Prescription and presbyopia

What does “prescription” mean?

To see clearly, light must come to a focus exactly on the retina. If the shape of the eye or cornea makes it focus in front or behind, that is called a refractive error.

• Short sight (myopia): distant things look blurry.
• Long sight (hyperopia): near things look blurry.
• Astigmatism: both near and far things can look blurred or distorted.
• Presbyopia: close-up vision gets harder in middle age.

Blurred sight is the most common symptom. Headaches, eye strain, squinting and trouble focusing when reading also happen. Some people have no symptoms, so regular exams matter.

Presbyopia

In youth the lens is soft and can change shape for near and far, which is what you see at the top of this site’s home page. From about forty it stiffens and changes shape less easily. Presbyopia is a normal part of ageing and cannot be stopped.

Ways to correct it:

• Reading glasses, with a strength set by an exam
• Bifocal or progressive glasses if you already wear glasses
• Multifocal contact lenses, or monovision, with one eye set for distance and the other for near
• Prescription drops that narrow the pupil for a few hours
• Surgery, for those the doctor considers suitable

Glasses, lenses or surgery?

Glasses are the simplest and safest option. Contact lenses are prescribed by an eye doctor, who also teaches safe use and cleaning. Surgery changes the shape of the cornea, and the decision is one to make with your doctor.

Who is LASIK suitable for?

You usually need:

• A prescription that has changed little over the past year
• A healthy cornea of sufficient thickness
• Good general eye health
• Realistic expectations

These usually rule it out:

• Keratoconus, a thin cornea or a corneal scar
• Severe dry eye
• An unstable or very high prescription
• A cataract that affects vision
• Advanced glaucoma
• Poorly controlled diabetes

What not to expect

People who expect perfect vision without glasses may be disappointed. Dryness, fluctuating vision, halos, glare and weaker night vision are common and usually temporary. Infection and serious loss of vision are rare, but they happen. Sometimes the correction is incomplete and glasses or further surgery are needed.

If you are happy with glasses or contact lenses, you do not need surgery. If you do have it, keep the record of your eye measurements from before and after, because it helps with any cataract surgery later.