In two studies, the first in a school in Peterborough and the second in a school in Norwich, more than 233 children aged 8-12 years received either an orthoptic examination, or an optometric examination, together with an examination using coloured overlays and a test of reading fluency. In both studies more than one-third of the children reported visual symptoms. More than one-third of the children chose to use an overlay, and they read more quickly with it than without. The colour of the overlay chosen was weakly related to the binocular amplitude of accommodation: overlays reflecting greater energy at long wavelengths were chosen more frequently by children with a higher amplitude of accommodation. Although the visual symptoms were strongly related to the use of an overlay, in neither study was the benefit from an overlay strongly related to the orthoptic or optometric findings. Nevertheless, children who used an overlay had slightly, but significantly, reduced mean binocular amplitude of accommodation and fusional reserves. On average, children with 'sensory' or 'motor' instability of the nonius strips of the Mallett unit read more slowly than others, as did those with poor stereopsis. However, 60% of those demonstrating sustained overlay use gave a normal response on the Mallett aligning prism test, compared with 80% of those who did not use an overlay for a sustained period. Another indicator of decompensated heterophoria, Sheard's criterion, did not differentiate subjects who used overlays from those who did not. Although binocular and accommodative anomalies do not appear to be the underlying mechanism for the benefit from coloured filters in most cases, there may be some individuals who respond to coloured filters and in whom these ocular motor factors require treatment. Children with visually precipitated symptoms and/or reading difficulties need both a careful evaluation of their accommodative and binocular status, and an investigation of the effect of coloured filters.

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4 s u b j r c t that lias held man's attention for centuries has been the graclual development of the eye, from the early one cell type to the complicated, intricate, and highly s p e c i a l i d mechanism which man possesses today. It is the aim of this and subsequent liqwrs to tracr the evolution of the visual apparatus from early protoplasm to its present specialised form, and in the hope that those who read may be encouraged t o go furthcr into it; study and possibly attempt some research. as this field of stutly is vast :ml n-idc :ind leaves many intere+ting antl fascinating :ivenues along which nxi can \vork.W e I~I K that response to light doesn't indicate an organ of vision, as many inorganic su1ist;inces possess this property. i.e., Photographic Plate. Photochemical changes in t l i i . living protoplasm differs from the inorganic world in form and complexity, Ixit not in nattrre. Claude Bernard states that the only response liberated hy thc stimulatiini (if a primitive organism is one of motion called Tropisnr (turning). The action is not confined to the animal world hut also to the regetable world. Tii thc locver class which have free movement, it is controlled hy light-P h o t o t r o~L i~~~. T n the case (If fixed plant life, the movement is limited to various parts o l the plant antl is known as Heliotropic movements. The leaves of plants, etc.; are usually situatvtl a t right angles to the sun's rays in order to catch as much of the light as possil)le---this is called Positivc Neliotuopisitr, while in thc case of the roots which grow away from the light-NegtrtiveHeliotropisrti. In the lowor unicc.llular forms of plxnts and animals the tropic movement is very siniilar Init in the 1iiglic.r forms the coniparatibility is less evident. Although the stimulating iiiechanisrii is photochemical in both plants and animals, there is a difference in thr manricr i n which the stimulus is coiiveyed and which effects take place.In plant, [lie traiiznii~sion i5 q a s~/ v~. The itimuluy i s conveyed to a distant point where tlic tlesit-etI I)IiototroI-'ic-response results. 111 aninials tIie stimulation of the photochcmical su1)stance produces a chemical reaction in the neighbouring cells. thus producing a phrase of excitation from the site c f stiinulation to the site where the reaction is procluccd. This is called Actizre transmission.Phototropic respori may bc, considered i n two stages. ( 1 ) F'hobi~. responsr (,fear). In tliia case thr r-carlion to the stiinulus is madc in an intleterniinate ulaiiner. whether positive or iiegativc.. This is nicely seen in the case (.If negative phototropism of tlica .-2iiioel~:~---whc~ii an amoeba moves towards a light spot on a inicroscopic slid(. a 1 cw-tion immediately begins when one of its pseudopotls touclies thc light area. .\lthtrugh the wactii ,ii is not immediately rrversrd. thc pi.jsition is eventually ari-ived at aftchimticli movement of the body.(2) 7 o p i c re>potisv ( Placts). In rcvrrsc' t o the al)i)ve condition where the reaction is indeterminate, this 1-esp...