Refractive error is a common condition which affects many people across the UK and around the world. Estimates from the World Health Organisation indicate that 153 million people over the age of five have some form of visual impairment due to uncorrected refractive errors – however, this does not have to be the case. Refractive errors are easily diagnosed, and they can be treated. Mr Alexander Ionides, consultant ophthalmologist from the world-leading Moorfields Eye Hospital, explains more about refractive error, and how it can be corrected.
What is refractive error?
Refractive error is actually the general term for a group of conditions which affect the way that light hits the retina, a layer of tissue found at the back of the eye. In those with refractive error, light hitting the retina is unfocused, which means vision is affected. Common types of refractive error include hypermetropia (otherwise known as being long-sighted), astigmatism, and myopia (being short-sighted).
In hypermetropia, individuals focus better on objects which are further away rather than near, while individuals with myopia have difficulty focusing on distant objects. In astigmatism, light focuses in more than one place in the eye, which can cause individuals to strain, experience headaches, or have blurred vision. Astigmatism can occur at the same time as long or short-sightedness.
What are the symptoms of refractive error?
Symptoms vary depending on the type of refractive error. In those with myopia, objects which are far away may appear as blurs, and vision may be blurry when attempting to focus on something distant.
In hypermetropia, headaches and eye strain are common symptoms experienced when trying to focus on something near, especially for longer periods of time (e.g reading, or studying).
Astigmatism may also cause blurred vision, eye strain, and headaches.
In young children, these symptoms may not be picked up, as the child does not think anything is wrong and they do not realise they have any vision problems. Regular screening is important for children under six years old. Screening should continue past this age, and adults should have their eyes checked every once in a while as refractive errors can develop later on in life.
How is refractive error corrected?
Refractive error is typically corrected by glasses or contact lenses. These help to create clearer vision and both are generally safe, effective options. Nowadays, however, many people seek to have their refractive error corrected permanently, through surgery.
Refractive surgery changes the shape of the cornea permanently, allowing light rays to focus more precisely on the retina. There are many types of refractive surgery available to patients nowadays. LASIK is currently the most popular corrective surgery available.
In patients with severe myopia, however, phakic intraocular lens surgery is sometimes indicated.
What is phakic intraocular lens surgery?
Phakic intraocular lens surgery, sometimes called phakic IOL, implants a type of lens directly into the eye in order to correct myopia. The eye’s natural lens itself is not altered in any way. The procedure implants a clear lens either behind the iris, or between the cornea and the iris, enabling light to focus properly on the retina. Phakic IOLs are often indicated in those who have moderate to severe myopia, where it is clear LASIK or other procedures will likely not correct their refractive error. Not everyone is suitable for LASIK or laser eye surgery.
Phakic IOLs are not like contact lenses in that once they are implanted, the patient cannot feel them in the eye. They work from inside the eye rather than being placed on the surface, providing a permanent correction of myopia.
Who is a candidate for phakic intraocular lens surgery?
Patients with a high level of myopia are generally considered to be candidates for phakic IOLs. The procedure is performed on adults rather than children. Candidates for phakic IOLs do not present with any eye disease or systemic condition, and should not have any additional ocular pathology to correct.
Are there any risks to consider?
There is no surgical procedure which does not carry risks, but the implantation of phakic IOLs is generally considered to be safe. It is, however, important to understand the risks before the procedure is performed, so you can decide if it is right for you. Your ophthalmologist will discuss the benefits and risks before you make the choice to undergo surgery.
Phakic IOL surgery may cause a loss in vision which cannot be corrected through wearing glasses or further surgery. Other vision problems which can occur include double vision, halos, or glares. Patients may also find that their vision is not 100% corrected (undercorrection).
Other risks include the development of a cataract, a cloudy cornea, retinal detachment, or increased intraocular pressure. This pressure may be treated with medication or further surgery. However, the risks of complications like this are minimal. Speak to your surgeon if you are concerned about any of the risks the procedure carries.
How successful is phakic intraocular lens surgery?
Phakic IOLs are a highly successful method of treatment for those with refractive errors such as myopia. Your ophthalmologist will arrange to see you for follow-up visits, as a permanent implant in the eye should be monitored correctly. Eye examinations are recommended at least once a year, but after surgery you will be monitored more closely and follow-up visits will be arranged to make sure everything is going as well as expected.