A Theodore Hamblin trial lens set, used by opticians to determine a patient’s spectacle prescription, made in mid‑20th‑century London, cased in a blue silk lined fitted box.
 
What it is and how it was used:
The case contains rows of plus (white) and minus (black) spherical trial lenses, 54 in total, ranging from +20.0 to −20.0 dioptres, designed to be placed in the trial frame in front of the patient’s eye while refining refraction. The central scale in dioptres helps the practitioner step powers up and down systematically during testing.​
 
Age and maker:
Theodore Hamblin Ltd operated as a high‑end London optician and optical‑instrument maker from the early 1900s, with the Wigmore Street / W.1 branding used prominently in mid‑century advertising and on instrument cases.​
 
Also included is a trial frame with engraved degree scales and three lens slots for each eye and with adjustable arms and nose bridge width.
 
The case measures 12.8 x 18cm (5" x 7").