Undeclared variable in script after assigning to worksapce

function varargout = EyeDistance(varargin)

gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @EyeDistance_OpeningFcn, ...
                   'gui_OutputFcn',  @EyeDistance_OutputFcn, ...
                   'gui_LayoutFcn',  [] , ...
                   'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
function EyeDistance_OpeningFcn(hObject, eventdata, handles, varargin)

handles.output = hObject;
handles.video = videoinput('macvideo','FaceTime HD Camera');
set(handles.video, 'ReturnedColorspace', 'RGB');
handles.hImage = image(zeros(720, 1280, 3), 'parent', handles.cameraAxes);
guidata(hObject, handles);

function varargout = EyeDistance_OutputFcn(hObject, eventdata, handles) 
varargout{1} = handles.output;

% --- Executes on button press in startCamera.
function startCamera_Callback(hObject, eventdata, handles)
preview(handles.video,handles.hImage);

% --- Executes on button press in captureImage.
function captureImage_Callback(hObject, eventdata, handles)
pause(1);
handles.I = getsnapshot(handles.video);
stop(handles.video);
imshow(handles.I, 'Parent', handles.cameraAxes);
assignin('base','I',handles.I);

% --- Executes on button press in cropFace.
function cropFace_Callback(hObject, eventdata, handles)
DetectFaceandEyes;
imshow(face, 'Parent', handles.cameraAxes);

----------DetectFaceandEyes.M----------

NotYet = false;
%C = webcamlist;
%cam=webcam('macvideo','FaceTime HD Camera');
%preview(cam);
while ~NotYet
    %tic;pause(0.10);toc;
    %I = snapshot(cam);
    faceDetect = vision.CascadeObjectDetector();
    bbox=step(faceDetect,I);
    if ~isempty(bbox)
        NotYet = true;
        break;
    end
end
%closepreview;
%clear('cam');
face = imcrop(I,bbox);

Undefined function or variable 'I'.

Error in DetectFaceandEyes (line 9)
    bbox=step(faceDetect,I);

Error in EyeDistance>cropFace_Callback (line 108)
DetectFaceandEyes;

Error in gui_mainfcn (line 95)
        feval(varargin{:});

Error in EyeDistance (line 42)
    gui_mainfcn(gui_State, varargin{:});

Error in
matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)EyeDistance('cropFace_Callback',hObject,eventdata,guidata(hObject)) 
Error while evaluating UIControl Callback

[CS Researcher]

You need to pass I to DetectFaceandEyes function. The function does not know what I is.