Actually we cannot see far (other galaxies, early galaxies, quasars) in some parts of the sky because we are in our own galaxy plane [1], so stars, but mostly gas and dust between them obscure significant portion of our field of view [2]. So it is not flat 90 degrees, but roughly two cones with 90 degrees openings in Milky way's plane perpendicular directions.

1. https://scitechdaily.com/gaia-spacecraft-discovers-parts-of-...

2. https://www.darkenergysurvey.org/supporting-science/large-sc...