This paper shall examine the various reasons for prescription addition of the eye of an individual. We will examine various common ailments and the reasons due to which these ailments cause a prescription addition. The areas which will be studied in this section are Presbyopia, Anisometropia, squints, the various debilitating effects of diabetes mellitus and juvenile stress myopia. These issues will be studied with respect to their relevance in prescription addition. The other major issue which will be studied is the difficulties in dispensing eye prescriptions. This issue is an often neglected issue, but it has a big effect on the patient as it is the patient who is eventually denied suitable eye care. The dispensing issues which will be examined are aphakic prescriptions, iseikonic lenses, pediatric dispensing, low vision aids and protective spectacles. These dispensing issues will be examined from the patient's viewpoint.
As mentioned earlier there are numerous causes due to which prescription addition occurs. The most common is Presbyopia, which is caused due to increased age. The main cause of presbyopia is the reduced suppleness of the lens in the human eye. This suppleness is required to focus the objects near the eye. The Ciliary muscle which helps the eye to focus becomes less efficient. The lens loose their ability to alter their focusing power, the capsule which contains the lens in the eye loses its suppleness. The combination of these two factors results in a decrease in the ability to accommodate (reduced accommodation) (Woodruff 2001).This results in progressive prescription addition with the passage of time.
Anisometropia is caused due to the differences in the dioptric values between both eyes of a single person. This is generally caused either due to refractive surgery causing a difference in the ability of both eyes. Other reasons are overcorrections of myopic and hyperopic patients. Lastly, Anisometropia is also caused, if one eye is significantly more astigmatic than the other. Irregular astigmatism can cause an imbalance in the refractive power of both the eyes (Woodruff 2001). Prescription addition due to Anisometropia are caused primarily because of either surgery causing a difference in the refractive power between either eyes or the overcorrections of myopic and hyperopic patients.
A squint refers to a state where the eyes are not aligned in the same direction Squints are caused by many reasons and occur more in children. As we are focusing on prescription additions, squints especially those that arise from hypermetropia (long sightedness) are treated with the relevant prescription addition. Then the child will be assessed for the decrease of the degree squint and the child's prescription will be changed accordingly. There are various reasons for the occurrence of squints and consequent prescription addition (for the correction of the squint) amongst children. Illnesses like viral fever, measles, and meningitis are known to cause squints. Injury to the nerves attached to the eye muscles can also cause squint.