This case report highlights how the Scleral 5Z Toric lens can be used to fit a healthy eye with high amounts of regular astigmatism to provide comfortable, stable and sharp vision in a contact lens.
Video of case report
This patient, a 25 year old male, reported to our practice to investigate his contact lens options. He is a university student in the health area and plays basketball at a high level.
He has high amounts of astigmatism and came to his appointment wearing spectacles, which he was very happy with.
RE: +5.50/-4.50 x 168 VA:6/5
LE: +5.25/-4.25 x 11 VA:6/5
He had tried several different contact lens options in the past. Customised soft toric disposable lens had good comfort but the vision was poor and fluctuated. Rigid gas permeable bitoric corneal lenses were tried but were poorly tolerated due to comfort despite providing good vision. They had also popped out twice during basketball games!
Discouraged by this our young patient got the opinion of a corneal specialist who told him a clear lens extraction was the only permanent opinion. After discussion of his options we decided to fit a toric periphery scleral lens to improve comfort and stability of the lens and vision when the patient needed to be without his spectacles.
CAPTION:Corneal topographies and fundus images in Medmont Studio showing the regular limbus-to-limbus WTR astigmatism.
Corneal topographies show limbus to limbus regular with-the-rule corneal astigmatism corresponding to the spectacle prescription. Interestingly his fundus photos shows his high astigmatism with the horizontal vessels appearing clearer than the vertical, not unlike a fan and block chart might appear!
His visible iris diameter measurement was a large 12.0mm so we started trial fitting with the larger 17.5mm 5ZR set. To establish the sag of our initial lens we first measured the sag of the flat meridian at a 10mm chord in Medmont. This gave 1556um in the RE and 1565um in the LE. Adding 2300um to this amount gives a starting sag value of ~3850um in each eye.
From the fitting set we elected to start with Lens 14 (3900um / 8.2mm / Standard SLZ / plano / 17.5 ) in the right eye and a lens with more sag in the left: Lens 16 (4100um / 8.0 / Flat SLZ / -1.00D / 17.5 ).
Whilst comfortable, the rotationally symmetrical trial lenses rocked along the vertical meridian allowing bubbles beneath the lens and making it difficult for the patient not to blink the lens out! A topography over these trial lenses after only a few minutes showed significant with-the-rule flex of around 2 diopters. Over-refraction through the lens at this point also showed -2.00D of astigmatism with axis 180.
CAPTION:Topography over the rotationally-symmetrical trial lenses shows significant flex on the toric anterior surface.
Given the difficulties keeping the lens in the eye it was decided to proceed to an initial lens order. As it was clear that significant differences in the sag value would be required to prevent flex in the lens it was decided to order the lenses with 500um difference (to account for ~2.50D of flex) between the meridians. A base curve of 8.2mm was decided on as it was the average of the principal meridians of the each cornea. The trial lens appeared to fit very steep horizontally so an increased flat scleral landing zone (SLZ) was used in this meridian and a standard SLZ zone was used vertically.
The first lenses ordered were as follows: RE: 5Z T XL / 8.2 / 3850 x 4350/ Incr. Flat x Standard / 17.5 / +3.50
LE: 5Z T XL / 8.2 / 3850 x 4350 / Incr. Flat x Standard / 17.5 / +3.00
1st follow up visit
Following a delivery and teach appointment the patient returned wearing his new lenses after 1 week. He reported the comfort was excellent and the vision generally very good, he had played a game of basketball a few days before with no problems. He did comment the vision sometimes misted up after a few hours. He also found that his insertion technique sometimes ended up with a few bubbles beneath the lens. On several occasions there was some redness of the eyes following removal.
RE: VA: 6/7.5, OR +0.25/-1.00 x 165 (VA: 6/5) LE: VA: 6/5, OR +0.50/-0.75 x 170 (VA: 6/5)
A topography over the lens showed very slight flex R>L still present in the vertical meridian. This explains the WTR astigmatism present in the over-refraction.
CAPTION:Corneal Topography over the scleral lenses showing slight flex in the vertical meridian R>L.
Central clearance was excessive as shown by the OCTs and with a view through the slit-lamp at 45 degrees to the visual axis. A measurement with the OCT software shows clearance of R 424um and L 415um.
CAPTION:OCT showing the central clearance of the initial scleral lenses. The top image is the right eye.
An alternative method to measure the central clearance is to compare the clearance by comparison with a known corneal thickness (measured with a pachymeter) or comparison with the central scleral lens thickness, which will vary but tends to fall between 300-400um (this can easily be verified with a thickness gauge).
CAPTION:Digitally enhanced images showing the central clearance of the scleral lens in the the R and L eye.
The excessive clearance was most likely allowing a slight mucous build up to accumulate beneath the lens and cloud the vision. Some of this buildup can be seen in the OCT images below. Mucus is a normal inflammatory response to irritation, expected in a neophyte wearer. Topical anti-histamine drops can help with this, along with ensuring there is not excessive apical clearance for the mucus to accumulate in and ensuring the lenses are very clean (cleaning with a dedicated rigid lens cleaner such as Lobob and a cotton tip can help here). Some patients find they prefer to remove and reinsert the lens with fresh saline midway through the day, which is not a bad management strategy anyway to avoid stagnation and de-oxygenation of post-lens fluid. Most new wearers will only be bothered by a mucus response for a short time as their eyes become accustomed to the lens.
Scleral Landing Zone (SLZ)
The fit of the lens appeared reasonable although the lens did appear a little tight in the SLZ, especially horizontally. You can see this on the slit-lamp images as the edge of the lens appears to occlude the conjunctival vessels.
CAPTION:Slit lamp images of the lens fit in the RE
The OCT also shows the ‘toe’ of the lens digging into the conjunctiva, rather than distributing the pressure evenly across the landing zone.
CAPTION:OCT of the horizontal meridian of the RE showing a slightly steep SLZ.
CAPTION:Slit lamp images of the lens fit in the LE.
CAPTION:OCT of the horizontal meridian of the LE also showing a slightly steep SLZ.
To improve the scleral fit, a new pair of lenses were ordered with,
- less central clearance
- slightly more sag difference to reduce subtle lens flex
- flatter SLZ to have the lens more evenly spread the pressure on the conjunctiva at the edge of the lens and avoid redness on removal.
The new lens parameters ordered were: RE: 5Z T XL / 8.2 / 3600 x 4200 / Extra Increased Flat x Flat / 17.5 / +3.50 LE: 5Z T XL / 8.2 / 3600 x 4200 / Extra Increased Flat x Flat / 17.5 / +3.00
2nd follow up visit
The patient returned 2 weeks after picking up his new lenses. He reported vision with his new lenses was improved compared to his first lenses and was now as good as his glasses. He was noticing much less hazing as the day continued. Comfort was also reported to be excellent. Vision with each lens was 6/6+2 after 4 hours of wear.
Topography over the lenses showed no obvious flexure.
Central clearance was much improved, measuring in the low 200um. This clearance could be further decreased into the 100-50um range if desired with the predictability afforded by modern lathe technology.
CAPTION:Decreased apical clearance in the new lenses as seen with the slit-lamp and OCT.
Scleral Landing Zone (SLZ)
The edge appearance was also improved with the flatter SLZ in the new lenses. There is very little conjunctival impingement. Upon removal, aside from some mild staining atop small pingueculae in each eye, there is no evidence of lens impression or abrasion. The cornea is also devoid of defect.
CAPTION:Scleral landing zone profiles of the new right lens. Note the decreased conjunctival blanching.
CAPTION:Scleral landing zone profiles of the new left lens. Note the decreased conjunctival blanching.
CAPTION:NaFl images of the cornea and conjunctiva immediately after lens removal. Note the only staining present is over the mild pingueculae.
The SLO image of the anterior lens surface as we were carrying out the OCT measurements showed that after a blink the surface was quick to dry out, indicating poor wettability. This could be seen with the topographer also albeit to a lesser extent.
CAPTION:SLO image of the anterior scleral lens surface, the speckled reflection seen was not present immediately after a blink, only after the lids were kept open for 2-3 seconds.
To improve wettability a detergent-based lens cleaner (Lobob) was added to the patient’s cleaning arsenal rather than just a multi-purpose solution (Menicare plus) for cleaning and disinfection. The next image shows the lens of a different patient (but with the same Boston XO material) with complaints of haze developing throughout the day. This haze was eliminated after switching to Lobob instead of Boston Advance Cleaner.
CAPTION:A different patient’s scleral lens with poor wettability and vision. This resolved with the use of Lobob daily cleaner.
Overall the patient was very happy with the outcome of his scleral lens fitting. His vision was comparable with his glasses, was stable even during high level competitive sport and comfortable throughout the day. He will be reviewed in 2-3 months for an aftercare to check the health of his eyes have not been compromised and the patient is adhering to his lens care regime.
Careful assessment of the cornea for signs of hypoxia and toxicity is important during follow-up visits as even with the high Dk materials used in modern scleral fitting, the thickness of the lens and tear reservoir can pose barriers for oxygen to pass to the cornea. A key concept here is that a toric cornea can achieve great vision with a spherical back optic zone. The difference in sagittal height of the peripheral areas is key, as this controls stability and flexure on the eye.
This case shows that specialty scleral lenses are not just reserved for diseased or compromised corneas but can be a useful and effective tool in treating regular ametropias in practice.