Intracorneal ring segments - vision correction for people with keratoconus or irregular corneas
What are intracorneal ring segments?
Intracorneal ring segments are small corneal implants that are used to reshape the cornea and improve vision. The ring segments are made out of polymethyl methacrylate (PMMA) - a high-tech, rigid, acrylic material that is designed to last a lifetime and can safely be implanted in the body without stimulating inflammation or rejection. PMMA has been used for implants within the eye for many decades and has a long track record as a safe and well-tolerated material that does not stimulate inflammation or rejection.
An asymmetric corneal ring segment one week after implantation
Intracorneal ring segments are transparent and very thin. They measure only a fraction of a millimeter in thickness and are difficult to see with the naked eye once implanted.
Ring segment implants come in a large number of shapes and sizes and are custom fitted to match the precise shape of your cornea. There are several different types of ring segments available including Kerarings, Ferrara rings, Intacs, and others. All types of intracorneal ring segments work in a similar way to modify the shape of the cornea. Despite the small size, corneal ring segment implants can dramatically improve the shape of the cornea and typically result in significant improvements in vision.
Who can benefit from surgery with intracorneal ring segments?
Corneal ring segments are commonly used to correct irregular corneal shape and improve vision. Insertion of intracorneal ring segments may be used to improve the vision in a range of conditions including:
Keratoconus
Contact lens intolerance
Pellucid marginal degeneration
Corneal transplants with significant residual or irregular astigmatism
Previous corneal trauma or scarring that is associated with significant astigmatism
Irregular astigmatism associated with previous radial keratotomy.
Post LASIK corneal ectasia
Poor vision due to irregular astigmatism that cannot be corrected with glasses
People of all ages can have corneal ring segment implantation. Insertion of ring segments is a permanent but reversible procedure. It is also possible to adjust the ring segment position and replace or remove the implants if required in the future.
The most common reason for corneal ring segment surgery is for visual rehabilitation in patients with keratoconus.
How do intracorneal ring segments improve vision?
A normal cornea is approximately half a millimeter thick and has a very regular shape. The cornea is the most important structure in the eye that focuses light to enable clear vision. The cornea alone provides two-thirds of the focusing power of the eye. Clear focus and good vision require a symmetrical cornea.
In certain eye conditions, an irregularly shaped cornea can be the cause of significant visual impairment. Insertion of intracorneal ring segments in these conditions can be used to flatten abnormally steep regions of the cornea to improve the overall corneal shape. Improving irregular astigmatism with intracorneal ring segments will typically improve vision and/or enable correction with glasses.
Corneal ring implants are very thin. They typically measure just 0.1mm to 0.3mm thick
During surgery after numbing the eye, a very small corneal incision is created that is approximately 80% depth of the cornea. This step is usually completed with a diamond knife or a laser to ensure the correct depth for intracorneal ring implantation. A thin corneal tunnel is then created to accommodate the ring implant. The implant is then carefully moved into position within the tunnel. The ring is precisely aligned to improve the shape of the cornea. In some cases, two rings or an asymmetric ring may be required.
What can I expect during surgery?
Insertion of intracorneal ring implants is typically completed under a local anaesthetic while you are awake. The procedure is not painful and the cornea is completely numb during the surgery. Mild irritation or a gritty sensation later that day when the anaesthetic wears off is common. During the surgery, you will see a bright light and feel some movement. The operation is not painful and most people are pleasantly surprised with how easy it is. In some cases, a longer-acting anaesthetic can be used if required and the eye can be covered with a patch overnight.
It is not unusual to have some mild irritation over the first few days and you may be a little sensitive to bright lights. Some people can find that simple sunglasses are helpful in the first few days after surgery.
What outcomes can I expect after surgery?
Around 80% of people will notice a good improvement in vision following intracorneal ring implantation surgery. Up to 20% of people may find their vision has not improved significantly. A small fraction of people may find the vision is worse. If the vision fails to improve it may be necessary to adjust the position of the corneal implant, add a second implant or replace the implant. If there is a problem or the vision fails to improve, it is possible to remove the implant if required.
Although most people will notice a significant improvement in vision following implantation of an intracorneal ring implant, often some additional refractive correction is required to optimise the vision. It is not uncommon to require some fine-tuning with glasses, a contact lens, or further surgery with an ICL to achieve the best possible vision. Further refractive correction is more likely to be required in cases where the preoperative status of the cornea is very irregular or the vision is very poor. In severe cases, it may not be possible to fully correct the vision and/or a corneal transplant may be required. Insertion of intracorneal ring segments does not prevent corneal transplantation in the future if required.
It is possible to remove an intracorneal ring implant if there are any problems or the results are not as expected. In this case, the cornea will typically revert back to the preoperative shape and the vision is likely to revert to how it was before surgery.
What are the risks of surgery?
Corneal ring implantation is a safe procedure with a long track record of good results. It is uncommon to see poor results or complications resulting from surgery. The specific risks and benefits of corneal ring implantation relating to the correction of your vision will be discussed at your appointment.
Can you see the ring implants?
Intracorneal ring segments are made out of transparent PMMA and are typically very difficult to see with the naked eye in normal lighting conditions.
The corneal implants are made out of PMMA - a tough, transparent acrylic material
The transparent intracorneal ring implant is only visible at high magnification in certain lighting conditions. Here you can see it casting a shadow onto the brown iris.
In most situations the ring implants are not easily visible to the naked eye
This is the same cornea as pictured above under normal room lighting. It is very difficult to see the implant even with a magnified view.
Visibility can vary with different eye colours and in different lighting conditions. In some lighting conditions, it may be possible to see the implanted ring segment if you look very carefully. The ring implants can be viewed in the clinic using a microscope to ensure they are correctly positioned.
How long is the recovery and what can I expect during this time?
You will notice a big change in your vision immediately after surgery. It can take a few days for the vision to settle. It takes three months for the cornea shape to fully adjust after surgery.
After your surgery you will be given some eyedrops to help prevent infection and speed your recovery. Postoperative clinic visits will be arranged to track your progress and ensure a trouble free recovery.
How long does the surgery last?
Corneal ring implant surgery is a permanent vision correction procedure that is reversible. The implants are designed to last a lifetime. Although the surgery provides a permanent correction in vision, there are still other things including other eye diseases or changes in corneal shape that may affect vision in the future. Intracorneal ring implant surgery does not protect against other causes of visual impairment and it is important to have regular eye checks to ensure your eyes remain healthy and your vision is stable.
What are the alternatives to corneal ring segments?
There are several other surgical and non-surgical options that may be used in combination with corneal ring segments or as an alternative to improve vision. Simple non-surgical options may include glasses or contact lenses. Surgical options to permanently correct the vision may include ICL surgery, refractive lens exchange or corneal transplantation.
Corneal ring segment surgery is best suited to correct visual impairment that is associated with irregular astigmatism or an abnormal corneal shape. If there is significant corneal scarring or opacity, then a corneal transplant may be required. For very thin corneas, corneal ring segment implantation may not be possible.
How can I find out more?
To see if you would be a good candidate for vision correction with intracorneal corneal ring implants please book an appointment. A full assessment including corneal tomography is usually required.
You can book an appointment online or call Gaynor on ☎ 0800 CATARACT (0800 228 27 228) or (07) 834 6335. If you need an appointment to discuss keratoconus, cross-linking, or vision-correction surgery please get in touch and we will do our best to arrange an appointment within the next 1-2 weeks.
For any other questions please feel free to email info@jamesandeye.co.nz
