The eye accommodates to dynamically change the power of its natural lens. This modifies and enhances the visual focus point of objects to obtain sharp images in the retina.
The increase or decrease of the optical power is achieved through the increase or decrease of the curvatures of the anterior and posterior structures of the crystalline becoming rounder or flatter.
What is the ampaccommodation length? Find out below at Área Oftalmológica Avanzada.
What is the ampaccommodation length?
La ampAccommodation litude is the maximum capacity of the eye to focus with the lens, it is measured in diopters and its maximum capacity is 15.00 dp. As a person ages, the lens loses its accommodative power and the ampaccommodation lititude decreases considerably.
How is the ampaccommodative latitude?
La ampLititude of accommodation (AA) is the maximum increase in ocular power that corresponds to the inverse of the closest distance that a patient can see clearly at a long distance, using the appropriate optical correction.
La ampAccommodative lititude can be measured using any of the following methods:
Hofstetter formula
It is done by calculating the result with one of the following formulas:
- AmpMinimum lititude = 15 – 0.25 X age.
- AmpMean height = 18.5 – 0.30 X age.
- AmpMaximum lititude = 25 – 0.40 X age.
Donders method or approach
The approach method to measure the ampAccommodation lititude aims to measure subjective AA in monocular mode.
The examination consists of showing the patient the test of optotypes and bringing it closer progressively until the patient states that they cannot see it clearly. Subsequently, the distance, the closest point, is measured, and its inverse in meters yields the value of the accommodation diopters.
For this test to be valid and without errors, it is very important to correctly measure the fuzzy near distance. This method presents the error that as the optotype test approaches, its size increases, therefore, it can overestimate the AA by 2,00 dp.
Negative lens method
The negative lens method, also called Sheard's method, also measures the ampaccommodation length in monocular condition. To perform this test, ophthalmologists use the phoropter placing the usual distance refraction and the test for near vision that corresponds to a visual acuity from 20/20 to 40 centimeters away.
To perform the test, negative crystals are used in the phoropter from 0,25 dp onwards, until the patient cannot see the visual acuity test clearly. In this method the ampPatient accommodation length is the power of the negative lens used plus the accommodation to focus at 40 cm distance. The formula would be as follows: AA (Initial Lens – Final Lens) + 1/d.
What pathologies does it detect?
Through an examination of ampof accommodation, the following conditions can be diagnosed:
- Lazy eye or amblyopia.
- Accommodation paralysis.
- Pupil from Adie.
- Excessive hyperopic undercorrections
- Excessive myopic undercorrections.
