Necesito una lente bifocal.

In Spanish, the subject pronoun is often omitted because the verb ending already shows who the subject is.

• Necesito = I need
• The -o ending tells you it is yo.

So Necesito una lente bifocal is the normal, natural way to say it.

You can say Yo necesito una lente bifocal if you want extra emphasis, contrast, or clarity, for example:

• Yo necesito una lente bifocal, pero él no.
  I need a bifocal lens, but he doesn’t.

In this sentence, lente is treated as a feminine noun, so it takes una.

• una lente bifocal

This is something you should mostly learn as a set phrase. Noun gender in Spanish does not always match any logic from English.

Also, usage can vary by region. In Spain, learners will often hear other more common words depending on what is meant:

• gafas = glasses
• lentilla = contact lens

So una lente is grammatically understandable, but the most natural choice in real life may depend on the situation.

Necesito is the first-person singular present tense of the verb necesitar.

• necesitar = to need
• necesito = I need

A few related forms:

• necesitas = you need
• necesita = he/she/you need
• necesitamos = we need

So the sentence structure is simply:

• Necesito = verb
• una lente bifocal = direct object

In Spanish, adjectives usually come after the noun.

So:

• una lente bifocal
• literally: a lens bifocal

That is the normal word order.

English often puts adjectives before nouns, but Spanish usually places them after:

• una casa grande = a big house
• un coche rojo = a red car
• una lente bifocal = a bifocal lens

Because many Spanish adjectives do not change for gender.

Bifocal is one of those adjectives. It stays the same in the singular:

• una lente bifocal
• un cristal bifocal

But it does change in the plural:

• lentes bifocales

So the pattern is:

• singular: bifocal
• plural: bifocales

The plural would be:

• Necesito unas lentes bifocales.

Changes:

• una → unas
• lente → lentes
• bifocal → bifocales

In Spain, if you mean bifocal glasses as a pair, a more natural phrase may often be:

• Necesito unas gafas bifocales.

That is often more idiomatic than talking about a single lente, unless you really mean one lens.

Yes, with a singular countable noun like lente, the article is normally needed.

So:

• Necesito una lente bifocal. ✅

Without the article:

• Necesito lente bifocal. ❌

That sounds incomplete or unnatural in standard Spanish.

In the plural, however, Spanish sometimes allows article omission more easily depending on context:

• Necesito lentes bifocales. ✅
• Necesito unas lentes bifocales. ✅

Both can work, though the version with unas feels more specific.

Because necesitar takes a direct object in Spanish. It does not normally need a preposition like de or a here.

So you say:

• Necesito una lente bifocal.

Not:

• Necesito de una lente bifocal. ❌

This is similar to English I need something.

More examples:

• Necesito ayuda. = I need help.
• Necesitamos dinero. = We need money.

It depends on what you mean.

In Spain:

• gafas is the usual word for glasses
• lentilla is commonly used for a contact lens
• lente usually refers to a lens as an object

So if you mean:

• one lens: una lente bifocal can make sense
• a pair of bifocal glasses: unas gafas bifocales is often more natural
• a bifocal contact lens: you might hear una lentilla bifocal

So the sentence is grammatically fine, but the most natural vocabulary depends on the exact situation.

A simple pronunciation guide is:

• Necesito → neh-theh-SEE-toh
• una → OO-nah
• lente → LEN-teh
• bifocal → bee-foh-KAL

In much of Spain, the c before e in necesito is pronounced like the th in think:

• ne-the-si-to

In many other Spanish-speaking places, it sounds like an s:

• ne-se-si-to

Both are valid Spanish pronunciations, but for Spain Spanish, the th sound is very common.

Yes, but the meaning changes.

• Necesito una lente bifocal. = I need a bifocal lens.
• Quiero una lente bifocal. = I want a bifocal lens.

Necesito expresses necessity.
Quiero expresses desire or preference.

So if the idea is that it is medically or practically necessary, necesito is the better choice.