666

neurological signs, air encephalography was of no furtherdiagnostic value. Berlin’s findings are similar : of 57

patients on whom air studies were performed, only 1

showed a localised abnormality-a traumatic cyst,known to be of some years’ standing-and only 4 othersshowed significant generalised ventricular dilatation.Moreover, in reviewing another group of 81 proven casesof supratentorial brain tumour, he found that 3 hadnormal air pictures one year after the onset of epilepsy,and another 1 four years after the onset.The facts certainly cast doubt on the value of this

investigation in grand-mal epilepsy without focal signs.On the other hand, the diagnostic value of focal fits orthe presence of focal signs is well illustrated ; for inBerlin’s series of subsequently proven brain tumourspresenting with epilepsy, 59% had jacksonian attacks,and in 85% either jacksonian attacks or neurologicalsigns of a focal lesion developed within a year of theirinitial fit. These figures support the growing impressionamongst neurologists that epilepsy of late onset may stillbe of "

idiopathic "

type with a relatively good prog-nosis. This does not relieve us of the necessity of investi-gating such cases fully, because the occasional slow-

growing neoplasm, which does present in this way, maybe readily and successfully treated. Negative findingsfrom a full investigation enable the clinician to give areassuring prognosis with added confidence; and con-

tinuing freedom from a focal element in the pattern ofthe seizures, and from neurological signs, suggests thatthis confidence has been justified.

1. The Use of Optical Aids for the Partially Sighted. N.I.B.Bulletins, no. 19. The National Institute for the Blind, 224,Great Portland Street, London, W.1. 1953. Pp. 16.

NEW OPTICAL AIDS

MANY of the partially sighted can read comfortablyif the type is large enough. The National Institute forthe Blind has done much research on the use of largetypes, and its committee on the education of the partiallysighted found that books in 18-point type-

that is, in type of this sizecould be read comfortably by most of the children tested.The cost of producing enough books in this type is

prohibitive, however ; and the same applies to booksreproduced in large type by ’ Photostat.’ In 1946, ajoint committee of the Institute and the London CountyCouncil was appointed to advise on the use of opticalaids for this group of handicapped people, and has nowreported.1 The committee concentrated on magnificationby lenses or projection, and on handwriting. When partof a page of type is seen with both eyes through a lens,two monocular images, which do not coincide, are

formed. One of them is farther from the lens than theother, and displaced to one side of it. Moreover thedistance separating the two images varies as the sightsweeps across the lens from one side to the other. The

eyes have thus to make constantly changing efforts ataccommodation and convergence, in the attempt to fusethe two images into one. In some people this causesheadache and eye-strain, but the committee says this isnot necessarily harmful. It was decided, however, toexperiment with lenses of greater magnification and awider field of vision than any on the market. With the

cooperation of the research department of ImperialChemical Industries Ltd., two aspheric plastic lenseswere produced, one 41/2 in. in diameter, the other 6 in.,and both having a magnification of 3. with focal lengthsof 6 in. The magnification was satisfactory but the distor-tion and chromatic aberration could not be quite over-come with lenses of this type. Nevertheless plastic lenses-once the mould has been made-can be produced verycheaply, though they are, however, easily scratched.They can easily be protected by two sheets of plainglass, but these introduce annoying reflections. In the

earlier models, electric lamps were fitted along the lens-stand, so as to shine on the page, and coloured filterswere often used to cut down glare ; for this purposeamber seemed to be the most satisfactory colour. Whenfluorescent lighting was introduced, however, these smallreading lights proved unnecessary, since it was possibleto get good illumination throughout the schoolroom;they carried, in any case, the inconvenience that a plughad to be fitted to every desk.The aim of the committee was to examine lenses

capable of covering the whole width, and half the length,of a page of an average-size book, and they studied threelenses in particular : .

The Lenslite ’ (glass), 8 in. focal length, plano-convex,magnification 2-5.The ’London’ or ’E.D.L.’ (glass), 11 in. focal length, biconvex,

magnification 1’ 9.The ’ Britex ’ (plastic), 10 in. focal length, aspheric,

magnification 2.

These were tried in schools for the partially sighted, andit was found that the children liked the London ’ andthe ’ Britex ’ about equally, and better than the Lens-lite.’ These were children whose visual acuity rangedfrom 3/60 to 6/18’ though most of them had less than 6;3s.They were also tried with hinocular loupes, consisting ofa pair of spherical lenses worn as spectacles over theordinary correction spectacles, with the bridge of theloupes resting on the lower part of the nose. The pair oflenses forming these loupes are as though taken from eachedge of a single large lens ; and as a result there is a singleoptical centre, and the reader does not have to make anyeffort to converge the eyes to look at a page held at thefocal length of the lens combination. (The magnificationis about 2.) Loupes of course, can be carried about moreeasily than lenses mounted on a reading stand, and theydraw less attention to the user. The children, however,did not show any particular preference for the loupesover the mounted lenses.

Magnification by projection can be achieved either byenlarging the projected print by means of lenses, with orwithout mirrors, or by microphotography of printedreading matter, which is then projected on to a screen.The first is done by the various types of episcope (whichproject on to a screen at a distance from the apparatus),and also by other devices which, by a system of mirrors,project the print on to a ground-glass screen containedin the apparatus itself. The magnification, with bothtypes of apparatus, can be varied-with the episcope byvarying the distance of the projector from the screen,and in the combined units by the choice and positioningof lenses. Any printed book can be read with these typesof apparatus ; but the contrast between the print andbackground is poor, and the machines are expensive.Moreover, it is hard to get the pages of the book flat, sothere is some distortion ; and every time afpage is turnedthe book has to be adjusted so as to bring the first lineinto the correct position for reading. Print can also be

photographed on to a microfilm and projected on to ascreen ; this device has been developed in America forpatients obliged to lie flat in bed : the print is projectedon to the ceiling, and a simple switch panel, managed bythe patient, controls the movements of the film. Thefilms are 100 ft. long and carry 1600 pages, which movefrom right to left.2 An apparatus of this type was installedlast year at the Miller General Hospital, Greenwich.3 Thejoint committee is conducting experiments to assess thevalue of these microfilm projectors for individual, notfor class, use.

Coloured " blackboards," and different-coloured chalks.have been used in some schools to help partially sightedchildren to read handwriting easily. The children in oneschool prefer blue chalk on a yellow board, but preferencesvary.

2. See Lancet, 1945, ii, 31.3. Ibid, 1952, ii, 943.