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Filed under Opthalmology

Last modified 22/04/2025

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J

J See Jaeger test types.

jack-in-the-box phenomenon See phenomenon, jack-in-the-box.

Jackson’s crossed cylinder test See test for astigmatism, cross-cylinder.

Jaeger test types Test types for measuring visual acuity at near. They consist of ordinary printers’ types of various sizes and are arranged as words and phrases. Depending on the size of test types read, acuity is recorded as J.1, J.2 in ascending size up to J.20. The smallest Jaeger (J.1) subtends an angle of 5’ at 450 mm from the eye.

See acuity, near visual.

Jannelli clip See clipover.

Javal’s grid See grid, Javal’s.

Javal’s method See method, Javal’s.

Javal’s rule See rule, Javal’s.

jaw-winking phenomenon See phenomenon, jaw-winking.

Jensen procedure See transposition.

jerk nystagmus See nystagmus.

jnd See threshold, differential.

joint See hinge.

Jones I test See test, Jones I.

Jones II test See test, Jones II.

Table J1

Approximate relationship between the Jaeger system, the point system (or N notation) and the Snellen equivalent

		Snellen equivalent at 40 cm
Jaeger	point	(m)	(ft)
1	3.5	6/7	20/23
2	4.5	6/8	20/27
3	5.5	6/11	20/37
4	6.5	6/13	20/43
5	7.5	6/14	20/47
6	8	6/15	20/50
7	9.5	6/17	20/57
8	11	6/20	20/67
9	12	6/24	20/80
10	13	6/26	20/87
11	14	6/28	20/93
12	16	6/30	20/100
13	18	6/36	20/120
14	22	6/45	20/150

Julesz random-dot stereogram See stereogram, random-dot.

jump The displacement of the image of an object occurring when viewing across the borderline between two portions of different power in a bifocal or trifocal lens. The jump is eliminated by placing the optical centres on the dividing line; the lens is then called a no jump bifocal (e.g. a monocentric bifocal with a straight dividing line) (Fig. J1). Syn. image jump; prismatic jump.