Biomedical subjects

A J Adams

Publications and source records attributed to A J Adams.

At least 37 records · Page 2Linked to original sources

PubMed1994

The effect of parental history of myopia on children's eye size.

OBJECTIVE: To evaluate whether eye size and shape are different in children based on their parental history of myopia. DESIGN: A community-based cohort study of schoolchildren (aged 6 to 14 years), the Orinda (Calif) Longitudinal Study of Myopia. SETTING: Four campuses of the Orinda Union School District, a predominantly white, high socioeconomic status community. PARTICIPANTS: A cross-sectional volunteer sample of 716 children (662 non-myopic) in the first, third, and sixth grades in 1989, 1990, and 1991. All children in those grades were eligible for inclusion in the study. INTERVENTION(S): None. MAIN OUTCOME MEASURES: Refractive error (measured by autorefraction), corneal curvature (measured by photokeratoscopy), crystalline lens power (measured by video phakometry), and axial ocular dimensions (measured by ultrasonography). RESULTS: With prevalent cases of myopia excluded and grade in school and "near work" controlled for, children with two myopic parents had longer eyes and less hyperopic refractive error (analysis of covariance, P < or = .01) than children with only one myopic parent or no myopic parents. A model incorporating parental history is only improved by the addition of near work for the prediction of refractive error. CONCLUSIONS: Even before the onset of juvenile myopia, children of myopic parents have longer eyes. These results suggest that the premyopic eye in children with a family history of myopia already resembles the elongated eye present in myopia.

Adolescent↗

PubMed1994

Visual evoked potentials in three-dimensional color space: correlates of spatio-chromatic processing.

Visual evoked potentials (VEPs) were measured for sinusoidal gratings with spatio-chromatic modulation defined in a three-dimensional color space. The spatio-chromatic modulation of the gratings can be decomposed into contributions from an achromatic luminance varying component, an isoluminant component which modulates only the activities of L cones and M cones, and an isoluminant component corresponding to modulation of only S-cone activity. The emphasis of this report is the nature of VEPs resulting from isoluminant spatio-chromatic modulation. The VEP response was characterized along a number of spatial, temporal, and chromatic stimulus dimensions: contrast, spatial frequency, chromaticity in the isoluminant plane, chrominance/luminance ratio, orientation, and temporal frequency. Isoluminant VEPs resulting from stimuli modulating L and M cones are compared with those from S-cone modulation. When appropriate spatiotemporal conditions are employed, both types produce robust VEPs; however, the S-pathway VEPs show considerably longer latencies than do those from LM-pathway activation. The VEP results are compared to psychophysical and single unit electrophysiological observations. VEP latencies exhibit the lowpass character of psychophysical chromatic contrast sensitivity functions but VEP amplitudes show bandpass tuning along both the S and LM axes. An oblique effect, i.e. shorter latencies for horizontal and vertical gratings than for diagonal, is observed in the isoluminant VEP. S-pathway VEPs are used to demonstrate an electophysiological correlate of transient tritanopia. Normative amplitude and latency data for VEPs from selectivity stimulated chromatic mechanisms provide a baseline for clinical electrodiagnostic applications.

Adaptation, Ocular↗

PubMed1994

The effect of cycloplegia on measurement of the ocular components.

PURPOSE: The purpose of this study was to examine the effect of cycloplegic agent on the measurement of refractive error and the ocular components. METHODS: We compared two commonly used topical cycloplegic agents, 1% tropicamide and 1% cyclopentolate, for their effect on the measurement of refractive error (by Canon R-1 autorefraction), accommodative response (by Canon R-1 autorefraction and by the conventional, subjective "pushup" method), crystalline lens power (by video phakometry and by calculation), and axial ocular dimensions (by A-scan ultrasonography) in 20 emmetropic to moderately hyperopic children. RESULTS: Comparison of refractive error at each drug's reported time of maximum cycloplegia (30 minutes for tropicamide and 60 minutes for cyclopentolate) showed that distance autorefraction in the vertical meridian differed by +0.20 +/- 0.30 diopters (D) (P = 0.008). The average difference was +0.07 +/- 0.10 mm for anterior chamber depth (P = 0.004), -0.03 +/- 0.05 mm for crystalline lens thickness (P = 0.025), -0.65 +/- 0.69 D for phakometrically measured crystalline lens power (P < 0.001), +0.03 +/- 1.55 D for calculated crystalline lens power (P = 0.94), and -0.09 +/- 0.19 mm for vitreous chamber depth (P = 0.062, all paired t tests; positive signs denote greater values with cyclopentolate). Residual accommodation was 0.47 and 0.67 D greater with tropicamide when measured by autorefraction and the pushup method (P = 0.013 and 0.08 respectively, paired t test). All significant differences were consistently in the direction of poorer cycloplegia with tropicamide. CONCLUSIONS: Although tropicamide, as expected, showed poorer cycloplegia compared to cyclopentolate, the degree of difference appeared to be small, with minimal effect on the measurement of distance refractive error and the ocular optical components.

Accommodation, Ocular↗

PubMed1994

Diabetic short-wavelength sensitivity: variations with induced changes in blood glucose level.

PURPOSE: To investigate variations in diabetic short-wavelength sensitivity with acute, induced changes in blood glucose level. METHODS: Increment threshold measures were obtained for short-wavelength-sensitive and middle/long-wavelength-sensitive cone pathways after an induced, acute change in blood glucose level in diabetic observers. RESULTS: Diabetic observers showed an increase in short-wavelength sensitivity, but no change in middle/long-wavelength sensitivity, with a rapid drop in blood glucose level. CONCLUSIONS: Experimentally induced changes in diabetic blood glucose levels can directly affect diabetic short-wavelength sensitivity.

Adolescent↗

PubMed1993

Blue-on-yellow perimetry can predict the development of glaucomatous visual field loss.

OBJECTIVE: The purpose of this investigation was to determine whether blue-on-yellow (B/Y) perimetry is capable of predicting the onset and location of impending glaucomatous visual field loss in patients with ocular hypertension. DESIGN: A Humphrey Field Analyzer (Humphrey Instruments, San Leandro, Calif) was modified to perform B/Y perimetry to isolate and measure the sensitivity of short-wavelength-sensitive mechanisms. Participants were tested annually with standard white-on-white (W/W) and B/Y automated perimetry for a period of 5 years. PATIENTS: The study population consisted of 38 patients with ocular hypertension and 62 age-matched normal control subjects. RESULTS: Initially, all 76 ocular hypertensive eyes had normal W/W automated perimetry results, with 67 eyes having normal and nine eyes having abnormal B/Y test results. Five years later, five of the nine ocular hypertensive eyes with initial B/Y abnormal results developed glaucomatous visual field loss measured by standard W/W automated perimetry, while none of the 67 ocular hypertensive eyes with initially normal B/Y results developed abnormal W/W perimetry results. CONCLUSIONS: Blue-on-yellow perimetry deficits are an early indicator of glaucomatous damage and are predictive of impending glaucomatous visual field loss for standard W/W automated perimetry. To our knowledge, this is the first prospective, long-term longitudinal study that demonstrates the ability to predict the onset of glaucomatous visual field loss in patients with ocular hypertension on the basis of psychophysical testing.

Adult↗

PubMed1993

Progression of early glaucomatous visual field loss as detected by blue-on-yellow and standard white-on-white automated perimetry.

OBJECTIVE: To determine whether blue-on-yellow perimetry reveals progression of glaucomatous damage before it is evident with standard white-on-white perimetry. DESIGN: A Humphrey field analyzer (Humphrey Instruments, San Leandro, Calif) was modified to perform blue-on-yellow perimetry to isolate and measure the sensitivity of short wavelength-sensitive mechanisms. Participants were tested annually with standard white-on-white automated perimetry and blue-on-yellow automated perimetry for 5 years. PATIENTS: Sixteen patients with early glaucomatous visual field loss in one or both eyes and 62 age-matched normal control subjects. RESULTS: At baseline, 25 (78.1%) of the 32 eyes exhibited larger deficits with blue-on-yellow perimetry, five (15.6%) had equivalent loss with both tests, and two (6.3%) had larger deficits with standard white-on-white perimetry. Seven (21.9%) of the 32 eyes demonstrated evidence of progressive visual field loss with standard white-on-white perimetry in 5 years, while the other 25 eyes (78.1%) were relatively stable. Deficits with blue-on-yellow perimetry were twice as large as deficits with white-on-white perimetry in the stable group and were three to four times as large in the group with progressive field loss. CONCLUSIONS: Blue-on-yellow perimetry is effective in predicting which patients with early glaucomatous visual field loss are most likely to have progressive loss. The rate of progressive loss is greater with blue-on-yellow perimetry than with standard white-on-white perimetry.

Adult↗

PubMed1993

Certain host-donor strain combinations do not reject brain allografts after systemic sensitization.

To investigate the factors related to allogenic brain graft rejection, rat cortex from either LEW-RT1l or BN-RT1n rats was transplanted into brains of several isogenic and allogenic inbred strains: F344-RT1l, LEW-RT1l, BN-RT1n, AO-RT1u, PVG-RT1c, PVG-RT1u, and PVG-RT1l. Each donor and host combination was subsequently subdivided into two subgroups. One group was systematically sensitized twice with donor skin tissue and another group served as a sham-sensitization control. Four weeks after the second sensitization, host brains were examined histologically, and the percentage volume of each graft that showed increased cellularity was estimated. Expression of major histocompatibility complex (MHC) and T cell antigens was also studied immunocytochemically. Almost all grafts in sham-sensitized animals from all groups were accepted with minimal or no reaction. However, two strains (AO-RT1u and F344-RT1l) showed considerable cell infiltration and expression of MHC antigens even without sensitization. After sensitization, almost all allogenic strain combinations showed greater signs of rejection-related responses. The severity of the tissue reaction, however, varied considerably between groups. All grafts from BN-RT1n donors were rejected severely in all host strains. For LEW-RT1l donors, grafts survived well in some host strains (BN-RT1n, AO-RT1u, PVG-RT1c, and PVG-RT1u), even with MHC + non-MHC disparity. Curiously, F344-RT1l hosts rejected LEW-RT1l grafts even though the two strains have the same MHC loci, but different minor histocompatibility (mH) loci. For both donor strains, experimental autoimmune encephalomyelitis-susceptible hosts tended to show more vigorous rejection responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1993

Automated perimetry and short wavelength sensitivity in patients with asymmetric intraocular pressures.

Automated visual field testing [white-on-white (W-on-W) perimetry] and perimetry of short wavelength sensitive mechanisms [blue-on-yellow (B-on-Y) perimetry] were conducted in both eyes of patients with large asymmetries in intraocular pressure (IOP) between eyes (average difference = 19.9 mm Hg). Overall visual field sensitivity was significantly (P < 0.05) depressed in the eyes with higher IOP by an average of 2.33 dB, in spite of the fact that all but two of the eyes with higher IOP demonstrated visual field sensitivities that were within normal limits. None of the eyes with lower IOP were outside of normal sensitivity limits. B-on-Y perimetry revealed similar findings, except that three of the fellow eyes with relatively lower IOP also demonstrated abnormalities. Our results are consistent with the hypothesis that the diffuse loss in visual field sensitivity in glaucoma is related to IOP. In addition, it appears that short wavelength sensitive mechanism may reveal early glaucomatous losses in patients with elevated IOP.

Adult↗

PubMed1993

Size induction transcends the cardinal directions of color space.

Certain psychophysical phenomena occur separately for color and for luminance stimulation. Separate psychophysical effects have also been elicited along different directions in equiluminant colour space. Whereas in most studies in which separate luminance and color effects have been reported the authors have used successive-adaptation approaches, less is known about the separateness of color and luminance processing under simultaneous conditions. A study is reported in which simultaneous size induction was examined for several different color directions thought to be 'cardinal' for early stages of processing. The perceived size of a test object was influenced by the size of the surrounding objects regardless of the color direction of the test and induction objects. The results indicate that simultaneous size induction occurs at a level of processing at which information conveyed by color and by luminance mechanisms is compared and contrasted to influence visual perception.

Attention↗

PubMed1993

Impact of new and emerging instrumentation in optometry.

Traditional tests of vision emphasize visual acuity, visual fields, and testing for hereditary color vision defects. New instrumentation for testing vision has proliferated due to advances in our knowledge of the visual system, the availability of new technologies, the introduction of computers into practice, and the expanded scope of optometric practice. Each is discussed in relation to the subsequent symposium papers by other authors.

Color Perception↗

PubMed1993

Initial cross-sectional results from the Orinda Longitudinal Study of Myopia.

BACKGROUND: Although investigations of human refractive error development and normal ocular growth have been conducted for the last 50 years, no previous study of refractive error and the ocular components has measured all the ocular components. METHODS: The Orinda Longitudinal Study of Myopia was initiated to characterize the development of refractive error and normal eye growth in a sample of predominantly Caucasian children ages 6 to 14 years. RESULTS: Cross-sectional results from 530 children ages 5 to 12 years in the 1st, 3rd, and 6th grades are presented. CONCLUSIONS: This sample's refractive error decreased toward emmetropia with age from an average of +0.73 D at age 6 years to an average of +0.50 D by age 12 years. Between the ages of 6 and 12 years, the vitreous chamber elongated (by 0.52 mm) and the crystalline lens power decreased (by 1.35 D); surprisingly, the crystalline lens thinned by 0.14 mm during this same time period.

California↗

PubMed1993

Comparison of cyclopentolate versus tropicamide cycloplegia in children.

This double masked study compares the cycloplegic effects of tropicamide 1% and cyclopentolate 1% in 20 nonstrabismic, nonamblyopic, hyperopic 6- to 12-year-old children with a mean refractive error = +1.48 +/- 1.10 diopters (D). Unlike previous studies which used only amplitude of accommodation to measure the depth of cycloplegia, this study compares refractive error as determined by retinoscopy, distance subjective refraction, and distance autorefraction (Canon R-1). In addition, we compare the amplitude of accommodation as measured by subjective push-up and objective autorefraction methods. There is no statistically significant difference between cyclopentolate and tropicamide for either cycloplegic retinoscopy or distance subjective refraction. Autorefraction measurement of refractive error shows a statistically significant but clinically unimportant bias (0.14 +/- 0.30 D) toward more hyperopia with cyclopentolate. Both drops reveal latent hyperopia, and the mean latencies are not statistically different between the two cycloplegic agents. Latent hyperopia is not systematically related to the degree of hyperopia after tropicamide, but this relation is significant after cyclopentolate. No differences were found between refractive results with either agent at 30 min compared to 60 min after drop instillation. When measured objectively with the autorefractor, accommodation is inhibited more effectively by cyclopentolate than by tropicamide. Our results suggest that although tropicamide is not as effective as cyclopentolate in inhibiting accommodation it is, nevertheless, a useful cycloplegic agent for measuring distance refractive error of low to moderate hyperopia in school-aged children.

Accommodation, Ocular↗

PubMed1993

Application of the spatiochromatic visual evoked potential to detection of congenital and acquired color-vision deficiencies.

Visual evoked potentials were recorded in response to spatiochromatic stimuli modulated in different directions in cone-activation color space from subjects with congenital and acquired color defects. This technique was effective for detection and classification of both mild and severe forms of congenital deficits. Results suggest that the visual evoked potential is useful for early identification of color abnormalities in acquired deficits such as diabetes and that it is sensitive enough to detect regional retinal losses of sensitivity (e.g., as in central serous choroidopathy). The spatiochromatic visual evoked potential provides a systematic and sensitive indication of different color-vision anomalies.

Adult↗

PubMed1992

Perceptual ambiguity and the short wavelength sensitive visual pathway.

Visual illusions and ambiguous figures are difficult to perceive when presented in a manner which stimulates only chromatic pathways. This perceptual limitation could indicate that these pathways are unable to mediate form perception, or it may reflect the relative visibility of the stimulus, regardless of the pathway utilized. To examine this issue, an ambiguous figure (illusory Necker cube) was presented to the short wavelength sensitive (S) cone pathway which is thought to convey only chromatic signals. Although few observers could recognize the cube when presented in isolation to S cones, the same reduction in recognition was found when the cube was detected by achromatic pathways at a level of visibility comparable to that conveyed by S cones. Our results indicate that for this object recognition task, visibility of the stimulus is the relevant variable, rather than the particular pathway traversed. Prior experience was also found to be important determinant of object recognition.

Color Perception↗

PubMed1992

Lightness induction in the S-cone pathway.

Lightness induction is classically regarded as a contrast phenomenon limited to pathways which process luminance information. To determine if lightness induction can also occur in the chromatic domain, this phenomenon was studied with stimuli visible only to the short wavelength sensitive (S)-cones which have post-receptoral connections limited to chromatic pathways. The lightness of an object visible only to S-cones was found to be dependent on the relative intensity of its background in a manner similar to achromatic, luminance stimuli. Less intense (dark) backgrounds made the object appear lighter, while more intense (light) backgrounds made the same object appear darker. These results indicate a commonality among lightness induction effect in the processing of chromatic and luminance information.

Adaptation, Ocular↗

PubMed1992

Cortical potentials evoked by short wavelength patterned light.

Pattern-evoked cortical potentials (PECPs) were recorded in response to the onset of blue and black, square wave gratings superimposed on a bright orange background. Several lines of evidence, including spectral sensitivity and the absence of response in a tritanopic subject, indicate that the measured cortical potentials reflect input from S cones. Spatial and temporal tuning of this response are comparable to psychophysical measures of the S-pathway. In agreement with previous studies of achromatic and chromatic spatial processing, a comparison of the response to patterns of different complexity indicates that spatial processing in the S-pathway can be described by linear systems analysis. An oblique effect for the S-pathway is demonstrated. Additional findings which bear on the nature of postreceptoral processing in the S-pathway are considered. Included are measurements from a patient with diabetic retinopathy. This study underscores the potential importance of the S-pathway for spatial information processing.

Adult↗

PubMed1992

A video technique for phakometry of the human crystalline lens.

Accurate measurement of the dioptric power of the human crystalline lens is important in any study of ocular development and refractive error. Previous studies have used comparison ophthalmophakometry, measuring crystalline lens curvature and power from still flash photographs of Purkinje images I, III, and IV. This report presents a video-based technique for in vivo measurement of crystalline lens power suitable for use with children. The repeatability and validity of this video system were evaluated in comparison to a still photograph system through the measurement of anterior and posterior lens curvatures of 40 normal adults. The video system's repeatability (95% limits of agreement) was +/- 0.52 diopters for the anterior lens power, +/- 0.73 D for the posterior lens power, and +/- 0.88 D for the total lens power. The repeatability of the still flash photography system was +/- 0.78 D for the anterior, +/- 1.43 D for the posterior, and +/- 1.84 D for the lens power as a whole. An indirect method of calculating lens power using other ocular component measures gave a repeatability of +/- 1.78 D. The validity of the video system was improved by having the camera and the light source closer to the optic axis of the eye. The bias induced by having a more off-axis configuration (40 degrees separation between camera and light source) was a +0.10 D overestimation of surface power for the anterior and +0.73 D for the posterior lens surface power compared to a more coaxial arrangement (20 degrees between camera and light source). The use of video phakometry improved the repeatability and the validity of lens curvature measures relative to still flash photograph comparison ophthalmophakometry and to an indirect method of calculating lens power. This was achieved through the system's ability to analyze multiple frames, the use of a collimated light source, and the placement of the light source for the Purkinje images closer to the eye's optic axis.

Adult↗

PubMed1992

The repeatability of measurement of the ocular components.

Studies of the ocular components of refraction typically neglect issues of repeatability of measurement methods or analyze method comparison/repeatability data inappropriately using correlation. The authors have examined the repeatability of refractive error measures (retinoscopy, subjective refraction, and Canon R-1 autorefraction, noncycloplegic and cycloplegic), axial dimension measures (Allergan-Humphrey A-scan ultrasound), and corneoscopy (keratometry and KERA photokeratoscopy), and the agreement between different refractive error and corneal measurement methods on 40 pre-presbyopic normal adults. The authors plotted the difference versus the mean of two different measurement occasions (repeatability), or two different methods (agreement), to determine the bias (mean of the differences relative to zero) and 95% limits of agreement of each technique. The most reliable measure of refractive error was autorefraction with cycloplegia, with 95% limits of agreement of +/- 0.32 diopters. Cycloplegic autorefraction had no statistically significant bias compared to cycloplegic subjective refraction. Cycloplegic retinoscopy was the least reliable refractive error measure, with repeat measures on two separate occasions extending over 95% limits of agreement of +/- 0.95 D. Anterior chamber depth was reliable to +/- 0.29 mm, lens thickness to +/- 0.20 mm, and vitreous chamber depth to +/- 0.37 mm. Corneal curvature measures show keratometry to be more reliable (to +/- 0.87 D) than photokeratoscopy (+/- 2.02 D) with a statistically significant bias (paired t-test, P less than 0.0001) of 0.57 D flatter for photokeratoscopy.

Adult↗