A angle

acromial angle

acute angle

alpha angle

alveolar angle

anterior chamber angle

biorbital angle

cardiophrenic angle

carrying angle

caudal angle

cavity angle

cephalic angle

cephalometric angle

cerebellopontine angle

cervicofemoral angle

Cobb angle

angle of convergence

costal angle

costophrenic angle

costovertebral angle

craniofacial angle

facial angle

flat angle

gamma angle

gonial angle

Hilgenreiner epiphyseal angle

angle of incidence

angle of inclinication (of the hip)

angle of jaw

angle of mandible

metafacial angle

obtuse angle

occipital angle

ophryospinal angle

parietal angle

pontine angle

prophy angle

pubic angle

Q angle

angle of refraction

right angle

sacrolumbar angle

sacrovertebral angle

sphenoid angle

sternal angle

angle of Treitz

venous angle

visual angle

angle 

1. The figure formed by two intersecting lines or planes at one point. 2. The direction from which an object is viewed. 3. The form produced by a change in direction of a line or plane.
angle alpha Angle between the visual axis and the optical axis formed at the first nodal point of the eye. The visual axis usually lies nasal to the optical axis on the plane of the cornea (positive angle alpha). It is, on average, equal to about 5º in the adult eye. If it lies temporal to the optical axis, the angle is denoted negative (Fig. A9). Symbol: α. See angle lambda.
angle of altitude 1. The angle through which the eyes have turned up or down from the primary position by a rotation about the transverse axis (x-axis). 2. The angle between the plane of regard and the subjective horizontal plane. Syn. angle of elevation.
angle of anomaly Angle between the line of visual direction of the fovea and the line of visual direction of the abnormal corresponding point of the same deviated eye. It is usually represented by the difference between the objective and subjective angles of deviation in abnormal retinal correspondence. See line of direction; abnormal retinal correspondence.
angle of the anterior chamber Angle at the periphery of the anterior chamber formed by the root of the iris, the front surface of the ciliary body and the trabecular meshwork. Syn. angle of filtration; drainage angle; irido-corneal angle. See gonioscope; Shaffer and Schwartz van Herick method; Smith's method; shadow test.
apical angle See prism angle.
angle of azimuth The angle through which the eyes have turned right or left from the primary position by a rotation about the vertical axis.
Brewster's angle See angle of polarization.
contact angle Angle formed by a surface and a tangent to a sessile drop of fluid (usually water) at the point where the drop meets the surface. This angle indicates the degree of wettability of that surface. The more wettable (or hydrophilic) the material, the smaller the angle, being equal to 0º for a completely hydrophilic material when water spreads evenly over that surface. Hydrophobic surfaces can have contact angles greater than 90º, e.g. silicone rubber in which the angle is about 120º (Fig. A10). Syn. wetting angle. See sessile drop test.
angle of convergence Angle between the lines of sight of the two eyes which are in a state of convergence. The angle is positive when the lines of sight intersect in front of the eyes, and negative when they intersect behind the eyes. Note: some authors regard the angle of convergence as the rotation of one eye only towards the fixation point, and refer to the angle of convergence of both eyes, defined above, as the total angle of convergence or the total convergence. The total angle of convergence required for binocular fixation of a target is equal toorconvergence (in Χ) = convergence (in ma)✕ PD (in cm)where d is the distance between the target and the midpoint of the base line and PD the interpupillary distance. Syn. angle of triangulation. See metre angle; prism dioptre; line of sight.
critical angle That angle of incidence which results in the refracted ray travelling along the surface between the two media (angle of refraction equal to 90º). If the angle of incidence is greater than the critical angle, the ray is totally reflected. If, however, the angle of incidence is smaller than the critical angle, the ray is refracted (with some light reflected). The critical angle i_c is given by the following formulasin i_c = n/n′where n and n' are the indices of the media on each side of the surface, with the light travelling from the high index medium n to the low index medium n′ (Fig. A11). Syn. limiting angle. See fibre optics; reflecting prism; total reflection; refractometer.
angle of deviation 1. Angle through which a ray of light is deviated on reflection by a mirror, or refraction by a lens or prism. 2. Angle between the visual axis (or line of sight) of the deviated eye in strabismus and the straight-ahead position while the other eye fixates straight ahead. It can be assessed subjectively by having the patient report simultaneous perception (e.g. the lion in the cage seen in the amblyoscope) or objectively as measured by the practitioner either with the amblyoscope or using prisms and cover test, or by the Hirschberg test. Syn. angle of squint; angle of strabismus. See angle of anomaly; incomitance; Hirschberg's method; Javal's method; Krimsky's method; minimum deviation of a prism.
angle of divergence Angle between the lines of sight of the two eyes which are in a state of divergence.
drainage angle See angle of the anterior chamber.
angle of elevation See angle of altitude.
angle eta See stereoscopic visual acuity.
external angle See canthus.
angle of filtration See angle of the anterior chamber.
angle gamma The angle between the optical axis and the fixation axis.
angle of incidence Angle between the incident ray and the normal to the surface at the point of incidence in either reflection or refraction at a surface separating two media.
irido-corneal angle See angle of the anterior chamber.
angle kappa Angle between the pupillary axis and the visual axis, measured at the nodal point. Symbol: κ. See angle lambda; line of sight.
angle lambda Angle between the pupillary axis and the line of sight formed at the centre of the entrance pupil. It is this angle which is measured clinically as it is almost equal to angle alpha. Symbol: λ. See pupillary axis; line of sight.
limiting angle See critical angle.
metre angle (ma) Unit of convergence which is equal to the reciprocal of the distance (in metres) between the point of fixation assumed to lie on the median line and the base line of the eyes. Thus, if an object is located at 25 cm from the base line, each eye converges through 4 ma; at 1 metre, 1 ma, etc. Metre angles of convergence can be converted into prism dioptres of convergence by multiplying by the subject's interpupillary distance expressed in cm. Example: for a PD of 6.0 cm, a convergence of 5 ma = 30 Χ. See angle of convergence.
minimum angle of resolution (MAR) The angle subtended at the nodal point of the eye (or the centre of the entrance pupil) by two points or two lines which can just be distinguished as separate. See visual acuity; log MAR chart.
palpebral angle See canthus.
pantoscopic angle Angle between the spectacle plane and the frontal plane of the face when the superior edge of the lens is farther away from the face than the inferior edge (Fig. A12). Syn. pantoscopic tilt. See retroscopic angle.
angle of polarization The angle of incidence at which the reflected light is maximally polarized. At this angle, the reflected and refracted rays are 90º apart (Fig. A13). This angle i is given by the equationtan i = n₂/n₁and measures 56.7º when the first medium n₁ is air and the second medium n₂ is a glass with an index of refraction equal to 1.523. Syn. Brewster's angle. See polarized light.
prism angle The angle between the two refracting surfaces of a prism. Syn. apical angle; refracting angle (this term is deprecated because of the confusion with 'angle of refraction').
recession angle A tear between the longitudinal and circular muscles of the ciliary body. It is most often noted following blunt trauma to the anterior segment. It is typically followed by hyphaemia. This form of injury predisposes the individual to elevated intraocular pressure (i.e. increased risk of glaucoma) in the future. With a gonioscope, angle recession appears with an abnormally wide ciliary body band with a prominent scleral spur and some torn iris processes. There are also marked variations in the width and depth of the angle in different quadrants of the eye. See cyclodialysis; hyphaemia; iridodialysis; ciliary muscle.
angle of reflection Angle between the reflected ray and the normal to the surface at the point of incidence.
angle of refraction Angle between the refracted ray and the normal to the surface at the point of emergence.
retroscopic angle Angle between the spectacle plane and the frontal plane of the face when the superior edge of the lens is closer to the face than the inferior edge. Syn. retroscopic tilt. See pantoscopic angle; frontal plane; spectacle plane.
angle of squint See angle of deviation.
angle of stereopsis The difference between the angles subtended at the centres of the entrance pupils of the two eyes by two points located in space at different distances from the eyes. See stereoscopic visual acuity; Howard-Dolman test; three-needle test.
angle of strabismus See angle of deviation.total a. of convergence See angle of convergence.
angle of triangulation  See angle of convergence.
viewing angle See visual angle.
visual angle The angle subtended by the extremities of an object at the anterior nodal point of the eye. If the object is far away, the point of reference can be the centre of the entrance pupil or even the anterior pole of the cornea. Syn. viewing angle.
wetting angle See contact angle.
refracting angle   See angle, prism." >Fig. A9 Angle alpha" >Fig. A10 Different contact angles α between a drop of fluid and a contact lens material" >Fig. A11 Critical angle i_c and total internal reflection (i, angle of incidence; i′, angle of refraction)" >Fig. A12 Pantoscopic angle PA" >Fig. A13 Ray of non-polarized light AO is incident to the surface at the polarizing angle. Most of the light is transmitted across the surface and partially polarized, the rest being reflected and polarized maximally (i.e

Table A8 Critical angle (in degrees) beyond which all the light is reflected at the surface separating various transparent substances from air or water
substance		refractive index n		critical angle ic
				in contact with air n′ = 1		in contact with water n′ = 1.333
water		1.333		48.6		-
spectacle crown glass		1.523		41.0		61.1
flint glass (dense)		1.62		38.1		55.4
flint glass (extra dense)		1.706		35.9		51.4
PMMA		1.49		42.2		63.5
CR-39		1.498		41.9		62.9
polycarbonate		1.586		39.1		57.2
diamond		2.42		24.4		33.4

Table A9 Relationship between viewing distance and total convergence in metre angles and prism dioptres for 4 interpupillary distances (PD in cm)
object distance from cornea (cm)		metre angle (ma)		convergence (in prism dioptres)
				PD: 6.0			6.4		6.8				7.0
200		0.5			3.0		3.2			3.4				3.5
100		1.0			6.0		6.4			6.8				7.0
67		1.5			9.0		9.6			10.2				10.5
50		2.0			12.0		12.8			13.6				14.0
40		2.5			15.0		16.0			17.0				17.5
33		3.0			18.0		19.2			20.4				21.0
25		4.0			24.0		25.6			27.2				28.0
20		5.0			30.0		32.0			34.0				35.0
16		6.25			37.5		40.0			42.5				43.7
14		7.14			42.8		45.7			48.5				50.0

A angle

acromial angle

acute angle

alpha angle

alveolar angle

anterior chamber angle

biorbital angle

cardiophrenic angle

carrying angle

caudal angle

cavity angle

cephalic angle

cephalometric angle

cerebellopontine angle

cervicofemoral angle

Cobb angle

angle of convergence

costal angle

costophrenic angle

costovertebral angle

craniofacial angle

facial angle

flat angle

gamma angle

gonial angle

Hilgenreiner epiphyseal angle

angle of incidence

angle of inclinication (of the hip)

angle of jaw

angle of mandible

metafacial angle

obtuse angle

occipital angle

ophryospinal angle

parietal angle

pontine angle

prophy angle

pubic angle

Q angle

angle of refraction

right angle

sacrolumbar angle

sacrovertebral angle

sphenoid angle

sternal angle

angle of Treitz

venous angle

visual angle

angle 

1. The figure formed by two intersecting lines or planes at one point. 2. The direction from which an object is viewed. 3. The form produced by a change in direction of a line or plane.
angle alpha Angle between the visual axis and the optical axis formed at the first nodal point of the eye. The visual axis usually lies nasal to the optical axis on the plane of the cornea (positive angle alpha). It is, on average, equal to about 5º in the adult eye. If it lies temporal to the optical axis, the angle is denoted negative (Fig. A9). Symbol: α. See angle lambda.
angle of altitude 1. The angle through which the eyes have turned up or down from the primary position by a rotation about the transverse axis (x-axis). 2. The angle between the plane of regard and the subjective horizontal plane. Syn. angle of elevation.
angle of anomaly Angle between the line of visual direction of the fovea and the line of visual direction of the abnormal corresponding point of the same deviated eye. It is usually represented by the difference between the objective and subjective angles of deviation in abnormal retinal correspondence. See line of direction; abnormal retinal correspondence.
angle of the anterior chamber Angle at the periphery of the anterior chamber formed by the root of the iris, the front surface of the ciliary body and the trabecular meshwork. Syn. angle of filtration; drainage angle; irido-corneal angle. See gonioscope; Shaffer and Schwartz van Herick method; Smith's method; shadow test.
apical angle See prism angle.
angle of azimuth The angle through which the eyes have turned right or left from the primary position by a rotation about the vertical axis.
Brewster's angle See angle of polarization.
contact angle Angle formed by a surface and a tangent to a sessile drop of fluid (usually water) at the point where the drop meets the surface. This angle indicates the degree of wettability of that surface. The more wettable (or hydrophilic) the material, the smaller the angle, being equal to 0º for a completely hydrophilic material when water spreads evenly over that surface. Hydrophobic surfaces can have contact angles greater than 90º, e.g. silicone rubber in which the angle is about 120º (Fig. A10). Syn. wetting angle. See sessile drop test.
angle of convergence Angle between the lines of sight of the two eyes which are in a state of convergence. The angle is positive when the lines of sight intersect in front of the eyes, and negative when they intersect behind the eyes. Note: some authors regard the angle of convergence as the rotation of one eye only towards the fixation point, and refer to the angle of convergence of both eyes, defined above, as the total angle of convergence or the total convergence. The total angle of convergence required for binocular fixation of a target is equal toorconvergence (in Χ) = convergence (in ma)✕ PD (in cm)where d is the distance between the target and the midpoint of the base line and PD the interpupillary distance. Syn. angle of triangulation. See metre angle; prism dioptre; line of sight.
critical angle That angle of incidence which results in the refracted ray travelling along the surface between the two media (angle of refraction equal to 90º). If the angle of incidence is greater than the critical angle, the ray is totally reflected. If, however, the angle of incidence is smaller than the critical angle, the ray is refracted (with some light reflected). The critical angle i_c is given by the following formulasin i_c = n/n′where n and n' are the indices of the media on each side of the surface, with the light travelling from the high index medium n to the low index medium n′ (Fig. A11). Syn. limiting angle. See fibre optics; reflecting prism; total reflection; refractometer.
angle of deviation 1. Angle through which a ray of light is deviated on reflection by a mirror, or refraction by a lens or prism. 2. Angle between the visual axis (or line of sight) of the deviated eye in strabismus and the straight-ahead position while the other eye fixates straight ahead. It can be assessed subjectively by having the patient report simultaneous perception (e.g. the lion in the cage seen in the amblyoscope) or objectively as measured by the practitioner either with the amblyoscope or using prisms and cover test, or by the Hirschberg test. Syn. angle of squint; angle of strabismus. See angle of anomaly; incomitance; Hirschberg's method; Javal's method; Krimsky's method; minimum deviation of a prism.
angle of divergence Angle between the lines of sight of the two eyes which are in a state of divergence.
drainage angle See angle of the anterior chamber.
angle of elevation See angle of altitude.
angle eta See stereoscopic visual acuity.
external angle See canthus.
angle of filtration See angle of the anterior chamber.
angle gamma The angle between the optical axis and the fixation axis.
angle of incidence Angle between the incident ray and the normal to the surface at the point of incidence in either reflection or refraction at a surface separating two media.
irido-corneal angle See angle of the anterior chamber.
angle kappa Angle between the pupillary axis and the visual axis, measured at the nodal point. Symbol: κ. See angle lambda; line of sight.
angle lambda Angle between the pupillary axis and the line of sight formed at the centre of the entrance pupil. It is this angle which is measured clinically as it is almost equal to angle alpha. Symbol: λ. See pupillary axis; line of sight.
limiting angle See critical angle.
metre angle (ma) Unit of convergence which is equal to the reciprocal of the distance (in metres) between the point of fixation assumed to lie on the median line and the base line of the eyes. Thus, if an object is located at 25 cm from the base line, each eye converges through 4 ma; at 1 metre, 1 ma, etc. Metre angles of convergence can be converted into prism dioptres of convergence by multiplying by the subject's interpupillary distance expressed in cm. Example: for a PD of 6.0 cm, a convergence of 5 ma = 30 Χ. See angle of convergence.
minimum angle of resolution (MAR) The angle subtended at the nodal point of the eye (or the centre of the entrance pupil) by two points or two lines which can just be distinguished as separate. See visual acuity; log MAR chart.
palpebral angle See canthus.
pantoscopic angle Angle between the spectacle plane and the frontal plane of the face when the superior edge of the lens is farther away from the face than the inferior edge (Fig. A12). Syn. pantoscopic tilt. See retroscopic angle.
angle of polarization The angle of incidence at which the reflected light is maximally polarized. At this angle, the reflected and refracted rays are 90º apart (Fig. A13). This angle i is given by the equationtan i = n₂/n₁and measures 56.7º when the first medium n₁ is air and the second medium n₂ is a glass with an index of refraction equal to 1.523. Syn. Brewster's angle. See polarized light.
prism angle The angle between the two refracting surfaces of a prism. Syn. apical angle; refracting angle (this term is deprecated because of the confusion with 'angle of refraction').
recession angle A tear between the longitudinal and circular muscles of the ciliary body. It is most often noted following blunt trauma to the anterior segment. It is typically followed by hyphaemia. This form of injury predisposes the individual to elevated intraocular pressure (i.e. increased risk of glaucoma) in the future. With a gonioscope, angle recession appears with an abnormally wide ciliary body band with a prominent scleral spur and some torn iris processes. There are also marked variations in the width and depth of the angle in different quadrants of the eye. See cyclodialysis; hyphaemia; iridodialysis; ciliary muscle.
angle of reflection Angle between the reflected ray and the normal to the surface at the point of incidence.
angle of refraction Angle between the refracted ray and the normal to the surface at the point of emergence.
retroscopic angle Angle between the spectacle plane and the frontal plane of the face when the superior edge of the lens is closer to the face than the inferior edge. Syn. retroscopic tilt. See pantoscopic angle; frontal plane; spectacle plane.
angle of squint See angle of deviation.
angle of stereopsis The difference between the angles subtended at the centres of the entrance pupils of the two eyes by two points located in space at different distances from the eyes. See stereoscopic visual acuity; Howard-Dolman test; three-needle test.
angle of strabismus See angle of deviation.total a. of convergence See angle of convergence.
angle of triangulation  See angle of convergence.
viewing angle See visual angle.
visual angle The angle subtended by the extremities of an object at the anterior nodal point of the eye. If the object is far away, the point of reference can be the centre of the entrance pupil or even the anterior pole of the cornea. Syn. viewing angle.
wetting angle See contact angle.
refracting angle   See angle, prism." >Fig. A9 Angle alpha" >Fig. A10 Different contact angles α between a drop of fluid and a contact lens material" >Fig. A11 Critical angle i_c and total internal reflection (i, angle of incidence; i′, angle of refraction)" >Fig. A12 Pantoscopic angle PA" >Fig. A13 Ray of non-polarized light AO is incident to the surface at the polarizing angle. Most of the light is transmitted across the surface and partially polarized, the rest being reflected and polarized maximally (i.e

Table A8 Critical angle (in degrees) beyond which all the light is reflected at the surface separating various transparent substances from air or water
substance		refractive index n		critical angle ic
				in contact with air n′ = 1		in contact with water n′ = 1.333
water		1.333		48.6		-
spectacle crown glass		1.523		41.0		61.1
flint glass (dense)		1.62		38.1		55.4
flint glass (extra dense)		1.706		35.9		51.4
PMMA		1.49		42.2		63.5
CR-39		1.498		41.9		62.9
polycarbonate		1.586		39.1		57.2
diamond		2.42		24.4		33.4

Table A9 Relationship between viewing distance and total convergence in metre angles and prism dioptres for 4 interpupillary distances (PD in cm)
object distance from cornea (cm)		metre angle (ma)		convergence (in prism dioptres)
				PD: 6.0			6.4		6.8				7.0
200		0.5			3.0		3.2			3.4				3.5
100		1.0			6.0		6.4			6.8				7.0
67		1.5			9.0		9.6			10.2				10.5
50		2.0			12.0		12.8			13.6				14.0
40		2.5			15.0		16.0			17.0				17.5
33		3.0			18.0		19.2			20.4				21.0
25		4.0			24.0		25.6			27.2				28.0
20		5.0			30.0		32.0			34.0				35.0
16		6.25			37.5		40.0			42.5				43.7
14		7.14			42.8		45.7			48.5				50.0