This case study highlights the value of fitting a scleral contact lens on a cornea with a large diameter penetrating keratoplasty.
A 57 year old male patient was diagnosed with keratoconus approximately 36 years ago. He wore rigid gas permeable (RGP) lenses for a number of years before receiving a penetrating keratoplasty (PK) in the Left Eye (LE).
The patient was referred to me in 2005 from an ophthalmologist to fit the Right Eye (RE) with a keratoconic lens. The RE was not considered for a corneal graft as the LE was still being treated for corneal rejection.
Topography from the Oculus Keratograph showed the RE had severe keratoconus with a prominent central ectasia and Sim K values of 6.20 mm x 5.17 mm and a corneal cylinder of -10.80D. The final lens fitted was a C2 toric design / BC 5.25 / Diameter 8.6 / Power -35.50D.
In 2008 the patient developed complicated glaucoma, coupled with corneal decomposition and chronic corneal ulceration in the LE, which persisted through various treatment options from two ophthalmologist. Unfortunately the end result was a loss of visual acuity to finger count in the LE.
In 2010 he started to develop acute hydrops in the RE and it was decided to do a penetrating keratoplasty. He did not respond well to the corneal graft and had multiple graft infections and ultimately developed a graft rejection.
A year later, in 2011, a second corneal graft was performed by another surgeon. Due to the state of the corneal periphery, the surgeon decided to perform a large diameter penetrating keratoplasty (LDPK), also known as sclerokeratoplasty.
Again the corneal graft started rejecting with the standard topical corticosteroid treatment. Consulting with an immunologist, the patient was placed on aggressive topical and systemic immunosuppressive drugs. He also developed increased intraocular pressure for which he was prescribed chronic glaucoma medication.
The patient was then closely monitored over a period of 2 years. Eventually the graft started to stabilise to a point where the patient could be referred back for RGP lens fitting in 2013.
Examining the anterior aspect of the eye, the patient presented with a large diameter penetrating keratoplasty with the radially interrupted sutures still present.
Peripheral corneal edema was visible with corneal neo-vascularisation present at the 4, 10 and 12 o’clock positions of the cornea.
Due to the nature of the graft, where the recessed conjunctiva is reattached to the limbus by bipolar cautery and sutures, the conjunctiva now presents as irregular and shows diffuse hyperaemia.
Further examination of the anterior aspect of the eye showed a complete iris prolapse. Posteriorly the patient had a pseudophakic intraocular lens. Fundus examination showed a glaucomatous optic disc with cup disc ratio of 0.7 x 0.8, the rest of the fundus appeared unremarkable.
Using the Medmont topographer a composite topography map was taken of the RE and imported into EyeSpace contact lens design software. The topography showed an irregular corneal surface with a corneal cylinder of 4.65D at an oblique axis.
The tear layer was extremely unstable as can be seen from the above Medmont placido rings and spectacle refraction proved challenging. The best corrected visual acuity with a trial frame was an intermittent 6/24 (0.25).
The patient’s chief concern was that he was not eligible to renew his drivers licence with his current visual acuity and was fully dependent on his wife and family for transport.
As the cornea was prone to rejection, all the sutures still present, and early neo-vascularisation present in the corneal periphery, it was important not to mechanically assault the corneal surface with a contact lens. After careful consideration it was decided to fit the patient with a scleral contact lens.
The scleral contact lens holds many benefits for this patient. Most importantly the lens itself will vault the corneal surface and only rest on the scleral conjunctiva, eliminating the risk of corneal mechanical trauma. Added benefits was the dry corneal surface will be permanently lubricated with saline captured between the lens bowl and the eye and no foreign bodies could flush underneath the lens causing abrasion or discomfort to the patient.
Fitting the EyeSpace scleral RS lens
The first step in fitting the EyeSpace scleral RS contact lens is to determine the correct sagittal height or sag of the lens. One way to determine the sag value of the initial diagnostic lens is to make use of the Medmont mean weighted value measured at a chord length of 10 mm. To this value add another 2300 microns to calculate the suggested diagnostic lens sag value measured at a chord length of 15 mm.
In this case the mean weighted value was 1788.9; added to that the 2300 microns and the initial suggested sag value calculated to 4088.9 microns.
The diagnostic scleral lens with the closest sag value was fitted on the eye:
Lens 3 / 5ZRS / 8 / 4040 / Flat / -1.00 / Diam 16.5 mm.
The sagittal height of the lens was not sufficient and required about a 100 to 150 microns more to achieve the appropriate post lens tear thickness (PLTT). A second diagnostic lens with a sag height of 4135 microns was fitted to confirm that the correct sagittal height for the final lens should be 4150 microns.
The 8.00 mm back optic zone radius (BOZR) of the 1st trial lens gave good alignment over the corneal surface .
Scleral landing zone (SLZ)
The next step was to determine the correct scleral landing zone (SLZ). When fitting the EyeSpace scleral RS lens it is important that the SLZ aligns correctly in all the meridians of the sclera. OCT is preferable in evaluating the accuracy of the SLZ angles, but in the absence of an OCT, the SLZ angles can be judged using a slit lamp.
Using the slit lamp, observe the limbal and para limbal zones under the SLZ in all the meridians for any edge compression leading to blanching or para limbal congestion. In this case it was particular difficult to judge the SLZ due to the irregular conjunctival tissue and excessive hyperaemia.
After observing the different SLZ angles, the Flat SLZ angle appeared to give the best alignment in the 4 major meridians.
Rotational symmetric (RS) or toric?
The next step was to determine if the scleral lens design should be a rotational symmetric (RS) or toric (T) design. The flat SLZ already appeared evenly aligned in all the meridians which favors the RS design. However, the best technique to determine if a toric design is needed, is to let the diagnostic lens settle on the eye for 20 minutes and take a topography map of the lens on the eye and observe for any lens flexing.
In this case the lens flex or lens cylinder visible on the topograpgy was 0.5D, which equates to approximately 90 microns of sag difference between the steep and flat meridians of the lens. The 0.5D cylinder had very little effect on the visual acuity of the patient and coupled with the evenly aligned SLZ, it was decided to use the RS or rotational symmetric design for this patient.
The EyeSpace scleral RS lens power is determined by the sum of the trial lens power, over refraction power, and change in BOZR between the diagnostic lens and final lens (SAM/FAP).
In this case the trial lens was -1.00D and over refraction with a trial frame was -11.00D, measured at a vertex distance of 13 mm. The final lens BOZR remained unchanged from the diagnostic lens which then required no further power adjustments requiring the SAM/FAP rule.
The overall lens power was calculated as -1.00D + -9.75D (vertexed) = -10.75D
Final lens parameters
The final lens was ordered through EyeSpace with the following parameters:
OD: 5ZRS / 8 / 4150 / Flat / -10.75D / Diam 16.5 mm / Clear.
The EyeSpace scleral RS lens was dispensed 2 weeks later.
Evaluation of the EyeSpace scleral RS lens revealed that the lens power was slightly over corrected and had to be adjusted by +0.50D, resulting in a total lens power of -10.25D.
The final visual acuity with the scleral contact lens was 6/7.5-2 (0.8-2). The patient reports that he is comfortable with his EyeSpace scleral RS lens, much more than with his previous RGP lenses, and he can wear the lens on average for about 12 to 14 hours per day.
Most importantly for the patient, his corrected visual acuity with the EyeSpace scleral RS lens made him eligible to renew his drivers license, restoring his independence.
The EyeSpace scleral RS contact lens range is a valuable option for eye care providers to correct irregular corneas and should be considered as a first fit for complicated penetrating keratoplasties.