LCD Dot Matrix Failure Modes

If the LCD is still fully readable, i.e., if all of the segments are still functioning, then it may just not be getting enough power. If it's powered by batteries, replace them. This sounds most likely to me. The LCD cell is not getting enough power from the drive electronics to fully switch from clear to opaque at normal angles. It only partially switches, allowing the LCD to be readable from a high angle but not straight on.

If it uses an inverter, the inverter may be failing. Or it could be the grounding (earthing) has failed.

If the LCD segments look really 'shiny', like metallic compared to the area immediately surrounding each segment, then the LCD may be 'dc plating' internally. This happens when the drive electronics fail leaving a net dc bias voltage across the LCD cell. Then the internal metal oxide begins to plate onto the glass. The LCD won't last long if this is happening.

But like I said, I'd try replacing the batteries first, if it uses batteries.

The OP said LCD, not CRT!

There is commonly a polarizing film somewhere in the LCD assembly (or possibly two at right angles). It could be that a film has been knocked off. Viewing any flat surface at a 45° angle naturally polarizes the light, thereby making visible the difference between correctly and incorrectly polarized light.

To check this possibility, view the display through one of the lenses of a pair of polarized sunglasses, and rotate the glasses through 90°.