(The information below is based on OS X El Capitan. For additional updated information, go to Low Vision Accessibility Settings for MacBooks (February 2019).
There are many accessibility options built-in to Apple Computers. Many of these options can be selected by going to the Apple Menu (Apple symbol in the top left corner of the screen) > System Preferences > Accessibility then selecting the accessibility category: Display, Zoom, VoiceOver, Descriptions, Captions, Audio, Keyboard, Mouse and Trackpad, Switch Control and Dictation.
When Dock Magnification is on, the cursor moves over the dock symbols, the symbol with the focus becomes larger. You can also adjust the length and size of the dock by changing the Size slider. Apple Menu > System Preferences > Dock, then select Magnification and move slider to the desired level of magnification.
Reducing the transparency changes the bright white transparent areas of the desktop and app windows to gray. Apple Menu > System Preferences > Accessibility > Display, then select Reduce Transparency.
Change the desktop background picture that is less busy or fewer colors. Apple Menu > System Preferences > Desktop & Screen Saver > Desktop, then browse through the picture folders and select the desired picture.
This will reduce the transparency and will also make borders darker and more visible. Apple Menu > System Preferences > Accessibility > Display, then select Increase Contrast.
This will maintain an increased cursor size. You can also temporarily increase the cursor by quickly moving your finger back and forth on the trackpad or rapidly move the mouse. The pointer will briefly enlarge. To maintain a larger cursor: Apple Menu > System Preferences > Accessibility > Display, then move Cursor Size slider.
When in Icon View (top left option in the Finder window – four tiny squares symbol), move Icon Size slider. Click the Text Size pop-up menu and choose a text size by using the up/down arrows.
When in List View (second option at the top of the Finder window – horizontal lines symbol), select Text Size in the pop-up menu and choose a text size by using the up/down arrows.
When in the Column View (third option at the top of the Finder window – three columns symbol), select Text Size pop-up menu and choose a text size by using the up/down arrows.
To increase items in the Finder and Mail sidebars: Apple Menu > System Preferences > General > Sidebar Icon Size and choose Large.
Apple Menu > System Preferences > Accessibility > Zoom.
Set your preferences (you can select both).
Use keyboard shortcuts to zoom.
Use scroll gesture with modifier keys to zoom.
Choose Zoom Style: Full Screen or Picture-in-Picture (zoom window which can be moved around the screen).
To set options for zoom or zoom window, select More Options. This pop-up window enables you to set the maximum and minimum zoom ranges and how the screen image moves.
To quickly set Zoom options, press Option-Command-F5.
To Zoom In on the screen: Apple Menu > System Preferences > Accessibility > Zoom.
When “use keyboard shortcuts to zoom” is selected, you can zoom by pressing Option-Command-Equal Sign. (Press the three keys simultaneously.) To Zoom Out, press Option-Command-Minus Sign. (Press the three keys simultaneously.) To toggle Zoom, press Option-Command-8.
When “Use scroll gesture with modifier keys to zoom” is selected, you can zoom in by holding down the Control key (or other modifier key) and swiping up with two fingers on your trackpad.
For more Zoom options, go to Zoom Pane of Accessibility
To Zoom In on Safari Webpages: When in Safari > View > Zoom In (or press Command-Plus Sign. Repeat multiple times to continue zooming in.
To Zoom In on just the text and not the images, choose Zoom Text Only.
If you never want to see small text sizes in Safari Webpages: Safari > Preferences > Advanced, select “Never use font sizes small than” then select your font size.
How to Zoom in on Mac (2014)
Zoom Feature on a Mac Using a Mouse: Video
By Diane Brauner