Shared care in refractive surgery--Part 1.
The days when vision correction options were restricted to spectacles or contact lenses are long gone. Refractive surgery to correct myopia, hyperopia, astigmatism and presbyopia is widely available and increasing competition between clinics has made this an affordable option for many. Advances in the field of laser and non-laser treatments now mean that refractive surgery may be a viable option for an even greater range of patients.
Optometrists must be the primary healthcare professionals that patients go to for advice when considering their vision correction options. Even if an optometrist does not provide any refractive surgery affiliated services within their practice, patients expect them to be knowledgeable enough about the field to give good advice pertinent to their eyes and their visual correction.
Patients are demanding with their questions too. In this internet age, most patients will have researched the subject beforehand and even watched videos of surgical procedures. Patients are more informed than ever before. However, the internet is not always a reliable source of information and so patients will seek their optometrist's opinion for both verification of the facts and reassurance from a trusted professional.
This series aims to equip the optometrist with the knowledge to provide information about the type of treatments available and whether the patient is potentially suitable. Later articles in this series will look at the normal post operative management and potential complications that may be encountered in the shared care of refractive surgery patients.
TREATMENT OPTIONS Laser refractive surgery
The cornea is the major refractive surface of the eye and laser refractive surgery can correct myopia, hyperopia and astigmatism by permanently reshaping it. There are two options for patients considering this form of correction: laser-assisted in situ keratomileusis (LASIK) and laser-assisted sub-epithelial keratectomy (LASEK). Both involve exposing the stromal tissue and using a computer controlled excimer laser to ablate the cornea according to a pre-calculated plan that is based upon the patient's corneal topography and wavefront aberrations. The manner in which the stroma is exposed differentiates the two procedures.
With LASIK, a flap just below Bowman's membrane is created on the cornea using a microsurgical blade (microkeratome) or with a femtosecond laser. The first method is the traditional way of creating a flap and makes a physical cut across the cornea, allowing the top layer to be lifted and moved aside. The femtosecond laser is now widely used in LASIK flap creation and this has proved popular with patients who find the thought of an 'all-laser' technique less daunting than one which uses a blade. The femtosecond laser is focused to the required depth and the laser energy creates a layer of bubbles, separating the stromal cells at that level. An instrument is then inserted to cleave the cornea at that plane, thus creating a flap.
Once the flap has been lifted and peeled back to expose the stroma, the excimer laser is used to ablate the cornea to its new profile. After treatment, the flap is repositioned and smoothed into place. The epithelium generally remains intact and eventually, surface epithelial cells migrate over the edges of the flap to create a living bond (see Figure 1).
The prescription range treated with LASIK varies from clinic to clinic and can be between +6.00 and -9.00 dioptres (in the highest powered meridian), with a maximum of six dioptres of astigmatism. The hyperopic treatment range is smaller than with myopes as the visual outcome is increasingly variable with high hyperopes. With myopes, the limiting factor is the total amount of tissue removed from the central cornea and the subsequent corneal profile, which may lead to poor visual quality and in cases of excessive corneal thinning, ectasia.
With LASEK, the surface epithelium is weakened using an alcohol preparation such as 20% ethanol and then lifted and moved to one side. Some surgeons use a blunt edged oscillating instrument called an epithelial separator to create a flap; this technique is termed epi-LASIK and aims to reduce the damage to epithelial cells from the alcohol used in LASEK.
After the laser has been employed, the flap is repositioned and a bandage contact lens placed over the top. In most cases and the surface epithelium completely regenerates eventually leaving no trace of a flap behind. Patients undergoing this technique generally feel more discomfort than with LASIK, but less pain than with the older technique of photorefractive keratectomy (PRK) due to a lesser degree of epithelial trauma.
Surface treatments like this carry an increased risk of corneal haze and scarring. This risk can be minimised by only treating low to moderate myopes or with the use of topical steroids postoperatively. For moderate myopes, some surgeons will apply the antimetabolite mitomycin C to the stromal bed intra-operatively to reduce the risk further.
Monovision laser treatments can be considered for presbyopic myopes and low hypermetropes, where the non-dominant eye is deliberately under-corrected. Most patients are able to tolerate up to 1.75 dioptres of anisometropia and so if a patient's reading addition is greater than this they should be counselled carefully on the expectations of modified monovision. Where possible, the patient should try the proposed monovision correction with contact lenses prior to surgery. Blended monovision is another variation offered by some clinics. The use of nonlinear aspheric treatment profiles, which exaggerate the natural prolateness of the cornea, increases depth of field to compensate for up to 1.50 dioptres of reading addition. The dominant eye can then be treated for distance and intermediate vision with the non-dominant eye treated for intermediate and near vision.
Multifocal laser treatments use the principle of ocular aberrometry and aspheric laser ablation profiles to create a correction that is similar to those seen with centre-distance multifocal contact lenses. Introduced around 10 years ago, it has yet to be granted FDA approval and can only be accessed in the US via clinical trials. Although available in the UK, it is not widely marketed. This may be due the possible increased risk in terms of glare, haloes and reduced visual quality when compared to traditional laser treatments. Reversibility is also a consideration should cataract become an issue.
These implants can be offered to presbyopic patients that do not have a distance refractive error without having any significant loss of contrast or visual quality. They can also be used in conjunction with laser refractive procedures. There are a few types of implant available; the Kamra inlay uses the pinhole principle to increase depth of field; the Raindrop (see Figure 2, page 56) uses a method of corneal reshaping; and the Flexivue Microlens creates multifocal vision by using an in-cornea lens.
Astigmatic keratotomy (AK) is a corneal refractive procedure that consists of making fine microscopic arcuate incisions or relaxing incisions with a surgical blade at the limbus (see Figure 3). These cuts are made for the purpose of flattening the steepest part of the cornea in an attempt to obtain a more spherical surface. AK permanently changes the shape and focusing power of the cornea. During the initial healing process, there may be some discomfort, which may last several days. The goal of AK is to improve vision by reducing the astigmatic error only and so it is often used in conjunction with other refractive surgery procedures such as refractive lens exchange. Any residual myopia, hyperopia or astigmatism can still be corrected with either further incisions, or a laser refractive procedure.
Phakic intraocular lenses
With phakic intraocular lenses (pIOL) an additional lens is placed either in front of or directly behind the iris. It is a possible solution for those patients who are limited by either a high refractive error or a thin cornea from having laser surgery and are too young to be considered for refractive lens exchange. The advantage with this treatment is that patients retain their accommodation for near vision tasks. Long term there is a small risk of endothelial cell loss and shallowing of the anterior chamber as the natural lens thickens with age and so annual review with the treating clinic is advised. The pIOL can be removed in the future should the patient develop cataract and need phacoemulsification in their later years.
Refractive lens exchange
Refractive lens exchange (RLE), also known as clear lens exchange, involves phacoemulsification of the crystalline lens and the insertion of an artificial lens implant (see Figure 4) before cataract is present. The procedure is the same as for cataract surgery and is considered to be a good option for patients who are presbyopic or cannot achieve a good level of vision for all distances with laser refractive surgery. Optical biometers such as the Zeiss IOL Master and the Lenstar by Haag Streit have enabled surgeons to calculate the lens implant power required to a high degree of accuracy. Any significant residual prescription that remains can be treated with a laser refractive procedure if necessary.
Multifocal lens implants
For presbyopes, multifocal or accommodating lens implants may help them meet the challenge of near vision tasks. Multifocal implants have improved greatly in recent years with most patients able to achieve a good standard of distance and near vision. The side effects of significant glare or reduced contrast are much less common with improved lens designs and the use of different lens types in the dominant and less dominant eye.
PATIENT SUITABILITY CRITERIA
Patients are usually advised by clinics to have an eye examination before booking for an initial consultation. The following findings during an eye examination are indicative of unsuitability for elective refractive surgery.
History and symptoms
Any symptoms reported by the patient need to be investigated and resolved prior to refractive surgery. For example, if the patient has diplopia or photopsia and floaters, this will need to be investigated and a specialist opinion sought before refractive surgery can proceed.
Absolute general health contraindications
Patients in the following categories are unlikely to be considered suitable for elective refractive surgery (see Table 1):
* Significant autoimmune disease--for example rheumatoid arthritis, systemic lupus erythematosus--there may be an increased risk of inflammatory complications in these cases (1)
* Immune suppression--conditions such as HIV or if the patient is taking immune suppression drugs means that there is an increased risk of infection
* Systemic steroids--patients that have a condition requiring constant steroid use may also be at a higher risk of developing infections.
In addition, patients in the following categories will not be considered for LASIK/LASEK:
* Pregnancy--during pregnancy and lactation the refraction may vary and there is an altered wound healing response. The patient must wait six months after giving birth or cessation of breast-feeding
* Amiodarone--the interaction of the laser with the corneal deposits found with the use of this drug is unknown
* Roaccutane--this drug causes decreased tear production. Patient suitability can be considered if the drug is stopped or substituted with the GP's consent for six months before treatment.
Relative general health contraindications
Patients with the following relative contraindications may not be suitable for treatment, but can still attend for the initial consultation. The clinic may require extra information from the patient's GP before proceeding (see Table 1):
* 5-Hydroxy-tryptamine drugs (for example sumatriptan)--there is an increased risk of vascular occlusion when the intraocular pressure is raised during LASIK treatment. The patient can be considered if they are able to change to an alternative drug with the GP's consent for at least one month before treatment. This contraindication does not apply to LASEK or lens replacement surgery
* Tricyclics/lithium based medication--such patients may have obsessive, compulsive or perfectionist personality traits or suffer from a significant level of depression. Therefore, these patients can have expectations of surgery that are too high and are at increased risk of dissatisfaction postoperatively. Care must be taken not to discriminate against such patients and the GP should be consulted before treatment takes place
* Epilepsy--the patient must be able to remain relatively still during the surgical procedure. Therefore, patients that have had an epileptic episode within the last 12 months may be considered unsuitable for treatment
* History of frequent fainting--these patients may have a low threshold for vasovagal attack. Patients that have a known history of a low oculo-cardiac reflex would also be unsuitable
* Diabetics can have an increased risk of epithelial complications after LASIK treatment, (2) so the clinic may require more information about a patient's blood sugar levels before deciding upon suitability for treatment
* Any active or uncontrolled atopic disease would be contraindicated until it is well controlled as it is a risk factor for post-operative inflammation. (3)
Absolute ocular health contraindications
The following contraindications relate to LASIK and LASEK only unless stated (see Table 2):
* Significant diabetic retinopathy is an absolute contraindication for all elective refractive surgery as it can accelerate the progression of the disease with sight-threatening consequences (4,5)
* In patients diagnosed with glaucoma, the optic disc is compromised. During LASIK treatment, the intraocular pressure (IOP) is raised to above 90mmHg, which may cause further damage to the optic disc; this contraindication applies to LASIK only. Topical steroids used post-operatively may also affect IOP management in glaucoma patients. (6,7) Subsequent narrowing of the anterior chamber following pIOL implantation may also cause some issues with IOP management and it is, therefore, contraindicated in glaucoma patients
* In dystrophies where the cornea is abnormally thin, for example, keratoconus, LASIK and LASEK would reduce the corneal thickness even further and may cause keratectasia. Signs of subclinical keratoconus such as inferior steepening of the cornea, even where corneal thickness is adequate are a contraindication to corneal surgery. (8,9) Lens implant calculation is less reliable with keratoconic eyes and so RLE is approached with caution
* History of ocular inflammatory disease--eyes that have recurrent inflammatory conditions will be more susceptible to inflammatory attack after surgery, (1) which may be difficult to control
* Herpetic ocular disease--there is evidence that this can be reactivated by laser eye surgery (10-12)
* Fuchs' endothelial dystrophy--endothelial decompensation and poor flap adhesion has been associated with this condition; (13,14) this contraindication also applies to elective lens surgery due to the risk of long-term corneal oedema which may take months to resolve and result in permanently reduced vision
* Unstable refractive error--the prescription must be fairly stable before refractive surgery is carried out. A change of more than 0.50 dioptres spherical equivalent in 12 months or less is deemed unstable. This contraindication does not apply to presbyopes undertaking RLE
* Cataract--patients with evidence of cataract are not suitable for laser refractive or pIOL surgery. Phacoemulsification and IOL implant would be a more appropriate option in these cases.
Relative ocular health contraindications
* Dry eye/ocular surface disease--in some patients their condition may be temporarily worse after LASIK treatment. In patients where the dry eye is mild, it is unlikely to interfere with their suitability. The surgeon will decide upon suitability for treatment on a case-by-case basis
* Blepharitis/meibomian gland dysfunction--all signs of blepharitis must be treated prior to any treatment as it may induce post-operative infection or inflammation (see Figure 5). (15) The surgeon will expect the patient to adopt lid hygiene measures where appropriate and in some cases use medication prior to treatment.
Contraindicated eye examination findings
* Binocular vision status--if the patient has diplopia controlled by prisms or where decompensated heterophoria is corrected by the use of prism in spectacles, refractive surgery may not be suitable as it does not correct this element of the spectacle prescription
* Significant amblyopia--in cases where the best corrected acuity of the amblyopic eye is less than 6/12, treatment of the other eye may be contraindicated. Some exceptions to this may be allowed if, for example, the patient does not drive.
Other ocular considerations
* Mild ametropia/emmetropia patients with very good unaided vision and who only need spectacles to correct presbyopia are unsuitable for most treatments. The treatment range offered will vary from clinic to clinic. In some instances, monovision in some form may be an acceptable option after careful discussion with the surgeon.
Primary open angle glaucoma--a direct family history of this condition is relevant as there may be a significant long-term decrease in intraocular pressure measurements after laser refractive or RLE surgery. It is important that pre- and postoperative IOP measurements and visual fields are recorded by the patient's own optometrist. This will help to avoid the risk of glaucoma being missed in its early stages in the future.
The optometrist can start preparing the patient for their surgery preoperative assessment by managing their expectations and discussing the following points:
* An absolute zero prescription is not necessary for good vision
* Not all patients achieve 6/6 uncorrected vision after treatment
* They may need more than one treatment to achieve the desired visual outcome?
The patient may well go on to ask about the potential visual outcome and a typical discussion might include the following points:
* The possibility of over or under correction which if significant can often be rectified
* The effect of presbyopia and the loss of unaided near vision for presbyopic myopes unless opting for a multifocal lens implant
* The probability of temporary dry eye post LASIK treatment and the effect on vision
* The temporary exaggeration of glare, haloes and starburst post LASIK/LASEK treatment
* The potential loss of up to two lines of best-corrected visual acuity with high hypermetropes.
The treating surgeon is best placed to discuss surgical complications as rates will vary from surgeon to surgeon, and patients are increasingly demanding in their requests for statistics. However, it is useful to inform the patient that the most significant risk after surgery is infection and inflammation; this is usually prevented and controlled by the use of eye drops postoperatively.
Accurate corneal pachymetry, topography and keratometry are essential to the refractive surgery work up. Prior to pre-operative assessment, soft contact lens wearers need to leave their lenses out for one to two weeks and rigid lens wearers must leave lenses out for at least four weeks due to the possibility of corneal warpage and oedema.
This article has highlighted the key role that the practitioner can play in guiding patients on the suitability for elective refractive surgery, managing their expectations and identifying contraindications to treatment. Subsequent articles in this series will explore the typical and atypypical outcomes and their management.
Course code: C-39332 Deadline: February 20, 2015
To be able to explain to patients about the options for refractive surgery (Group 1.2.4)
To be able to advise patients on their suitability for refractive surgery based upon clinical findings (Group 2.2.5)
To be able to explain to patients about different types of refractive surgery (Group 1.2.4)
: REFLECTIVE LEARNING
Having completed this CET exam, consider whether you feel more confident in your clinical skills--how will you change the way you practice? How will you use this information to improve your work for patient benefit?
Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk/cet/exams. Please complete online by midnight on February 20, 2015. You will be unable to submit exams after this date. Answers will be published on www.optometry.co.uk/cet/exam-archive and CET points will be uploaded to the GOC every two weeks. You will then need to log into your CET portfolio by clicking on 'MyGOC' on the GOC website (www.optical.org) to confirm your points.
Visit www.optometry.co.uk/clinical, click on the article title and then on 'references' to download
Michelle Hanratty BSc (Hons) MCOptom
Michelle Hanratty is a hospital optometrist based at Optegra Birmingham Eye Hospital. The author of LASIK--A Handbook for Optometrists and numerous articles in optometry journals, Ms Hanratty has extensive experience in clinical optometry and refractive surgery. She is an examiner for the College of Optometrists and has been training and assessing optometrists entering the optometry profession since 2001
Table 1 General health contraindications Absolute contraindications Contraindicated elective refractive procedures Significant autoimmune disease All Systemic steroids All Immune suppression All Pregnancy LASIK/LASEK Amiodarone LASIK/LASEK Roaccutane LASIK/LASEK Relative contraindications Contraindicated elective refractive procedures 5-Hydroxytryptamine LASIK Tricyclic or lithium-based medication All Epilepsy All History of frequent fainting All Diabetes All Active atopy All Table 2 Ocular health contraindications Absolute contraindications Contraindicated elective refractive procedures Significant diabetic retinopathy All Glaucoma LASIK, pIOL Corneal thinning dystrophies LASIK/LASEK History of ocular inflammatory All disease Herpetic ocular disease LASIK/LASEK Fuchs' endothelial dystrophy All Unstable refractive error LASIK/LASEK, pIOL Peripheral retinal degenerations/ All retinal detachment Cataract LASIK/LASEK, pIOL Relative contraindications Potentially contraindicated elective refractive procedures Dry eye, Sjogren's syndrome LASIK Blepharitis All
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|Title Annotation:||CET: REFRACTIVE SURGERY|
|Date:||Jan 24, 2015|
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