You have carefully selected your patient, taken the necessary measurements, ordered the lenses and now they have arrived in your practice (read part one of our guide). What happens next?
[CaptionComponent="1992"]Lens collection
The collection of orthokeratology (from now on referred to as ortho-k) lenses is very similar to the collection of ‘standard’ rigid gas permeable (RGP) lenses. Firstly, the parameters on the label are confirmed to match the order (Figure 1). Then, on insertion, there are a number of points where the process may differ:
- To reduce the chance of getting air bubbles under the lens in the reverse zone and reducing the effectiveness of the tear film, the lens should be inserted in a horizontal plane with the lens full of a suitable solution (RGP) conditioning solution (such as saline, rewetting drops). The lens should be inserted directly on to the centre of the cornea. At the beginning this can be achieved by placing a mirror on a flat surface and the patient leaning over it to insert the lenses.
- During sleep, the lenses do not move much on the eye and can be quite tight- fitting in the morning on waking. It is important that the lens is mobile on the eye before it is removed. Instruct the patient that it can help to use rewetting drops on waking and to wait about 30 minutes before removing the lenses. Should the lens still be immobile, it is also possible to massage the eye through closed lids or to use the lower lid to press on the limbus to release the lens. The lenses can then be removed by using the lid margins under the bevel and squeezing them together.
- It is not necessary to build up the wearing time with ortho-k lenses like it is with first-time use of RGPs, as the main reason for this ‘build-up’ time is due to discomfort during blinking. As the eyes are mainly closed during wear, the discomfort is not an issue.
Material and colour
During the collection appointment, the lenses should be worn for about 30 minutes so the fit can be checked with fluorescein (Figure 2). An ideal fit would be:
- A 1-4mm central fit zone – the size of this zone depends on the prescription and will become bigger as the prescription reduces and the epithelial cells are redistributed.
- Regular equally wide-edge lift under the bevel
- About 1mm movement during blinking
- No or very few air bubbles under the lens
- A plano over-refraction with the lenses in situ
It is also possible, after 30 minutes, to see a change in the corneal shape with the topographer, and patients usually comment that their glasses feel too strong when they put them back on after removing the lenses. The ideal target is summarised here:
What is the target corneal shape?
- A 4-5mm diameter centrally flattened zone that is centred on the pupil to give good visual acuity and contrast sensitivity in normal lighting conditions
- A concentric, regular steep ring zone in the mid-peripheral cornea around the central zone. The more regular the ring, the better the lens centration
- A peripheral cornea whose geometry is unchanged
While the lenses do not move on the eye during the night, they are more prone to deposits. Daily cleaning with an RGP surface cleaner is recommended and can be followed by storage in either an RGP conditioning solution (such as Boston Advance or Total Care) or a one-step peroxide system (such as AOSept or EasySept). Protein removal should also be carried out on a monthly basis.
During the first week of wear, the patient should be made aware that certain activities that require sharp vision may not be possible, such as driving at night, and the residual correction will need to be compensated for using alternative correction. This is most easily done with daily disposable contact lenses.
It is possible, due to the negatively powered tear film under the lens, to wear ortho-k lenses during the day to achieve full correction.
However, it is not recommended that the user wear the lenses for more that 18 hours a day.
It is useful to give the patient written information, with some ‘frequently asked questions’ answered, to give them confidence during the first couple of weeks.
Aftercare Appointments
At the start of the ortho-k journey, the fitting of the lenses, unaided vision, residual correction and change in shape of the cornea must be checked frequently and patient and practitioner must be prepared for this number of appointments. The recommended aftercare schedule is as follows:
1 First morning after overnight wear (with lenses in)
2 Morning after the third or fourth night of wear (with lenses in)
3 Morning after a week (patient to bring lenses to appointment)
4 Morning after three to four weeks (patient to bring lenses to appointment)
5 Afternoon or evening after three to four weeks (to check regression)
6 Regular check-ups at least every six months (patient to bring lenses to appointment). The lenses should be changed after a year.
Aftercare after the first overnight wear
On the morning after the first night of wear, the patient should attend for their aftercare wearing their lenses and they should not attempt to take them out before the appointment. The lenses should be checked on the eye with and without fluorescein.
- Movement – lenses that are worn while sleeping tend to move very little and sometimes can be stuck on the eye by suction. For this reason, it is important that the patient has not tried to remove the lenses themselves before the practitioner has checked they are mobile. If the lens is not mobile, the patient should be instructed to massage the limbal area through closed lids. The patient must be able to tell if the lenses are moving or not. Removal of an immobile lens can result in epithelial damage, ocular discomfort and photosensitivity.
- Centration – the lens should sit central on the cornea and move slightly with blinking.
- Air bubbles – there should be no air bubbles under the lens. It is also important to check for deposits under the lens.
- Vision/visual acuity – this should be checked with the lenses in situ and an over-refraction carried out.
- Fluorescein – it should be possible to already see the ‘typical’ ortho-k fluorescein pattern (Figures 3).
The lenses should then be removed by the patient and cleaned as per previous instructions.
It is possible at this moment that the patient will become aware that they can see better without any correction than they could the evening before.
Bear in mind that a patient who previously has -3.00DS of myopia may already have reduced their correction to only -1.00DS after the first night of wear.
The following checks should be undertaken after removal of the lenses:
- Vision, residual refraction and visual acuity
- Corneal check – minimal staining may be visible. This can happen because during the first night the cornea is adapting to having the lenses in and the majority of the shape change occurs during this first night.
- Air bubble pits – when a lens is too steep centrally, it is possible to get air bubbles in the tear reservoir. These can press on the cornea, leaving a small pit similar to dimple veil. These disappear quickly.
- Corneal shape change – this is checked with the topographer and should already start to show a central flattening and mid-peripheral steepening, although it is unlikely that there will be a full circle (Figures 4a and 4b)
- Correction of the residual refraction – This can usually be corrected using daily disposable lenses or, if you have a lab on site, with a simple pair of distance glasses. The patient should expect the correction to regress during the day, especially during the first week. Ensure the patient has enough contact lenses to last until their next aftercare appointment. I tend to give them the correction they had on the first morning, plus a few with a weaker prescription for the next couple of days.
Subsequent aftercares
The aftercares after three/four nights and a week will follow the same pattern. For the three-day aftercare, the patient should attend wearing the lenses again to double check the mobility of the lenses. The patient can then attend all subsequent aftercares after removing the lenses, but should always bring their lenses with them so they can be checked for deposits or any other damage. Usually after three to five nights, the residual correction is minimal and the patient should not require contact lenses or glasses during the day. The regression will still be noticeable and correction may be required for driving at night or for other activities that require excellent distance visual acuity.
It is a good idea to do all the aftercare appointments at the same time of day (when possible early morning), so that the topography pictures and refraction can be better compared. Also, as the lenses have not been removed too long before the appointment, it would still be possible to see any staining or air bubble pits.
Between the first two appointments the fluorescein picture can change significantly. The central flat zone will become larger as the epithelial cells start to migrate and the mid-peripheral cornea will become steeper.
After about a month an aftercare appointment should take place in the afternoon or evening, as well as in the morning, to enable the practitioner to quantify any regression. The morning aftercare may show a slight overcorrection (positive sphere shift). If this is still present in the afternoon, it is possible to reduce the wearing schedule to every second night.
The patient should be informed that they can try this wearing schedule and see for themselves if the vision remains stable or if they see a significant regression during the second day. If the patient is happy with the level of vision they have with the new wearing schedule, they can continue. If not, they can revert to nightly wear and try to change the schedule again after another month when the cornea is more stable.
Yearly aftercare
After a year of regular wear, the lenses should be replaced. If an over-refraction is found when the lenses are worn, the central BOZR can be altered to compensate for changes in refraction. The BOZR will be made flatter when the myopia has increased and steeper when it has decreased. The peripheral curve and eccentricity must only be adjusted very occasionally.
Topography pictures
Ortho-k lenses can only be fitted when the practitioner has a topographer. The fit of the lenses can only be seen by the change in shape of the cornea, as the lens sits differently when viewed on the slit lamp compared with on a closed eye during sleep. It is also helpful if the topographer has the software required to compare topography pictures with one another so the exact change in corneal shape can be monitored.
Figures 5a to e show the topography transformation throughout this period for one of my patients. The fluorescein picture gives a good idea of how the lens is fitting, but cannot quantify the change in corneal shape like the topographer can.
[CaptionComponent="1997"][CaptionComponent="1998"][CaptionComponent="1999"][CaptionComponent="2000"][CaptionComponent="2001"]Ideal fitting — Bull’s eye
The ideal picture is a well-centred flattened central zone centred on the pupil with a regular steeper ring around it. The peripheral cornea should remain unchanged and the picture should have no distortion. This is called a bull’s eye.
Flat fitting — Smiley face (Figure 6)
When the lens is fitted too flat, the central flat zone is usually small and the lens tends to decentre mostly upwards and/or temporally. The lower edge of the lens lifts from the cornea and the tear film under the central zone is too shallow or non-existent. The lens must be made steeper and the sag increased. This is achieved by steepening the peripheral curve and/or reducing the eccentricity. The topography difference picture looks like a smile, hence ‘smiley face’.
[CaptionComponent="2002"]Steep fitting — Central islands
When the lens is too steep, the tear film is too deep and therefore the flattening pressure is reduced. Small areas remain steeper resulting in central islands. The peripheral zone is too wide and air bubbles may collect under the lens. To reduce the central tear film thickness, the lens needs to be flattened and the sag decreased by increasing the peripheral curve (r02) and/or increasing the eccentricity.
Changing the fit of the lens
The fit (sag) of an ortho-k lens can be adjusted by changing the shape of the peripheral curve (r02 and eccentricity). The sag can also be changed by adjusting the (?) value in microns when the other parameters remain the same. When the total diameter is adjusted this changes the centration of the lens. The flat central zone (r0) has no impact on the fitting of the lens and is only needed to give the required correction.
Regression
The correction, unfortunately, does not remain stable for the whole day after lens removal. The cornea is always trying to return to its original shape. For this reason, the topography pictures look different if they are taken in the morning or evening. The aim is for a slight over-correction (+0.50DS) in the morning, leading to an emmetropic eye in the afternoon or evening. This change is often so minimal that the patient does not notice the difference. The average correction change during the day is about 0.50DS. Regression is, however, very individual and can be very different for each patient.
Reversibility
If the ortho-k lenses are not worn for a longer period of time than one day, the cornea will revert to its original shape and the myopic error will return. After a few days most of the error will be back, but it takes a lot longer for the corneal epithelial cells to completely redistribute themselves again. It is, therefore, recommended that if the patient wants to undergo corrective laser eye surgery they should wait about six months before having surgery.
Read more
Part one: An introduction to orthokeratology
Experiences of orthokeratology – revealing case studies
The next and final article will feature a number of case studies showing what potential adjustments may need to be made when everything does not go as planned with the initial lenses.
Lisa Crouch is a UK-qualified optometrist practising at Visilab GlattzentrumSwitzerland and specialising in orthokeratology and complex contact lens fitting
