Maths Abrahamsson

Risk factors in amblyopia.

Any intervention to prevent serious amblyopia is based on the knowledge about normal versus subnormal visual development. Our ability to predict with high degree of certainty which children will develop amblyopia will be dependant on the characteristics of various risk factors for initiating the development of squint or amblyopia. We have used longitudinal studies of population based cohorts of young children to define some of these risk factors such as refractive errors. Three hundred and ten children with an astigmatism 1.0 D at one year of age were refracted yearly between the age one and four years. Astigmatism and anisometropia were found to be highly variable during infancy and early childhood. Longitudinal follow-up seems to be needed to separate the normal from the abnormal refraction development, which initiates the development of the amblyopia. Children with constant or increasing astigmatism or anisometropia between one and four years were ‘at risk’.In parallel we have studied important factors for successful treatment of amblyopia. Based on these findings we conclude that a population screening at four years of age seems to be advantageous in Sweden in order detect and successfully treat most cases of amblyopia.

Accommodative facility training with a long term follow up in a sample of school aged children showing accommodative dysfunction

The primary aim of this project was to study the effect of flip lens-training on the accommodative function in a group of children with accommodative dysfunction and subjective symptoms such as asthenopia, headache, blurred vision, and avoidance of near activity. We also wanted to measure the accommodative facility among the children in comparison with a control group. Another aim of the study was whether flip lens-training increased accommodative facility, and to find out if it also had a positive effect on their asthenopia and related problems also in long term. Following the training period the accommodative facility and accommodative function significantly increased and two years after finishing the training period no child had regained any subjective symptoms and the objective findings were almost the same as at the end of facility training period. These results suggest that accommodative facility training is an efficient method built on loss of symptoms among children with accommodative infacility.

The neonatal development of the light flash visual evoked potential.

Aims. To follow visual development longitudinally in the normal neonate using the flash visual evoked potential (VEP) and to find indications for a relationship between potential development and visual development. Methods. Twenty healthy infants, born at term, were included in the study. Flash and patterned flash VEPs were used. The first VEP was recorded the day of birth or just postnatally, and succeeding recordings were performed the following weeks and months. Results. The data revealed different types of VEP in the neonatal period suggesting great variablity in visual function on the day of birth. In the early development a potential of long latency and duration preceded the development of a more compound potential of shorter latency. The two types of responses seemed to coalesce during early development; the first late response was attenuated and was eventually integrated in the more mature VEP. At approximately five weeks of age changes in the VEP were simultaneous with the development of responsive smiling and another visual behaviour of the infants. Conclusions. The results showed many similarities between the VEP development in infants and in immature animals. In developing animals geniculo-cortical and extra-geniculate visual afferent pathways evoke two types of VEPs similar to those recorded in the present study. The early responses were also similar to previous recordings from children with lesions in the geniculo-striatal pathway or primary cortex. Our interpretation of the results was that the human VEP also consists of responses evoked by afferents running both in geniculo-cortical and extra-geniculate pathways and that the two types of responses could be separated in the VEP in the neonatal period. These findings are important for our understanding of conditions with a delay in visual maturation, for example intracranial haemorrhages, hydrocephalus, pre/dys-maturity and `idiopathic delayed visual maturation.

Visual acuity, amblyopia, and ocular pathology in 12- to 13-year-old children in Northern Mexico

PURPOSEnThe aim of this study was to establish visual acuity (VA) and the prevalence of amblyopia and other ocular disorders in a population of 12- to 13-year-old children in Mexico who have not been vision screened.nnnMETHODSnA total of 1,035 12- to 13-year-old children were examined in a field study. The examination included VA, stereopsis, cover testing, refractive retinoscopy, and examination of the red reflex and posterior pole. In cases with unexplained subnormal VA, visually evoked potential/visually evoked response was also performed.nnnRESULTSnA >or=20/20 in at least one eye was found in 93% of the subjects. Bilateral VA <or=20/40 was found in 0.3% of cases. None of the subjects had bilateral VA <20/60. Amblyopia (<or=20/40) was found in 26 subjects (2.5%). In 10 cases, the cause of subnormal VA was unexplained. Ocular albinism was found in 3 cases, whereas strabismus was found in 24 subjects (2.3%). There were very few ocular opacities or posterior pole abnormalities.nnnCONCLUSIONSnThe visual status in the Mexican 12- to 13-year-old children tested was good. The prevalence of amblyopia was similar to that in other unscreened populations.

The effects of accommodative facility training on a group of children with impaired relative accommodation—a comparison between dioptric treatment and sham treatment

The effects of accommodative facility training were evaluated by comparing training with plano lenses and ±2.00u2003D lens flipper sets. Thirteen children with symptoms and signs of accommodative dysfunction were included in the study. Seven started with 2 weeks of plano lens training before proceeding to traditional dioptric flipper training; later, one patient from this group was lost to follow‐up. The remaining six children used powered flipper training from the start. The positive (PRA) and negative relative accommodation (NRA) were examined every second week. During the initial training period both the PRA and the NRA decreased in the sham treatment group (P=0.010 and P=0.102, respectively), while the PRA and the NRA increased during the dioptric training in both groups (P=0.102 and P=0.033, respectively). The result of this study indicates that accommodative facility training has a real effect on the amplitude of relative accommodation in patients with impaired relative accommodation.

Prevalence of myopia among 12- to 13-year-old schoolchildren in northern Mexico.

Purpose. The aim of this article was to report the prevalence of refractive errors, mainly myopia, among 12- to 13-year-old children in a metropolitan setting in Mexico. Methods. A total of 1035 schoolchildren were examined in a field study in Monterrey, Mexico. The examination included best-corrected visual acuity and refraction during cycloplegia. A sample of the children was sent to a pediatric eye clinic and underwent cycloplegic refraction with an autorefractor. Results. We found a prevalence of myopia (≥−0.5 D SE) of 44%, whereas bilateral myopia was present in 37% of the children. In the total sample, high myopia (≥−5D) was found in 1.4%. The prevalence of myopia was significantly higher in girls. Only 20% of children with bilateral myopia used prescription glasses; 8% had prescribed glasses, but did not use them. Hyperopia (≥+1 D) was present in 6.0% of the total population, and astigmatism (≥−1.5 D) was present in 9.5%. Conclusions. The prevalence of myopia among 12- to 13-year-old children in Mexico is high. The majority of cases are low grade, and a large number of the myopic children do not have, or do not use, prescription glasses.

A new glare test based on low contrast letters--evaluation in cataract patients.

Abstract A new simple glare test was designed and evaluated regarding clinical usefulness and reproducibility. The ability to recognize letters of equal size and varying contrast was determined with the absence and presence of glare sources above and below the letters. Ten patients with cataract, visual acuity of at least 0.3 and glare problems, and three age matched controls were tested, as well as one patient with glare complaints and exophoria, one with lens subluxation and one with cataract and no glare problem. The test was found to be cheap and simple to produce and useful for clinical testing. Normal eyes had no detectable reduction of letter contrast sensibility with glare. All cataractous eyes had a letter contrast sensivitity without glare that was well below that of the controls and under glare conditions they all had a drop in visual function that was unrelated to their visual acuity. The reproducibility was of a magnitude similar to that of other low contrast letter tests. Our conclusion is that this test will be a valuable tool in the evaluation of cataract patients providing information not only about glare‐induced visual loss but also about contrast sensitivity, separating eyes with increased intraocular light scattering from normal eyes.

Evaluation of a clinical glare test based on estimation of intraocular light scatter.

A glare test based on psychophysical estimation of intraocular light scatter and using a flickering, annular glare source was evaluated. The parameters determining the accuracy of the test were studied. In particular the influence of background light and flicker frequency were investigated and optimum values for best accuracy were found. Based on these findings a versatile and simple apparatus was constructed. Forty patients with various degrees of cataract were investigated in a clinical study. Patients, who subjectively experience severe glare problems, indeed show high glare values as measured with the apparatus. No obvious relation between visual acuity and glare score was found. In comparison with glare tests using a stationary glare source the use of a flickering glare source is advantageous in terms of sensitivity and accuracy

Glare disability as a cause of deterioration of vision in cataract patients

Patients with developing cataracts often experience the most marked consequences of their disease under glare conditions (Miller and Benedek, 1973). They begin to have difficulties in recognition of faces under bright light conditions. They often give up driving at night because they experience that oncoming headlights make the road signs undertectable and they often complain about reading problems and some patients may even avoid being outdoors since their vision drops dramatically under bright light conditions. Due to the complaints of our cataract patients it is important for us to evaluate the lenticular scatter as a cause of visual disability and to test glare disability during the preoperative evaluation in cases with turbid ocular media. Slitlamp exqnination gives only information about the backscattered light

Patterned light flash evoked short latency activity in the visual system of visually normal and in amblyopic subjects

Abstract In a previous experimental study on anaesthetized cat it was shown that a short latency (35–40 ms) cortical potential changed polarity due to the presence or absence of a pattern in the flash stimulus. The results suggested one pathway of neuronal activation in the cortex to a pattern that was within the level of resolution and another to patterns that were not. It was implied that a similar difference in impulse transmission to pattern and non‐pattern stimuli may be recorded in humans. The present paper describes recordings of the short‐latency visual evoked response to varying light flash checkerboard pattern stimuli of high intensity in visually normal and amblyopic children and adults. When stimulating the normal eye a visual evoked response potential with a peak latency between 35 to 40 ms showed a polarity change to patterned compared to non‐patterned stimulation. The visual evoked response resolution limit could be correlated to a visual acuity of 0.5 and below. In amblyopic eyes the shift in polarity was recorded at the acuity limit level. The latency of the pattern depending potential was increased in patients with amblyopia compared to normal, but not directly related to amblyopic degree. It is concluded that the short latency, visual evoked response that mainly represents the retino‐geniculo‐cortical activation may be used to estimate visual resolution below 0.5 in acuity level. The possible value of the method in analyzing general maturation and lesions in the visual system is discussed.