Supporting safe laser eye surgery

Dave Walsha, Sales and Marketing Director of Electro Mechanical Systems explores the role of precise laser alignment in the development of corrective eye surgeries.

According to UK Biobank data, around 4% of the UK’s population has had laser vision correction (LVC) since the nation’s first laser eye surgery was carried out in the late 1980s. In the years since, there have been significant improvements in LVC effectiveness, healing times and safety.

Due to its relatively low risk and high success levels, LVC has become one of the most popular elective surgeries, with conservative estimates suggesting over 100,000 Brits undergo the procedure each year.

As well as correcting vision problems such as short-sightedness (myopia), long-sightedness (hyperopia) and astigmatism, laser eye surgery can also be used to treat more serious conditions that can cause blindness. These include diabetic retinopathy and complications after cataract surgery.

The beginnings of LVC

In the three and a half decades since the UK’s first LVC procedure was undertaken, the methods used have greatly evolved. 

Early procedures involved mechanical microkeratomes, which are surgical instruments with an oscillating blade used to create a thick, hinged flap in the cornea during laser eye surgery. The ophthalmologist would then lift the flap and correct the patient’s vision using a laser to reshape the corneal tissue. While safe, the procedure can be uncomfortable for the patient and is prone to complications stemming from the way the cornea is cut. For example, if the flap is too thick, this can cause the cornea to bulge forward, leaving the patient with suboptimal vision.

Mechanical microkeratomes may also suffer from power losses and the jamming of mechanical parts. While these devices have advanced in recent years, microkeratomes are now much less widely used in LVC surgeries than they once were.

With around half of the global population predicted to be myopic by 2050, femtosecond-based laser eye surgery is likely to continue growing and evolving.”

Femto first

Today, the most common LVC method uses a femtosecond laser. Named after its laser pulses that last only a femtosecond (10-15 seconds), the laser technology paved the way for Femto Laser-Assisted in Situ Keratomileusis (LASIK) procedures. Femto LASIK allows for precise and predictable flap creation, with the vision correction then conducted using an excimer laser. The short duration of the laser’s pulses means that creating the flap takes around ten seconds per eye, increasing patient comfort when compared with mechanical microkeratome LVC. Femto LASIK can also improve healing times due to its less invasive nature.

In recent years, small incision lenticule extraction (SMILE) has also emerged as an alternative. Although this procedure is currently only suitable for patients with myopia or astigmatism, it still offers several benefits. For patients with dry eyes, thin corneas or higher levels of myopia who would not be eligible for LASIK surgeries, SMILE offers a viable option since it does not involve the creation of a flap.

Instead, the ophthalmologist uses a femtosecond laser to carve a six-millimetre disc of corneal tissue, which is then removed through a two-to-four-millimetre keyhole incision made by the same laser. The elimination of the potential complications caused by the corneal flap allows patients to resume physical activity more quickly than with Femto LASIK.

Stepper motor support

Be it Femto LASIK or SMILE, none of the modern methods of laser eye correction would be possible without motor-controlled femtosecond laser alignment. When it comes to moving the prisms, filters and mirrors that allow for precisely defined and rapid pulses, stepper motors are the ideal choice.

Stepper motors differ from other motor types, such as servo motors, in that they can operate with high precision even in an open-loop control system. This means that an encoder is not required, simplifying both the electrical and software configuration required for an accurate drive system. Stepper motors have exceptional stopping accuracy and responsiveness, making them well suited to applications that demand high levels of precision, including LVC microsurgeries where optical components need to be positioned and aligned. 

To ensure high motion control performance, there are several things to consider before selecting a stepper motor. In order to function effectively without an encoder, the chosen motor should match the application’s size and rating requirements. You should also think about the application’s required step resolution, power supply and speed profile.

EMS is a leading supplier of FAULHABER Precistep motors, which range from six to 66 millimetres in diameter. Precistep motors can hold their position even when the power supply is turned off, thus avoiding the earlier issue faced by mechanical microkeratome procedures during power loss. Their long service life also means that ophthalmologists needn’t worry about reduced equipment performance or downtime.

With around half of the global population predicted to be myopic by 2050, femtosecond-based laser eye surgery is likely to continue growing and evolving. Precise motion control is essential not only to improve the effectiveness of the procedures, but also to ensure their safety.