|Year : 2020 | Volume
| Issue : 4 | Page : 245-248
Advanced keratoconus with very low pachymetry – Can contact lens avoid corneal surgery?
Radhika Natarajan, Amrutha Mahalakshmi Anandan, Manokamna Agarwal
Department of Cornea and Refractive Surgery, Medical Research Foundation, Sankara Nethralaya, Chennai, Tamil Nadu, India
|Date of Submission||16-May-2020|
|Date of Decision||20-Jul-2020|
|Date of Acceptance||18-Sep-2020|
|Date of Web Publication||16-Dec-2020|
Dr. Radhika Natarajan
Deputy Director, Department of Cornea and Refractive Surgery, Medical Research Foundation, Sankara Nethralaya, Chennai - 600 006, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Clinical relevance: Keratoconic eyes with low pachymetric values, precluding safe CXL can show significant improvement in vision with newer scleral Contact lenses(CL), which was not possible with older rigid CLs. Purpose: To describe diagnostic and management difficulties in keratoconic eyes with pachymetry too low for CXL (Collagen Cross linking)necessitating surgery for improving tensile strength, yet having significant improvement in vision with newer rigid contact lenses such that immediate keratoplasty can be deferred. Methods: Case records of 16 patients (20 eyes) were reviewed. All patients had advanced keratoconus with low pachymetric values but had significant improvement in vision with rigid CLs. CXL was not safely feasible in these eyes and immediate surgical treatment for tissue strengthening was deferred as they had good vision with newer rigid CLs. Patients were kept under close observation due to the risk of developing corneal hydrops. Results: Mean age was 25.68 years. Mean best-corrected visual acuity with glasses was 0.54logMAR, whereas, with rigid CLs was 0.18logMAR. Mean steep-keratometry (K) was 62.66D. Mean central pachymetry, highest posterior surface elevation, and pachymetry at thinnest location was 314.4, 119.6 and 313.61microns respectively. Mean follow-up was 4 years. Conclusion: Advanced keratoconic eyes may have pachymetric values too low for CXL, therefore needing keratoplasty for tissue strengthening and yet can have good vision with rigid CLs. Quantitative analysis of further progression of keratoconus in these eyes is difficult as imaging techniques become unreliable in advanced stages of the disease. Significant improvement in vision with newer rigid and scleral CLs makes the decision to operate, purely for tissue building, difficult.
Keywords: Collagen cross-linking, keratoconus, pachymetry, rigid contact lenses, scleral lenses
|How to cite this article:|
Natarajan R, Anandan AM, Agarwal M. Advanced keratoconus with very low pachymetry – Can contact lens avoid corneal surgery?. TNOA J Ophthalmic Sci Res 2020;58:245-8
|How to cite this URL:|
Natarajan R, Anandan AM, Agarwal M. Advanced keratoconus with very low pachymetry – Can contact lens avoid corneal surgery?. TNOA J Ophthalmic Sci Res [serial online] 2020 [cited 2021 Apr 23];58:245-8. Available from: https://www.tnoajosr.com/text.asp?2020/58/4/245/303649
| Introduction|| |
Keratoconus is a degenerative disorder of the cornea, characterized by progressive stromal thinning and conical ectasia that results in irregular astigmatism and associated vision loss. Collagen cross-linking (CXL) is a minimally invasive procedure which aims at halting the progression of the disease by increasing the biomechanical strength of the stromal tissue. However, even after halting the progression of disease, the patient needs surgical or nonsurgical aid for visual rehabilitation.
To safely perform CXL, a minimum corneal thickness of 400 μ is needed to avoid damage to the corneal endothelium. For corneal thickness <400 μ, modifications in Riboflavin concentration, ultraviolet-A fluence, and corneal thickness have been tried and are still under study. In advanced keratoconus, where pachymetric values are too low for CXL, the usual surgical options not only to improve vision but also to strengthen the cornea are deep anterior lamellar keratoplasty (DALK) and rarely penetrating keratoplasty. However, when these eyes have significant improvement in vision with newer rigid contact lenses (CLs), the decision to operate purely for thickness building becomes a dilemma. Nonetheless, deferring immediate keratoplasty may pose a risk of acute hydrops in progressive keratoconus cases. This paper describes this management dilemma in such advanced keratoconic eyes, where newer rigid CLs were considered over surgical management in very thin keratoconus corneas.
| Materials and Methods|| |
This was a retrospective study in a tertiary eye care center in India. It was approved by the Institutional Review Board and adhered to the tenets of the Helsinki declaration. Case records of all patients diagnosed with keratoconus, based on results from slit-lamp microscopy, corneal topography, and tomography, including pachymetry, were reviewed. Twenty eyes of 16 patients were enrolled in the study. Inclusion criteria were advanced keratoconic corneas (simK >55) with thinnest pachymetry values too low (<360 μ) for even hypotonic CXL but with significant improvement in vision with rigid CLs. Exclusion criteria were keratoconic corneas with adequate pachymetry for CXL, keratoconic corneas without significant improvement in vision with rigid CLs due to dense apical scarring, and keratoconus with or after hydrops.
| Results|| |
Twenty eyes of 16 patients were studied. The mean age was 25.68 years (range 12–40 years). Twelve patients (75%) were male and 4 (25%) were female. Two eyes had treated vernal keratoconjunctivitis. One patient had atopic dermatitis and diabetes mellitus.
On slit-lamp examination, all the twenty eyes had Fleischer ring and Vogt's striae. Twelve eyes had apical scarring.
The mean best-corrected visual acuity with spectacles was 0.54 logMAR (range 0.10–1.00, standard deviation [SD] = 0.31). Mean best-corrected visual acuity with CLs was 0.18 logMAR (range 0.00–0.50, SD = 0.13). Nineteen eyes had near vision of N6 and one eye had a near vision of N12. In two eyes, though the vision was improving to only 0.50 logMAR with CLs, as the patients were satisfied with the vision for daily activities, immediate keratoplasty was deferred.
Topography, tomography, and pachymetric values
Mean steep simK was 62.66D (range 56.33D to 76.97D, SD = 5.88D) and flat simK was 52.34D (range 49.2D to 67.60D, SD = 5.41D). In six eyes, the mires were distorted due to high irregular astigmatism. Hence, we were unable to get a reliable keratometry reading. The mean of the highest posterior surface elevation and pachymetry at the thinnest location, recorded on tomography (PentacamHR, Oculus, Germany), was 119.6 μ (range 41–213 μ, SD = 40.75 μ) and 313.61 μ (range 186–357 μ, SD = 39.31 μ), respectively. In two eyes, we were unable to get a reading as the quality of imaging was unreliable due to advanced keratoconus. Mean central pachymetry (ultrasonic pachymeter, Tomey, Japan) was 314.4 μ (range 186–386 μ, SD = 48.21 μ). Ultrasonic pachymetry was used as it records the minimum value among pachymeters. This was corroborated and confirmed with Pentacam pachymetry after incorporating correction.
Rigid contact lens fitting
Two eyes were fitted with rigid gas permeable CLs (CLASSIC company, Bangalore, India), 5 with Rose-K lenses (Menicon Co., Ltd, Nagoya, Japan), and 6 with PROSE (Prosthetic Replacement of the Ocular Surface Ecosystem, Boston Foundation for Sight, Needham Heights, Boston, MA, USA). Thirteen (65%) eyes had good tolerance to the CLs. Seven (35%) eyes developed reduced tolerance and fitting difficulties over a period of time. Among these seven eyes, five eyes which were fitted with rigid gas permeable CLs in the first visit were shifted to PROSE lenses in subsequent visits, one eye which was fitted with Rose-K lens was shifted to PROSE lens, and one eye which was fitted with rigid gas permeable CL was shifted to Rose-K lens. Following the shift, these seven eyes also had good tolerance. None of the patients developed any contact lens-related complications. Patients on rigid gas permeable lenses and Rose-K lenses changed their CLs every 2–3 years and those on PROSE lenses every 4–5 years once. The mean tomography values of patients in different contact lens groups are enumerated in [Table 1].
|Table 1: Mean tomography values of patients in different contact lens group-pachymetry at the thinnest location (Pentacam HR, Oculus, Germany), highest posterior elevation map (Pentacam HR, Oculus, Germany), Simulated K|
Click here to view
The mean follow-up was 4 years (range 1 month to 11 years).
All 20 eyes had advanced keratoconus on presentation. Their visual acuity improved significantly with rigid CLs. Although they were kept on regular follow-up, quantitative analysis of progression was not possible as the quality of imaging became unreliable or unrecordable in advanced disease. However, seven patients were shifted from corneal to corneoscleral or scleral lenses for a better fit, possibly indicating progression.
| Discussion|| |
Several studies have confirmed the efficacy and safety of CXL making it the standard of care for stabilizing progressive keratoconus. The aim of CXL is to create new chemical bonds (cross-links) between collagen fibrils and other extracellular matrix proteins in the corneal stroma through localized photopolymerization, thereby causing corneal stiffening and halting further progression of the disease. However, in the conventional CXL protocol, a minimum de-epithelialized corneal thickness of 400 μ is recommended to avoid potential irradiation damage to the corneal endothelium. This limits the use of CXL in advanced progressive keratoconic corneas with pachymetry values <400 μ.
Even after trial of several modifications to the conventional protocol, namely transepithelial CXL, CXL with hypo-osmolar riboflavin, accelerated CXL, customized pachymetry-guided epithelial debridement, and incorporating adaptive fluence (still under study), currently, these cannot be safely used in corneas with pachymetry values <350 μ.
Furthermore, quantitative analysis of disease progression in these advanced keratoconic eyes is difficult as imaging techniques become unreliable or unrecordable. Hence, in these keratoconic corneas with progressive ectasia, the feasible surgical treatment options available are DALK and penetrating keratoplasty for improvement in corneal tensile strength as well as vision. Other surgical options such as Bowman layer transplantation and small incision femtosecond laser-assisted intracorneal concave lenticule implantation have also been reported in the literature, but are still under study. It is worthwhile to note that every surgical procedure has its own inherent risks that need to be taken into consideration when planning for the rehabilitation of such patients, especially when corrected visual acuity is good.
With the advancement in contact lens technology, the other available nonsurgical option for advanced keratoconus is scleral lenses. The advantages of scleral lenses compared to corneal lenses in the correction of irregular corneas are numerous. Mini scleral and scleral lenses provide a more stable and better-centered fit than conventional rigid gas permeable CLs. As these lenses do not touch the cornea, scar formation is not exacerbated. The optical quality is also good because of the liquid layer between the contact lens and the cornea. Most of all, the overall comfort is better, thereby improving the quality of life for many patients with advanced keratoconus.
In a paper by Koppen et al., they have shown that the use of specialty lenses, specifically scleral lenses, led to a decreased need for corneal transplants in severe keratoconus as defined by steep keratometry more than 70 Diopters. However, in the subset of patients with no improvement in vision even with scleral lenses and therefore consequently requiring surgical intervention, DALK is preferred over penetrating keratoplasty as in the former, the patient's endothelium is retained, thereby eliminating the chances of endothelial rejection. However, rarely, in cases with deep stromal and endothelial scarring, penetrating keratoplasty is the preferred option. Some issues with DALK include risk of Descemet's membrane perforation intraoperatively requiring conversion to open sky penetrating keratoplasty. Postoperatively, the patient can develop interface haze, infective keratitis, or vascularization. Furthermore, while the post DALK cornea may be stronger, it may still have surgery and suture-related astigmatism persisting after suture removal. This may warrant the use of CLs even after the surgery. Freedom from CLs is not a guarantee after DALK.
Keratoconic eyes with low pachymetric values, precluding safe CXL, can show significant improvement in vision with the newer scleral CLs [Figure 1] which were not possible with the older rigid CLs. Hence, the decision to operate to improve the corneal tensile strength becomes difficult, especially when ongoing disease progression cannot be ascertained quantitatively in these advanced cases [Table 2]. On the other hand, even though there is a significant improvement in vision with these lenses, the tissue tensile strength issue is not addressed. Hence, deferring immediate keratoplasty poses the risk of the patient developing acute hydrops over time, though, in our case series of 20 eyes of 16 patients, no patient developed hydrops in the follow-up period.
|Figure 1: Slit-lamp image (a) and posterior elevation map (b) of the patient with advanced keratoconus with low pachymetric value but good vision with rigid contact lenses|
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|Table 2: Examples of difficulty in analyzing progression quantitatively in advanced keratoconus difficulty in the documentation of disease progression in advanced keratoconus as imaging techniques become unreliable or unrecordable|
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| Conclusion|| |
This paper reports eyes with advanced keratoconus with pachymetry values too low for safe CXL. The standard surgical options to improve corneal tensile strength as well as vision in these eyes are DALK and penetrating keratoplasty. However, they showed a significant improvement in vision with rigid CLs. Hence, immediate keratoplasty was deferred in these eyes. They were kept under close observation due to the risk of developing hydrops. As imaging techniques were unreliable or unrecordable in these eyes due to advanced disease, it was difficult to quantitatively analyze the progression of keratoconus. This paper highlights the management dilemma between operating for strengthening the cornea when contact lens vision is good and risking corneal hydrops in such eyes.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]