How is the exterior suffering?

The buddha says jivhā, rasā, jivhāviññāṇaṃ, jivhāsamphasso, vedayitaṃ and all the other sensual stuff are afflicted with bad things

The tongue, brethren, is afflicted, savours are afflicted, tongue-conseiousness, is afflicted, tongue-contact, is afflicted, that weal or woe or neutral state experienced, which arises owing to tongue-contact,- that also is afflicted.

Afflicted with what?

Afflicted with birth, decay and death, sorrow and grief, woe, lamentation and despair.

So I declare.

http://obo.genaud.net/dhamma-vinaya/pts/sn/04_salv/sn04.35.029.wood.pts.htm#p1

It is the sensation created by the touch of the object which is suffering regardless of whether it is pleasant, unpleasant or neutral. The whole sphere of sensations is unsatisfactory.

External objects are not suffering until you come in contact and it creates a sensation. Anything physical object you have not experienced is not unsatisfactory to you. You don't know about it and not registered in your mental model of the world. For someone who experiences it, it will be unsatisfactory. To experience an object you need contact: the object, faculty and attention to the faculty.

Your mental model of the world is all that you have experienced. So everything you have experienced is unsatisfactory hence the world at large is unsatisfactory.

Also, the world is the 5 aggregates. Past experiences leave an impression in sanna and what is experienced now is registered through consciousness and recognised though sanna - which essentially builds your mental model of the world. Physical objects which are in your world is what is unsatisfactory to you. Objects in another's world unsatisfactory to them. External objects on their own are not unsatisfactory.

Essentially what is know wold to a being is unsatisfactory. Everything in the known world is unsatisfactory. Anything which is unknow becomes unsatisfactory then it is experienced, until then it is not known hence neither satisfactory nor unsatisfactory. What you crave for is also unsatisfactory as you might not get it.

The faculty (e.g. eye) itself is not suffering. It is the sensation produced which lead to suffering.

If there are an eye and an external object and attention which gives rise to eye consciousness. This results in a sensation due to contact.

This is very well explained in MN 38:

"On seeing a form with the eye, he is infatuated with pleasing forms, and gets upset over unpleasing forms. He dwells with body-mindfulness unestablished, with limited awareness. He doesn't discern, as it has come to be, the awareness-release & discernment-release where those evil, unskillful qualities cease without remainder. Engaged thus in compliance & opposition, he relishes any feeling he feels — pleasure, pain, neither-pleasure-nor-pain — welcomes it, & remains fastened to it. As he relishes that feeling, welcomes it, & remains fastened to it, delight arises. Now, any delight in feeling is clinging/sustenance. From his clinging/sustenance as a requisite condition comes becoming. From becoming as a requisite condition comes birth. From birth as a requisite condition, then aging-&-death, sorrow, lamentation, pain, distress, and despair come into play. Such is the origination of this entire mass of stress & suffering.

"On hearing a sound with the ear...

"On smelling an aroma with the nose...

"On tasting a flavor with the tongue...

"On sensing a tactile sensation with the body...

"On cognizing an idea with the intellect, he is infatuated with pleasing ideas, and gets upset over unpleasing ideas. He dwells with body-mindfulness unestablished, with limited awareness. He doesn't discern, as it has come to be, the awareness-release & discernment-release where those evil, unskillful qualities cease without remainder. Engaged thus in compliance & opposition, he relishes any feeling he feels — pleasure, pain, neither-pleasure-nor-pain — welcomes it, & remains fastened to it. As he relishes that feeling, welcomes it, & remains fastened to it, delight arises. Now, any delight in feeling is clinging/sustenance. From his clinging/sustenance as a requisite condition comes becoming. From becoming as a requisite condition comes birth. From birth as a requisite condition, then aging-&-death, sorrow, lamentation, pain, distress, & despair come into play. Such is the origination of this entire mass of stress & suffering.

The word 'dukkha' here means 'unsatisfactory' or 'cannot bring happiness'. It does not mean 'suffering', as translated by Sri Lankan N.K.G. Mendis, Indian Acharya Buddharakkhita and Thai Bhikkhu Buddhadasa:

"What do you think of this, O monks? Is form permanent or impermanent?"

"Impermanent, O Lord."

"Now, that which is impermanent, is it unsatisfactory or satisfactory?"

"Unsatisfactory, O Lord."

"Now, that which is impermanent, unsatisfactory, subject to change, is it proper to regard that as: 'This is mine, this I am, this is my self'?"

"Indeed, not that, O Lord."

SN 22.59

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277. "All conditioned things are impermanent" — when one sees this with wisdom, one turns away from suffering. This is the path to purification.

278. "All conditioned things are unsatisfactory" — when one sees this with wisdom, one turns away from suffering. This is the path to purification.

279. "All things are not-self" — when one sees this with wisdom, one turns away from suffering. This is the path to purification.

Dhammapada

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"Vipassana" means "seeing clearly," having direct insight into the truth of aniccam (impermanence), dukkham (unsatisfactoriness) and anatta (not self).

Buddhadasa

The Buddha said:

Open are the doors to the Deathless to those with ears.

MN 26

Answer to this query is related to birth-time or the causes&conditions(old action) which results in the the formation of eye. Answer is already in the link you have given

Reference

And what is old action?

The eye is old action. It should be seen as produced by choices and intentions, as something to be felt.

Sutta goes on saying

And what is the cessation of action?

When you experience freedom due to the cessation of deeds by body, speech, and mind.

Furthermore,

And what’s the practice that leads to the cessation of action?

It is simply this noble eightfold path, that is: right view, right thought, right speech, right action, right livelihood, right effort, right mindfulness, and right immersion.

This is called the practice that leads to the cessation of action.

I see that the translation in your link interprets the Pali word dukkha as "suffering". Other translations have it as "painful" or "stressful" or "unsatisfactory". Whatever word we use, the point being made about external phenomena is that they are not going to make us happy. The gorgeous potential romantic or sexual partner, the object my eye rests upon, may inspire in me a pleasurable feeling, but that happiness is not going to last. That happiness is not a support for the freedom from suffering that the Buddha is teaching us about.

Because they are notself, because they are impermanent, they cannot provide lasting happiness, though we tend to think they will. Instead, we'll end up discovering the things we see (hear, touch, smell, taste, think of) will disappoint us. They'll change, or disappear, causing us to suffer.