Age affected saccadic latency, accuracy, and velocity. For each parameter there was a different pattern of development and decline probably related to the way in which the portion of the brain that controls each function develops and ages.

We have developed a lightweight plastic goggle with rigid contact lens inserts that can be applied to the eyes of newly hatched chicks to explore the range and accuracy of the developmental mechanism that responds to retinal defocus. Convex and concave lenses of 5, 10, 15, 20 and +30D were applied to one eye on the day of hatching. The chick eye responds accurately to defocus between -10 and +I5D, although hyperopia develops more rapidly than myopia. Beyond this range there is first a levelling off of the response and then a decrease. The resulting refractive errors are caused mainly by increases and decreases in a.xial length, although high levels of hyperopia are associated with corneal flattening. If + 10 D defocusing lenses are applied nine days after hatching the resulting myopia and hyperopia are equal to about 80% of the inducing power. After one week of inducing myopia and hyperopia with ± !0 D lenses, the inducing lenses were reversed. In this case, the refractive error did not reach the power of the second lens after another week of wear. Instead, astigmatism in varying amounts (0-12 D) was produced, being greater when reversal was from plus to minus. Finally, astigmatism can also be produced by applying 9 D toric inducing lenses on the day of hatching. The astigmatism produced varies from 2 to 6 D, and the most myopic meridian coincides with the power meridian of the inducing lens. This astigmatism appears to be , primarily due to corneal toricity. Furthermore, the greatest magnitude of astigmatism was produced when the piano meridian of the inducing lens was placed 45" from the line of the palpebral fissure.

PURPOSE: Most studies of visual development have concentrated on visual development of infants. Only a few studies have extended this to children and determined the point at which visual function becomes truly adult-like. Yet from a clinical and research perspective it is important to know this. This review paper is a discussion of the development of visual acuity and contrast sensitivity into childhood. METHODS:The literature on subjective (measured with preferential looking or psychophysical methods) and objective (visually-evoked potential) measures of visual acuity and contrast sensitivity was examined with particular emphasis on studies of children over the age of 5 years and those articles that compared different age groups and those that made a comparison with adults. RESULTS: Visual acuity was found to be fully mature between the ages of 5 and the mid teenage years, while contrast sensitivity was found to mature fully between the ages of 8 to 19 years. Thus, there is still no clear answer to the fundamental question of when these basic aspects of visual function mature, but it may be later than previously thought. CONCLUSIONS: Further studies are needed to answer this basic question more precisely and objective measures, such as VEP, may be able to answer this question better than psychophysical methods. KEY WORDS: visual development; visual acuity; contrast sensitivity; critical period; visually-evoked potential. RESUMEN OBJETIVO: La mayoría de los estudios sobre desarrollo visual se han centrado en el desarrollo visual de bebés. Sólo unos pocos estudios han ampliado el intervalo de edades estudiadas para incluir a niños y han determinado en qué momento la función visual alcanza un estado verdaderamente equiparable al de un adulto. Sin embargo, desde una perspectiva clínica y de interés científico, es importante conocer este dato. En este artículo de revisión se analiza el desarrollo de la agudeza visual y de la sensibilidad al contraste a lo largo de la infancia. MÉTODOS: Se analizaron los artículos científicos existentes sobre medidas de agudeza visual y de sensibilidad al contraste, tanto subjetivas (medidas con la técnica de mirada preferencial o por métodos psicofísicos) como objetivas (potenciales visuales evocados), centrándonos particularmente en aquellos estudios realizados en niños mayores de 5 años y en aquellos artículos donde se compararon diversos grupos de edad entre sí o con un grupo de adultos. RESULTADOS: Se encontró que para la agudeza visual el ojo alcanza un estado plenamente maduro a una edad comprendida entre los 5 y los 15-16 años, mientras que para la sensibilidad al contraste el ojo alcanza la madurez plena a una edad comprendida entre los 8 y los 19 años. Así, todavía no disponemos de una respuesta clara a la pregunta fundamental de cuándo estos aspectos de la función visual acaban de madurar, pero es posible que esto suceda a una edad más tardía de la que se creía hasta ahora. CONCLUSIONES: Es necesario realizar más estudios para poder dar una respuesta más precisa a...

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Light-weight translucent plastic goggles with convex or concave rigid contact lens inserts were applied unilaterally to the eyes of young chicks. Convex and concave cylindrical lenses produced astigmatic refractive errors. The magnitude of the induced astigmatism was less than that of the inducing lens and varied with axis orientation. Decreased aperture size or interruption of the defocus resulted in a decreased response to refractive defocus. Slit apertures and spherical defocus produced variable amounts of myopia, hyperopia and astigmatism. Choroidal changes (increased thickness) were observed only in birds developing hyperopia or recovering from myopia.

Vision scientists have concentrated on studying two visual functions when it comes to assessing the sensory visual development in human: visual acuity and contrast sensitivity. The methods used to measure these visual functions can be either behavioral or electrophysiological. A relatively new technique for measuring the visual acuity and contrast sensitivity electrophysiologically is the sweep visual evoked potential (sVEP). This paper is a review of the literature on the sVEP technique: stimulus parameters, threshold determination, validity and reliability of sVEP are discussed. Different studies using the sVEP to study the development of visual acuity, contrast sensitivity, and vernier acuity are presented. Studies have demonstrated that the sVEP is a potentially important tool for assessing visual acuity and contrast sensitivity in non-verbal individuals with disorders affecting their visual system.

In the last 100 years, there appears to have been a myopic shift in clinic-based populations and myopia prevalence appears to follow a predictable pattern with age.

Near addition lenses are prescribed to pre-presbyopic individuals for treatment of binocular motor problems such as convergence excess and to control the progression of myopia. To date, no investigation has looked at the complete sequence of binocular motor responses during a period of near work with +2D lenses. This investigation evaluated changes to accommodation and vergence responses when young adults sustained fixation at 33 cm with +2D addition lenses. In addition, the effect of the accommodative vergence cross-link (AV/A) on the magnitude and the completeness of binocular adaptation to these lenses were evaluated. The results showed that +2D lenses initiate an increase in exophoria and convergence driven accommodation. The degree of the initial induced phoria was dependant upon the magnitude of the AV/A ratio. Vergence adaptation occurred after 3 min of near fixation and reduced the exophoria and convergence driven accommodation. The magnitude of vergence adaptation was dependant upon the size of the induced phoria and hence the AV/A ratio. The completeness of adaptation was seen to vary inversely with induced exophoria and thus the AV/A ratio.