You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lens.m
    path of file: ./repos/gkaModelEye/model/eye/species/+canine
    
    the code of the file until where you have to start completion: function lens = lens( eye )
% Returns the lens sub-field of an eye model structure
%
% Syntax:
%  lens = human.lens( eye )

    
function lens = lens( eye )
% Returns the lens sub-field of an eye model structure
%
% Syntax:
%  lens = human.lens( eye )
%
% Description:

% Inputs:
%   eye                   - Structure.
%
% Outputs:
%   lens                  - Structure.
%

%% Lens front surface
radii = [4.5 4.5 4.5];

% Create the quadric
Sfront = quadric.scale(quadric.unitSphere, radii);

anteriorLensPosition = -4.27;
Sfront = quadric.translate(Sfront,[-radii(1)+anteriorLensPosition 0 0]);

% Set the bounding box
bbfront = [-9 anteriorLensPosition -5 5 -5 5];


%% Lens back surface
radii = [5.2 5.2 5.2];

% Create the quadric
Sback = quadric.scale(quadric.unitSphere, radii);

posteriorLensPosition = -11.54;
Sback = quadric.translate(Sback,[radii(1)+posteriorLensPosition 0 0]);

% Set the bounding box
bbback = [posteriorLensPosition -9 -5 5 -5 5];


%% Assemble the system
lens.S = [quadric.matrixToVec(Sback); quadric.matrixToVec(Sfront)];
lens.boundingBox = [bbback; bbfront];
lens.side = [-1; 1];
lens.mustIntersect = [1; 1];
lens.index = [1.5361];
lens.label = [{'lens.back'};{'lens.front'}];
lens.plot.color = [{[0.75 0.75 0.75 0.75]};{[0.75 0.75 0.75 0.75]}];
lens.meta.navarroD = nan;

end