Design of multifocal contact lens with nurbs and shrinkage analysis on shell mold by injection molding process

DESIGN OF MULTIFOCAL CONTACT LENS WITH NURBS

AND SHRINKAGE ANALYSIS ON SHELL MOLD BY

INJECTION MOLDING PROCESS

DEPARTMENT OF

MECHANICAL ENGINEERING

PRECISION MANUFACTURING

LABORATORY

Taipei, May 4 2018

Dissertation defense for the Degree of Doctor of Philosophy

presented by Vu Thi Lien

Advisor: Prof. Chao-Chang A. Chen

Committee : Prof. Sen-Yeu Yang (Chair)

Prof. Jong-Woei Whang

Dr. Kuo-Cheng Huang

Prof. Pei-Jen Chung

Dr. Yi-Sha Ku

Prof. Chien-Yu Chen

Prof. Chao-Chang A. Chen

2 6/5/2018

OUTLINE

Conclusions and Recommendations

Introduction

A. NURBS multifocal CLs with given optical power distribution

B. NURBS multifocal CLs with uniform optical power in center-distance zone

C. Minimization of shrinkage error of shell mold in injection molding process

Specific studies

Overview of contact lens design

3

Presbyopia and correction methods

A loss of accommodation with age (>40) to focus on nearby objects

when the crystalline lens becomes harder and loses elasticity and

causes light to focus behind the retina.

https://www.improveeyesighthq.com/presbyopia.html

Progressive addition lens Multifocal contact lens Multifocal Lasilk

blur blur

http://www.eyelandeyedoc.com/eyeglass-lens- options/

http://video.visiondirect.com/v/1396813785/aom-consumer- moa-video-hi-res-mov-air-optix-contact/

http://www.allaboutvision.com/visionsurgery/presby-lasik.htm

Presbyopia corrections

Spectacles Contact lens

Surgery

(Effect is not long-lasting)

• Better vision

• More attractive

• More convenient (sport activities) • Not be affected by weather conditions

http://metroeyedocs.com/boomer-lens.html

Presbyopic eye Presbyopia correction with spectacles

http://www.eyes-and-vision.com/presbyopia-eye-disorder.html

Retina

Crystalline lens

4 6/5/2018

Multifocal CLs for presbyopia

“Image jump”

Focusing various vision distances

within the area of pupil on retina at the

same time (more natural)

Two vision distances (near and far)

Power distributions of CLs for presbyopic correction [42-44]

Dop=6.0 mm

http://www.bausch.com.sg/en/our-products/contact-lenses/lenses-for-presbyopia/biotrue- oneday-for-presbyopia/

5 6/5/2018

Power profiles of commercial simultaneous multifocal CLs

Additional (Add) powers (low, mid, high) from +0.75 to 3.50 D

[87]

[89]

The power profile of a zonal-aspheric

multifocal CL

6

Problem statement

Current problems for multifocal CL designs:

• Reduce the dependence of CLs on pupil sizes

• Increase Add powers (>3.5 D)

• Smooth lens surfaces

• Minimal machining errors

• The demand for presbyopia CLs is very high

with more and more requirements. • None of available multifocal CL designs

presents as the best design. Lens shapes, materials and manufacture

methods need to be continuously improved.

The Add range of commercial soft multifocal CLs [68]

Continuity problem of zonal aspheric designs

Curvature continuity ?

Smooth connection