To explain astigmatism, I use a model and describe how the natural eye works. I explain how light enters the eye, bends and lands somewhere inside the eye. If the focal point lands on the retina, we do not need glasses; if it lands in front or behind the retina, we need glasses to bring the focal point to the retina. Then I explain how an astigmatic eye creates two focal points, which will need two different prescriptions to bring both of those focal points to the retina. Patients will forget but understand in the moment and will appreciate the 30 seconds given to explain something they didn’t understand and often didn’t know they had.
To explain presbyopia, I use a system of 10 units, which I created years ago. It was designed as a simple method to ease the tension of and to provide more understanding of presbyopia.
The general loss of accommodation of 2.50 D can be compared to a loss of 10 units of accommodative strength if broken into 0.25 D steps. I describe to my patients that the focusing system has 10 units of energy, and over a 35-year period we will all lose those 10 units. The rate at which we do lose them is individual and depends on the amount of near work we do.
For example, if a patient presents to the clinic with a +1.50 D add, he has more than likely lost six units of his accommodate muscle energy and is performing with only four units of his initial ability. This patient would require six units (+1.50 D) of add support to return him to his full potential. These six units are added to his distance prescription to give him his best reading vision. With the six units of magnification plus his natural four units, the patient’s accommodative system is at 100 percent. The four natural units remaining will eventually be lost, and the patient understands that four more steps of change still lie ahead.