Common Questions About The Initial Screening

Browse our 101 questions and answers to gain more insight into the treatments offered at London Vision Clinic or contact one of our Patient Care Coordinators for more information.

How Long Is The Initial Screening?

For the video elaborating this FAQ please click here.

The initial screening usually takes 2 hours.

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Am I Suitable For Laser Eye Surgery?

If you want to learn more about this FAQ click here to watch the video.

The only way to know for sure if you are suitable for laser eye surgery is to attend an initial screening.

Where Is London Vision Clinic Located?

For the video explaining London Vision Clinic’s location please click here.

The London Vision Clinic address is 138 Harley Street, London W1G 7LA. We are just beside Regent’s Park in the heart of London. We’re within easy reach of the London Underground and many major bus routes. The shops, sights and attractions of Oxford Street and the West End are just minutes away.

Where Can I Park?

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The clinic is within London’s Congestion Zone. There is metered street parking on Harley Street and surrounding streets. The nearest underground car park is at London Portland Place, 6-7 Weymouth Mews, London W1N 3AA. Opening times are Monday to Friday 7am to 7pm; the car park closes on Saturday and Sunday. Daily tariffs are £10 for 2 hours, and £16 for 2 to 4 hours.

When Can I Have An Initial Screening?

For the video with more information on this FAQ please click here.

We hold initial screenings from Monday to Friday, between 9am and 3pm.

How Soon After The Initial Screening Can I Have My Laser Vision Correction Procedure?

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After we find you suitable, the next step is to have your ophthalmic exam, after which you are able to have the procedure on the next clinic day (Monday to Friday).

Can I Bring Anyone With Me To The Initial Screening?

Watch a video about this FAQ – click here.

Yes, you are more than welcome to bring someone with you to the initial screening. Your companion will be able to accompany you for most of the screening with the Patient Care Coordinator and the optometrist.

Will I Be Able To See Clearly After The Initial Screening?

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Your vision will be unaffected after the initial screening. During the ophthalmic exam, we instill eye drops in your eyes to dilate your pupils so that we can run some of our tests. Patients are often light sensitive and blurry for up to 4 hours after we instill them. Hence, it is advisable to bring sunglasses to this appointment and to not plan any activities that require good vision for up to 4 hours after this appointment.

Does Anything At The Initial Screening Cause Discomfort Or Pain?

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No. There is nothing done at the initial screening or ophthalmic exam that would cause any discomfort or pain.

How Long Is The Initial Screening Assessment Valid For?

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The results of the tests undertaken at the initial screening are valid for no longer than 3 months. This is to ensure that there has been no significant movement in your prescription and that any treatment plan is completely up to date.

Will There Be Any Pressure To Have The Laser Eye Treatment While I Attend The Initial Screening?

If you would like to watch the video relating to this question please click here.

No. We do not put pressure on anyone to have treatment. In fact, we have declined to treat patients who we feel are not ready for treatment, even after finding them medically suitable.

Laser eye surgery is an elective procedure and there is no need to have it done sooner than later. The sooner one has the procedure, the sooner the benefits will be realised, but only the patient can make this decision. Our goal at the initial screening, and in fact throughout the entire patient process, is to give you as much information as required to make an informed decision.

What Do I Need To Do To Prepare For The Initial Screening?

To watch a video answering this question please click here.

The Patient Care Coordinator will ask you a series of questions that are necessary to create your file, and you will have an opportunity to ask questions as well.

Many patients have asked if they need to bring past prescriptions to the initial screening. While past prescriptions are helpful, we do not rely on these to plan or treatment, and will always perform our own tests based on our screening protocol.

In terms of contact lenses, all you need to do is take them out on the morning of your initial screening. There are more stringent requirements for contact lens removal prior to surgery, but these are not necessary for the screening. You may also want to bring your glasses with you to the initial screening.

It would be helpful if you could read about the procedure (i.e. the UK Guide to Laser Eye Surgery) prior to your consultation, but not entirely necessary as everything will be explained at your consultation.

If you intend on booking your ophthalmic exam and/or surgical appointment, you should bring your diary and a method of payment with you in order to make the necessary arrangements.

What If I’m Found Unsuitable, What Are My Options Then?

Find out what options you have if found unsuitable – click here to watch the video.

If you are found unsuitable for laser eye surgery at London Vision Clinic, the optometrist can advise you on alternative treatment options which may include intra-ocular lenses or other procedures based on findings at the initial screening. Some contraindications may be temporary, and we may suggest you see us again at another time.

What Are The Differences Between Screenings At London Vision Clinic And At Other Laser Eye Surgery Clinics In The UK?

Find out what options you have if found unsuitable – click here to watch the video.

We perform one of the most thorough screenings for laser eye surgery in the UK. The following are some factors we have deemed important to include in our screenings (many of which are rare or unique in the UK)

Discovering your uniquely personal needs – The Patient Care Coordinator is responsible for gathering the necessary information that makes you unique, in terms of your most important priorities, and your life and work style as they relate to laser eye surgery.

Measuring your pupil size with certainty – We use Colvard infrared pupillometry in total darkness (with the best chance of detecting maximum natural pupil size). The best methods for determining this are either using infrared cameras or a low-level green slit light at the microscope (slit-lamp). Both have been shown to be effective methods.

Analysing every patient’s eyes with a wavefront aberrometer – Our clinical staff analyse everyone’s eyes with the wavefront aberrometer. This differs significantly from other clinics where some patients pay more to have a wavefront analysis that will influence their treatment plan.

Imaging your corneal topography and thickness using the most up to date methods – This is one of the most important safety factors in laser refractive surgery (along with front and back surface topography). We obtain two parameters to optimise the safety of surgery: The thickness at the thinnest point in the cornea and the shape of the 3D thickness profile of the cornea. Hand-held ultrasound devices used should preferably be of the 50MHz variety (many on the market are only 20-30MHz). We obtain multiple measurements of the central corneal zone, and record the thinnest measurement.

Orbscan provides a 3D thickness map of the cornea, which is essential for determining that the thickness profile of the cornea is normal, although the actual values for thickness provided are less accurate than the values we obtain by ultrasound. There is a new device now available called Artemis VHF digital ultrasound, which measures corneal thickness more accurately than either Orbscan or hand-held ultrasound devices and does so in 3D to ensure detection of the thinnest point and display the thickness profile of the cornea.

We use the Sonogage II (50MHz) hand-held probe and Orbscan II as well as Artemis VHF digital ultrasound scanning (the latter is usually used only if there is any question of suitability).

Scanning your eye with the ultrasound – During a pre-operative assessment for suitability, most laser refractive surgery practitioners will use an ultrasound probe called a pachymeter. This is a hand-held ultrasound probe that is the mainstay for accurate single point measurements of the corneal thickness. While pachymeter measurements are more accurate than those of the Orbscan are, we can only obtain them at single points, and cannot use them to adequately determine the thinnest point in the cornea. The accuracy of pachymetry is approximately 10-microns (SD). The most accurate of these devices has a +/- 5% chance of error.

The Artemis is the world’s first very high frequency (VHF) digital ultrasound eye arc-scanner. It takes advantage of the accuracy of ultrasound (and at very high-frequency) together with the 3D mapping capabilities of a scanner. In cases where there is any question regarding candidacy for surgery, we use the Artemis to be certain, and confirm safety or determine unsuitability. The accuracy of the Artemis is approximately 1-micron. It has a +/- 1% chance of error.

There is only one Artemis VHF digital ultrasound scanner in the UK (it was FDA approved in 2002), and it is available only at London Vision Clinic.

Measuring intra-ocular pressure – We measure your eye pressure using two different methods, Ocular Response Analysis and Tonometry (Goldmann). The Ocular Response Analyzer utilizes a rapid air impulse, and an advanced electro-optical system to record two applanation pressure measurements; one while the cornea is moving inward, and the other as the cornea returns. Due to its biomechanical properties, the cornea resists the dynamic air puff causing delays in the inward and outward applanation events.

Testing how you may benefit from Laser Blended Vision – If you are over 40, our optometrist will perform a Laser Blended Vision simulation in order to provide you with this option as a potential treatment plan.

Dilating your eyes to optimise treatment – Manifest, cycloplegic and analyser parameters are used to base calculations for treatment. We obtain both measurements and compare them to the wavefront aberrometer (higher order aberration) of a particular eye for optimal treatment planning.

Find out what options you have if found unsuitable – click here to watch the video.

Where Can I Learn More About The Screening And Assessment Technologies Used For Laser Eye Surgery?

If you would like to watch the video relating to this FAQ please click here.

Most laser eye surgeons use five technologies. These are:

  • Topography
  • Pachymetry
  • Artemis
  • Pupillometry
  • Wavefront analysis

At London Vision Clinic, our surgeons have chosen what they believe to be the “best of breed” technologies – meaning; they have reviewed different brands and chosen the ones that provide, in their opinion, the best outcomes – regardless of the surgeon conducting the treatment.

What Is Topography?

Click here for the video answering what topography is.

Topography measures the depth of the surface of your eye, your cornea. The picture produced by a topography machine looks like a map of a mountain range, with the different elevations shown in contrasting colours.

Topography is one of the most important safety factors in determining how suitable you are for laser eye surgery. The most basic kind of topography measures the shape of the surface at the front of your eye. The most detailed topography measures the shape of both the front and back surfaces of your cornea. Common topography machines are the Orbscan™, the Pentacam™ and the Galilei™.

Our laser eye surgeons chose the Orbscan II to perform corneal topography at London Vision Clinic. The Orbscan II machine provides the most detailed topography. It is the ‘gold standard’ across the world because of the sheer number of points it measures on your eye. This is the very best option for determining changes in the shape of your cornea. It provides a 3D map of your cornea, which is essential for determining whether it is too thin for surgery to be safe. We perform topography both before and after treatment.

What Is Pachymetry?

Please click here to watch a video explaining what pachymetry is.

A pachymeter is a hand-held device used to measure the depth of the thinnest point of your cornea. Along with front and back surface topography, the thickness of your cornea is one of the most important safety factors in laser refractive surgery. Your surgeon should review these measurements, topography and pachymetry, to make surgery as safe as possible.

Using a pachymeter together with a topography device provides very accurate data, and ensures that the thickness of these areas is within acceptable safety limits. Ask your surgeon what kind of pachymeter they are using – the 50MHz model gives more detailed information than a 20-30MHz device.

What Is Artemis?

Please click here to watch a video about Artemis.

Our surgeons work with the most advanced and accurate device to perform pachymetry, which is the Artemis™ VHF digital ultrasound. This measures corneal thickness more accurately than either the Orbscan or hand-held ultrasound machines. It produces a 3D image, which means it detects the thinnest point with great accuracy, and displays a profile of the depth of your cornea. This technology is currently only available in a handful of clinics around the world.

What Is Pupillometry?

To watch Mr. Glenn Carp explain pupillometry in a video click here.

Pupillometry measures the size of your pupils, the windows that let light into your eye. The measurement of your pupil size takes place in a darkened room to ensure that your pupils are open fully.

Accurate pupillometry is critically important because the laser is only capable of treating a defined area. Typically, this is a circle with a diameter of 6mm to 8mm, depending on the laser used. If your pupils were larger than the area treated by the laser, it would leave you with an untreated ring around the smaller circle corrected by the laser. It would be like looking through a clear patch in the middle of a smeared window.

This is why pupillometry is such an essential part of the assessment before surgery. The results will determine the type of laser eye treatment you need. Specific lasers that are capable of covering an area larger than their pupils can only treat some people with large pupils.

What Is Wavefront?

To watch a video about wavefront please click here.

This measures the unique imperfections of the surface of your eye, called ‘higher order aberrations’. These irregularities of your cornea and optical system affect the finer quality aspects of your vision, beyond the normal refractive errors of short-sightedness, long-sightedness, and astigmatism.

A wavefront aberrometer records data from several spots on the surface of your cornea. This produces a map of the imperfections on the surface of your cornea, as well as a visual system analysis that we feed into the laser to achieve better results. The laser must be able to receive these measurements and then apply them directly onto the cornea.

Different analysers measure different numbers of spots, ranging from as low as 60 to as high as 650. Our laser eye surgeons choose the Carl Zeiss WASCA wavefront aberrometer, which has the highest resolution on the market.

A low-resolution analyser is like a watercolour painting. It provides a general impression of the landscape. It measures just a few points and then uses a mathematical formula to work out an approximate image of the rest.

A high-resolution analyser will give as sharp a picture as a photograph. It records much more data, giving a more accurate map of the number and location of imperfections. This means the surgeon can plan your treatment precisely.

Wavefront treatment has received a lot of publicity. Some clinics promote wavefront as if it could cure any imperfections – in reality, it simply provides another method of measuring your eyes.

Does Every Patient Get Wavefront At London Vision Clinic?

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We test every patient with the wavefront aberrometer at the initial screening under dilated and undilated conditions. If we find higher order aberrations in the visual system, we will include a wavefront-guided component in the treatment plan. If we do not find higher order aberrations, we will omit this component.

What If I Am Currently Wearing Contact Lenses?

For the answer to this FAQ you can click here and watch the video.

When you schedule an initial screening, just remove your contact lenses on the morning of the Initial Screening. Also, bring in your glasses if available.

Prior to surgery, it is important to note the following: if you are wearing hard or gas permeable contacts, they must be out of your eyes at least six weeks prior to your surgery. Soft lenses must be out at least 1 week.

Contact lenses can “mold” the corneal surface, which changes the corneal curvature and may lead to a change in your refraction (prescription). To properly calculate the treatment to correct your refractive error, you will have to stop wearing contact lenses at some stage before your appointment. In time, the cornea will return to its natural shape and size. We are dedicated to providing you with the most accurate treatment, and this we can only achieve this if the corneal surface is stable and back to its natural shape.

For the vast majority of patients, the recommended minimum length of time for contact removal should suffice. However, the individual rate of corneal adjusting may vary. If your cornea is still adjusting at either the pre-operative or the surgery appointment, you will be required to reschedule your appointment for a later date. This will allow the cornea to return to its natural shape and refraction to stabilise, thus providing you with an opportunity to attain the best possible outcome. London Vision Clinic cannot reimburse for time off work, hotel, airline tickets or any other expenses incurred due to rescheduling.

The difference in the length of times to remove contact lenses listed below is to ensure that rescheduling of appointments if corneal “molding” is apparent does not inconvenience the majority of out-of-town patients.

Medical evidence suggests that we can reduce the likelihood of an enhancement with a lengthening of the time a patient has their contact lenses out.

Removal of contact lenses prior to Surgeon Consultation appointment with surgeon:

Contact lens typeLength of time lenses need to be out before the Surgeon Consultation appointment with the surgeon
All soft contact lensesAt least 1 week before
Extended wear soft lensesAt least 1 week before
Toric soft lensesAt least 2 weeks before
Rigid gas permeable (RGP) lenses
worn for 0 – 10 years
worn for 10 -20 years
worn for 20 – 30 years
At least 4 weeks before
At least 8 weeks before
At least 12 weeks before
True hard lenses (Polymethyl methacrylate)At least 12 weeks before

For the answer to this FAQ you can click here and watch the video.

If Another Clinic Finds Me Unsuitable, Why Should I Come To London Vision Clinic For Another Screening?

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Surgeons have different criteria for accepting or rejecting patients. This may seem strange, but there are good reasons. Every surgeon has different expertise, experience, and technology. These factors have a direct impact on the kind of patients the surgeon is able to treat. Many clinics may boast that they reject up to 25% of people at initial screenings. This is not a sign of quality. In fact, surgeons need to reject only about 10 per cent of the general population. If a surgeon turns away more patients, it may indicate a lack of experience or expertise or limited access to the latest technology. If a clinic disqualifies you, you should seek a second opinion.

In late February I saw an article in the Daily Mail re: laser treatment for the older person. I immediately rang and my call was answered by a gentleman – very calm and reassuring – who took my details and my lens prescription, and set up an appointment for me in London. I was so happy because another laser clinic had told me my prescription was impossible to correct. – Janet B. from Sevenoaks, Kent

Many patients, who were not found suitable elsewhere, are surprised to find that they were found suitable at London Vision Clinic. The reasons for this are similar to the reasons we give when answering why London Vision Clinic can treat higher prescriptions than the norm.

Do I Need To Bring Old Prescriptions To My Screening?

Please click here to watch the video relating to this FAQ.

Many patients have asked if they need to bring past prescriptions to the initial screening. While past prescriptions are helpful, we do not rely on these to plan or treat, and will always perform our own tests based on our screening protocol.

About The Initial Screening