Case 1
Probably the most challenging complication in our GP lens practice
is the condition most frequently referred to as 3 and 9 o'clock staining.
Since the introduction of rigid corneal lenses in the early 1950s this
phenomenon has been described in the literature. And it has been reported
that 80% of GP lens wearers show some degree of 3 and 9 o'clock staining,
but it is estimated to be of clinical significance in about 10-15%.
This 33 year old patient has been a in our practice
for a long time, almost always presenting with some degree
of 3 and 9 o'clock staining. She has been wearing rigid
lenses for over 20 years, which she has been overall satisfied
with.
OD S -2.50 = C-1.25x180 VA 20/20
OS S -2.25= C -1.50x175 VA 20/20
We have tried to fit her into hydrogel lenses for many times for this reason, but somehow her toric hydrogel lenses kept rotating, which probably has to do with the position of her eyelids. Furthermore she developed GPC on two occasions when wearing her hydrogels, which resolved quickly after going back into GP lenses.
On the last visit she presented with unacceptable grades of 3 and 9 o'clock staining: grade 3 OU (see picture) and moderate to severe conjunctival hyperemia (grade 2.5 OU).
What to do in these cases of 3 and 9 o'clock staining?
In the literature, in total ten possible treatment options for 3 and 9 o'clock staining can be found. Eight are related to lens parameters changes and of these, edge lift (or better: the edge clearance) is by far the most popular variable (mostly investigated and most often referred to). However, conflicting evidence is found regarding this variable: both increasing and decreasing the edge clearance is suggested to be beneficial in remedying 3 and 9 o'clock staining. Of importance to note is that by changing the edge lift, not just the edge clearance is changed but possibly a whole different fitting technique is introduced.
Larger edge lifts can lead to lid attachment fits, while with lower edge lifts interpalpebral fits can be created. The type of fit directly relates to other parameters that have been found to be useful in remedying 3 and 9 o'clock staining. These, however, also show conflicting evidence: both lens fits in alignment with the cornea and flat fits are advocated in the management of 3 and 9 o'clock staining. The same counts for diameter: either decreasing the total diameter or increasing it is suggested to remedy 3 and 9 o'clock staining. Lens positioning is related to the fit as well: it is suggested to avoid an inferior lens position, while centrally or superior lens position is said to decrease the chances on 3 and 9 o'clock staining.
Back surface geometry is another parameter that is subject to debate. Based on theoretical considerations it can be concluded that aligning the curves of the lens with the cornea as much as possible is likely to be decrease 3 and 9 o'clock staining, but scientific evidence to confirm this statement is not available.
More uniformity is found in the literature about the other remaining three variables for 3 and 9 o'clock staining. Decreasing edge thickness and creating a comfortable edge shape both seem to inhibit the eyelid-lens interaction, which might lead to a decrease in 3 and 9 o'clock staining. A good lens movement has been reported to be beneficial as well because of better mucine spreading and consequently proper wetting of the cornea. Furthermore, a clean and especially well wetting surface of the contact lens seems beneficial in prevention of 3 and 9 o'clock staining according to most authors.
Recently, we have found new evidence with regards to 3 and 9 o'clock staining, showing it is indeed a true tear film problem. First of all, the tear meniscus height in GP lens wearers was found to be statistically significantly lower than in non lens wearers: e.g. tear volume is subtracted for the anterior ocular surface by the (edge of) GP lens. Secondly, conjunctival staining was found to be more present in patients suffering from 3 and 9 o'clock staining, which is an indication of a dry eye disorder. Furthermore: blinking patterns are different in GP lens wearers and in particular in patients suffering from 3 and 9 o'clock staining: more partial or half blinks compared to full blinks were found in these patients. In addition to this: high edge lifts and interpalpebral fits (as opposed to lid attachment fits) cause more staining, which complies with the theory that blinking is inhibited because of discomfort by the lens edge.
These new insights will hopefully be beneficial in aiding 3 and 9 o'clock staining management. Particularly in the light to moderate cases, it is expected to be of value. For the true severe cases (grade 3 and up), other possibilities might be needed. Other types of lens modalities might be needed to solve the case (as in this particular case).
Case 2
Another very common problem in the GP lens practice is corneal warpage. This 35 year old patient presented with severe visual acuity problems when wearing her glasses and the following topography pattern, and in addition mentioned the presence of discomfort with her current GP lenses.
 |
(Marco van Beusekom, Visser Contactlenzen) |
The impact of the influence that RGP (and also hydrogel) lenses can have on the corneal epithelium has become clear in pre-exams for laser refractive surgery. RGP lens wearers frequently need to stop wearing their lenses for many weeks before surgery for the cornea to return to its baseline shape, and the same is true prior to orthokeratology treatment. It is becoming increasingly clear that RGP lenses can significantly influence corneal topography. One refractive surgery centre in the Netherlands reported that 95% of all retreatments for refractive reasons were performed on previous RGP lens wearers. Currently, it is advised to stop RGP-lens wear for at least 8 weeks prior to laser surgery, and after these 8 weeks to evaluate the cornea at 2-week intervals until the topography is stable (0.5D change or less compared to the last visit). Work by Wang et al supports this approach; the mean recovery time for corneal warpage in RGP lens wearers was 8.8 ± 6.8 weeks in their study. Extra care should be taking with long time lens wearers, PMMA lens wearers and back-surface aspheric multifocal lenses (that are fitted steeper than the flattest keratometry readings, sometimes up to 3D steeper). This can easily create corneal warpage and in theses cases it can take much longer than 8 weeks before the cornea is recovered.
Therefore it seems wise (apart from the gain in comfort) to respect the shape of the cornea as much as possible. If the surface area of contact is maximized between the lens and the cornea, the weight of the lens is distributed over the largest possible area of the cornea. In this situation the force per unit of surface area applied to the cornea is minimized, and the likelihood of corneal distortion is reduced. It has been shown that lenses that are fitted 0.3mm steeper than the flattest meridian induce corneal steepening after a short time of lens wear. In a recent orthokeratology study, patients showed significant central corneal flattening (0.61 ± 0.35D; p=0.01) within 10 minutes of open-eye lens wear, showing the vulnerable nature of the epithelium and the speed with which it can be altered. Alterations of corneal topography in RGP contact lens wearers have been reported by many researchers. The resting position of the lens on the cornea seems to play an important role; the topography of warped corneas is usually characterized by a relative flattening of the cornea underlying the RGP contact lens in its resting position. Lenses that ride high, for example, produce flattening superiorly and result in a relatively steeper contour inferiorly.
One of the main causes of corneal warpage is not respecting the shape of the cornea if corneal astigmatism is present. Non-toric lenses on with-the-rule corneas will create pressure in the horizontal meridian. Textbooks generally advice to use back toric designs when the corneal toricity is 2.5-3.0D or more. However, using non-toric lens designs on toric corneas below these values could easily lead to topographical changes and spectacle blur as well. Steep lenses, as little as 0.3mm (accounting for a 1.5D steep fit) will give significant corneal changes. In addition to this, corneal toricity may increase or decrease towards the periphery and thus influence fitting characteristics. Peripheral corneal toricity has been found to be one of the major factors determining the success of toric hydrogel lens fitting. Since RGP lenses rest mostly peripherally, this influence should not be neglected. Central cornea astigmatism is easier to deal with than limbal to limbal corneal astigmatism when fitting RGP lenses. Corneal topographers can aid in assessing the degree of peripheral astigmatism. If not available, a standard non-toric trial lens can be placed on the eye and the fluorescein pattern will aid the practitioner in the assessment of how much corneal toricity is present and whether this is acceptable or not.
Central versus Limbus to Limbus corneal astigmatism
|
 |
|
Increasing corneal astigmatism towards the periphery (note the difference in amount of astigmatism in the 3mm, 5mm and 7mm central zones shown in the table on the right)
(Colpa Optiek, the Netherlands)
|
If lower degrees of corneal toricity are present (in particular when peripheral corneal toricity can be seen), edge toric back-surface geometries with one spherical and one aspheric meridian can be used. This was the case in the reported patient above. After leaving her out of lenses for eight days, she was refitted with an edge toric lens since her corneal astigmatism was limited to -1.50D – with-the-rule. One meridian was fitted with an e-value of zero, while the flattest meridian was fitted with an e-value of 0.8. It is advised to use large diameters since the toricity increases towards the periphery (9.8 was used in this case). Be aware that, when evaluated these lenses with a radiuscope, the lenses are spherical centrally (and only start to diverge towards the periphery of the lens). The lenses are marked in the flattest meridian to make evaluation of the position of the lens in situ possible. No or limited signs of rotation during lens wear should be visible, and usually this is the case. Often, front toric optics are added to the lens.
Apart from an increase in lens comfort, the corneal warpage was resolved in this patient with the current lens design.
 |
Fluorescein pattern of an edge toric lens on a with-the-rule astigmatic cornea – note the dots in the 3 and 9 o'clock positions, marking the meridian with the highest eccentricity
|
