SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Ophthalmologists today need to be able to determine visual acuity accurately more and more frequently. The result depends not only on the optotypes but also on the investigation methods used. Possible errors are discussed.
Preoperative and posteroperative visual acuities for Landolt ring targets and for a grating target of comparable retinal illuminance produced by two-beam interference were assessed in patients with anterior segment disease. Good preoperative interferometric acuities (6/12 or better) were found in over half of the cases in which Landolt acuities were 6/90 or worse. In general, good preoperative interferometric acuities were predictive of good postoperative Landolt acuities. However, poor interferometric acuities in patients with opacified media did not preclude good Landolt acuities postoperatively. We conclude that interferometric acuity testing can provide valuable information about potential macular resolution capacity in some cases. Both the strengths and weaknesses of interferometric acuity testing must be appreciated for successful application.
Strabismus, the misalignment of the visual axis of one eye relative to that of the other eye, reduces visual acuity in the affected eye. Several processes contributing to that loss are: amblyopia, which results in a chronic acuity loss whether or not the fellow eye is viewing; strabismic deviation, which shifts the image of an acuity target onto more peripheral, and therefore less acute, retina when the fellow eye fixates; interocular suppression and binocular masking, which reduce visibility in the strabismic eye due to neural influences from the other eye. We measured the losses due to these processes in nine small-angle strabismic subjects. Amblyopia reduced acuity by a median of 34% relative to its value in subjects with normal binocular vision, and strabismic deviation produced a loss of 44%. Suppression and masking together reduced acuity by 20%, and therefore had substantially less effect than the other factors.
Ninety-five patients with Stargardt's macular dystrophy were appraised for visual loss with age by both life-table analyses and cross-sectional procedures. The probability of maintaining a visual acuity of 20/40 or better in at least one eye was 52% by age 19, 32% by age 29, and 22% by age 39. In the population studied, once a patient's visual acuity dropped below 20/40, it tended to decrease rapidly and stabilize at 20/200. Fluorescein angiograms obtained on 64 of the 95 patients showed a "dark choroid" in 55 (85.9%). This finding, therefore was present in the majority of the patients, although its absence does not rule out Stargardt's macular dystrophy.
We describe two patients with spontaneous retinal pigment epithelial tears through the fovea who have maintained at least 20/40 visual acuity for 1 year and 3 years following the rip. Both patients had long-standing serous detachments of the retinal pigment epithelium associated with age-related macular degeneration prior to the development of the tear. Each tear was at least five disc areas in size and centered on the fovea. Foveal fixation was documented despite the presumed absence of pigment epithelium. This observation suggests either that there may be remaining or redundant pigment epithelium or that pigment epithelium directly beneath the central macula is not required for maintenance of 20/40 visual acuity.
OBJECTIVE: To determine the association between changes in visual acuity (VA) and frequent falls in older women. DESIGN: Prospective cohort study. PARTICIPANTS: Two thousand two elderly community-residing women participating in the Study of Osteoporotic Fractures with measurements of VA at baseline and a follow-up examination 4 to 6 years later (mean of 5.6 years). METHODS: Binocular VA with habitual correction was measured under standard illumination using Bailey-Lovie charts at baseline and fourth examinations. Change in VA was stratified into 5 categories: no change or VA gain, loss of 1 to 5 letters, loss of 6 to 10 letters, loss of 11 to 15 letters, and loss of >15 letters. A separate analysis considered decline in VA as the loss of >or=10 letters (>or=2 lines) on the Bailey-Lovie acuity measure between baseline and follow-up examinations. MAIN OUTCOME MEASURES: Data on falls were obtained from postcards sent every 4 months after the follow-up examination. Frequent falling was defined as >or=2 falls during a 1-year period after the follow-up examination. RESULTS: Compared with women with stable or improved VA, women with declining acuity had significantly greater odds of experiencing frequent falling during the subsequent year. Odds ratios after adjustment for baseline acuity and other confounders were 2.08 (95% confidence interval [CI]: 1.39-3.12) for loss of 1 to 5 letters, 1.85 (95% CI: 1.16-2.95) for loss of 6 to 10 letters, 2.51 (95% CI: 1.39-4.52) for loss of 11 to 15 letters, and 2.08 (95% CI: 1.01-4.30) for loss of >15 letters. In the analysis of visual decline defined as a loss of >or=10 letters, heightened risk of frequent falling was evident in each of 2 subgroups defined by splitting the sample on baseline VA, with borderline significant evidence of a more pronounced effect in those women with baseline VA of 20/40 or worse (P value for interaction, 0.083). CONCLUSIONS: Loss of vision among elderly women increases the risk of frequent falls. Prevention or correction of visual loss may help reduce the number of future falls.
The Stiles-Crawford effect (SCE) of the first kind has often been considered to be important to spatial visual performance in that it ameliorates the influence of defocus and aberrations. We investigated the influence of SCE apodization on visual acuity as a function of defocus (out to +/-2 D) in four subjects. We used optical filters, conjugate with the eye's entrance pupil, that neutralized or doubled the existing SCE. With an illiterate-E task, the influence of the SCE was more noticeable for myopic defocus than for hypermetropic defocus, was generally more noticeable for high-contrast than for low-contrast letters, and increased with increase in pupil size. The greatest influence on visual acuity of neutralizing the SCE, across the subjects and range of conditions, was deterioration of 0.06 (4-mm pupil), 0.16 (6-mm pupil), and 0.29 log unit (7.6-mm pupil).
Controversy surrounds the averaging of visual acuity scores. We examine this debate and provide a series of guidelines and worked examples to enable investigators to select an average (e.g. arithmetic mean, geometric mean, median) appropriate for their data.
We have estimated the total number, distribution and peak density of retinal ganglion cells (RGCs) in retinal wholemounts of several species of microchiropteran (echolocating) bats. The estimates are based on counts of Nissl-stained, presumed RGCs. The total number of presumed RGCs varies among the species: from about 4,500 in Rhinolophus rouxi to about 120,000 in Macroderma gigas. In addition, in two species (Nyctophilus gouldi and M. gigas), the estimates are based on counts of positively identified RGCs retrogradely labelled with the enzyme horseradish peroxidase injected into the retinorecipient nuclei. In these two species, the numbers and distributions of retrogradely labelled RGCs and Nissl-stained presumed RGCs are very similar. In all six species studied, the peak-density regions of presumed (or positively identified) RGCs are located in the inferotemporal retinae, and the RGC isodensity lines tend to be horizontally elongated. However, the RGC densities in the high-density regions are only 2-4 times greater than those in the low-density regions in the superior retinae. The somal sizes of RGCs vary from 5 to 16 micron in diameter and are unimodally distributed. There is no indication of the existence of distinct morphological classes of RGCs. The axial lengths of microchiropteran eyes vary from 1.8 mm in R. rouxi to 7.0 mm in M. gigas. For all species the posterior nodal distance (PND) was assumed to be 0.52 of the axial length of the eye. This assumption is based on the analysis of published data concerning schematic eyes of nocturnal vertebrates. These derived values of the PNDs allowed us to calculate the retinal magnification factors and the number of RGCs per degree of visual angle. From these, the upper limits of visual acuity were derived on the basis of the assumptions of the sampling theorem. The estimated upper limits of visual acuity of the six species of echolocating bats vary from about 0.35 cycles/degree in R. rouxi to about 2 cycles/degree in M. gigas. This range is quite similar to the range of visual acuities in murid rodents.
In summary, these finding show us several things. First, we know that with surgery keratoconus patients can be rehabilitated to achieve excellent vision. A postoperative average visual acuity of 20/20 after an average preoperative visual acuity of 20/500 is a most positive outcome. Secondly, the average amount of postoperative astigmatism of 3.5 diopters shows that even after totally removing a corneal button and replacing it with 360 degrees of sutures we can still achieve a relatively small amount of residual astigmatism and a relatively spherical cornea. Thirdly, with the exception of one primary donor failure, a total of one hundred percent clear grafts, even after the occurrence of two graft rejection episodes, indicated an extremely high success rate of keratoplasty in keratoconus.
In the early postoperative stage giant cells often appear on IOLs. Independent of this, a foreign-body reaction may start about 3 months after surgery from posterior synechia. Foreign-body reaction occur more frequently in diabetic patients or patients with glaucoma. In a prospective trial, we examined the surface of the IOLs from 115 patients with diabetes or glaucoma using specular microscopy. We compared the maximal density of the cells to visual acuity. One week and 1 month after surgery, the maximal density of giant cells was between 0 und 20/mm2; vision (median) was independent of the giant cell density in all groups between 20/25 and 20/30. Three months after surgery, the maximal density of giant cells was between 0 und 35/mm2; vision (median) was 20/25 in patients with no giant cells or cell densities up to 15/mm2. Seven patients had cell densities between 16 and 35/mm2; visual acuity (median) was 20/125. The difference was significance was (P < or = 0.05). Six months and 1 year later after surgery, the maximal density of giant cells was between 0 and 41/mm2; the vision (median) in patients with giant cell densities up to 15/mm2 was between 20/20 and 20/25. In five examinations the cell densities were found to be in the range of 16 to 40/mm2; visual acuity (median) was 20/80 in these cases. The difference is not significant (P < or = 0.05). A foreign-body reaction with more than 15 giant cells/mm2 is a rare complication of cataract surgery with lens implantation. Three months after surgery, this complication correlates with poor vision.
Toxaemia of pregnancy associating hypertension and proteinuria can cause maternal and ocular complications. Maternal ocular involvement is classically described with loss of visual acuity due to serous retinal detachment. We report a case of a 31 year old woman who just complained of severe deterioration of visual acuity. During her stay at the hospital we discovered a pregnancy complicated by a HELLP syndrome. Resturation of vision has been obtained after fetal expulsion and medical treatment against hypertension.
Ophthalmologic examinations for cataract, glaucoma, diabetic retinopathy, macular degeneration and visual acuity were performed on 2631 of the 3977 members of the Framingham (Massachusetts) Heart Study population still living in 1973-1975. The subjects ranged in age from 52 to 85 years. This monograph presents the detailed protocols and record forms for screening and diagnostic examinations, definitions of the specific abnormalities and characteristics used to screen for each disease, criteria for suspicion and diagnosis of diseases, detailed tables of the basic data from the study, evaluation of quality of the data, and discussion of selected findings. The tables provide data on the number and proportion of persons and of eyes with each type of abnormality and each disease, by age and sex. Where appropriate, the data are further classified by location of abnormality, severity, bilaterality and associated visual acuity limitation. The study was sponsored by the National Eye Institute.
Most elderly visually disabled people have lower levels of visual acuity for both reading and getting about in their homes than would be inferred from clinic measurements. Even with optimum optical correction, performance can be much improved by simple modifications to existing facilities, individual advice, and in most cases the addition of a simple adjustable reading lamp.
PURPOSE: We set out to determine whether the children who have low compliance (measured electronically) with occlusion therapy for amblyopia are those with insufficient increase of visual acuity. METHODS: In 14 newly identified amblyopic children (mean age 4.3+/-1.9 years), compliance was measured electronically over a period of 1 week, 6 months after the start of occlusion therapy. Compliance was measured with an Occlusion Dose Monitor (ODM). The measurements took place during planned domiciliary visits. The children were diagnosed with anisometropia (n=5), strabismus (n=4) and anisometropia and strabismus (n=5). Compliance was expressed in percentages of the electronically registered time compared with the prescribed occlusion time. Satisfactory acuity increase following 6 months of occlusion therapy was defined on reaching any of the following criteria: acuity increase expressed as a ratio between acuity of the amblyopic eye and acuity of the good eye of more than 0.75, acuity of the amblyopic eye exceeding 0.5 as measured on the E-Chart or Landolt-C, or three LogMAR lines of increase in acuity. RESULTS: Measured compliance averaged 80% in the eight children who had a satisfactory acuity increase and 34% in the six children who had an unsatisfactory visual acuity increase. Children with low acuity increase had statistically significantly lower compliance (P=0.038). CONCLUSION: The general assumption among orthoptists, that compliance with occlusion therapy for amblyopia is low in children with insufficient acuity increase, has been validated by electronic, objective means.
Visual evoked cortical potentials (VECP) were recorded from 10 subjects with normal visual acuity (VA) 1.0. Reversing square-wave gratings of 16 different spatial frequencies were used as stimuli. In all 10 subjects significant increase in power at the stimulation frequency was observed in the Fourier spectrum. The VA, calculated from the Fourier spectra, ranged from 0.4 to 1.0. The described method for VA measurement is entirely objective, and the examination can be performed very rapidly and conveniently with the aid of a computer. However, the results indicate that the reliability of the measurement in individual cases may be doubtful.
A Q-switched neodymium: YAG laser was used to perform 67 posterior capsulotomies in 67 patients. A clear visual axis was produced in all the eyes. The visual acuity improved by one or more Snellen lines in 90% of the eyes, and the final visual acuity was 20/40 (6/12) or better in 78% of the eyes. Cystoid macular edema developed in two patients after capsulotomy. Increases in intraocular pressure were most prevalent in the early postoperative period. No significant correlation was found between the acute pressure rise and the laser energy used, a previous history of glaucoma or the presence of an intraocular lens. After 6 months of follow-up none of the eyes showed a permanent pressure elevation.
When visual acuity, as assessed by interference fringes before and after cataract surgery, is compared without regard to the stage of the disease, the correlation is much higher than for preoperative and postoperative letter acuity but is still rather moderate (about 0.4 to 0.5). If, however, the cases are classified according to the visibility of the red fundus reflex, those with a readily visible reflex result in a correlation as high as r = .85, whereas those with a considerably diminished reflex range much lower, and those with a mature or almost mature cataract become erratic. In these examinations it is preferable to ask the patient to indicate only the direction of the fringes, since this criterion was found to be better defined than fringe visibility.