I have a 13-year-old male patient who has problems with seeing print in books clearly. He is 6/5 in each eye with no distance refractive error. He has an accommodative amplitude of 4 DS in each eye and a near point of convergence of 20 cm. He also has a 20 prism dioptre exophoria at near with slow recovery. He is due to start back at school after the summer break next week. He has struggled with school work for the last two years. There are no signs of eye or neurological disease. I have referred him to a local government eye hospital but the next available appointment is in three months time. What should I do?
I would expect a patient of this age to have an accommodative amplitude of around 20 DS and a near point of convergence of less than 10 cm. It sounds very much like he has accommodative insufficiency (AI) and convergence insufficiency (CI) and that he has had it for some time. These two conditions are notorious for causing educational underachievement. It is sensible to refer for further investigation because sometimes this level of AI and CI can have sinister causes.
However, in the meantime, this boy needs your help. A good way to start is to advise multifocal glasses with base-in prism. The add can be determined by determining what power of lens gives clear near vision probably between +1.50 and +2.50 DS. Bear in mind that reducing the accommodative stimulus will reduce the convergence ability even more so it is very important to include base-in prism. The amount of prism can be determined using a near Mallett Unit if you have one or by the amount of prism it takes to improve the rate of recovery of the near exophoria. Prism can be incorporated across the whole lens as the patient will make use of the prism for near vision where he needs it and adapt to it for distance vision where he doesn’t need it.
The ideal lens form, in this case, would be a bifocal with a large flat top segment set so the edge of the top sits at the level of the middle of the pupil. This gives a large and obvious reading zone which will be easy for the patient to locate when he needs to read and easy to look above when he is looking in the distance. However, it is likely that wearing bifocals in early teenage years will attract negative attention from peers. This could result in the patient refusing to wear the glasses. A slightly less ideal lens form is a varifocal. But this is less likely to attract negative attention than the bifocals and more likely to be worn. However, it may prove more difficult for the patient to locate the reading section. Choosing a varifocal with a large reading area and instructions on how to use varifocals will assist with this.
With the help of his educators and the use of glasses this patient’s educational achievement will rapidly start to improve even while he is waiting for his hospital appointment.