Methods Of Presbyopic Add Determination

Presbyopic add simply means the difference between the distance correction and the reading correction. When determining presbyopic add of an individual the optometrist should keep the following basic principles in mind;

• Find the distance error first and correct it.
• A suitable plus lens addition should be made over the distance correction to get the near correction.
• Near point should be fixed based on patient’s profession.
• Prescribe the weakest plus lens with which the patient sees clearly at near point since overcorrection will result in asthenopic symptoms.
• The near correction added should be such that about one-third (1/3) of the amplitude of accommodation should remain as reserve. In general, it is better to under-correct than to overcorrect presbyopia.

The following methods are used in determining presbyopic add;

Best Visual Acuity Subjective (Plus Build Up)

In this method, plus lenses are added binocularly above the patient’s subjective finding (#7) until he/she reads the smallest letters on the near point card placed at the customary working distance. The total lens in place is subtracted from the subjective finding to get the presbyopic add. This test can also be performed monocularly but the binocular method is preferred because the monocular method results in greater near addition due to lack of convergence accommodation.

Dynamic Retinoscopy

In this method, the preferred near working distance of the patient is used to perform the test and the plus lens that neutralizes the with-motion is taken as the tentative presbyopic add.

Bichrome Method                    

Testing monocularly, plus lenses are added until the red chart at near is clearer for each eye. Reduce the plus lens binocularly until the green chart is clearer and the plus lens remaining is the presbyopic add.

Based On Age

         Age                                                   Add

40 – 45 years                                          +1.00D

45 – 50 years                                          +1.50D

50 – 55 years                                          +2.00D

55 – 60 years                                          +2.50D

60 – 75 years                                          +3.00D

Based on Amplitude of Accommodation

Add = working distance in diopter – 1/2AA

i.e 100/d(cm) – 1/2AA

Example; Calculate the add of working distance 40cm if the patient has an amplitude of accommodation of +2.50.

Add = 100/40 – 1/2(2.50) = +1.25D

Cross Cylinder Method

The difference between the 14A net or 14B net finding (whichever is higher) and the distance correction is the reading add.

Example; #14A net = +4.00D, #14B net = +3.00D, #7 = +1.00D.

Add = +4.00 – 1.00 = 3.00D

Balancing PRA and NRA

Add = NRA – 1/2(PRA + NRA)

Example; Calculate add if positive relative accommodation is -0.50 and negative relative accommodation is +2.00.

Add = +2.00 – 1/2(0.50 + 2.00) = 0.75D

NOTE: This method is less accurate.