1. Purpose The von Graefe phoria test is a subjective method of evaluating the presence, direction, and the magnitude of the phoria.

(a) Controlling accommodation Controlling accommodation is also important when evaluating the phoria using the von Graefe procedure. It is vital to emphasize this in the instructional set to the patient. Often clinicians merely ask the patient to look at one image and report when the other is right above or below. To ensure more accurate accommodation, the clinician should state

I want you to look at the lower image, and it is very important to keep it clear at all times. While you keep it clear, tell me when the upper image moves directly above the lower image.

Although the instruction to keep the target clear is not always included in phoria testing, a lack of attention to this issue may lead to variability and poor reliability.

Another issue that should be considered, particularly in young children, is whether the patient understands the task. Clinicians often use the following instructional set to try to explain the objective of the test:

Look at the bottom line and tell me when the top line moves directly above it, like buttons on a shirt.

Although this may be helpful for older children and adults, we have found that children who are 7 years old and younger do not perform well with this analogy. To promote an understanding in young children, we suggest an actual simple demonstration outside the phoropter using one’s fingers. The young child is asked to look at the examiner’s fingers, which are held one directly over the other. We use the following instructional set:

Look at the finger on the bottom and tell me when my top finger is right over my bottom finger. (Demonstrate by misaligning your fingers and then bringing them back to alignment.) Now let’s try it; tell me when to stop.

Using this method allows the examiner to determine whether the child has an understanding of what is expected.

Although the von Graefe procedure is commonly used in clinical practice, a study by Rainey et al. (20) indicated that this procedure is the least repeatable of the various tests used to measure the phoria.

(b) Reliability Rouse et al. (21) reported a high level of intraexaminer reliability, both within and between sessions, using the von Graefe method of assessing the phoria in children 10 to 11 years old.

3. Expected values At distance, the expected value is 1 exophoria, with a standard deviation of ±1Δ (Table 1.4). The mean expected value at near is 3 exophoria, with a standard deviation of ±3Δ (19) for children and young adults; for presbyopes, the mean expected values are 1 esophoria, with a standard deviation of ±1Δ at distance, and 8 exophoria with a standard deviation of ±3Δ at near.

1. Purpose This technique is a subjective method of evaluating the presence, direction, and the magnitude of the phoria.

(a) Controlling accommodation With the modified Thorington test, it is important for the clinician to emphasize that the patient keep the letters on the chart clear during the test procedure. In a study by Rainey et al. (20), the results of seven different procedures of assessing the phoria were compared to determine the repeatability of the clinical tests. The authors compared the estimated cover test, prism-neutralized objective cover test, prism-neutralized subjective cover test, von Graefe continuous presentation, von Graefe flash presentation, the Thorington method, and the modified Thorington method. They found that the modified Thorington procedure was the most repeatable method, whereas the von Graefe methods had the poorest repeatability.

(b) Testing outside the phoropter An important advantage of this technique is that it can be used for patients who are difficult to test with a phoropter. For this reason, the modified Thorington technique has value with children younger than 7 or 8 years. As indicated above, it has also been shown to be the most repeatable method of assessing the phoria.

3. Expected values At distance, the expected value is 1 exophoria with a standard deviation of ±1Δ (Table 1.4). The mean expected value at near is 3 exophoria, with a standard deviation of ±3Δ (19).