Die kornea fokus die sonlig op die retina.

In Afrikaans, die is the definite article and usually means the.

So in:

• die kornea = the cornea
• die sonlig = the sunlight
• die retina = the retina

A helpful point for English speakers: Afrikaans does not change the for gender or number. It is very often just die.

Afrikaans verbs are much simpler than English verbs in this respect. The verb usually does not change form depending on the subject.

So:

• Ek fokus = I focus
• Jy fokus = you focus
• Die kornea fokus = the cornea focuses

Unlike English, Afrikaans does not add -s for he/she/it in the present tense.

Yes, in this simple main clause it is very similar to English:

• Die kornea = subject
• fokus = verb
• die sonlig = object
• op die retina = prepositional phrase

So the structure is basically:

Subject + Verb + Object + Prepositional phrase

That makes this sentence quite straightforward for an English speaker.

Op usually means on or onto, but in this context it is best understood as on(to) or onto in the sense of directing light toward a surface.

So:

• op die retina = onto the retina / on the retina

With verbs like fokus, Afrikaans often uses op just like English uses on in focus on or focus onto.

Sonlig is a compound noun:

• son = sun
• lig = light

Together, sonlig means sunlight.

Afrikaans, like Dutch and German, often forms compound nouns as one word. So an English speaker should get used to seeing ideas packed into a single noun like this.

It is basically a scientific/medical word, and it is very close to English cornea. Many anatomical terms in Afrikaans look familiar to English speakers.

Here:

• kornea = cornea
• retina = retina

So this sentence is quite easy vocabulary-wise if you already know the science terms in English.

A rough English-friendly guide would be:

• kornea ≈ kor-NAY-ah
• retina ≈ reh-TEE-na or reh-TEE-nah

And the whole sentence roughly:

Die kornea fokus die sonlig op die retina
≈ dee kor-NAY-ah FOH-kus dee SON-likh op dee reh-TEE-na

A few notes:

• die is usually pronounced like dee
• fokus has a clear k sound, not an English s/z ending
• g in lig is often a throaty Afrikaans sound, which English speakers may find difficult at first

Because this sentence is a normal present-tense statement with a lexical verb:

• fokus = focuses

Afrikaans does not need an extra helper verb here. It simply says:

Die kornea fokus die sonlig op die retina.

Literally, that is very close to:

The cornea focuses the sunlight onto the retina.

You probably could in a very literal or unusual way, but sonlig is the natural standard word for sunlight.

Afrikaans often prefers a compound noun where English also has a single established word. So sonlig is the best choice here.

It is the normal way to talk about a body part in a factual/scientific statement. Afrikaans often uses the definite article where English also uses the in general anatomical descriptions.

So die retina does not necessarily mean one specially identified retina in conversation. It can simply refer to the retina as the anatomical structure.

Yes. Even though the nouns are singular, the sentence can express a general truth:

Die kornea fokus die sonlig op die retina.

This works like an English textbook statement such as:

The cornea focuses sunlight on the retina.

So singular forms with die can still describe how something generally works in science or anatomy.