Practitioners > Frequently Asked Questions > General Fitting Questions

General Fitting Questions

General fitting questions from fitters and replies by Paul Rose

last updated 2021.1.8


Q: I’ve been working with patient who claimed he is using RGP. To start with we suggest to get his topography result but it’s sooo impossible for him to get this done. Will keratometry be enough and ask fitter to bring trials?

A: Yes, keratometry readings are sufficient for your first choice of trial lens but they give no information on corneal shape like topographers do, so therefore no indication on the choice of the appropriate Rose K design. If the patient has been diagnosed with keratoconus then I suggest initially to use the regular Rose K2 (KC) trial set.

Q: If you increased the edge lift, as all the peripheral curves are altered, does this not lower the overall sag of the lens, and would you not need to steepen the base curve to compensate ?

A: Yes, changing the edge lift does change the overall lens sag. When an edge lift other than standard is ordered the laboratory automatically makes a change to the BC to change the sag so it matches the standard lift trial lens.

Q: To select the first Rose K can you use the BestFit Sph of elevation maps?

A: The Rose K fitting guides are based on mean 3 sim K's or K readings.  Using best sphere from the elevation map will invariably produce a much flatter value so unfortunately using best fit sphere from elevation maps would not be appropriate.

Q: When we change edge lift by +1.50, with ideal BC, should we steepen the BC by 0.1 steep?  Because some time the lens goes flat with increasing the edge!

A: The laboratory will automatically change the edge lift to compensate for the lower sag with the increased lift, so in the majority of cases the central fit will remain the same as your trial lens when you change the edge lift value.  However, depending on where the lens is bearing, in some cases the change is insufficient and the BC may require steepening further.  Unfortunately this is not predictable so my advice is not to change the BC when you change the lift.

Q: Do you use anesthetic eye drops for the first fitting?

A: Yes, I always use corneal anesthetics for new patients but not for patients who are already wearing lenses. This makes it more comfortable for the patient and reduces the tearing to give a more accurate fluorescein pattern and reduces fitting time. 

Q: Can I start my test with average K in all situations ?

A: Yes, before we had topographers this was all we had to use and we still fitted keratoconus successfully. The only downside is that it does not show you the corneal shape so gives no indication for the best choice of Rose K design.

Q: How would you amend a lens that is too tight in the mid periphery despite a good central fit and despite flattening the periphery to achieve an ideal 0.6-0.8 fl peripheral band width? I find this happens with steep central cones.

A: When you change the edge lift this also affects the mid-peripheral fit, as all curves change outside the back optic zone to the edge of the lens change. Try increasing your edge lift to a maximum before the lens becomes unstable. Also making the lens smaller if this is an option or changing the design to Rose K2 NC can also help this problem.

Q: What is the difference in lens design between Rose K PG and Rose K IC?

A: They are a similar design.  However IC has a larger back optic zone and a lower edge lift value than PG.

Q: If palpebral apertures are small or where the lens is lid attached, would you still assess fit in the central position or wherever it naturally settles?

A: Always assess the fit with the lens centered over the pupil even if it does not locate here for the majority of time.  On blinking the lens will travel over the central area and I therefore still find that this is the best position to assess the fit.

Q: Is there relation between diameter and the power of lens? For example, if we change diameter, will the power change?

A: No, power will not change if you change the diameter.  Power change is affected only by the Base Curve.

Q: Does Rose K2 XL work on the cornea or sclera?

A:  Rose K2 XL lands nearly entirely on the cornea just inside the limbus. It lifts off over the sclera.

Q: Why we chose as small a diameter as we can rather than large diameter in Rose K2 ?

A: Irregular corneas often have peripheral astigmatism. Therefore the further we go out from the center of the cornea the greater the sag difference becomes in the two meridians. Thus, the larger the lens diameter the more the corneal asymmetry needs to be considered.

Q: Is there any specific requirements when to use ACT?

A: When you want to change the edge lift considerably in only one meridian. Remember with XL you will also affect the fit on the peripheral cornea as well as outside the limbus.

Q: Can OCT help correct fitting and if so how many microns for each area?

A: An OCT is useful in verifying your final lens but fluorescein is easier to use for the fitting.  For XL, aim for 35 to 50 microns clearance at the highest point on the cornea. In the periphery and edge lift of between 50 to 60 microns in all meridians.

Q: TP > Can I anticipate whether I’ll need a TP lens looking at the Topo (Fourier analysis) ?

A: Unfortunately not as topographies are often not accurate enough outside 5mm and this is where the TP is applied on the lens. I have tried to do this but was unsuccessful.

Q: For a XL lens steepen the base curve to give movement to the lens will not have frothing effect?

A: Frothing or bubbles under the lens can only come from insertion, an edge lift that is too high, or a diameter that is too small. Steepening the BC will not cause frothing.

Q: How do you manage hypoxia problems with XL lenses?

A: Make sure the lens is not binding.  If it is, can you increase the edge lift or steepen the BC? Also do a topography over the lens in situ to make sure it is not warping as this will also cause binding.

Q: If I change the edge lift, will this change the fit over the cornea?

A: In corneal lenses if you change the edge lift value the laboratory will automatically change the BC value to reflect the change in sag so that it will fit like your trial lens. With XL, changing the edge lift value does not affect the central fit unless the lens is resting heavily on the sclera and not the cornea.

Q: Is it appropriate to rectify toric edge problems by just ordering a smaller diameter Rose K XL?

A: NO, this is not appropriate. Diameter in XL is completely dependent on the patient's HVID.  The edge lift must be judged separately from the diameter.  The diameter needs to give 1.3 to 1.5 mm overlap outside the limbus.

Q: Why do we have to steepen the BC to increase the movement? 

A: With a flat lens the minimal tear layer between the lens and the cornea over the flat area produces large capillary forces between the surfaces causing suction and reducing movement. You have to misalign these surfaces by going steeper with the BC to reduce this capillary force. Try taking two pieces of flat glass with a think layer of water between, force them together and then try to pull them apart.  It is impossible because of the capillary forces.

Q: Which gain of visual acuity do you recommend for ordering a front toric lens?

A: Usually one line of vision makes it justified but I gauge this by the patient's reaction.  If they notice a significant improvement when you hold the cyl over the spherical trial lens then I will incorporate the cyl.

Q: Can toricity be measured by tomographer like Pentacam to adjust TP? 

A: In my experience I have not found this to be accurate enough to predict the amount of TP. 

Q: When you say you judge the EL at 3 and 9 o'clock, do you also assess the 12 and 6 o'clock but not adjust the EL from their appearance as much?

A: With corneal lenses and keratoconus, we judge the edge lift in the horizontal meridian as this will normally be where it is the tightest and this can cause issues.  If the edge lift is a little more open in the vertical meridian then this will often not be an issue.

Q: Which is the clearance on limbus zone with RoseK XL in situ? 

A: Around 20 microns.

Q: How can you identify the cone you have without a topography image using a keratometer?

A: Unfortunately you cannot identify the cone type from a keratometer. You need to assume it is an oval cone so initially try the Rose K2 KC design and then assess the fitting pattern which will show whether it is an oval or nipple cone.

Q: During the fitting process we have seen patients where as we steepen the lens, the central touch still remains. We have a theory in my hospital department that if the edge is too tight, as you steepen, it tightens further and squashes the soft KC cornea up so it still looks flat centrally. Do you think this is the case?

A: I assume you are referring to corneal lenses here? If so I have not ever experienced cases where the BC is steepened and the central touch remains the same.  With Rose K designs, always attain the correct BC first before assessing the edge lift. However it is difficult to judge exactly how flat a BC is and often this is underestimated so that a steeper BC can still show touch.  I cannot see how a corneal lens could cause the apex to protrude further.

Q: My question is why Dr. Rose considered a semi scleral lens instead of a fully scleral? Semi scleral versus scleral please.

A: The smaller the lens the less you have to be concerned about fitting scleral toricity.  Also smaller lenses are in my experience easier to insert and remove.

Q: If a TP and FS cylinder is required for a XL design contact lens, should the TP be added before the FS cylinder, or at the same time?

A: It can be done at the same time. However if you are finding you require a FS cyl then ALWAYS do a topography over the trial lens in situ to make sure it is not warping which would induce the cyl.  Adding a TP to XL will often prevent lens warpage which then may mean you do not require the FS cyl.

Q: Do before you assess, like a semi scleral, need to let the XL lenses settle for a certain amount of time?

A: Get the correct fit and then let XL settle for a further 20 mins only before doing a final assessment.

Q: Can we consider that when using ACT, the central sagittal depth increases a bit?

A: Not necessarily. Most often the central fit over the pupil remains the same.

Q: If we choose TP in corneal lens, is there a scale or a proportion that we have to follow to change BC?

A: I do not publish a scale.  However the standard TP of 0.8 requires a BC steeping of 0.05.  A TP of 1.6 would require twice this of 0.1.  As a rough guide the BC will require to be steepened by about 50% of the toricity amount.

Q: Why would you not just go to the RoseK XL lens straight away as it seems to cover most aspects of KC and seems more comfortable initially when compared to a corneal lens ?

A: If a patient can tolerate a corneal lens comfortably then why cover the whole cornea, which can have disadvantages, if you do not need to?  Also corneal lenses are easier to handle than larger lenses like XL.  Also they are considerably less expensive which is important in some markets.

Q: What are my options if ACT design is applied in a case where it's needed, but the lens position results in too low centration?

A: I assume this is with a corneal lens. Flattening the BC, increasing the diameter, increasing the edge lift or decreasing the amount of ACT can help the lens to locate higher.  If this does not help then try the Rose K2 PG design which has a larger BOZ and larger diameter but would require increased lift for keratoconus.

Q: When is needed a back toric design in KC patients?

A: A full back surface design is required when a TP design still does not provide the optimum fit.  If the degree of TP toricity required is greater than 1.8 then you probably need a full back surface toric. Back surface torics are very under-utilised around the world.

Q: What time you suggest to use to evaluate toric scleral lens rotation to get back in their place? I mean, when we can consider returning movement slow or high?

A: A lens with a TP should orientate itself correctly within 10 seconds of insertion.

Q: How can we adjust if we have lifted superior edge not inferior ?

A: You can adjust the edge of the lens either inwards or outwards anywhere around the clock. If you want to change the edge lift only outside of the limbus then use the quadrant specific edge lift option where a different edge lift can be ordered in each different quadrant. If you order an increased lift this will move the edge of the lens away from the eye and the notation will be + For example a +1.00 is a standard increased lift. If you want to tuck the edge in then we use a decreased lift and the notation is minus  (- ).

Q: Should we account for lens settlement when judging apical clearance?

A: It is common for the lens to settle slightly, about 0.05 to 0.1mm , so yes leave the lens slightly on the steep side at the fitting.

Q: Why does a steeper BC increase the movement?

A: With a flat lens a very thin tear layer between the cornea and the lens back surface is created. This causes a large capillary force between the two surfaces which reduces the lens movement.

Q: What's the central thickness of Rose K2 XL?

A: It depends on the power but for minus powers over -7D it is 0.14. For lower powers it is thicker up to 0.2mm.

Q: Can we order toric edge values below 1.2?

A: Yes you can have toric periphery values from 0.4 to 2.0 in 0.2 steps.

Q: What can we do about fogging effect after 3-4 hrs of wearing?

A: If possible reduce the tear film depth by flattening the BC and also increase the edge lift as much as possible.

Q: What to change if the patient finds that the lens is difficult to remove?

A: If possible increase the edge lift.

Q: From what age can an XL be applied? Is an extended wear up to 7 days possible?

A: From any age as long as the patient or parents can handle the lens competently. XL is not recommended for extended (overnight) wear.

Q: Sclerals are good for dry eye, would that be specific for aqueous deficient or would meibomian dropout dry eye also be good candidates?

A: Would be good for both scenarios.

Q: Have any similar studies (regarding IOP) been performed on corneo-sclerals as you are aware of? (If a more tricky cornea need a bit more steep lens than ideal - it might be a bit tricky to remove thus potentially also affecting IOP?)

A: No not that I am aware of but as the suction forces are less with C Sl's we would expect them to have less effect on IOP's. Yes a steep BC can increase suction but edge lift is the main factor.

Q: Has there been issues with pterygiums?

A: XL can accommodate pterygiums by using reverse ACT over the raised area. You can also use the SSACT options which defines a smaller segment for the increased lift than normal ACT. Please look at the special options fitting guide on

Q: What is the reason for difficulty in removal of the lens (lifting from periphery)?

A: There are 3 reasons why a RoseK2 XL lens can be difficult to remove. 1. A tight edge. 2. A BC overly steep or flat even slightly. 3. The lens has warped. This can be checked by taking a topography over the lens in situ. It should be spherical unless a front surface cylinder has been added.

Q: How to manage patients using Rose K2 XL but having tears particles?

A: I assume you refer here to particles in the tear layer which causes "midday fogging". Minimise the tear layer thickness over the highest point on the cornea, and maximise the edge lift to ensure tear exchange. Also changing the insertion solution from non-preserved saline to specific scleral lens insertion solution which has a similar PH to the tears can help.

Q: The choice of the diameter of the IC is HVID -1mm ?

A: This depends on several factors such as the cone position and whether the IC lens is locating and moving correctly. But as a "rule of thumb" for IC it should be HVID -  0.6mm

Q: Which parameter would you change first to improve lens comfort providing lens is feather touch over the cone?

A: The edge lift influences the comfort of the lens more than any other one factor. In the corneal lens designs a tight edge lift will be less comfortable but in the XL design an edge lift that is excessive will be uncomfortable.

Q: I have experienced few cases while fitting on keratoconus patients the landing of the lens is happening on limbus or on sclera even though the corneal diameter is 12mm or more.

Please guide on this concern.

A: This would suggest that your choice of edge lift is too tight. For a 12mm HVID the XL design should always land inside the limbus unless the edge lift is tight causing the lens to bear on the limbus and also on the conjunctiva.

Q: What do you do if the Rose K2 NC is too flat on the cone with a bubble in the center at the insertion of the lens (bubble doesn't come from the EL) ?

A: Try filling the lens on insertion with an overnight storage solution such as Menicare. Also reducing the overall lens diameter can help as this also reduces the back optic zone diameter. Fit the lens optimally however so you have feather touch at the highest point on the cornea which may not be the cone apex if there is scar tissue present. If all this fails piggyback the Rose K2 NC over a  daily soft disposable lens.

Q: Is it true that a portion of keratoconic patients are not able to obtain sharp vision with any corneal lens design due to the distortion of the back surface of the cornea?

A: Yes, certainly this is true. If the back surface of the cornea is too distorted this will make it impossible to achieve good vision even with the optimum fit. Not being able to achieve satisfactory vision for the patient in these cases is an indication for a full thickness corneal graft.

Q: Patient with XL 7.4mm, central fit perfect, problem  diameter is small, lens exactly on the edge of cornea so no landing area, I will increase diameter to16.50, but I don’t know what to do with edge lift, need help.

A: If you have an optimum BC and edge lift with your trial XL  lens but want to make changes to the diameter, you do not need to make any adjustment to either the edge lift or the BC when changing the diameter from the trial lens . Simply use the the edge lift value that looked optimum with the trial lens. However for corneal lenses changing the diameter from the trial lens does require a change in the BC.