Contact Lens Exam vs. Eye Exam: Why You Need Both

Patients ask this constantly: I just had an eye exam. Why do I need another appointment for contacts?

It is a fair question with a straightforward answer. A glasses prescription describes how light needs to bend before it reaches your eye. A contact lens prescription describes an object that sits directly on your cornea, all day, against living tissue that needs oxygen. Those are different problems.

What a glasses exam gives you

A comprehensive eye exam measures your visual acuity, determines your refractive error, checks eye pressure, and evaluates the health of the front and back of your eye. It produces a spectacle prescription: sphere, cylinder, axis, and — if needed — an add power for reading.

That prescription is measured at a lens sitting roughly 12 millimeters in front of your eye.

What a contact lens exam adds

Move that lens to zero millimeters and several things change.

The power changes. For stronger prescriptions, the effective power required at the corneal surface differs from the power required at spectacle distance. This is not a rounding error.

The shape of your cornea matters. Contact lenses have to match corneal curvature. Too flat and the lens slides. Too steep and it suctions down, restricting tear exchange. Corneal measurements — keratometry, and sometimes full topographic mapping — determine base curve and diameter.

Your tear film matters. A lens divides the tear film. If yours is already unstable, a lens that works perfectly on paper will feel unbearable by 4 p.m. Tear quality is assessed before a material is chosen.

Oxygen matters. Different lens materials transmit oxygen at very different rates. Corneas do not have blood vessels; they get oxygen directly from air through the tear film. The wrong material worn too long causes corneal swelling and, over years, new blood vessel growth into the cornea.

The fit has to be observed. A trial lens goes on the eye and the doctor watches how it centers, how it moves with each blink, and how it settles. This cannot be predicted from numbers.

The follow-up nobody schedules

A contact lens fitting is not complete on day one. You wear the trial lenses, live in them, and return so the doctor can look at the cornea after it has been under a lens. Small problems — mild swelling, surface dryness, a lens that rides high — are visible and correctable at that stage, and invisible to you until they are not.

Specialty fits

Not every eye takes a standard lens. Eyepic’s optometrists fit:

• Toric lenses for astigmatism, which must resist rotating on the eye
• Multifocal lenses for presbyopia
• Lenses for irregular corneas, including post-surgical and keratoconic eyes
• Daily disposables, which solve most compliance and hygiene problems at once

Wearing lenses safely

The most common complications are entirely preventable.

Never sleep in lenses unless the lens is specifically approved for it and your doctor has cleared you. Never rinse lenses or a case with tap water — Acanthamoeba, a rare but devastating corneal infection, lives in it. Replace the case every three months. Replace lenses on schedule, not when they feel worn out; the schedule is based on deposit accumulation, not comfort. Do not top off old solution.

And if an eye becomes red and painful, remove the lens and call your doctor the same day. A corneal ulcer moves fast.

Book a contact lens exam

Eyepic Eye Care fits contact lenses at all four practices, with opticians and optometrists working together:

• Park Slope Eye Care — 334 9th St, Brooklyn · (718) 504-8660
• Graham Eye Care — 102 Graham Ave, Brooklyn · (718) 690-2177
• Flatbush Eye Care — 1054 Flatbush Ave, Brooklyn · (718) 223-5707
• Harlem Eye Care — 2249 2nd Ave, New York · (212) 201-1201

Mention contact lenses when you book so enough time is reserved. Or call 1-877-239-3742.

Frequently asked questions

Can I do both exams in one visit? Usually yes, if you tell us in advance. It takes longer than a glasses exam alone.

Can I use my glasses prescription to buy contacts online? No. They are different prescriptions, and a contact lens prescription legally requires a fitting.

How often do I need a contact lens exam? Annually. Contact lens prescriptions expire sooner than glasses prescriptions.

My contacts feel fine. Do I still need a check-up? Yes. Most early corneal changes cause no symptoms at all.