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Laser eye surgery terminology – do you know your LASIK from your keratectomy from your lenticule?


Laser eye surgery terminology – do you know your LASIK from your keratectomy from your lenticule?

So, you know you want laser eye surgery. You’ve most likely heard of LASIK. But that’s where it probably ends.

As laser eye surgery is a medical procedure, the ophthalmic industry will use terms that the average patient may not understand. So, here is a guide to a few of the terms you may read or hear when you’re considering laser eye surgery.


In surgery, to ablate is to remove (see ASLA).

ASLA (Advanced Surface Laser Ablation) also known as PRK (Photorefractive keratectomy)

Advanced surface laser ablation (also known as photorefractive keratectomy) was the first laser eye surgery option introduced and is still in use today. The procedure involves removing the epithelial layer (the top layer of the cornea). This layer naturally regenerates and will reform after surgery.

Once the layer is removed, the excimer laser is used to reshape the cornea. Correcting short-sightedness (myopia) entails removing tissue in the middle to create a flatter surface. Correcting long-sightedness (hyperopia) requires removing tissue from the corneal edges. Excimer lasers correct astigmatism by reducing corneal irregularity and providing a more even surface in order to provide even light refraction.


A deviation of a spherical curve (the cornea) resulting in distorted images. In classic Greek, the ‘a’ is ‘without’, while the ‘stigmata/stigmat’ refers to a point – so it is literally ‘without point’. Astigmatism is a common refractive error that can be corrected with laser eye surgery.

Epithelial layer

The cornea consists of five layers, and the top layer is called the epithelial layer. Laser eye surgery involves the epithelial layer (the epithelium) and the stromal layer (the stroma).


A dictionary definition of excimer is ‘an unstable excited molecule which is formed by the combination of two smaller molecules and rapidly dissociates with emission of radiation, utilised in some kinds of laser’.

An excimer laser uses gas to produce energy through which the cornea can be permanently reshaped without the need for any heat. No burning occurs.


A femtosecond laser is used in LASIK laser eye surgery to create a flap of tissue which can be lifted and replaced back into it’s original position. The word ‘femtosecond’ relates to the amount of time it takes for a single pulse – a ‘femtosecond’ converts to approximately one quadrillionth of a second.

The purpose of the femtosecond laser is to create the ‘flap’ in LASIK laser eye surgery.


In Greek, ‘hyper’ means ‘beyond’ and ‘ops’ means ‘eye’. Hyperopia refractive error refers to ‘overcorrect/over measure’. You may know hyperopia as long-sightedness or far-sightedness. Laser eye surgery can correct hyperopia.


Refers to the surgical removal of a layer of the cornea.


Keratomileusis refers to the reshaping of the cornea in order to correct a refractive error – ‘kerato’ relating to the cornea, and ‘mileusis’ a reference to the Greek term for ‘carving’. Granted, this is not the most elegant description of laser vision correction.

LASIK – ‘laser in-situ keratomileusis’ (laser eye surgery)

The term LASIK refers to ‘laser-assisted in-situ keratomileusis’. This type of laser eye surgery differs from ASLA (or PRK) in the way a surgeon accesses the cornea. Instead of removing the entire epithelial layer, process requires creating a flap.

With the flap open, a surgeon alters the corneal tissue. With the procedure completed, the flap is closed. As the eye does not have to recreate the entire epithelial layer, recovery time is much faster.


‘Lenticular’ refers to something that is curved on both sides. Lenticule is the term for a ‘disc-shaped piece of corneal tissue’. A precise measurement is created, as determined by the individual’s refractive error – when it is removed, the curvature of the cornea is reshaped and vision is corrected.


In Greek, ‘ops’ refers to ‘eye/look‘, ‘myein’ to ‘shut’. Myopia literally means ‘trying to see like a mole’. You may know ‘myopia’ better as short-sightedness or near-sightedness. Laser eye surgery can correct myopia.


Refractive refers to the measurement of the focusing characteristics of the eye. A refractive error is created when the light focusing through the cornea and lens does not focus clearly on the retina. This can be due to an incorrect eye length, or incorrect power or curvature of the cornea or lens.

SMILE – ‘small incision lenticule extraction’

The term SMILE means small incision lenticule extraction. This form of laser vision correction does not require the surgeon to create a corneal flap. Instead, the procedure entails making a tiny keyhole incision to remove the lenticule created by the femtosecond laser.

The SMILE technique may offer a solution for patients suffering from chronic dry eyes or for individuals diagnosed with having a thin cornea.


The layer of the cornea that sits under the superficial epithelial layer. This is the layer that requires reshaping during laser eye surgery in order to correct vision.

The future?

Really, you don’t need to know these terms – simply know that, since the 1980s, laser eye surgery has helped tens of millions of people enjoy improved vision. Techniques continue evolving, and the type of technique needed to achieve the best results varies from patient to patient.

Find out more about laser eye surgery.

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