The Scleral Lens Education Society: Case Report 1
Management of Keratoconus and Corneal Graft with the use of Rigid Gas Permeable Semi-Scleral (Corneo-scleral) Contact Lenses
Dirk J Booysen Dip. Optom FOA(SA), MCOptom(UK), TMOD(PCO), CAS(NECO), DOptom(Aston) 248 Voortrekker Road Monument Krugersdorp Republic of South Africa dirk@dirkbooysen.co.za
Abstract
Keratoconus is a bilateral asymmetric non-inflammatory corneal degeneration characterised by localised corneal thinning which leads to ectasia or protrusion of the thinned cornea. The corneal thinning and protrusion can occur anywhere on the cornea but is most commonly found in the inferior and central cornea and this leads to high myopia and irregular astigmatism that affects the visual acuity and the patients quality of life. The most important objectives of non-surgical treatment is firstly to halt progression and the secondly to provide visual rehabilitation. Contact lenses are extremely beneficial to correct vision in many patients but does not slow or halt progression of ectasia.
This case report deals with the use of rigid semi-scleral (corneo-scleral) gas permeable contact lenses to visually rehabilitate a patient with keratoconus, post penetrating keratoplasty corneal irregularity and high myopia.
Key Words
Keratoconus, keratoplasty, scleral lenses, corneal ectasia
Introduction
Keratoconus is a bilateral asymmetric non-inflammatory corneal degeneration characterised by localised corneal thinning which leads to ectasia or protrusion of the thinned cornea 1,2. The corneal thinning and protrusion can occur anywhere on the cornea but is most commonly found in the inferior and central cornea and this leads to high myopia and irregular astigmatism that affects the visual acuity and the patients quality of life 1. Keratoconus, pellucid marginal degeneration, keratoglobus and progressive iatrogenic ectasia is classified under "ectatic corneal diseases" while conditions such as Terriens marginal degeneration, dellen and inflammatory melts are not classified as ectatic diseases but "thinning disorders" of the cornea 2. Keratoconus typically presents during the second decade of life during puberty and progresses until the forth decade when it stabilizes 1.
Histopathologically , there are three signs that typically characterise keratoconus; corneal thinning, Bowman's layer breaks, and iron deposits within the corneal epithelium's basal layer (Fleischer's rings) 1. The epithelial basal cells degenerate and decrease in density and grow toward Bowman's layer which often show breaks filled with collagen from the stroma. In the stroma the number of lamellae, keratocytes are decreased leading to changes in the gross organization of the anterior stroma lamellae and collagen fibrils particularly around the apex of the cone 1. The corneal nerves have thicker bundles, reduced density and sub-epithelial plexuses compared to normal corneas 1.
Descemet's membrane and the endothelium are usually unaffected until the late stages of the disease when breaks can occur leading to disruption of the endothelial pump mechanism which results in corneal hydrops 1. Despite intensive research into the aetiology and pathogenesis of keratoconus, the causes and mechanisms for its development are poorly understood and there is no primary pathophysiologic explanation for keratoconus 2. However, several hypotheses have been proposed which include genetic, environmental, biochemical, mechanical and biomechanical mechanisms. Furthermore keratoconus associations with other diseases are well documented 1,2.
Keratoconus can be managed non-surgically or surgically depending on the severity of the disease. Even in the case of corneal hydrops, non-surgical management should be attempted before keratoplasty 2. The most important objectives of non-surgical treatment is firstly to halt progression and the secondly to provide visual rehabilitation. Among the non-surgical treatment measures verbal guidance regarding the importance of not rubbing one's eyes and effective treatment of ocular allergy with topical multiple-action anti-allergic medication are probably the most important to halt progression of the disease 1,2. Contact lenses are extremely beneficial to correct vision in many patients but does not slow or halt progression of ectasia 1,2. The flowchart from Gomes et al, 2015 explains the treatment options available to the keratoconus patient (Figure 7).
Case Report
This 66 year old Indian lady has a history of keratoconus and high myopia. I first saw her in the mid 1990's for treatment and visual rehabilitation for her keratoconus. Unfortunately those records were lost as she consulted other practitioners in the interim (records older than 10 years are destroyed).
She has subsequently had multiple eye surgeries, including cataract extraction with IOL implants, YAG capsulotomies, retinal surgery in both eyes, and penetrating keratoplasty in the left eye only. Her initial visit took place on the 30th January 2015. My findings were as follows.
R. +3.00/-2.00×180 20/400 L. +1.00/-2.00×10 20/200 GAT IOP was 16mmHg in both eyes corrected to right 16+6 = 22mmHg and left 16-4 = 12mmHg (Dresden correction algorithm). Axial length was measured using the Pachscan 300 AP (Sonomed), right eye 27.80 mm and left 28.82 mm.
Biomicroscopy revealed a central corneal scar (in the visual axis) in the right eye most likely due to corneal hydrops or previous rigid gas permeable lens wear (Figure 1). The left eye showed superior lid ptosis as well as penetrating keratoplasty with clear cornea and no evidence of rejection (Figure 2). The pupil was offset nasally and there was a superior temporal irredectomy. Both eyes were pseudophacic with well-placed IOL's and YAG capsulotomies. There were no signs of lid disease and the tear break up time was 10 seconds in both eyes. Pentacam scans are attached showing central protrusion of the right cornea with curvature of 52.7/53.9 dioptres and thinnest pachymetry of 391 microns (Figure 3 & 5). The left eye shows a temporal elevation and nasal depression of the cornea in keeping with the irregular surface created by the corneal surgery. Curvature was 43.4/57.10 dioptres and thinnest pachymetry was 496 microns (Figure 4 & 6). The external anterior chamber depth (measured form the corneal epithelium) measured by the Pentacam was right 4.27mm and left 4.67mm. Dilated examination of the fundus showed posterior staphyloma as well as chorioretinal atrophic and macular changes in both eyes.
Contact Lens Examination and Fit
Although penetrating keratoplasty is not a contraindication for scleral lens wear, care has to be taken to ensure that the scleral lens does not trigger graft rejection which is normally preceded by microcystic oedema of the graft tissue. In these cases it is of utmost importance to choose a lens with appropriate corneal clearance and sufficiently high Dk values to ensure corneal health 3 Van Der Worp, 2015 classifies a semi-scleral lens as having a diameter of 12.5 to 15.00 mm sharing bearing on the cornea and sclera (Figure 18) 3, this lens design can also be classified as a corneoscleral lens 4. Although complete corneal clearance would be preferable in this case I decided to fit a rigid corneo-scleral design for this patient due to her difficulty in handling (removing) larger diameter steeper lenses. The lens rests partly on the cornea as well as the sclera and as long as no mechanical insult occurs to the cornea and the fit is closely monitored this fitting modality works well. On the 10th February 2015 she came in for trial lens fitting. My trial lens selection is roughly based on measured anterior segment depth + 0.30 mm = right 4.27 + 0.30 = 4.57 mm and left 4.67 + 0.30 = 4.97 mm (Figure 8). Figures 9 to 12 show the results of the lenses on the eye. Over refraction was right +8.00 and left +3.00 and visual acuity was right 20/100 (PH = 20/100) and left 20/100+ (PH = 20/80). Both initial trial lenses were flat showing very little corneal clearance in the right eye and no corneal clearance in the left eye which was also evident after removal of the lenses (Figure 11 and 12). Limbal clearance was adequate in both eyes. The sagittal depth was increased to right 4.6@15.60mm and left 5.03@15.60mm and the peripheral curves and diameter altered to 14.60mm/1.20mm and 16.00mm respectively in order to obtain more acceptable corneal as well as limbal clearance and adequate scleral fitting relationships (Figure 13). Because of the corneal irregularity the corneal clearance varied between 70 to 120 microns in the right eye and 60 to 120 microns in the left eye depending on which corneal meridian was measured, limbal clearance along the horizontal was 210 microns in the right eye and 230 microns in the left eye. Due to "sinking" of the scleral lenses during wear the lens will have some bearing on the cornea which may vary during wear 3. The goal is to minimise this bearing to maintain corneal health. Regular visits are required to re-evaluate the fit and to look for signs of corneal staining and to ensure that the bearing of the rigid corneo-scleral lenses are minimal. Over refraction on the second set of lenses was right +6.50 and left +2.00 with acuity of 20/100 and 20/80 right and left respectively.
Final corneo-scleral lenses were ordered as per figure 13 and dispensed on the 23rd February 2015. The fluorescein patterns indicated acceptable corneal as well as limbal clearances of right 80/160 microns and left 70/170 microns respectively (Figures 14 and 15). She was instructed on different lens insertion and removal techniques and felt most comfortable using a DMV plunger to remove and insert the lenses. The lens bowl was filled with unpreserved saline (Alcon Polyrinse®) before insertion. Hydrogen peroxide was recommended as a disinfection system (AO Sept®) after cleaning and rinsing the lenses with a surfactant (Crystal Cleaneralcohol based surfactant) and saline respectively. Alcohol based surfactant cleaners are very effective in removing surface lipid and protein deposits with manual rubbing. In combination with hydrogen peroxide sterilization this cleaning regime is very effective for all types of contact lenses. Hydrogen peroxide was specifically selected for this patient due to her rural location and the significant risk of Acanthamoeba infection due to poor drinking water quality which makes the use of multipurpose solutions and rinsing with tap water extremely risky. A two-step 3% hydrogen peroxide solution is 99.9% cysticidal providing contact times of at least four hours are employed 5. Hydrogen peroxide also provides excellent antimicrobial and antifungal efficacy. It works by penetrating the lens material and cleans by expanding the lens matrix and oxidizing microbes. Because of its hypotonic nature and pH of 4.00, H2O2 is also able to break protein and lipid bonds, remove trapped debris and penetrate bacterial biofilms6. H2O2 is highly effective against all microorganisms when used in a 3% concentration but is non-selective in its activity.
Unfortunately this lady struggled with removal of the lenses and although the addition of a toric peripheral curve could have improved the lens fit and removal, this technology is not currently available in South Africa necessitating the addition of small peripheral fenestrations in the periphery of both lenses to facilitate lens removal. "It has been suggested that in theory, more "suction" of the lens can occur in non-fenestrated lenses and that fenestrated lenses can be easier to remove and can improve the exchange of metabolic debris, but no scientific evidence for these theories are available" 3. In some cases the negative pressure under the lens can be such that the conjunctiva can be sucked underneath the lens and even through the fenestration 3. Fortunately in this case the fenestrations solved the removal problem without trapping the conjunctiva.
The next follow-up visit took place on the 30th March 2015 and again on the 14th April 2015. At both these visits she had no adverse reaction to the lenses and both corneas remained clear with no NAFL staining. He vision remained stable and she reported that she could wear the lenses up to eight hours per day. The last visit was on the 27th May 2015. Once again no adverse reactions were seen and both lenses were clean. Her corneas were clear; there was no ocular inflammation and no NAFL staining present. The patient also reported that she was much more adept at inserting and removing the lenses than before. Her vision has remained at 20/100 and 20/80 and she was able to wear the lenses up to 8 hours per day comfortably. An additional unexpected benefit of the scleral lens on the left eye was that the ptosis of the superior lid was reduced – possibly due to the lens shape and thickness.
Differential Diagnosis
Pellucid marginal degeneration (PMD): Bilateral asymmetrical corneal thinning in the inferior periphery with protrusion superior to the band of thinning. PMD can co-exist with keratoconus and keratoglobus. Corneal topography show a "butterfly" pattern with severe astigmatism and diffuse steepening in the inferior cornea 7-9 Keratoglobus: Rare congenital, non-progressive disorder with a circular uniformly thinned cornea. Onset is at birth. Maximal thinning occurs in the mid-periphery of the cornea with protrusion central to the area of maximal thinning 7-9 Iatrogenic ectasia: After lamellar refractive surgery such as Laser in situ keratomileusis (LASIK), and rarely surface ablation (PRK), an ectasia similar to keratoconus can develop.
Treatment is similar to that of keratoconus 7-9 Posterior Keratoconus: Uncommon, sporadic unilateral, non-progressive increase in the curvature of the posterior corneal surface. The anterior surface is normal and visual acuity may be unimpaired due to the similar refractive indices of the cornea and aqueous humour.
Two types are recognized; Generalis, where the entire posterior surface curvature increases and Conscriptus, where the increase in curvature is localized either centrally or paracentrally 7-9
Discussion
Oxygen delivery to the cornea is impacted by the scleral lens and the tear lens thickness, especially if the scleral lens was thicker than 350 microns and the tear layer thickness exceeds 200 microns 10. In order to minimize hypoxia induced swelling with scleral lenses, lenses with high Dk values (>150), maximal centre thickness of <250 microns or less, and tear lens thickness not exceeding 200 microns should be used 10. This theoretical model has been validated clinically, large scleral lens wear results in 2-3% corneal oedema at the end of the wearing period if the lens and tear layer is thicker than 300 and 200 microns respectively 3. Compan et al, 2014 also suggested that scleral lens materials should have at least a Dk of 125 with a thickness of 200 microns and a tear film thickness of 150 microns or less to meet oxygen tension of 55mmHg – which is considered the minimum critical barrier to avoid clinically significant hypoxia 11. Thinner tear lens thickness or lower corneal clearance seems to have a positive effect on the Dk/t of the system ensuring long term corneal health.
However, care should be taken to ensure that the corneal clearance is maintained during lens wear. It is known that clearance decreases naturally due to "sinking" of the lens during wear into the conjunctiva and this should be kept in mind when fitting the lenses 3.
Although this lady did well with the contact lenses with no adverse effects reported during period of wear reported here, her visual acuity remained poor. Right and left 20/100 (PH = 20/100) and 20/80 (PH = 20/80) respectively. From the axial length it is evident that the myopia in this patient is primarily axial in nature. According to the Gullstrand # 1 schematic eye, the axial length of the emmetropic eye is 24,4 mm and 1 mm = 2.67D of refractive power 12.
Myopic individuals are prone to degenerative changes throughout all tissues of the eye with the retina particularly vulnerable to myopic retinopathy. Myopic fundus changes seem to be a function of increasing myopia and age as they are uncommon and mild in myopic children 13. Ocular pathology associated with increased axial length (high myopia) of the eye include; optic nerve crescents, peri-papillary atrophy, chorioretinal atrophy, choroidal neovascularization, Foster-Fuchs spots, lacquer cracks, posterior staphylomas, posterior vitreous detachments, rhegmatogenous retinal detachments, lattice degeneration, cataracts, and primary open angle glaucoma 7,9,13. Myopic crescents occur in all eyes with axial lengths over 28.5mm and posterior staphylomas are present in 19% of eyes with axial lengths over 26.5mm. Foster-Fuchs spots are present in 3.2% of eyes with pathological myopia 13. Posterior vitreous detachment starts earlier in myopia and 53.5% of all retinal detachments without prior intraocular surgery occurred in myopes. Lattice degeneration is found in ± 8% of the population, more commonly in myopes between -3.00 and -10.00D. The odds ratio for primary open angle glaucoma is 3:1 for <- 5.00 and 1:3 for low myopia (-0.25 to -5D) 13.
Multiple surgeries were performed on this lady all with a high risk of post-operative complications. Common post-operative complications of penetrating keratoplasty include wound leaks, flat anterior chamber with increased IOP, endophthalmitis, persistent epithelial defects, primary graft failure, problems related to sutures, post-operative astigmatism, corneal ulcers, recurrence of disease, and graft rejection 9. The prevalence of endothelial graft rejection is around 21% 9. Symptoms include pain, photophobia, redness, and decreased vision. Patients must be educated with regard to these symptoms especially if they wear contact lenses that may stimulate the immune response which may lead to rejection 9.
Dilated examination of the fundus revealed degenerative myopia (posterior staphyloma, chorioretinal atrophy, secondary macular degeneration) as well as signs of previous retinal surgery in both eyes 9,13. The macula in both eyes were involved with the result that the visual prognosis is poor. Optical coherence tomography shows the pathology clearly in the right eye. The macula in the left eye appears more normal with evidence of a substantial epiretinal membrane and loss of the foveal pit 9,13 (Figures 16 & 17). According to the retinal surgeon no further surgery is indicated at present and he will evaluate the situation regularly. Visual prognosis is therefore guarded.
Conclusion
In this case follow-up visits are extremely important to look for evidence of graft rejection in the left eye and to assess the fit of the corneo-scleral lenses to prevent further complications and potential vision loss. Although the lady has now used the corneo-scleral lenses successfully for more than six months she visits my practice as well as the treating ophthalmologist/retina specialist every three months for follow-up and adjustments. Her vision has remained stable and although she cannot drive legally she is able to work and care for her family.
Figures
Figure 1 Right eye with central corneal scar Figure 2 Left eye with penetrating keratoplasrty and ptosis Figure 3 Pentacam of the right eye Figure 4 Pentacam of the left eye Figure 5 Pentacam Scheimpflug images of the right eye showing corneal scar Figure 6 Pentacam Scheimpflug images of the left eye showing penetrating keratoplasty Figure 7 Keratoconus treatment flowchart. Management by contact lenses (CLs), corneal crosslinking (CXL), intra-corneal ring segments (ICRS), photorefractive keratectomy (PTK/PRK), deep lamellar keratoplasty (DALK), penetrating keratoplasty (PK) 2
Right Radius DiameterLeft RadiusDiameter Sag 4.4955
@15.6
Sag 7.50 8.60 4.9453
@15.6
6.89 8.60 7.70 12.00 7.09 12.00 8.70 13.80 8.70 13.80 13.00 14.80 13.00 14.80 14.40 15.60 14.40 15.60 Plano Tyro 97 Plano Tyro 97
Figure 8 initially selected trial lenses Figure 9 Anterior OCT of the right eye with initial trial lens in situ, note "feather touch" and minimal corneal clearance as well as corneal scarring Figure 10 Anterior OCT of the left trial lens in situ showing an alignment fit with no cornea clearance Figure 11 First trial lens on the right eye; note the flat fluorescein pattern and effect of the low clearance on the cornea after lens removal Figure 12 First trial lens on the left eye; note the flat fluorescein pattern and effect of the low clearance on the cornea post lens removal
Right Radius DiameterLeft RadiusDiameter Boston XO2 Boston 7.20 8.60 XO2 6.75 8.60 Dk 141 Dk 141 Sag 4.6905
@15.6
Sag 7.40 12.00 5.0392
@15.6
7.00 12.00 EOP 18% @ 0.25mm EOP 8.70 13.80 19% @ 0.2mm 8.70 13.80 13.00 14.80 13.00 14.80 14.60 16.00 14.60 16.00
+7.00 +2.00
CT CT 250µm 200µm
Figure 13 Final semi scleral lens parameters for the right and left eye respectively Figure 14 Final lens on the left eye; note improved fluorescein pattern, peripheral fenestration, and minimal corneal clearance fit of the lens Figure 15 Final lens on the right eye; note the improved fluorescein pattern appearance and fit of the lens Figure 16 Figure 17 Figure 18 Classification of RGP contact lenses, from "A Guide to Scleral Lens fitting, 2nd Edition" 3