Reading view is a cool new feature Microsoft released as part of Internet Explorer 11 in Windows 8.1. Reading view allows you to focus on the main content of the Web page you want to read, without the distractions of related (or unrelated) content surrounding the story. When you visit a compatible web page, IE will show a Reading View icon at the bottom next to the URL, just tap it to enjoy reading the web page in Reading view mode. While other browsers like Safari too provide this same feature, Microsoft detailed their effort to create this experience. One of the highlight is that, Microsoft created a whole new font called Sitka.
IE 11 reading view takes advantage of a brand new font for Windows 8.1, called Sitka. It was developed for Microsoft by Mathew Carter, in collaboration with the Advanced Reading Technologies team that previously developed Clear Type text rendering to work well for online reading as well as in print.
One of the advantages of the Sitka font comes from the optical scaling addressed by its different weights. Research has shown that different letter spacing, stroke sizes, and x-height can have a positive effect on the readability of different sizes of text. An optical family contains styles specifically optimized for each size and use case – rather than trying to be one-size-fits-all, like many of the typefaces common on the Web. Thus, you can get terrific legibility in text, and style in display sizes, all with the same family. Reading view for example uses Sitka Small, which is designed with thinner strokes, larger x-height, and looser letter spacing, for image captions, and Sitka Banner, designed with thicker strokes and tighter letter spacing, for the article titles.
In this picture we show three of the optical weights of Sitka at the 2.0em size. From this you can see how the tighter letter spacing and thinner widths employed in Sitka Heading are a better reading choice for text at this size.
In this picture again we show the same three optical weights of Sitka this time at the 0.8em size. It is easy to see how the greater x-height, and looser letter spacing employed in Sitka Small is substantially better for reading the text at this size.
Sitka was also the first typeface family designed with scientific legibility studies integrated directly into the design process. Most fonts do not undergo legibility studies. Those few that do are studied after the font is nearly done. Sitka, however, was repeatedly tested throughout the design process.
Additionally reading view uses a larger than average size font because research has shown that reading speed increases at larger sizes (up to a plateau at very, very large sizes).
Read about it in detail from the link below.
Source: Internet Explorer blog
Note: Both Microsoft-news.com and WMPoweruser supports this Reading View feature in IE11.