Why did Frodo go temporarily blind in The Two Towers?

[Carantalath]

In the Two Towers, in the chapter The Taming of Smeagol, one of the nazgul is heard while Frodo's climbing down the cliff. He lets go of the cliff and falls onto a ledge and yells to Sam saying that he can't see. Why couldn't he see? Was it because of hearing the nazgul scream? And why did he get his sight back after seeing the rope? I'm very confused.

 

[Celebthôl]

it may have been due to him bumping his head, and this caused hi to tempererily go blind, also it may have been really dark there.

Thôl

 

[Anamatar IV]

I think it was because it was very dark there and he was able to see the elven rope because since it was elven it gave off a sort of light or shine in darkness.

 

[Ithrynluin]

'Climb back, I suppose,' said Frodo.
'Easy said,' objected Sam. 'Better wait till morning and more light.'
`No! Not if I can help it,' said Frodo with a sudden strange vehemence.
`I grudge every hour, every minute. I'm going down to try it out. Don't
you follow till I come back or call!'

'All right, all right! I'm here. But I can't see.'
Frodo was calling with a weak voice. ,He was not actually very far
away. He had slid and not fallen, and had come up with a jolt to his
feet on a wider ledge not many yards lower down. Fortunately the
rock-face at this point leaned well back and the wind had pressed him
against the cliff, so that he had not toppled over. He steadied himself a
little, laying his face against the cold stone, feeling his heart pounding.
But either the darkness had grown complete, or else his eyes had lost their sight. All was black about him. He wondered if he had been
struck blind. He took a deep breath.

Quickly Sam unslung his pack and rummaged in it. There indeed at the bottom was a coil of the silken-grey rope made by the folk of
Lórien. He cast an end to his master. The darkness seemed to lift from
Frodo's eyes, or else his sight was returning. He could see the grey line as it came dangling down, and he thought it had a faint silver sheen.Now that he had some point in the darkness to fix his eyes on, he felt less giddy. Leaning his weight forward, he made the end fast round his waist, and then he grasped the line with both hands.

It seemed to Frodo as if he had gone blind, because the darkness was so complete.
The rope obviously has a glow of its own...some strange elvish properties that we humans call magic.

 

[Carantalath]

But doesn't it also say that Sam could see Frodo below him? If it was a complete darkness, wouldn't Frodo be hidden from Sam's view?

 

[Ithrynluin]

It was complete darkness from Frodo's point of view. Sam was higher up and things were probably more visible from up there.

 

[kohaku]

I doubt it would have been darker on the side of the cliff than at the top, certainly not to the point that Frodo would be completely unable to see. I think it is something he experienced alone that was not caused by extra darkness around him. It may have been some combination of fear from the nazgul and the fall, and from the blinding flash of lightning. A psychological blindness, you might say, and the magic of the elven rope brought him out of it.

 

[Mablung]

I think I read somewhere the rope was made with some ithildin though I can't find a quote to back that up does anyone remember something similar?

 

[Carantalath]

Sorry, I don't know what the rope was made of.

Could the blindness be because of being stabbed by the nazgul at Weathertop? In Moria, it is said that Frodo's hearing and sight were increased in the dark. Maybe because he was stabbed by the nazgul and almost turned into one, he just had a memory of the darkness then.

Maybe Frodo could see the rope because it was made by the elves, who were associated with light and healing, it cleared his head and he could see again.

Is this probable?