What is Heterophoria method?
What is Heterophoria method?
The heterophoria method involves comparing distance align- ment to near alignment and factoring in the effect of interpupillary distance on the amount of convergence that is needed at near. 1-4 For most esotropic patients, the dif- ference between the distance and near de- viation is a function of the AC/A ratio.
How is AC ratio calculated?
Purpose: The two most commonly used clinical methods of determining a high AC/A ratio are: 1) the gradient method, and 2) the distance/near disparity method. Significant differences can be found not only between these two methods, but also in the different techniques for the gradient method alone.
What is a normal AC A ratio?
Mean Gradient AC/A for patients with a normal Clinical AC/A was 2:1, below the range traditionally thought of as normal. Mean Gradient AC/A for patients with a high Clinical AC/A was 5:1.
How is phoria calculated?
Distance phoria = 2 exo. AC/A ratio = 3/1; PC/A ratio = 2/1. These two ratios have additive properties. For every 1 D change in accommodative demand, 5pd of convergence are generated (3 accommodatively and 2 proximally).
Why is AC a ratio important?
Purpose: : Measurement of the AC/A ratio is important in the diagnosis and treatment of strabismus. The AC/A ratio can indicate the cause of strabismus and help to guide the management. Whether a ratio is considered to be high or low is often based on a so-called normative range that lies between 3-5:1.
What does a low ac a ratio mean?
Because an AC/A ratio of less than 3:1 is considered low, as little as an 8 Δ difference between distance and near would be sufficient to fit the diagnosis of CI.
What is a normal urine albumin creatinine ratio?
A ratio of albumin (mcg/L) to creatinine (mg/L) of less than 30 is normal; a ratio of 30-300 signifies microalbuminuria and values above 300 are considered as macroalbuminuria. On a standard urine dipstick, 10-20 mg/dL is the minimal detection limit of protein.
What is AC C ratio?
3. AC/A Ratio Definition: The measurement of the convergence induced by accommodation per diopter of accommodation Purpose: To determine the change in accommodative convergence that occurs when the patient accommodates or relaxes accommodates a given amount. 4.
What is a low ac a ratio?
What is accommodative convergence in relation to AC A ratio?
The accommodative convergence/accommodation (AC/A) ratio gives the relationship between the amount of convergence (in-turning of the eyes) that is generated by a given amount of accommodation (focusing effort).
Why we measure AC A ratio?
Is the heterophoria at near different from at distance?
Depending upon the amount of convergence that accompanies each dioptre of accommodation (the magnitude of the AC/A ratio, section 5.11 ), the heterophoria at near may be very different from that which exists at distance.
When is heterophoria said to be asymptomatic?
Heterophoria is usually asymptomatic. This is when it is said to be “compensated”. When fusional reserve is used to compensate for heterophoria, it is known as compensating vergence. In severe cases, when the heterophoria is not overcome by fusional vergence, sign and symptoms appear. This is called decompensated heterophoria.
How is the cross cover test used to detect heterophoria?
In other words, one or both eyes are not properly fixated to an object of interest. However, we must know that the eyes have a fusional vergence system which corrects this misalignment. The cross-cover test, or alternating cover test is usually employed to detect heterophoria.
How is heterophoria related to the visual axis?
In order to understand how heterophoria occurs, we must understand of how the eye can maintain proper fixation with non aligned visual axis. Heterophoria is actually the misalignment of the visual axis of both eyes. In other words, one or both eyes are not properly fixated to an object of interest.