Final answer:
When fitting multifocal lenses, it is important to consider the patient's original prescription, as well as the accurate measurement of pupillary distance and alignment of focal points with line of sight for different vision tasks. Vision problems such as myopia and hyperopia are corrected by concave and convex lenses, respectively, and these conditions, along with presbyopia, dictate the type of multifocal lenses needed.
Step-by-step explanation:
When fitting multifocal lenses (MFs), which are used to correct presbyopia among other vision issues, certain rules are important to remember. Always take into account the patient's original prescription (ORx), which indicates the corrective power needed for each eye. Multifocals are designed to provide different strengths of vision correction, often for near, intermediate, and distance vision, within the same lens.
Vision problems like myopia (nearsightedness) and hyperopia (farsightedness) could require glasses for sharp vision at different distances. With myopia, objects far away appear blurred, and a concave lens corrects this condition. Hyperopia is the opposite, where near objects are not seen clearly, and a convex lens is used for correction. Presbyopia, which often prompts the need for reading glasses, generally begins after the age of 40 when the lens of the eye becomes less flexible, making it hard to focus on close objects.
Common signs of myopia include squinting, eye strain, and difficulty seeing distant objects. Signs of hyperopia include a hard time focusing on close objects and potentially aching eyes or headaches after prolonged focus work. Knowing these signs helps in accurately determining the need for and type of multifocal lenses a person may require.
When fitting for ORx, careful measurement of the pupillary distance and consideration of the patient's daily activities and needs are essential. Furthermore, ensuring the multifocal focal points align with the patient's line of sight for different tasks is also critical.