Biomedical subjects

K D Fern

Publications and source records attributed to K D Fern.

7 recordsLinked to original sources

PubMed1994

Resistance to occlusion: sensitivity to induced blur in 6- to 12-month-old infants.

BACKGROUND: Resistance to occlusion and fix and follow are often used to make inferences about the acuity of young children. In this study, the acuity of 6- to 12-month-old infants was degraded monocularly to elicit resistance to occlusion or loss of fixation. METHODS: Occlusion foils and optical blur were used to simulate monocular acuity reduction. Two different targets, a mechanical rabbit and a "flickering" light were used for fixation. RESULTS: More infants resisted occlusion when viewing the rabbit than the light. Resistance to occlusion was observed in the majority of infants when acuity was degraded to the level expected for 6 to 12-month-old infants (20/80-20/300). CONCLUSIONS: The sensitivity of resistance to occlusion is influenced by the test target and if an interesting target is used, resistance to occlusion may be a useful tool for detecting interocular acuity differences in 6- to 12-month-old infants.

Amblyopia↗

PubMed1990

Motion coherence in infants.

Two perpendicular square-wave gratings (i.e. plaids) were used to investigate motion coherence in 1-, 2- and 3-month-old infants. The direction of motion of the stimulus was judged by an adult observer, on the basis of the induced optokinetic nystagmus (OKN) in an eight-alternative eye movement voting paradigm. Infants as young as 1 month of age demonstrated OKN in the direction consistent with motion coherence. There was no significant difference among the performances of 1-, 2- or 3-month-old infants. However, the percentage of trials on which infants demonstrated OKN in the coherence direction was less than that obtained from adults tested with the same paradigm. Movshon, Adelson, Gizzi and Newsome (1985) have suggested that the cohered motion of a complex pattern may be processed after the orientation of the components of the pattern, perhaps in the middle temporal area of the visual cortex (MT). The present results suggest that either young infants and adults process the motion of complex patterns similarly or that the OKN consistent with the direction of motion coherence observed in infants involves subcortical nonoriented visual centers rather than the higher level process which is presumed to occur in adults.

Adult↗

PubMed1989

Visual acuity outcome in isometropic hyperopia.

Refractive amblyopia may occur as a unilateral or bilateral condition. Although bilateral refractive amblyopia may account for 1 to 2% of all refractive amblyopia, there is little consistent information in the literature regarding isoametropic amblyopia resulting from bilateral hyperopia. Hence, this retrospective study investigated the prevalence of reduced aided acuity in patients aged 10 years and younger (mean age 3.97 years) with 5 D or more of isometropic hyperopia and considered the following factors that may influence visual acuity: (1) age at first correction; (2) magnitude of hyperopia; and (3) duration of refractive correction of the hyperopia. The results indicate that the majority of patients (87%) have aided acuity poorer than 6/6 at initial correction of refractive error. However, if the full hyperopic correction was worn for 1 year or longer, only 43% of these patients demonstrated acuity poorer than 6/6 and none showed acuity poorer than 6/12. The magnitude of the hyperopia appeared to have the greatest influence on the visual acuity outcome both at initial correction of refractive error and 1 year or longer after correction. Duration of correction also influenced the visual acuity outcome, but to a lesser extent than the magnitude of refractive error. In contrast, the age of first correction showed little correlation with visual acuity either at the time of first refractive correction or after a minimum of 1 year of correction.

Age Factors↗

PubMed1987

Contour interaction function in the preschool child.

Contour interaction was investigated in 12 preschool children 3 to 4 years of age, and compared to the results obtained from 5 normal adults tested under an identical paradigm. Observers viewed the display from a distance at which they could identify the location of a gap (up or down) in an isolated C correctly on 90 to 95% of the trials. The isolated C and C's with bars tangentially located at various positions above and below the test optotype were intermixed randomly. Percent correct was plotted as a function of the angular subtense of the gap width of the test optotype. A significant decrease in performance was found when the bars were positioned at 0.71 to 1.42 times the angular subtense of the gap for both the preschool children and the adults. The results suggest that preschool children demonstrate contour interaction that is quantitatively similar to adults. Because the spacing of letters on standard acuity charts is typically larger than the range over which contour interaction occurs, the poorer acuity often measured with charts compared to isolated letter presentation in preschool children suggests that factors other than contour interaction (perhaps attentional factors) are involved.

Adult↗

PubMed1986

Contour interaction in the preschool child.

Preschool children show poorer visual acuity when tested with multiple optotypes than when tested with isolated optotypes. This difference in performance could be the result of contour interaction or the greater distractions imposed by a multiple optotype display, which may be beyond a young child's ability. To differentiate between these alternatives, isolated and surrounded visual acuity were measured in children aged 2 to 7 years by pairing a Landolt C with an O. The surrounded optotypes were identical to the isolated optotypes with the exception of the flanking bars located at 2.5 times the minimum angle of resolution (MAR) of the optotype. A two-alternative forced choice interleaved paradigm was used to measure surrounded and isolated visual acuity defined as 75% correct. When the test demands were equated by measuring isolated and surrounded acuity using a single optotype, poorer visual acuity was obtained with surrounded optotypes. This suggests that preschool children, like adults, show contour interaction.

Adult↗

PubMed1986

Visual acuity of the preschool child: a review.

The need for visual acuity assessment in preschool children has long been recognized, yet there are no standardized visual acuity norms or screening criteria. This report reviews the literature on distance visual acuity in the preschool child. The areas of review include: methods of assessment of visual acuity; visual acuity norms obtained with these tests; reasons for the variations in reported visual acuity norms; variations in referral criteria for vision screenings; testability reported for various visual acuity tests; and important design principles and recommendations for preschool visual acuity tests. It is concluded that a well designed preschool visual acuity test should consist of high contrast Snellen optotypes without directional components that progress in 0.1 log steps down to a level of 6/3. To improve testability, a matching or forced choice response should be used. Of the tests that have been standardized, STY-CAR (Sheridan-Gardiner) comes closest to meeting these criteria.

Child↗

PubMedDate not supplied

Testing stereopsis in the preschool child: is it clinically useful?

The evaluation of stereoacuity should provide an unambiguous assessment of binocular function in infants and young children. Unfortunately, clinical measures of stereopsis in these young patients often result in stereotheresholds poorer than the criteria suggested to differentiate normal from anomalous binocular vision. Thus, two experiments were conducted to determine whether the large stereothresholds frequently demonstrated on tests designed for young children are diagnostic of normal binocular function in preschool children. The first experiment investigated the salience of the monocular cues in the Lang and Frisby stereotests in normal preschool children (2 to 5 years old). None of the children who passed either the Frisby or the Lang stereotest under binocular conditions were able to pass either test monocularly, even after passing the test binocularly. In the second experiment, preschool children with abnormal binocular vision were tested with the Lang and Frisby stereotests to determine if large disparities (730 to 800 seconds of arc [arcsec]) could be passed without normal binocular vision. None of the children with strabismus passed either stereotest. However, two children with anisometropia passed the Frisby test and one of these children also passed the Lang test. These results suggest that in the absence of other clinical findings to the contrary, the demonstration of gross stereopsis with either the Frisby (730 arcsec) or Lang (733 or 800 arcsec) test in the preschool child implies normal binocular function. Thus, clinical tests of stereopsis for infants and preschool children, like those used routinely for adults, can provide evidence of binocular function without approaching stereothreshold.

Amblyopia↗