Negative relative accommodation

Negative Relative Accommodation (NRA) is a term used in the field of optometry and ophthalmology to describe a specific measure of the eye's ability to maintain clear, single vision as objects move closer to the person or as the eyes converge. This measure is crucial in diagnosing and managing various binocular vision disorders and in prescribing corrective lenses.

Definition

Negative Relative Accommodation is the maximum amount of minus lens power that can be added to a patient's current refractive correction before the patient first reports blur at a specified working distance, typically at near (about 40 cm). It is a measure of the flexibility of the eye's accommodation system, which allows for maintaining focus on objects as they move closer to the observer.

Clinical Importance

NRA is an important diagnostic parameter for identifying issues related to the accommodative and binocular vision systems. It helps in diagnosing conditions such as accommodative insufficiency, convergence insufficiency, and other forms of eye strain that are often associated with tasks requiring sustained near vision, like reading or computer work. Understanding a patient's NRA can guide the development of a comprehensive treatment plan, which may include eyeglasses, vision therapy, or both.

Measurement

The measurement of Negative Relative Accommodation is typically performed using a phoropter or trial lenses in conjunction with a standardized reading chart. The patient is first corrected for near vision, and then minus lenses are added in 0.25 diopter increments until the patient reports blur. The amount of minus lens power added to the patient's near correction at the point of blur represents the NRA value.

Relation to Positive Relative Accommodation

NRA is often measured in conjunction with Positive Relative Accommodation (PRA), which is the maximum amount of plus lens power that can be added to a patient's current refractive correction before blur is reported at a specified working distance. Together, NRA and PRA provide a comprehensive view of the accommodative flexibility of the eyes, which is essential for diagnosing and managing accommodative and binocular vision disorders.

Treatment and Management

Management strategies for issues identified through NRA measurements may include prescription of corrective lenses with specific accommodative support, vision therapy exercises to improve accommodative flexibility and endurance, and ergonomic adjustments to reduce visual stress during near tasks.

Conclusion

Negative Relative Accommodation is a key measure in the assessment of the accommodative and binocular vision systems. Its evaluation is essential for diagnosing vision disorders related to accommodation and convergence, and for guiding effective treatment plans to improve visual comfort and performance in near tasks.