Sarah Kher-Alla ¹ MBBS BSc, Saeed Azizi² FRCOphth MBBS BSc, Adnaan Haq³ FRCOphth MBBS BSc

¹Basingstoke and North Hampshire Hospital, Aldermastone Road, Basingstoke, RG24 9NA, Foundation doctor

²Moorfields Eye Hospital NHS Foundation Trust, City Road, EC1V 2PD, Ophthalmology registrar

³Moorfields Eye Hospital NHS Foundation Trust, City Road, EC1V 2PD, Ophthalmology locum consultant

Introduction

Keratoconus is a progressive, non-inflammatory eye disorder leading to corneal thinning and irregular astigmatism (1). The cornea is the window of the eye, which acts as a covering of its anterior chamber and refracts approximately 60% of the light entering the eye. Keratoconus is marked by thinning and projection of the cornea; which can progress to lead to high myopia and asymmetrical astigmatism (2).  This condition has an incidence of one in two thousand, is most common in early adolescence and is believed to be caused by a combination of genetics, as well as environmental influence such as allergens (3).

A diagnosis of keratoconus is made through a slit lamp bio-microscopy of the anterior segment with imaging such as corneal topography. The treatment options for Keratoconus have become more diverse, ranging from conservative management, such as avoiding eye rubbing, topical therapy, contact lenses, to surgical procedures such as cross-linking, intracorneal stromal rings, penetrating keratoplasty and deep  anterior lamellar keratoplasty (DALK) (4).  Early diagnosis is vital for countermeasures to be put in place in order to arrest the progression. Treatments such as Corneal cross-linking are only applicable to non-advanced cases of keratoconus (5).

Case report

A 28-year-old male presented to cornea clinic for follow up regarding his long-standing diagnosis of Keratoconus, which is more advanced in his left eye. He initially presented to the eye clinic in 2012, and since then his visual acuity in both eyes have gradually gotten worse. Prior to this appointment he was treated conservatively with contact lenses and topical anti-histamine therapy and topical lubricants to prevent irritation of the eye and eye rubbing. The contact lenses were rigid gas permeable, which provide a strong rigid structure in aims to retain the spherical shape of the eye, instead of conforming to the irregular shape of the cornea of an eye. The visual acuity was 6/9 OD best corrected vision (BCV) and 6/60 OS with glasses. Pentacam Kmax showed a Kmax (maximal keratometry) score of 56.2D OD and 69.8D OS. Kmax is a reliable parameter to show disease progression, which in turn determines treatment choice, such as collagen cross-linkage (6). In addition to this the patient exhibited the following signs which were classical for keratoconus progression:

• Corneal thinning (earliest sign)
• Munson’s sign (protrusion of the lower eyelid in the downgaze)
• Superficial scarring of the left cornea
• Acute hydrops (a condition of the breakdown in Descemet’s membrane, which consequently allows aqueous into the stoma leading to decreased visual acuity and pain)

On examination via slit lamp, his intraocular pressures were within normal range, healthy optic nerves and maculae in both eyes. He admitted to not being compliant with his current prescriptions of Sodium hyaluronate 0.2% eye drops (for dry eyes), as well as Olopatadine 1 mg in 1 ml eye drops (anti-histamine). This has resulted in worsening of his itchy and dry eye symptoms, which has prompted continuous eye rubbing and worsening of his condition. Due to advanced keratoconus in the left eye, the patient was offered Deep anterior lamellar keratoplasty (DALK) surgery to the left eye with a high chance of conversion to penetrating keratoplasty. It was also made clear the importance of adhering to the usage of eye drops after the operation. As the patient had previously missed important follow up appointments at MEH, the importance of continuity of care was emphasised to alert the patient to the potential complications.

Effect of Deep anterior lamellar keratoplasty (DALK)

DALK is a surgical procedure involving removal of the corneal stroma down to the Descemet’s membrane, to give a partial-thickness (lamellar) transplant. Previously penetrating keratoplasty (PK), which involves a full-thickness corneal graft, was the gold-standard treatment of choice for corneal stromal diseases. Thus, PK may have complications such as graft rejection, irregular astigmatism and corneal opacification. Whereas, in DALK those risks may be less, as the recipient Descemet’s membrane and endothelium are preserved. Another advantage of DALK is less risk of traumatic rupture as the endothelium is left intact and hence more efficient visual rehabilitation. As mentioned to the patient, DALK procedures can pose some challenges such as a perforation, which may necessitate the conversion to penetrating keratoplasty (PKP) (7). Rates of conversion to PK are relatively low, with only 2 in 100 requiring this (8).  

Postoperatively, topical corticosteroids and antibiotics are administered as prophylaxis to these complications. Patients are then routinely monitored for inflammation, infection, graft rejection, astigmatism and suture-related issues. In comparison to PK, patients usually require less medication and time for rehabilitation (9).

A 18-month follow up study looking at 101 consecutive eyes with keratoconus to investigate whether having UV-CXL prior to DALK surgery affected the rate of complications or clinical outcome, such as best corrected visual acuity, endothelial cell density and central corneal thickness found no association (10). It may be postulated that the patient may have not achieved a better long-term outcome if he was eligible and offered UV-CXL prior to his DALK.

Conclusion

In summary, corneal replacement was deemed the best possible procedure for correction of this patient’s advanced keratoconus in his left eye due to his history of poor compliance with medications. NICE UK have outlined guidelines for various Keratoconus treatments, including DALK surgery’s indications and complications. Treating Keratoconus by a DALK procedure achieves substantial results for the quality of vision post-operatively, which we hope is the case for this patient. It is vital to understand the pathophysiology behind the progression of this disease early on to help reduce the risk of progression. Graft surgery for keratoconus patients can yield excellent results, albeit patient selection is key.

References

1. Salmon, A., Chalk, D., Stein, K. and Frost, A., 2016. Response to: Comment on ‘Cost effectiveness of collagen crosslinking for progressive keratoconus in the UK NHS’. Eye, 30(8), pp.1152-1153.
2. Ang, M., Tan, A., Cheung, C., Keane, P., Dolz-Marco, R., Sng, C. and Schmetterer, L., 2020. Optical Coherence Tomography Angiography: A Review Of Current And Future Clinical Applications.
3. Gillan, W., 2006. Keratoconus: a research and clinical symposuim. African Vision and Eye Health, 65(4), p.166.
4. Jack S.Parker., et al. 2015, Treatment options for advanced keratoconus: A review. Survey of ophthalmology.
5. Dahl B.J., Spotts E., Truong J.Q. Corneal collagen cross-linking: an introduction and literature review. Optometry. 2012;83:33–42. (Pubmed)
6. Guber, I., McAlinden, C., Majo, F. and Bergin, C., 2017. Identifying more reliable parameters for the detection of change during the follow-up of mild to moderate keratoconus patients. Eye and Vision, 4(1).
7. Sharma, N., Jhanji, V., Titiyal, J., Amiel, H. and Vajpayee, R., 2008. Use of trypan blue dye during conversion of deep anterior lamellar keratoplasty to penetrating keratoplasty. Journal of Cataract & Refractive Surgery, 34(8), pp.1242-1245.
8. Terry MA, Wall JM, Hoar KL et al. (2007) A prospective study of endothelial cell loss during the 2 years after deep lamellar endothelial keratoplasty. Ophthalmology 114:631-639.
9. Shimmura, S. and K. Tsubota. Current Opin Ophthalmol 2006;17:349–355.
10. Schaub, F., Enders, P., Bachmann, B., Heindl, L. and Cursiefen, C., 2020. Effect Of Corneal Collagen Crosslinking On Subsequent Deep Anterior Lamellar Keratoplasty (DALK) In Keratoconus.