General Information

Serial #

N/A

Part Number

1

Total Parts

3

AKA

N/A

Patents

N/A

General Description

Instrument is all metal, with exception of clear glass lenses; folding handle has silver metal finish; metal disks housing silvered mirror and rotating lenses have darkened finish.

Dimensions

Note: These reflect the general size for storage and are not necessarily representative of the object's true dimensions.

Length

9.4 cm

Width

3.1 cm

Height

N/A

Thickness

N/A

Weight

N/A

Diameter

N/A

Volume

N/A

Lexicon

Group

Medical Technology

Category

Instruments

Sub-Category

N/A

Manufacturer

AKA

DOWN

Country

England

State/Province

Unknown

City

London

Context

Country

Unknown

State/Province

Unknown

Period

Unknown

Canada

Part of a collection of medical instruments used by J.R Jackson and W.A.L. Jackson, father and grandfather of donor. [Ref. 1]

Function

Unknown

Technical

One of the early problems when using the direct ophthalmoscope with the light placed to the side was the need to tilt the mirror at an angle to the line of observation for the light to enter the patient's eye. This meant that the observer was viewing the fundus obliquely through the correcting lenses. For low lens powers this was not a problem but in the higher ranges it produced a reduction in vision and a shifting of the image due to the prismatic effect. In 1875 John Couper of the Royal London Ophthalmic Hospital overcame this problem by dissociating the round disc of lenses from the mirror. By this means the observer was able to look through the centre of the lenses perpendicularly. Couper's design, made by Pickard and Curry of London, went through several models and effectively made redundant the fixed-mirror design. Edward Loring of the USA improved on Couper's model in 1877 with his vertically tilting mirror. This consisted of a round mirror with the sides cut off, rotatable on its vertical axis. [Ref. 2]

Area Notes

Unknown

Details

Markings

Rotating lenses are labelled. "LONDON/ DOWN" stamped into back of mirror housing.

Missing

Appears complete.

Finish

Instrument is all metal, with exception of clear glass lenses; folding handle has silver metal finish; metal disks housing silvered mirror and rotating lenses have darkened finish.

Decoration

N/A