The Artisan Lens:

Effects on Vision Quality, the Corneal Endothelium and Vision-Related Quality of Life

Ruchi Saxena

Financial support for the publication of this thesis was provided by the following:

Prof Dr Henkes Stichting

Stichting Leids Oogheelkundig Ondersteunings Fonds

Alcon Nederland B.V.

Allergan B.V.

Christelijke Stichting tot Praktisch Hulpbetoonaan Visueel Gehandicapten van alle Gezindten

D.O.R.C. International

Ergra Low Vision

Laméris Ootech B.V.

Medical Workshop

Novartis Pharma B.V.

Oculenti Contactlenspraktijken

Ophtec B.V.

Pfizer B.V.

Stichting tot Verbetering van het Lot der Blinden in Nederland Théa Pharma

URSAPHARM Benelux B.V.

R. Saxena, 2009

No part of this thesis may be reproduced or transmitted in any form or by any means without the permission of the author.

Layout and print by Ridderprint, Ridderkerk ISBN/EAN: 978-90-5335-186-4

The Artisan Lens:

Effects on vision quality, the corneal endothelium and vision-related quality of life

De Artisan lens:

Effect op de kwaliteit van de visus, het corneale endotheel en de visus-gerelateerde kwaliteit van leven

Proefschrift

ter verkrijging van doctor aan de Erasmus Universiteit Rotterdam op gezag van de

rector magnificus

Prof.dr. S.W.J. Lamberts

en volgens besluit van het College voor Promoties

De openbare verdediging zal plaatsvinden op

woensdag 13 mei 2009 om 11.45 uur

door

Ruchi Saxena geboren te Lucknow, India

The Artisan Lens:

Effects on Vision Quality, the Corneal Endothelium and Vision-Related Quality of Life

Ruchi Saxena

Chapter11

General Introduction

1.2A Brief History of Correcting Refractive Error

1.1 Refractive Errors

Refractive errors are the most frequent disorders of the eye1. In the ideal refractive state, emmetropia, an image is focused directly on the retina, resulting in the perception of a sharp image in a healthy visual system (Figure 1.1.1). Such eyes do not require glasses or contact lenses to see sharply. Most eyes, however, have some degree of refractive error, although correction is not always required.

Figure 1.1.1 The Emmetropic Eye

(Courtesy of Ophtec BV)

In myopia (nearsightedness), the image appears focused anterior to the retina, producing a sharp image at near and a blurred image at distance (Figure 1.1.2). A concave lens (minus Diopter) is required to sharpen the image. The reverse is true in hypermetropia (also known as hyperopia or farsightedness), where the image is projected posterior to the retina, producing a blurred image at near and a sharper image at distance (Figure 1.1.3). A convex lens (plus Diopter) is required to produce a clear image. Astigmatism (cylindrical error) is the result of two different refractive powers between two perpendicular meridians (Figure 1.1.4). A cylindrical correction can correct this problem. Extreme cases of all these refractive errors can cause severe visual loss. Anisometropia is the presence of two significantly different refractive errors. In these situations, simple spectacle correction is not always suitable due to aniseikonia (different sized images) resulting from the different powers in the lenses; other options such as contact lenses or surgery can then be considered. When refractive errors and anisometropia are not corrected aptly, diminished binocular vision and/or amblyopia could result.

Refractive error is not static. Newborns are normally born hypermetropic (approximately +2.0 D) and emmetropise quickly to plano between 4 and 6 years of age. Lack of emmetropisation can lead to hypermetropia2.

10 Chapter 1

Figure 1.1.2 The Myopic Eye

(Courtesy of Ophtec BV)

Figure 1.1.3 The Hypermetropic Eye

(Courtesy of Ophtec BV)

Figure 1.1.4 The Astigmatic Eye

(Courtesy of Ophtec BV)

Myopia generally has its onset around puberty, although in pathologic myopia, negative refractive error is found earlier. Myopization can continue slowly until about the age of 30. The development of cataract in older individuals can cause rapid myopization, however some patients become more hypermetropic.