Semi finished SF CR-39 1.49 Flat Top-28 bifocal prescription reading optical lens blanks

I. Specification

II. Technical Data

• Flat Top Bifocal Lenses

A flat top 28 bifocal lens is offers correction for both near and far distances. It is a multifocal lens commonly prescribed for those suffering from both presbyopia and hypermetropia, a condition whereby, with age, the eye exhibits a progressively diminished ability to focus on near and far objects. The flat top lens includes a segment at the lower half of the lens with a prescription for reading (near distance). The width of the flat top 28 bifocal is  28mm wide at the top of the bifocal and looks like the Letter D turned 90 degrees.  Because the flat top bifocal is one of the easiest multifocal lenses to adapt to, it is one of the most popular bifocal lenses in the world. It's distinct "jump" from distance to near vision gives wearers two well-demarcated areas of their glasses to use, depending upon the task at hand.   The line is obvious because the change in powers is immediate with the advantage being it gives you the widest reading area without having to look too far down the lens. It is also easy to teach someone how to utilize the bifocal in that you simply use the top for distance and the bottom for reading.

• The definition of semi finished lens

Semi-finished lens is the raw blank used to produce the most individualized RX lens according to the patient's prescription. Different prescription powers request for different semi-finished lens types or base curves. 

• The process of semi finished lens

The starting point for freeform production is a semi-finished lens, also known as a puck due to its resemblance to an ice hockey puck. These are produced in a casting process that is also used to manufacture stock lenses. The semi-finished lenses are produced in a casting process. Here, liquid monomers are first poured into moulds. Various substances are added to the monomers, e.g. initiators and UV absorbers.

• What's the importance of a good semi-finished lens to RX production

a. High qualified rate in power accuracy and stability

b. High qualified rate in cosmetics quality
c. High optical features
d. Good tinting effects and hard-coating/AR coating results
e. Realize the maximum production capacity
f. Punctual delivery

Not just superficial quality, semi-finished lenses are more focus on the internal quality, such as precise and stable parameters, especially for the popular freeform lens.