Binocular vision, phorias & tropias, Cyloplegic refraction, Manifest/Latent/total hypermetropia

Question 1

Orthophoria

Answer 1

The visual axes always remain directed towards the fixation target even when fusion is prevented

Question 2

Heterophoria

Answer 2

The visual axes are directed towards the fixation target during normal binocular vision but deviate when fusion is prevented

Question 3

Compensated heterophoria

Answer 3

Is a heterophoria which does not give rise to symptoms because fusional reserves are sufficient to maintain binocular alignment. A heterophoria may be fully or partially compensated.

Question 4

Uncompensated heterophoria

Answer 4

Is the part , or whole, of the heterophoria which gives rise to symptoms.

Question 5

Symptoms that may be caused by uncompensated heterophoria

Answer 5

*Blurred vision
*Intermittent diplopia
*Difficulty changing fixation
from DV to NV
*Headaches/aching eyes
(frontal & temporal usually)
*Rarely, vertigo or nausea

Question 6

Local sign

Answer 6

The direction in space associated with a particular point on the retina

Question 7

Corresponding points

Answer 7

A pair of retinal points (one in each eye) with the same local sign

Question 8

Horopter

Answer 8

The plane in space that contains all the points which stimulate corresponding retinal points.
OR
The plane in space that contains all the points that are seen in binocular single vision.

Question 9

Panum’s Fusional Area

Answer 9

An area on the retina of one eye that corresponds to a point on the retina of the other eye.
OR
The area on the retina of one eye within which an image can fall and still be fused with the image on the corresponding point of the other eye.

Question 10

Physiological diplopia

Answer 10

The double vision (usually noticed) produced in normal binocular subjects by all objects closer or further than the horopter

Question 11

Relative accommodation

Answer 11

The change in accommodation which can occur while keeping a fixed amount of convergence

Question 12

Relative convergence

Answer 12

The change in convergence that can be exerted while keeping accommodation fixed

Question 13

Fusional reserve

Answer 13

The amount of prism that the eyes can overcome while maintaining single vision

Question 14

AC/A Ratio

Answer 14

The accommodative convergence/accommodation ratio is the change in convergence that occurs with one dioptre of accommodation

Question 15

Metre-angle

Answer 15

Is a unit which can be used to measure convergence. An eye viewing an object at 1 metre exerts 1MA (metre-angle) of convergence and for an object at 1/2 metre it would be 2MA. It is independent of the subjects PD.
Convergence in MA is numerically the same as the accommodation required.

Question 16

Monocular clues to depth perception

Answer 16

*Overlapping of objects
*Geometric perspective
*Aerial perspective
*Light & shadow
*Movement & parallax

Question 17

Unilateral squint

Answer 17

Occurs in one eye only, subject always fixates with the same eye with the other eye deviating

Question 18

Alternating squint

Answer 18

Only fixates with one eye at a time but can use either eye and often can voluntarily switch from one eye to the other eye

Question 19

Constant squint

Answer 19

Present ALL the time

Question 20

Intermittent squint

Answer 20

Sometimes has binocular fixation but at other times, usually when tired, will only use one eye allowing the other eye to deviate

Question 21

Comitant or (Concomitant) squint

Answer 21

Is one which the angle between the visual axes is always the same regardless of the direction of gaze

Question 22

Incomitant or (Non-comitant) squint

Answer 22

Has a variable angle and is usually due to one or more of the extrinsic ocular muscles being defective. This means when the eye makes a movement that does not use this muscle , the angle of squint may be very small or even disappear altogether but when it looks in the direction normally covered by this muscle the squint becomes larger.

Question 23

Grades of Binocular Vision
Grade 1: Simultaneous
Perception

Answer 23

*Lowest grade of binocular
vision

*Px who achieves this level is capable of perceiving an object with both eyes simultaneously

*This grade is sometimes subdivided into Simultaneous Vision and Simultaneous Macular Vision

*Means subject can perceive a small detailed object with both eyes simultaneously

*Grade 1 can be investigated with a synoptophore using different slides for right and left eyes

*If subject is able to perceive both slides simultaneously, Grade 1 binocular vision is present

*Slides with small detailed pictures are used to investigate Simultaneous Macular Vision

Question 24

Grades of Binocular Vision
Grade 2: Fusion

Answer 24

*For a subject to achieve this level of binocular vision it is necessary for the images in the two eyes to be combined into the single percept

*Synoptophore is used with two slides with pictures that have much in common but each has some detail that is not present in the other

*The subject should be able to fuse the two main pictures (the house or Mickey Mouse) into a single image and to also see all the monocular details (both trees or the hammer and peg).

Question 25

Grades of binocular vision
Grade 3: Stereopsis

Answer 25

*Highest grade of binocular vision

*Means the subject is able to perceive objects as solid and to recognise that object are at different distances

• The synoptophore slides used to investigate this have small differences which the brain uses to give the sensation of
  3 dimensions to objects

Question 26

Manifest Hypermetropia

Answer 26

Maximum amount of plus sphere which is accepted by a hyperope during subjective refraction whilst maintaining clear distance vision

Question 27

Latent Hypermetropia

Answer 27

Any remaining part of the total hypermetropia which is hidden by spasm of the ciliary muscle