EN ISO 18369-1:2006

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Ophthalmic optics - Contact lenses - Part 1: Vocabulary, classification system and recommendations for labelling specifications (ISO 18369-1:2006)Optique ophtalmique - Lentilles de contact - Partie 1: Vocabulaire, systeme de classification et recommandations pour l'étiquetage des spécifications (ISO 18369-1:2006)Augenoptik - Kontaktlinsen - Teil 1: Begriffe, Einteilung von Kontaktlinsenmaterialien und Empfehlungen für die Schreibweise von Kontaktlinsenspezifikationen (ISO 18369-1:2006)Ta slovenski standard je istoveten z:EN ISO 18369-1:2006SIST EN ISO 18369-1:2006en,fr,de11.040.70Oftalmološka opremaOphthalmic equipment01.040.11Zdravstveno varstvo (Slovarji)Health care technology (Vocabularies)ICS:SIST EN ISO 8321-1:2002SIST EN ISO 8321-2:2000SIST EN ISO 8320-2:2002SIST EN ISO 11539:2001SIST EN ISO 8320-1:20031DGRPHãþDSLOVENSKI
STANDARDSIST EN ISO 18369-1:200601-december-2006

EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN ISO 18369-1
August 2006 ICS 01.040.11; 11.040.70 Supersedes
EN ISO 8320-1:2003,
EN ISO 8320-2:2001and EN ISO 11539:1999, and partly supersedes EN ISO 8321-1:2002 andEN ISO 8321-2:2000English Version
Ophthalmic optics - Contact lenses - Part 1: Vocabulary, classification system and recommendations for labelling specifications (ISO 18369-1:2006)
Optique ophtalmique - Lentilles de contact - Partie 1: Vocabulaire, système de classification et recommandations pour l'étiquetage des spécifications (ISO 18369-1:2006)
Augenoptik - Kontaktlinsen - Teil 1: Begriffe, Einteilung von Kontaktlinsenmaterialien und Empfehlungen für die Schreibweise von Kontaktlinsenspezifikationen (ISO 18369-1:2006) This European Standard was approved by CEN on 19 May 2006.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36
B-1050 Brussels © 2006 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN ISO 18369-1:2006: E

Foreword
This document (EN ISO 18369-1:2006) has been prepared by Technical Committee ISO/TC 172 "Optics and photonics" in collaboration with Technical Committee CEN/TC 170 "Ophthalmic optics", the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by February 2007, and conflicting national standards shall be withdrawn at the latest by February 2007.
This document supersedes EN ISO 8320-1:2003, EN ISO 8320-2:2001 and EN ISO 11539:1999 and partly supersedes EN ISO 8321-1:2002 and EN ISO 8321-2:2000.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
Endorsement notice
The text of ISO 18369-1:2006 has been approved by CEN as EN ISO 18369-1:2006 without any modifications.
NOTE: A-Deviations are given in Annex ZA (informative)

3 ANNEX ZA
(informative) A-deviations
A-deviation: National deviation due to regulations, the alteration of which is for the time being outside the competence of the CEN/CENELEC member.
This European Standard does not fall under any Directive of the EC. In the relevant CEN/CENELEC countries these A-deviations are valid instead of the provisions of the European Standard until they have been removed.
The legislative situation in Germany requires the unit "dioptre" be designated by the symbol "dpt" instead of "D".
This is to avoid conflict with the rules of ISO 1000 being the basic International Standard on symbols and units and with the respective basic resolution of the CGPM (International Conference on Weights and Mesures).
Identification of the regulation:
Gesetz über die Einheiten im Messwesen vom 02.07.1969 in der Fassung der Bekanntmachung vom 22.04.1985;
and
Ausführungsverordnung zum Gesetz über Einheiten im Messwesen (Einheitenverordnung - EinhV) vom 13.12.1985, § 1 und Anlage 1, Nr. 9.

Reference numberISO 18369-1:2006(E)© ISO 2006
INTERNATIONAL STANDARD
ISO18369-1First edition2006-08-15Ophthalmic optics — Contact lenses — Part 1: Vocabulary, classification system and recommendations for labelling specifications Optique ophtalmique — Lentilles de contact — Partie 1: Vocabulaire, système de classification et recommandations pour l'étiquetage des spécifications

ISO 18369-1:2006(E) ©
ISO 2006 The reproduction of the terms and definitions contained in this International Standard is permitted in teaching manuals, instruction booklets, technical publications and journals for strictly educational or implementation purposes. The conditions for such reproduction are: that no modifications are made to the terms and definitions; that such reproduction is not permitted for dictionaries or similar publications offered for sale; and that this International Standard is referenced as the source document. With the sole exceptions noted above, no other part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 • CH-1211 Geneva 20 Tel.
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copyright@iso.org Web
www.iso.org Published in Switzerland
ii
ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
iiiContents Page Foreword.iv Introduction.v 1 Scope.1 2 Terms, definitions and symbols.1 2.1 Terms and definitions.1 2.1.1 Basic terms.1 2.1.2 Contact lens parameters and design.3 2.1.3 Aspheric contact lenses.15 2.1.4 Bifocal and multifocal contact lenses.16 2.1.5 Scleral contact lenses and shells.18 2.1.6 Contact lens material properties.20 2.1.7 Tinted contact lenses.23 2.1.8 Contact lens manufacture.23 2.1.9 Packaging and labelling of contact lenses and contact lens care products.23 2.1.10 Contact lens usage and wear modality.25 2.1.11 Contact lens hygienic management and contact lens care products.26 2.1.12 Miscellaneous.29 2.2 Symbols.31 3 Classification of contact lens materials.32 Annex A (informative)
Specification of rigid contact lenses.35 Annex B (informative)
Specification of soft contact lenses.43 Bibliography.45 Alphabetical index.46

ISO 18369-1:2006(E) iv
ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
vIntroduction The ISO 18369 series applies to contact lenses, which are devices worn over the front surface of the eye in contact with the preocular tear film. This part of ISO 18369 covers rigid (hard) corneal and scleral contact lenses, as well as soft contact lenses. Rigid lenses maintain their own shape unsupported and are made of transparent optical-grade plastics, such as polymethylmethacrylate (PMMA), cellulose acetate butyrate (CAB), polyacrylate/siloxane copolymers, rigid polysiloxanes (silicone resins), butylstyrenes, fluoropolymers, and fluorosiloxanes, etc. Soft contact lenses are easily deformable and require support for proper shape. A very large subset of soft contact lenses consists of transparent hydrogels containing water in concentrations greater than 10 %. Soft contact lenses can also be made of non-hydrogel materials, e.g. flexible polysiloxanes (silicone elastomers). The ISO 18369 series is applicable to determining allowable tolerances of parameters and properties important for proper functioning of contact lenses as optical devices. The ISO 18369 series includes tolerances for single vision contact lenses, bifocal lenses, lenses that alter the flux density and/or spectral composition of transmitted visible light (tinted or pigmented contact lenses, such as those with enhancing, handling, and/or opaque tints), and lenses that significantly attenuate ultraviolet radiation (UVR absorbing lenses). The ISO 18369 series covers contact lenses designed with spherical, toric, and aspheric surfaces, and recommended methods for the specification of contact lenses. The vocabulary portion (2.1) of this part of ISO 18369 contains the terms and definitions primarily used in the contact lens field. A list of terms having special symbols is given in Table 1. The list of terms and definitions does not include all ISO terms, definitions, and symbols used in the contact lens field. It is intended to be a convenient reference source from which the contents have been compiled from the text of this and other ISO standards applicable to the manufacture, evaluation, measurement, labelling and marketing of contact lenses and contact lens care products. An alphabetical index was added for rapid finding of terms. Words are grouped under several topics by reference number according to the general category into which each word logically fitted. The preferred form of each term is listed on the first line after its reference number. Other admitted forms have been placed on subsequent lines after the preferred form. All admitted terms are given in bold-faced type. A few obsolete and superseded terms are listed for historical reference and convenience and as an aid to comprehension but are indicated as deprecated and are no longer to be used. Obsolete and superseded terms are not in bold-faced type so that they may be clearly identified as terms used historically. Figure 1 gives a schema of the classification and provides examples. It does not take into account all possible characteristics (hence resulting qualifiers) used in contact lens designation. Combinations of more than one qualifier are often used in contact lens designation.

ISO 18369-1:2006(E) vi
Figure 1 — Classification of contact lenses according to various characteristics
leads to various qualifiers used in their designation

INTERNATIONAL STANDARD ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
1Ophthalmic optics — Contact lenses — Part 1: Vocabulary, classification system and recommendations for labelling specifications 1 Scope This part of ISO 18369 identifies and defines the terms applicable to the physical, chemical and optical properties of contact lenses, their manufacture and uses. It provides a vocabulary of terms and, when appropriate, the international symbol and abbreviation associated with a specific term. This part of ISO 18369 also defines the terms relating to contact lens care products. It also incorporates the classifications of contact lens materials and gives recommendations for the labelling of the specifications of contact lenses. 2 Terms, definitions and symbols 2.1 Terms and definitions 2.1.1 Basic terms 2.1.1.1 contact lens any ophthalmic lens designed to be worn on the front surface of the eye NOTE This term includes contact lenses of plano power. 2.1.1.2 corneal contact lens contact lens having a total diameter less than the visible iris diameter and designed to be worn in its entirety on the cornea 2.1.1.3 scleral contact lens contact lens designed to be worn in front of the cornea and on the adjacent portion of the surrounding bulbar conjunctiva NOTE See 2.1.5 for specific terms concerning scleral contact lenses. 2.1.1.4 lenticular contact lens contact lens having a front optic zone made smaller than the total diameter NOTE This construction is conventionally used to reduce the centre thickness of a positive power contact lens or reduce the edge thickness of a negative power contact lens. 2.1.1.5 contact shell contact lens not designed to correct vision

ISO 18369-1:2006(E) 2
ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
32.1.1.16 contact lens accessory article intended specifically by its manufacturer to be used with a contact lens to enable the lens to be used in accordance with its intended purpose NOTE This term includes all devices recommended for use in the hygienic management of contact lenses, for hydrating contact lenses, or alleviating discomfort of contact lens wear by physical means. 2.1.1.17 contact lens care product contact lens accessory intended for use in maintaining the safety and performance of a contact lens after opening and removal of the lens from its primary container NOTE See 2.1.9 and 2.1.11 for specific terms concerning contact lens care products and the hygienic management of contact lenses. 2.1.1.18 other accessory for contact lenses item used for handling contact lenses or as a part of a contact lens care regimen excluding contact lens care products EXAMPLE Suction cup used to aid in the insertion of a contact lens onto or removal from the surface of the eye. NOTE This definition does not include the primary packaging (e.g. vials, blister packs or mailers) intended by the manufacturer to be used only for shipment of the contact lenses. 2.1.1.19 suction cup hand-held device designed with a small concave flexible tip intended to aid the insertion of a contact lens onto or removal from the eye by means of suction NOTE A suction cup is designed primarily for use with rigid corneal contact lenses. 2.1.1.20 contact lens container storage container contact lens case storage case container in which contact lenses are stored either dry or in a suitable solution by the user after removal from the primary container or the eye 2.1.2 Contact lens parameters and design 2.1.2.1 General terms 2.1.2.1.1 front vertex power Fv reciprocal of the paraxial front vertex focal length [ISO 13666:1998] NOTE The front vertex power is expressed in dioptres. 2.1.2.1.2 back vertex power F′v reciprocal of the paraxial back vertex focal length [ISO 13666:1998] NOTE The back vertex power is expressed in dioptres.

ISO 18369-1:2006(E) 4
optical decentration positioning of the optical centre at a point other than the geometric centre of the optic zone or central optic zone 2.1.2.1.12 contact lens axis line passing through the geometric centre, perpendicular to a plane containing the edge of a contact lens See Figure 2.

ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
52.1.2.1.13 back vertex point on the posterior contact lens surface lying on the contact lens axis See Figure 2. 2.1.2.1.14 vertex sphere imaginary spherical surface touching the back vertex NOTE The radius of curvature of the vertex sphere is the same as the steepest back optic zone radius, back central optic radius, or back vertex radius of an aspheric lens (see Figure 2).
Key 1 contact lens axis 2 centre of vertex sphere 3 back vertex 4 vertex sphere 5 peripheral junction thickness, tPJ0 6 overall posterior sagitta Figure 2 — Schematic representation of a tri-curve contact lens including symbols of the main parameters describing its back surface 2.1.2.1.15 sagitta sagittal depth sagittal height maximum distance from a chord, which is perpendicular to the axis of rotation of a surface, to the curved surface

ISO 18369-1:2006(E) 6
Key 1 front surface of contact lens 2 back surface of contact lens 3 vertex sphere 4 centre of vertex sphere 5 junction 6 specified point on the back surface of the contact lens; for radial and axial edge lift, specified point at the edge of the contact lens 7 axial lift, lA 8 radial lift, lR
Figure 3 — The difference between radial and axial lift 2.1.2.1.20 radial edge lift lER distance between a point on the back surface of a contact lens at the edge and the vertex sphere measured along the radius of curvature of the latter See Figure 3. NOTE This is often a value computed by the manufacturer and may be altered by the edging process.

ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
72.1.2.1.21 axial lift lA distance between a specified point on the back surface and the vertex sphere measured parallel to the contact lens axis See Figure 3. 2.1.2.1.22 axial edge lift lEA distance between a point on the back of a contact lens at the edge and the vertex sphere, measured parallel to the contact lens axis See Figure 3. NOTE This is often a value computed by the manufacturer and may be altered by the edging process. 2.1.2.1.23 spherical surface 〈non-aspheric〉 surface described by rotating a circle about a line containing its centre 2.1.2.1.24 spherical surface 〈non-toric〉 surface having the same radius of curvature for meridians in all directions 2.1.2.1.25 sagittal radius of curvature radius of curvature in the sagittal plane at a specified off-axis point on the surface NOTE 1 The radius at a specified point on the surface is equal to the distance along the normal at that point to its intersection with the axis of rotation. NOTE 2 The sagittal plane contains the normal to the surface at the specified point, but does not contain the axis of rotation, being perpendicular to the tangential plane. 2.1.2.1.26 tangential radius of curvature radius of curvature in the tangential plane at a specified off-axis point on a surface NOTE The tangential plane contains both the normal to the surface at the point specified and the axis of rotation. 2.1.2.1.27 bi-curve contact lens contact lens whose back surface is composed of two intersecting spherical zones 2.1.2.1.28 tri-curve contact lens contact lens whose back surface is composed of three intersecting coaxial spherical zones 2.1.2.1.29 multi-curve contact lens contact lens with a back surface that is composed of more than three intersecting spherical zones 2.1.2.1.30 aspheric contact lens contact lens with its front or back optic zone of aspheric form NOTE See 2.1.3 for specific terms concerning aspheric contact lenses. 2.1.2.1.31 toric contact lens contact lens with front and/or back optic zone of toroidal form

ISO 18369-1:2006(E) 8
ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
9 Key 1 tangent common to both circles 2 contact lens axis NOTE This is an example of a back surface of a contact lens. It is a bi-curve surface with a tangential junction T. The back peripheral zone would be formed by rotating the arc TE around the lens axis; the back optic zone is formed by rotating the arc YT around the lens axis. The back optic zone diameter is 2 LT; the total diameter is 2 EA; the overall posterior sagitta is YA. Figure 4 — Example of a tangential junction
Key 1 zone A 2 zone B 3 original junction of zone A and zone B 4 radius of curvature of the transition 5 transition Figure 5 — Example of a transition on the back surface of a contact lens

ISO 18369-1:2006(E) 10
ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
11 a)
Negative carrier
b)
Parallel carrier
c)
Positive carrier Key 1 optic zone 2 junction 3 edge Figure 6 — Different types of carrier 2.1.2.2 Radius of curvature NOTE 1 Radii relating to zones on the back surface of the lens are designated by a numerical subscript starting with zero (r0). The subscript becomes larger from the lens centre to the lens edge. See Figure 2. NOTE 2 Radii relating to the front surface of the lens have a double subscript, the first part of which is the letter “a”. The second part is a number from zero upward, for example, ra2. NOTE 3 In the case of an aspheric zone, a mathematical equation or expression may be used to describe the curvature of the zone. 2.1.2.2.1 back optic zone radius base curve radius r0 radius of curvature of the back optic zone of a surface with a single refractive element NOTE 1 On a toroidal zone there will be two radius values. NOTE 2 The term “base curve” used in a contact lens context must not be confused with the same term when used in a spectacle lens context (see ISO 13666:1998). 2.1.2.2.2 back central optic zone radius r0 radius of curvature of the back central optic zone of a multifocal contact lens

ISO 18369-1:2006(E) 12
ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
132.1.2.3.4 back central optic zone diameter Ø0 diameter of the posterior central optic zone of a concentric multifocal contact lens 2.1.2.3.5 back peripheral optic zone diameter Ø1, Ø2, . diameter of a posterior peripheral optic zone of a concentric multifocal contact lens 2.1.2.3.6 back peripheral zone diameter Ø1, Ø2, . diameter of a back peripheral zone NOTE This term may be preceded by first, second, third, etc. 2.1.2.3.7 front optic zone diameter Øa0 diameter of the front optic zone on a surface with a single refractive element 2.1.2.3.8 front central optic zone diameter Øa0 diameter of the anterior central optic zone of a multifocal contact lens 2.1.2.3.9 front peripheral optic zone diameter Øa1, Øa2, . diameter of an anterior peripheral optic zone of a multifocal contact lens 2.1.2.3.10 front peripheral zone diameter Øa1, Øa2, . diameter of a front peripheral zone NOTE This term may be preceded by first, second, third, etc. 2.1.2.4 Thickness NOTE It is common in France to use the symbol e for épaisseur, rather than t for thickness. 2.1.2.4.1 geometric centre thickness tC thickness of the contact lens or shell at its geometric centre 2.1.2.4.2 optical centre thickness tO thickness of the contact lens at its optical centre NOTE This symbol is used only if the optical centre does not coincide with the geometric centre.

ISO 18369-1:2006(E) 14
ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
Key 1 front surface of contact lens 2 vertex sphere 3 back vertex 4 centre of vertex sphere 5 contact lens axis 6 axial edge thickness, tEA 7 radial edge thickness, tER
a The radial edge thickness would normally be measured 0,2 mm to 0,8 mm from the edge of the contact lens. Figure 7 — The difference between radial and axial edge thickness 2.1.3 Aspheric contact lenses 2.1.3.1 aspheric zone zone with surface having a form generated by the rotating of a curve of continuously varying radius about the contact lens axis 2.1.3.2 bi-aspheric contact lens contact lens having both front and back optic zones of aspheric form 2.1.3.3 aspheric periphery contact lens contact lens with one or more back peripheral aspheric zones and a spherical back optic zone 2.1.3.4 aspheric bi-curve contact lens contact lens whose back surface is composed of two intersecting coaxial aspheric zones 2.1.3.5 aspheric tri-curve contact lens contact lens whose back surface is composed of three intersecting coaxial aspheric zones 2.1.3.6 aspheric multi-curve contact lens contact lens whose back surface is composed of more than three intersecting coaxial aspheric zones

ISO 18369-1:2006(E) 16
Key 1 carrier 2 central optic zone 3 peripheral optic zone Figure 8 — The surface of a solid, concentric bifocal contact lens 2.1.4.4 concentric multifocal contact lens contact lens having two or more optic zones of different power, each having coincident geometric centres 2.1.4.5 central optic zone innermost optic zone of a concentric bifocal or other multifocal contact lens

ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
172.1.4.6 peripheral optic zone optic zone surrounding the central optic zone of a concentric multifocal contact lens NOTE There can be more than one peripheral optic zone. 2.1.4.7 centre distance contact lens CD contact lens multifocal or progressive power contact lens where the maximum minus (or minimum plus) power is found in the central optic zone of the lens 2.1.4.8 centre near contact lens CN contact lens multifocal or progressive power contact lens where the maximum plus (or minimum minus) power is found in the central optic zone of the lens 2.1.4.9 solid bifocal contact lens one-piece bifocal contact lens non-composite bifocal contact lens bifocal contact lens formed from only one material 2.1.4.10 solid multifocal contact lens one-piece multifocal contact lens non-composite multifocal contact lens multifocal contact lens formed from only one material 2.1.4.11 fused segment contact lens multifocal contact lens made from materials of different refractive indices 2.1.4.12 segment height vertical distance of the segment extreme point above the horizontal tangent to the contact lens periphery at its lowest point See Figure 9. NOTE This dimension does not apply to concentric and diffractive multifocal contact lenses. 2.1.4.13 diffractive bifocal contact lens simultaneous image bifocal contact lens which utilizes diffraction as well as refraction to focus retinal images of distant and near objects 2.1.4.14 simultaneous image multifocal contact lens simultaneous vision contact lens (deprecated) bifocal or multifocal contact lens whose performance does not primarily depend on lens movement for different viewing distances NOTE It is intended that two or more zones continually cover the pupil area. 2.1.4.15 alternating image bifocal contact lens translating bifocal contact lens alternating vision bifocal contact lens (deprecated) translating vision bifocal contact lens (deprecated) bifocal contact lens whose performance depends primarily on movement of the contact lens to position either the near or the distance portion in front of the pupil See Figure 9.

ISO 18369-1:2006(E) 18
Key 1 distance optic zone 2 near optic zone 3 truncation 4 segment height Figure 9 — Example of an alternating image bifocal contact lens 2.1.5 Scleral contact lenses and shells 2.1.5.1 impression scleral contact lens scleral contact lens, the back surface of which has been produced by moulding from a cast of the eye of the wearer 2.1.5.2 impression scleral shell scleral shell, the back surface of which has been produced by moulding from a cast of the eye of the wearer 2.1.5.3 impression tray type of shell used to hold impression material in contact with the eye 2.1.5.4
preformed scleral contact lens scleral contact lens, not an impression lens, the back surface of which is of a specified form 2.1.5.5 back scleral size maximum internal dimension of the back scleral surface before the sharp edges have been rounded See Figure 10.

ISO 18369-1:2006(E) © ISO 2006 – All rights reserved
19 Key 1 displacement of optic d = (AB + CD)/2 2 scleral zone 3 optic-scleral junction 4 edge 5 centre of circle enclosing edge 6 centre of circle enclosing the optic zone 7 back scleral size = AD Figure 10 — Posterior view of a scleral contact lens or shell 2.1.5.6 displacement of optic d 〈scleral lenses〉 half of the difference between the maximum and minimum scleral chords See Figure 10. NOTE This assumes a rou
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