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At least 1,117 records · Page 62Linked to original sources

PubMed2006

Inferring myopia over the lifecourse from uncorrected distance visual acuity in childhood.

AIM: To report the usefulness of uncorrected distance visual acuity (DVA) at 16 years to "screen" for myopia status and to assess the lifetime risk of myopia, based on a national birth cohort. METHODS: 1867 members of the 1958 British birth cohort for whom there were data on acuity at 16 years had autorefraction, as part of a biomedical survey, at 45 years. Reduced uncorrected DVA at age 16 years (6/12 or worse in both eyes) was compared with adult refraction (spherical equivalent). RESULTS: Only a quarter of individuals in the population studied who had developed myopia by 45 years of age had reduced acuity at 16 years of age. Notably, half of all adults with moderate myopia (-2.99 to -5.99) and 31% (11/35) with severe myopia (> or =-6) had good uncorrected DVA in both eyes at 16 years of age. Thus, sensitivities were low, ranging from 16% for all myopia (cut-off point spherical equivalent -0.5) to 69% for severe myopia (cut-off point spherical equivalent -6). However, a high (91%) lifetime probability of primary myopia (spherical equivalent > or =-0.5) given a reduced uncorrected DVA at 16 years was found. CONCLUSION: In this population, reduced uncorrected DVA in childhood is an inaccurate and inappropriate intermediate "phenotype" for capturing adult myopia status. However, our findings support assessment of DVA in secondary school children as an effective method of identifying refractive error (both myopia and hypermetropia).

Adolescent↗

PubMed1994

Space-variant models of visual acuity using self-adjoint integral operators.

The purpose of this paper is to outline a more general approach to visual acuity experiments than the classical methods borrowed from the optical sciences. A theory based on integral operators with symmetric kernels replaces the standard use of filters constructed from windowed sines and cosines. This more general approach allows greater latitude in the range of phenomena to be modelled. It also permits all the standard techniques used in Fourier expansion of a stimulus and response to be generalized to a space-variant system such as the human visual field.

Cybernetics↗

PubMed2001

[Does supplementation of essential fatty acids influence the visual acuity and cognitive function of term infants?].

BACKGROUND: Norwegian health authorities recommend supplementation of essential fatty acids such as cod liver oil to term infants from four weeks of age. The essential fatty acids are seen as contributing to optimal development of the visual acuity and cognitive functions. This study reviews recent research on this issue. MATERIAL AND METHODS: We assessed six randomized controlled trials, published in 1998 and 1999, of which two evaluated visual function and four cognitive development. Outcome were measured by a number of standardized tests. We compared the results from our review with results from a Cochrane review which evaluated six studies published from 1995 to 1997. RESULTS: Only one of the tests used in the visual acuity studies showed significant effect at three out of the four age-related points in time at which the test was administered. Only one of the tests used in the cognitive development studies showed significant effect. INTERPRETATION: The studies reviewed here are in accordance with previous research and do not provide evidence for the claim that supplementation with essential fatty acids as such is significant in order to achieve optimal visual function and cognitive development in healthy term infants.

Child Development↗

PubMed1984

Immediate and long-term effects on visual acuity of surgically induced strabismus in kittens.

In order to isolate some of the factors responsible for strabismic amblyopia as well as to ascertain the time course of its development, frequent measurements were made of the visual acuity of the two eyes of kittens following imposition of surgically induced strabismus. Following behavioural training on a jumping stand, strabismus was induced in all but one animal by simple section of either the lateral (esotropia) or medial (exotropia) rectus muscle of one eye. The one exception was a kitten on which esotropia was induced by another common but more radical surgical procedure that involved removal of the body of both the lateral rectus and superior oblique muscles of one eye. There was a surprising difference between the immediate consequences for vision of section of the lateral and medial rectus muscles that were reflected by equally large differences in the magnitude of the amblyopia that developed eventually in the two situations. Following section of the lateral rectus muscle, there was an immediate reduction in the visual acuity of the operated eye of as much as 2 octaves after which vision returned to normal levels over 4 to 8 days. The acuity of the two eyes remained comparable for a few days after which the vision of the operated eye began to decline once more, signalling the onset of amblyopia some 10 to 12 days following imposition of strabismus. In contrast to the severity of these effects, the effects observed following section of the medial rectus were both mild and transitory. Furthermore, whereas all kittens that were rendered esotropic early developed amblyopia, none of the kittens that were made exotropic at the same age did so. Together, these results suggest that factors associated with the immediate consequences of the surgical procedure employed to produce a misalignment of the visual axes may contribute to the severity of the effects of surgically induced strabismus.

Age Factors↗

PubMed1986

Prediction of postoperative visual acuity in cataract patients using the Flying Corpuscle Viewer.

One hundred one cataract patients were tested preoperatively for macular function using the Flying Corpuscle Viewer, a portable blue field entoptic device which utilizes the slit lamp as a light source. Preoperative appreciation of the "Flying Leukocyte Corpuscles" (FLC) indicated a high probability of good postoperative visual acuity, while lack of appreciation of the blue field entoptic phenomenon preoperatively had no predictive value for postoperative visual acuity.

Adult↗

PubMedDate not supplied

Effects of intense continuous- and impact-type noise on pupil size and visual acuity.

The data obtained from these studies suggest that continuous noise at high levels will produce an increase in arousal, as indicated by pupil size, and that there is a tendency toward adaptation. At lower noise levels the effect is, at most, transitory. This papillary change does not appear to mediate a change in visual acuity. Impact noise such as that used here does not appear to produce reproducible changes in pupil size or visual acuity. For the noise conditions used here, concern for nonauditory sensory effects seems to be unwarranted.

Acoustic Stimulation↗

PubMed1990

[Margin of error in subjective assessment of visual acuity].

The frequencies for correct answers to individual Landolt-Cs were measured as a function of their size in 183 eyes ("psychometric function", 48 tests per acuity step, computer screen). An integrated Gauss function modified for assessing bias was fit (least squares) to the values of each subject. The mean value of the fitting function is a measure of visual acuity; its standard deviation is a measure of the reliability of the acuity measurements. The standard deviations are subject to a logarithmic normal distribution centered at a width of 1.5 steps. The distribution does not depend on age, sex or diagnosis (except for visual field defects). The width of the psychometric function is a universal number that is independent of the visual acuity itself (greater than 0.1). The distribution of acuity results measured according to DIN 58220 can be computed using the values of the psychometric function. For criteria 3/4, 3/5, 5/8 and 6/10, specified in the recently revised version of DIN 58220, one obtains standard deviations of the acuity measurements of 0.89, 0.84, 0.71 and 0.67 acuity steps. Compared to 3/4 the new criteria on average yield acuity values that are 0.55, 0.36, and 0.44 steps higher than previously. Given an actual acuity measurement value, confidence intervals are computed using Baye's formula. The results are presented as tables.

Humans↗

PubMedDate not supplied

Visual acuity and macular sensitivity in myopic eyes before and after laser in situ keratomileusis.

PURPOSE: To evaluate the changes in visual acuity (VA) and in macular sensitivity in myopic eyes subjected to laser in situ keratomileusis (LASIK) refractive surgery. METHODS: In 38 myopic eyes, VA by Snellen's table and macular sensitivity by scanning laser ophthalmoscope (SLO) microperimetry were assessed before and after 24 weeks after LASIK surgery. The myopic eyes were divided into three age-matched groups: Group A = from -5 diopters (D) to -7 D and normal SLO-macular sensitivity (15 eyes); Group B = from -8 D to -16 D and normal SLO-macular sensitivity (9 eyes); and Group C = from -8 D to -16 D and abnormal SLO-macular sensitivity. RESULTS: Group A and B eyes, at the first week after LASIK surgery, we observed a significant analysis of variance, p<0.01) reduction in VA and SLO-macular sensitivity with respect to baseline values, while after 12 and 24 weeks no differences (p>0.01) were found when compared to baseline. In Group C patients, at 1 and 4 weeks after surgical treatment, we observed a significant (p<0.01) reduction in VA and SLO-macular sensitivity with respect to baseline values. At 12 and 24 weeks the values of VA were reduced, but not significantly (p>0.01), while values of SLO-macular sensitivity were still significantly (p<0.01) reduced. CONCLUSIONS: LASIK could induce a reduction in VA and SLO-macular sensitivity in all myopic eyes during the 4 weeks following the surgery. This reduction is still present after 24 weeks only in eyes with the highest preoperative degree of myopia combined with the greatest reduction in macular sensitivity.

Adult↗

PubMed1995

[Visual acuity, refraction and color vision after implantation of foldable silicon lenses].

Implantation of intraocular lenses through a small opening is possible with phacoemulsification and foldable silicon lenses. There is little traumatic effect, which is positive for the healing process and the postoperative results of visual acuity and refraction. Because of alteration of the optic media, deteriorated sensation is possible. We investigated 28 patients with foldable silicon lenses after phacoemulsification. Pre- and postoperatively (1 day, 1 week, 3, 6, 12, 18 and 24 months) visual acuity and astigmatism were measured. As the testing of color vision is a sensitive method for the detection of disturbance in sensation because of altered optic media this was performed 24 months postoperatively using the pseudoisochromatic plates of Ishihara and Ichikawa and the color arrangement tests, Farnsworth Panel D-15 desaturated and the Farnsworth Munsell 100 hue test. The results of this study confirm quicker rehabilitation of visual function and a lower rate of operatively induced astigmatism. A slight blue color vision deficiency results as consequence to altered optic media, but there is no effect on daily life.

Aged↗

PubMedDate not supplied

[Increase in visual acuity in poorly-sighted patients by using spectral filters].

Tinted eyeglasses were selected for 768 poor-sighted patients aged 5-86 years with various ocular diseases. The frequency of tinted glasses utilization by poor-sighted patients was as follows: filter O2 was the optimal for 38% patients, filters G2 and K4 for 16-18%, and G1 for 11% patients. Filter G1 improved visual acuity by 19%, filters G2 and K4-K5 by 23%; the highest increment of visual acuity was observed with O2 filter: by 27%. Filters of different spectral characteristics and density may be useful in the same underlying ophthalmic disease, which is explained by the underlying disease and the presence, combinations, and severity of concomitant ocular diseases.

Eyeglasses↗

PubMed2004

A novel method for determining regional visual acuity in man and its application to a case of macular hole.

A novel method is described for measuring the regional visual acuity in the vicinity of the fovea. A letter is flashed for 100 ms in one of nine positions. The size of the letters is increased or decreased systematically until the size of a letter that can be identified correctly in 75% of cases is obtained for each of the nine positions. The method has been applied to the determination of the time course of development of the acuity changes associated with a macular hole in a single case. The relationship of these changes to other changes occurring in the retina or in perception is also described. With appropriate modification the method could be applied to other parts of the retina. Some even simpler tests are also described.

Fovea Centralis↗

PubMed1993

Risk of decreased visual acuity in full-thickness idiopathic macular holes.

We studied 169 eyes of 149 patients with a full-thickness idiopathic macular hole to ascertain the risk factors of enlargement of the hole or the surrounding retinal detachment and subsequent decreased visual acuity. Eyes were divided as follows: group A, 48 eyes with no posterior vitreous detachment and a hole 400 microns or smaller; group B, 77 eyes with no posterior vitreous detachment and a hole 400 microns or larger; group C, 13 eyes with posterior vitreous detachment and a hole 400 microns or smaller; group D, 31 eyes with posterior vitreous detachment and a hole 400 microns or larger. In group A, the macular hole enlarged in 37 eyes (77%); the retinal detachment enlarged in 35 eyes (73%); and visual acuity decreased by two or more Snellen lines in 28 eyes (58%). These percentages were significantly higher than those in group B (P = .01, P = .01, and P = .01, respectively), group C (P = .02, P = .01, and P = .01, respectively), and group D (P = .01, P = .05, and P = .01, respectively). Eyes without posterior vitreous detachment with a full-thickness idiopathic macular hole 400 microns or smaller may have a greater risk of an enlarged macular hole, surrounding retinal detachment, and subsequent visual loss.

Aged↗

PubMed1978

Image magnification, contact lenses, and visual acuity.

The optics of image magnification are derived. Necessary criteria for contact lens dispensing are explained and well-known approximations are demonstrated, along with their inherent limitations. The image size with spectacle lenses is contrasted with that of the corresponding contact lens, and the simple relationship between the two is demonstrated. Thus, no tables of contact lens image magnification are necessary for the clinical practitioner. Visual acuity as commonly expressed is not an exact measurement, but rather indicates that the patient has visual acuity equal to or better than the line read, but poorer than the next smaller line on the chart. It is shown how contact lens/spectacle interchange may be of significant social and legal benefit to selected groups of patients.

Contact Lenses↗

PubMed1991

Natural history of the development of visual acuity in infants.

A selective review of the contemporary understanding of development of infant visual acuity is presented together with recent developments in methodology to detect this change. References are confined, wherever possible, to human infant studies relating to factors explaining the development of acuity. Results obtained from a two year study of the development of grating acuity in normal infants are discussed briefly. The findings indicate the importance of establishing acuity norms and sensitivity of interocular acuity difference as an important parameter in the detection of monocular visual deficit in clinical practice.

Child Development↗

PubMedDate not supplied

Visual acuity norms in young children.

There are no universally accepted standards for visual acuity tests or norms in young (3-6-year-old) children, although acuity measurement is important in both clinical and screening settings. This review outlines the requirements for such standards. Although more research is needed, available data suggest that a standard test should meet the following requirements. It should utilize a letter optotype (tumbling E, Landolt C, or HOTV variant of the STYCAR), and single optotype with contour interaction bar surround. It should permit nonverbal pointing responses in younger children and verbal responses in older children. If an orientation-specifying method is followed, as with the E or Landolt C, the test should use a three-alternative choice--up, down, and sideways with a nondifferentiated left-right--rather than the traditional four alternative choice. A C-like O pseudo-optotype should be considered in a paired-comparison test format when the Landolt C is utilized, with a similar format for the tumbling E if a suitable pseudo-optotype can be derived. The optical grating test, which is widely used in infant testing, may underestimate acuity deficits and so is not a test of choice for determination of Snellen-equivalent acuity. A letter-based variant of the grating test may hold promise. Reduction in testing distance from 6 to 3 or 4 meters is recommended.

Age Factors↗

PubMed1978

[Postoperative astigmatism and visual acuity after cataract extraction with various operative methods (author's transl)].

UNLABELLED: The postoperative findings after cataract extraction with corneoscleral incision were compared with those after corneal incision in two groups consisting of 70 patients each. The criteria used were the degree and axis of postoperative astigmatism evaluated ophthalmometrically and the postoperative visual acuity. The preoperative values were taken into account. RESULTS: The mean values of astigmatism shortly after corneal incision were very much higher than those after corneoscleral incision, and they approached each other 6 months after cataract extraction. Patients who had an operation done with corneoscleral incision had a better visual acuity than those with corneal incision.

Astigmatism↗

PubMed1996

Clinical and surgical factors influencing corneal graft survival, visual acuity, and astigmatism. Corneal Transplant Follow-up Study Collaborators.

PURPOSE: To quantify clinical and operative factors that influence corneal graft outcome. METHODS: A multifactorial analysis was done on 2242 corneal grafts registered by the United Kingdom Transplant Service from July 1987 to June 1991. RESULTS: There was an increased risk of graft failure in patients with preoperative diffuse and other noncentral stromal edema, less-common eye diseases, small trephine size, difference in donor and recipient sizes greater than 0.25 mm, and use of mixed continuous and interrupted sutures. Visual acuity 3 months after surgery was poorer in patients who had glaucoma and low visual acuity preoperatively, small trephine size, and combined vitreous surgery. Use of interrupted sutures resulted in higher astigmatism at 3 months. CONCLUSIONS: After allowing for the effects of recipient factors, surgical factors significantly affected corneal graft outcome. No factors that showed significant benefits for graft survival also adversely affected visual performance. Details of medical history, clinical condition, and surgical method failed to predict more than a small proportion of observed variability in visual performance of functioning grafts.

Astigmatism↗

PubMed1999

Improvement of visual acuity in patients suffering from diabetic retinopathy after membrane differential filtration: a pilot study.

BACKGROUND: Membrane differential filtration is an extracorporeal treatment procedure which eliminates high molecular weight proteins and lipids from the blood. This pilot study was initiated to investigate the short-term effects on blood rheology and visual function in patients suffering from diabetic retinopathy. METHODS: Six patients with non-proliferative diabetic retinopathy, clinically significant macular edema (five patients, nine eyes) and inactive proliferative diabetic retinopathy (one patient, one eye) underwent a single treatment with a hollow fiber secondary plasma filter. The main parameter measured was visual acuity prior to and after treatment. Biochemical and rheological parameters (whole blood and plasma viscosity, and erythrocyte aggregation) were also measured. The mean follow-up was 25 (range 4-90) days after treatment. RESULTS: The mean improvement of visual acuity was 1.4 lines (SD 0.8 lines, p = 0.002) 24 h after therapy. This remained stable during the follow-up period. The rheological measures were significantly lowered. A significant reduction of total protein, fibrinogen, IgG, IgM, IgA, alpha-2-macroglobulin, total cholesterol, LDL and HDL was found. CONCLUSION: This study demonstrates the rheological impact of membrane differential filtration. It was shown that rheological changes correlated with clinical improvement in patients suffering from diabetic retinopathy with clinically significant macular edema.

Aged↗