacing cycloplegic retinoscopy with a noncycloplegic, “near” retinoscopy technique. We refracted a group of 31 infants (<2 years) and 43 children (>2 years) with both techniques, grading our level of confidence in the result. Near retinoscopy gave on average a less hypermetropic result than cycloplegic retinoscopy by 0.39 D. The difference was significant in infants and for low levels of examiner confidence. However, a repeatability study showed that much of the variability in the infant group could be attributed to the poor repeatability of either retinoscopy technique. Agreement between the two techniques is improved by changing the suggested adjustment factor from 1.25 to 1.00 D for children and to 0.75 D for infants.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We have examined the possible presence of color vision anomalies in 9 individuals (17 eyes, 1 blind) with fundus findings suggesting ocular albinism using the Ishihara plates, the 28-hue Roth test, and the Davico anomaloscope. Results indicate that four of these individuals show no sign of the anomalies expected in an albino in either of the two eyes. Of the remaining cases, two are simple deuteranomals in both eyes, according to Pickford's classification criteria. The rest have protanomaly; however, in these the deviation toward red appears in both eyes in only one subject, whereas in the other two subjects it appears in only one eye, their binocular color vision being basically normal. Our study shows that a large proportion of these albinos have photophobia, pendular nystagmus, strabismus, noticeable refractive errors (astigmatism and high myopia), and poor visual acuity [usually less than 6/30 (20/100) with correction]. The measurement of contrast sensitivity function (CSF) indicates that the frequency of 12 cpd cannot be perceived, even in binocular vision.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

A method published elsewhere for estimating dioptric power from meridional measurements is generalized here to allow for measurements of sagitta, lens thickness, and prismatic effect as well. Measurements may be of only one type or of combinations of types. Any number of measurements may be used. Within the usual limitations of first-order optics the method always works and gives all solutions when solutions exist. When no solutions exist it gives approximate solutions called least-squares estimates. At least one leastsquares estimate always exists. A wide class of ostensibly distinct problems reduces to a single standard routine that is easy to execute with matrix-handling software. If there is reason to believe that the dioptric power is of some particular form then constrained estimation may be applied to find that form.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We measured the Dk (oxygen permeability) of one specific hydrogel contact lens material (phemfilcon A, nominally 38% water content and ionic) by use of the conventional single chamber polarographic technique at 35°C. When corrected for the boundary and edge effect, Dk was found to be 13 x 10-11cm2ml O2/s ml mm Hg. (These units will be used for this term throughout the remainder of this report.) We also used the polarographic cathode as a model cornea to measure the Dk/L (oxygen transmissibility) of 7 powered contact lenses (-5 to +15 D) made from the same material by the same manufacturer. We found values ranging from 5 to 15 x 10-9cm ml O2/s ml mm Hg. (These units will also be used for this term throughout this report.) From analysis of these data, we found that any reasonable model (of the several previously proposed) for L could be used to predict the polarographically measured oxygen transmissibility of the low minus (-5 to - 1 D) powered contact lenses, but that plus powered lenses, at least on this measurement apparatus, give Dk/L values that are closer to predictions based on the observed Dk and central thickness rather than any version of average thickness.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

A 39-year-old white female presented with symptoms of constant diplopia onset with a first bifocal correction. The association of these conditions required a careful differential diagnosis and special management considerations. Testing indicated an esotropia with a longstanding nonconcomitant superior oblique paresis which became manifest when she began wearing bifocals. A regimen of horizontal vergence range training in combination with a relieving vertical prism in a near correction were prescribed. An amount of prism which allowed comfortable sensory-motor fusion through both the distance and near portion of a bifocal spectacle correction was eventually ascertained. Information regarding etiology, etiologic incidence, differential diagnosis, and management of superior oblique paresis is also presented.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Therapeutic doses of ibuprofen (2-4'-isobutylphenylpropionic acid) have been shown to have many deleterious effects on the nervous system. However, visual disturbances have been reported in fewer than 1% of the patients taking recommended doses of ibuprofen. The most commonly reported visual disturbances include: amblyopia, scotomata, and changes in color vision. To our knowledge, no studies have examined the effects of ibuprofen therapy on the contrast sensitivity function of an affected individual. Contrast sensitivity, Snellen visual acuity, color vision (D-15 test), and Goldmann visual fields were measured on 1 affected subject during and after ibuprofen therapy (800 mg/day for 2 days). Snellen visual acuity, color vision, and Goldmann visual fields were unaffected by the treatment. However, the contrast sensitivity was significantly depressed at low spatial frequencies while the subject was taking ibuprofen. The results, in concert with previous reports concerning the visual effects of ibuprofen, suggest that this drug can result in transient multifocal lesions of the visual pathway.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Although a laser-produced iridotomy effectively controls angle-closure glaucoma the iridotomy can cause annoying visual effects. One solution is to fit a toric contact lens with an opaque portion to cover the iridotomy.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID