Me dolían tanto los ojos que apenas podía parpadear.

Because doler works like gustar: the thing that causes the pain is the grammatical subject, and the person who feels it is shown with an indirect object pronoun.

So in Me dolían tanto los ojos:

• me = to me
• los ojos = the subject
• dolían = were hurting

Literally, it is closer to My eyes were hurting to me, although in natural English we say My eyes hurt.

Mis ojos dolían is understandable, but it does not sound like the normal Spanish way to express this idea.

Because the subject is los ojos, which is plural.

With doler, the verb agrees with the thing that hurts:

• Me dolía la cabeza = My head hurt
• Me dolían los ojos = My eyes hurt

So:

• singular subject → dolía
• plural subject → dolían

With body parts, Spanish usually uses the definite article (el, la, los, las) rather than a possessive adjective like mi or mis, as long as the owner is already clear.

Here, me already tells us whose eyes they are, so los ojos is the normal choice.

This pattern is very common:

• Me duele la espalda
• Se lavó las manos
• Nos duelen los pies

Using mis ojos is possible for emphasis or contrast, but it is not the default.

Me is an indirect object pronoun meaning to me.

In this sentence, it marks the person affected by the pain. So:

• Me dolían los ojos = My eyes were hurting / My eyes hurt

Spanish often uses this structure where English uses a possessive:

• Me duele la cabeza = My head hurts
• Te duelen las piernas = Your legs hurt
• Le duele el brazo = His/Her arm hurts

So me does not mean my; it means to me.

The imperfect is used because the sentence describes an ongoing situation in the past, not a single completed event.

• dolían suggests the eye pain was continuing
• podía suggests your ability was limited during that period

So the sentence paints a background state: the eyes were hurting so much that blinking was barely possible.

If you changed it to the preterite, it would sound more like a completed event or a specific moment:

• Me dolieron tanto los ojos que apenas pude parpadear

That version is also possible, but it feels more like a single episode viewed as finished. The original imperfect version focuses more on the ongoing experience.

Because tanto here is acting as an adverb, not as an adjective.

It modifies the idea of dolían—in other words, how much they hurt—so it stays in the invariable adverb form tanto.

The pattern is:

• tan/tanto ... que = so ... that

Here:

• Me dolían tanto los ojos que... = My eyes hurt so much that...

If tanto were directly describing a plural noun, then it would agree:

• tenía tantos problemas = he had so many problems

But in your sentence, it is not describing ojos directly.

It means so much / so ... that and introduces a result.

In this sentence:

• Me dolían tanto los ojos que apenas podía parpadear
• My eyes hurt so much that I could barely blink

The first part gives the intensity, and the que clause gives the consequence.

Very common similar patterns are:

• Estaba tan cansado que se durmió = He was so tired that he fell asleep
• Llovía tanto que no salimos = It was raining so much that we didn’t go out

Apenas means hardly, barely, or scarcely.

So:

• apenas podía parpadear = I could barely blink

It expresses that something was almost impossible or happened only to a very small degree.

You will often see it with this meaning in Spanish:

• Apenas podía hablar = I could barely speak
• Apenas dormí = I hardly slept

Because poder is followed by an infinitive when it means can / be able to.

So:

• podía parpadear = could blink / was able to blink

This is a standard verb pattern in Spanish:

• puedo ir = I can go
• podía ver = I could see
• no pudo abrirlo = he/she couldn’t open it

Only poder is conjugated here; parpadear stays in the infinitive.

Yes, Spanish word order is flexible, and that version is possible.

The original Me dolían tanto los ojos... sounds very natural and often puts the affected person and the experience first. If you say Los ojos me dolían tanto..., the focus shifts a little more toward the eyes.

Both are grammatically fine, but the original order is especially natural in everyday Spanish.

Yes, but it would not mean exactly the same thing in structure.

• Me dolían mucho los ojos = My eyes hurt a lot
• Me dolían tanto los ojos que... = My eyes hurt so much that...

So mucho simply states a high degree, while tanto ... que sets up a result: so much that...

If you want the second part que apenas podía parpadear, then tanto is the natural choice.

Yes. That sentence is correct too, but it gives a slightly different viewpoint.

• Me dolían ... podía ... → ongoing, descriptive, background feeling
• Me dolieron ... pude ... → more like a completed episode, seen as a whole

So the imperfect version feels more like describing what the experience was like, while the preterite version feels more like reporting what happened in a specific instance.