OPHTHALMIC LENSES

Ophthalmic Lenses

Ophthalmic Lenses

Introduction

This is the introduction part and it will be providing a clear structure that will be followed in the paper. This is paper will be presenting a Professional Qualifying Portfolio (PQP), and will analyze a case of the patient. In the discussion section we will be discussing the case and then will be dispensing a lens with justifications. The case will also be discussing what kinds of measures those have to be taken in order to justify the lenses that are recommended.

Patients normally come to an ophthalmologist to determine their refractive status of their eyes either diagnostic or treatment. So, ophthalmic dispensing is certainly a significant part of ophthalmology.The purpose of this article is to provide a brief resume of the types of spectacle lenses available to the patient for better vision (visual needs). The medical practitioners should know about the ophthalmic lenses to able to manage the patient's requirements.

Besides mechanical, manufacturing and aesthetic constraints, the shape of ophthalmic lens surfaces is designed aim at improving the optical quality, for different gaze directions, by means of minimizing some optical aberrations. The monochromatic aberrations that are normally considered are oblique astigmatism and curvature of field (also called mean power error), though the relevance of distortion has also been stressed. Recently, even some authors start to contemplate other higher order aberrations.

However, to control these aberrations, ophthalmic lens design is limited by the few available degrees of freedom. Aspherical surfaces were introduced, among other reasons, to increase the number of design parameters. The first aspheric lenses with convex surfaces appeared at the end of the 1970's. The majority of aspheric lenses are made aspheric on the front surface.

A fundamental question arises: given a single aspheric surface, which is the best strategy to maximize the optical quality? Following Schultz terminology [6], ophthalmic lens design can be considered as a case of large fields imaging with thin pencils. Schultz showed that, in general, such a system needs three aspheric surfaces to completely correct distortion, field of curvature and astigmatism. Within this fundamental constraint, in ophthalmic lens design several partial correcting strategies have been proposed; two of the most popular ones are the point focal and Percival designs that correct the oblique astigmatism and mean power error respectively. Nowadays, a typical strategy is to minimize the tangential power error. It has the advantage that if the real vertex distance is different from the value used in the design, the lens tends to behave as a point focal design (overestimation of the vertex distance) or as Percival design (subestimation of the vertex distance). In this work, I follow this approach.

The usual strategy in ophthalmic lens design is multi-parametric optimization. The method is based on searching for the coefficients of an analytical description of the lens surface which minimize a previously established merit function. This is performed with optimization algorithms. This procedure has the inherent problem of needing sophisticated optimization software, normally implemented in commercial optical design ...