Bagolini striated glasses test

Equipment
To test for binocular functions and cyclotropia, you need BSG, pen torch or a distant light source. Alternatively, trial frames and lens or lorgnette can be used. In some cases, the use of prisms is necessary.(Ansons and Davis, 2001, p.124)

Principles
Bagolini striated glasses are glasses of no dioptric power that have many narrow striations running parallel in one meridian. These glasses cause the fixation light to appear as an elongated streak. The lenses are usually placed at 135 degrees in front of the right eye and at 45 degrees in front of the left eye. Each eye receives a similar, fusible image, with the exception of the line, allowing simultaneous perception to be observed, rather than suppression. With both eyes, the patient should see a cross. This test is minimally dissociative for the assessment of retinal correspondence. (Ansons & Davis, 2001, p. 309)

Apart from testing binocular functions, Bagolini striated glasses can measure cyclotropia. The principle of the test is similar to that of double Maddox rod test. The glasses are placed in the trial frames with the striations vertical, giving rise to two horizontal line images when viewing a spotlight. If the patient has a vertical deviation, the lines will be seen one above the other. If there is little or no vertical separation, vertical prism can be used to separate the lines. The patient is asked if one or both lines are tilted. The lines can be straightened subjectively by rotating the glasses in the trail frame and the degree of cyclopropia recorded. (Von Noorden & Campos, 2002, p. 195-196)

Indications for use
The Bagolini Straited Glasses test is performed to determine whether a patient has normal retinal correspondence (NRC) or abnormal retinal correspondence (ARC). NRC is present when both foveas of each eye receive identical images (common visual stimuli) therefore the eyes are able to function optimally together and binocularity is present. ARC occurs when the fovea of one eye has a common visual direction with an extrafoveal area of the other eye (Ansons and Davis, 2001, p.145). This is a sensory adaptation that occurs when a constant deviation of the eye is present which facilitates the patient in achieving binocular single vision.

This test is also used to assess if a patient is pathologically suppressing visual stimuli, which happens when large strabismic deviations are present

Method
The test is performed under normal lighting conditions. The Bagolini glasses can either be used in trial frames or are set up in reversible lorgnette frames (Ansons and Davis, 2001, p.124) which are placed over the patients glasses who wear refractive correction. The examiner shines a torch light, directing it towards the the centre bridge of the Bagolini glasses i.e the patients nose ( so the light is at patients eye level) from distance (6m) or near (33 cms). The patient can also be tested in alternate positions of gaze (upgaze or downgaze). The test is usually performed at near.

The number and type of questions asked are contingent on whether the patient has binocularity present and the consequent responses to the testing questions. Ansons and Davis, 2001, p.124 explains that the patient is firstly asked about the position and number of lines seen and the number of lights visible. Examples of possible initial series of questions; How many lines can you see? Is one line positioned higher than the other? Do the lines form a cross or are they separate? How many lights are there? Do the lines intersect through the light?

The patient is then asked if they see the two lines at the same time or if one disappears. If both lines are seen to form an equal cross over the light, the patient is questioned if there are any gaps on any part of the lines. The patient is asked to describe or draw what they have seen (Ansons and Davis, 2001, p.124).

Recording and interpretation of results
The patient can be asked to describe or draw what they see. It is preferred by some clinicians to get the patient to draw what they see as the descriptions can be confusing.

When asking the patient to describe what they see, the clinician can prompt them by asking:
 * How many lights do you see
 * How many lines do you see
 * Do the lines cross
 * Are the two lines seen at the same time
 * Do the lines have any gaps in them
 * Which line is on the right/left (or which line is higher/lower)

Results
When interpreting results, the line associated with each eye is the line perpendicular to the lens in front of that eye. If the lens in front of the right eye is at 135 degrees, then the line on the results representing the right eye will be at 45 degrees.

One light: If the patient sees one light, that means that either they have fused the two images from each eye together, or are suppressing of one of the images.

Two lights: If the patient sees two lights, this is indicative of diplopia as the patient has an image from each eye but is unable to fuse the two. One line: If only one line is seen, this means one eye is suppressing. The eye that is suppressing is the eye which the corresponding line is not seen.

Two lines: If the patient sees two lines, this means that there is no suppression of either eye.

Disappearing line: The patient may report that they see one line, then the lines switch and they can only see the other line. This is the case in an alternating deviation, where there is always one eye suppressing, however the fixing eye is switching.

Broken line: If a line has a break in it, this means that there is a scotoma somewhere on the retina.

Normal binocular single vision
In a patient with normal binocular functions, the expected results would be a cross with the light where the two lines intersect.

Microtropia
In a patient with microtropia, the patient may see one light and two lines, with one of the lines having a small break in it. This is due to foveal suppression.

Esotropia
In a patient with an unsuppressed esotropia, the patient will see two lights with one line through each light. The line corresponding to the right eye will be on the right side, meaning the images are uncrossed.

Exotropia
In a patient with an unsuppressed exotropia, the patient will see two lights with one line through each light. The line corresponding to the right eye will be on the left side of the results, meaning the images are crossed.

Hypertropia/Hypotropia
In a patient with an unsuppressed vertical deviation, one line will appear higher than the other. If the image of the right eye is higher than that of the left, this means the right eye is lower than the left. This could be either a right hypotropia or a left hypertropia.

Harmonious Abnormal retinal correspondence
If the patient has a known deviation, but they report a cross as seen in a patient with normal binocular functions, this indicates the presence of harmonious abnormal retinal correspondence.

Inharmonious Abnormal retinal correspondence
If the patient reports that they see two lines, however only one of these lines crosses through the fixation light, this indicates the presence of inharmonious abnormal retinal correspondence.

This test merely detects the presence of a deviation, but does not identify which eye is the deviated eye.

Advantages and Disadvantages
Advantages: Performed in well-lit conditions and is less dissociative. Can measure cyclotropia

Disadvantages: Light sources can cause the patient confusion. It is a subjective test, relying on the patients responses. Miscommunication may result in inaccuracies. The results can be misinterpreted if the clinician does not take note of the orientation of the striations. Also extensive suppression may interfere with perception of the second stripe. (Von Noorden & Campos, 2002, p. 227-228)