Optical Marketplace

Perimeter Made By Theodore Hamblin Of London (Now Dolland And Aitchkinson)
Seems Complete And Un-Damaged With Some Cosmetic Marks, Easy Restoration.
They Have One Of These In The Museum At The College Of Optometry
Thanks To The College Of Optometry An arc perimeter is used to measure the angle of extent of the patient’s visual field by moving targets along the arc until they can no longer be seen and recording the result. The targets may be an integral part of the instrument running along a groove in the arc or they may be coloured discs on the end of hand-held wands that the optometrists holds against the arc in various places. The arc revolves so that the field can be assessed across any meridian. The instrument can also be used to identify the characteristics of the visual field such as scotoma (of which the physiological blind spot is an example that we all have).
The Lister perimeter, supplied by Theodore Hamblin Ltd, consisted of a rotating arc with sliding colour targets. There was a lamp holder with a directional shade. Note also the adjustable double chin rest, a round chart holder and an integrally mounted case of white, green and red colour targets.