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The soft lenses currently available commercially can be divided into a number of categories defined by the expected working life of the lens. Daily disposable lenses are intended to be worn once, then discarded. Planned replacement lenses are typically replaced at rather longer intervals typically either two weeks or one month.
There are a number of advantages to a short contact lens working life:
- The fewer times the lens has to survive handling and cleaning, the flimsier it can be. This allows it to be thinner, so it can transmit more oxygen
- Lenses made to be replaced frequently have less opportunity to collect deposits, so the use of group IV materials is practical. This makes mass manufacture commercially viable
- Fewer deposits means less chair time sorting out allergic and inflammatory reactions to them
- The need to obtain a new pack of lenses every so often can help with compliance with aftercare, although this is somewhat compromised if the patient obtains their lenses from an internet-based supplier
- Frequent replacement lenses need specific protein cleaners only rarely, especially with modern multipurpose solutions. Daily disposables need no disinfection either.
The choice of modality will depend on patient preference, bearing in mind their specific visual and physiological requirements.
Handling soft lenses
Patients are generally rather nervous around optometrists. There has been research that showed that people are more stressed having a sight test than they are during a dental appointment. Contact lens patients have the added stress of allowing someone to invade their personal space and stick a bit of plastic in their eye. The eye has a sophisticated defence mechanism to prevent things going into it. It is therefore important that the practitioner projects a calm demeanour, and avoids words like 'pain'. Like politicians we must sweeten the pill, and emphasise the immediate comfort likely to be experienced. This might not be absolutely true (unlike the pronouncements of politicians of course), but the best time to point out that the saline the lens was stored in might cause a tiny bit of stinging is probably when the lens is already in the eye, settling. It is essential that the practitioner be a source of calm and confidence. This is much easier to achieve if the practitioner is actually calm and confident, and competence in the handling of lenses will calm the nerves of both parties. The only way to achieve competence is by practice, but a little bit of technique can help as well.
Before touching a patient, thorough washing of the hands should occur, preferably in clear sight of the patient. In addition to the obvious antimicrobial benefits, this will serve to reassure the patient that they are in good (or at least clean) hands, and it may influence the patient's own approach to lens hygiene. Cold water may be best for the final rinsing, as rising mains water is less likely to contain Acanthamoeba.
Insertion of a soft lens
When handling soft lenses we must take a number of lens characteristics into account. Soft lenses are rather big compared to RGPs, and one of the challenges is therefore how to get something that size into the typical human palpebral aperture. Some of the thinner soft lenses are downright floppy, until they lose some water. They then distort and take on some of the characteristics of thin potato crisps, though possibly less comfortable on the eye. Thirdly it is easily possible to turn them inside out, and to insert them into the patient's eye in this state.
It follows therefore that our insertion technique should allow us to deliver a lens the right way round and reasonably hydrated to the right part of the eye without alarming the patient unduly, or needing to apply unreasonable force. Firstly we need to check that the lens is not inside out. Some lenses have markings that a sharp-eyed pre-presbyope, in good lighting, or on a slit lamp, might be able to see. For the most part, however, we need to do the following. Place the lens on the end of a finger and observe it from the side. The typical appearance of lenses the correct and wrong ways round can be seen in Figures 1a and 1b respectively. Next pinch the lens as shown in Figure 2. A lens the correct way round will fold inwards easily. A lens that is inside out will resist, and try to fold back on your fingers (Figure 3).
The next challenge to address is that of finding enough room to insert the lens. In general, this is best done by directing the patient to look to their left when inserting a lens into the right eye (and to their right when inserting a lens into the left eye) and either downwards or upwards (Figure 4).
The lens is applied to the temporal sclera, and centred on the cornea afterwards. If the patient's head is tilted back on the headrest, looking down and in will give the biggest target area on most people, as the upper lid can be pulled back further than the lower one. However, in many patients looking up and in will give a perfectly adequate target area and has the additional advantage with a nervous patient of allowing for Bell's phenomenon, where attempted reflex closure of the lids is accompanied by an upward rolling of the eyes to protect the cornea. There are also some soft lenses that are 'heavy' and tend to fall off the finger if the eye is approached from on high. The up-and-under approach works best for these. Ideally, a practitioner should be able to switch between techniques according to individual requirements. In either case the lids must be controlled. The upper lid is often best controlled by a thumb placed near the lid margin, which should allow sufficient control to be exerted without causing discomfort to the patient. The lower lid is generally controlled by the finger next to that bearing the lens. Most students put the lens on to the first finger for their early attempts at lens insertion, but for many practitioners the middle finger is longer. If the lens is placed on the end of this finger the extra length may allow some bending of the finger, which may assist insertion. Whichever finger is used, the lens should be placed on the tip, so that the area of contact between the finger and the lens surface is minimal. This makes it easier for the tear film to pull the lens from the finger. The approach to the eye should not be too slow. The longer it goes on the more likely the patient is to lose their nerve. The lens may dry out as well, especially on a hot day, and it may then be reluctant to leave your finger.
The technique for applying the lens to the eye is a little different to that used in RGP lenses. In the latter case one merely has to touch the lens to the eye and the tear film will claim it. A soft lens must be squashed gently on to the surface of the sclera, and it may help to slightly roll the finger. This will help to dispel any air pockets and help the lens to part with the finger. At this point we have a lens sitting on the upper or lower temporal sclera, probably a bit wrinkled and vulnerable to a sudden blink. It is important to retain control of the lids at this stage, while directing the patient to look towards the lens, then up, down, etc until the lens is centred on the cornea and most of the air expelled. We can then gently let the lids go.
Usually a soft lens is comfortable from the start. If it isn't, there are a number of possibilities:
- The saline that lenses are stored in becomes progressively acidic over time. If a lens has been in the bank for a long time it may take a few seconds for the pH to normalise, and the lenses may sting a little on insertion
- The lens may be damaged
- There may be a foreign body trapped under the lens
- There may be an air bubble.
If the saline is causing the discomfort, it will pass in a few moments. If the patient can manage it, have a look on the slit lamp. If not remove the lens, clean and rinse thoroughly and reinsert, provided the eye is not damaged. During professional examinations, candidates are sometimes observed massaging a newly inserted lens vigorously through the lids to clear trapped air. This is both unnecessary, as trapped air will usually find a way out unaided, and dangerous, as any foreign body under the lens will create pretty 'spirograph' patterns in the corneal epithelium and provide a potential source of entry for microbes.
Removal of a soft lens
It is generally not a good idea for the practitioner to attempt removal of a soft lens directly from the cornea. A heavy-handed approach might lead to mechanical abrasion of the cornea (Figure 5) similar to that seen at some aftercare appointments.
The technique usually favoured is essentially the reverse of insertion. The lens is decentred temporally using a finger, then the thumb is brought in to pinch the lens off the surface of the sclera (Figure 6).
Usually the upper lid needs to be pulled out of the way with a thumb or finger, and the lower lid may need to be controlled.
An alternative is a version of the common RGP removal technique where the lens is pinched out between the two lids, in this case direct from the cornea. The patient needs to have a wide palpebral aperture, as soft lenses are rather larger than RGPs, and the flexibility of the lens is also important. This method works best with 'stiffer' lenses such as silicone hydrogels and some torics.
Occasionally a patient will panic and develop blepharospasm. This can make removal of the lens impossible. Fortunately there is a trick which works 99 times out of 100. In a calm, confident tone of voice, tell the patient the following. 'When I say go, open your mouth as far as you can.' It is almost impossible to close the lids tightly and open the mouth wide at the same time. We are simply not wired up that way. Secondly, the drawing of attention towards the mouth, away from the eye, may also contribute to the effect. Either way, it will usually give you enough time to get the lens out.
If a lens is immobile, the practitioner should not attempt to take it out without irrigating the eye first. It is possible that there is little or no post-lens tear film present and the lens may be binding to the cornea. Removal of the lens in this state may take some of the epithelium with it. Irrigation can be a messy business, but the use of single dose saline is both hygienic and may limit leakage. The usual technique is to apply a generous quantity of paper towels to the side of the face below the eye to catch the excess (Figure 7).
It sometimes happens that the lens goes in and then goes AWOL. It's not where it should be, but it has not exited the eye either. In this case, evert the lids, as thin lenses do have a habit of hiding under the top one, and try instilling fluorescein, as it will stain a soft lens and make it more apparent. This is also a useful technique when looking for lens fragments. Irrigation of the eye may also be required. Occasionally a lens will roll itself up and hide well into the upper fornix. If the usual search is fruitless, get the patient back the next day. The lens can't do much harm up there in the short term, and it will probably work its way out in time. ?
? Ngaire Franklin and Andy Franklin are contact lens specialist optometrists practising in the South West