Negative relative accommodation (NRA)|| Positive relative accommodation (PRA)

Negative relative accommodation (NRA) is a term used in optometry to describe the ability of the eyes to adjust their focusing power to maintain clear vision on objects at different distances. It specifically refers to the range of accommodation where the eyes are relaxed or under less focusing demand.

Accommodation is the process by which the eyes change their optical power to focus on objects at varying distances. It involves the adjustment of the crystalline lens within the eye, allowing it to change shape and alter its refractive power. This allows us to see objects clearly both up close and at a distance.

In the case of NRA, it represents the amount of relaxation or backward movement of the focusing system required to view distant objects clearly after focusing on a nearby target. It is measured in diopters (D), which is a unit of measurement for optical power.

To determine NRA, an eye care professional typically uses a device called an accommodative target or lens bar. The individual is instructed to focus on a near target, and then the target is quickly changed to a distant one. The examiner measures the amount of accommodation relaxation needed for clear vision at the distant target.

NRA is an important measurement in assessing the accommodative system and its efficiency. It provides valuable information about the flexibility and range of the eyes' focusing abilities. An imbalance or abnormality in NRA can indicate certain vision conditions such as accommodative insufficiency or a reduced ability to relax the focusing system. These conditions may result in symptoms like blurred vision, difficulty shifting focus between near and distant objects, eye strain, and headaches.

By evaluating NRA along with other accommodative parameters, eye care professionals can diagnose and manage various vision disorders. Treatment options may include prescription glasses or contact lenses, vision therapy exercises, or other interventions aimed at optimizing the accommodative system and improving visual comfort and clarity at different distances.