US Dog Tag Covers

[uscob]

Can anybody help me with the meanings of the Inscriptions on these Dog Tag Covers:

PD
Temple
DBL E/S
Contact Lens no need as clear
RX Date
R maybe right
L maybe left
Add
Seg Ht

[bodes]

It's obviously information to aid any corpsman/medical personal, with a soldier who may be incapable of discussing his medical care requirements....

[Steve B.]

That was to record the information required for prescription eyeglasses.

[uscob]

Thanks so far.
What does the single lines mean exactly?