Spark ImageWise – 2- Cornea

Unilateral Keratoconus

Dr. Prabhat Nangia, Dr. Sarang Lambat, Dr.  Vinay Nangia
Suraj Eye Institute, 559 New colony, Nagpur

Case description 
A male, 13 years of age, came to us with chief complaint of diminution of vision in both eyes, more in left eye (OS) since 5 years. On examination, uncorrected visual acuity was 6/24 in right eye (OD) and 6/60 in OS. Best corrected visual acuity was 6/9, N6 in OD with refractive error of -4.00DS/+2.00DC at 100 degrees, and 6/9, N6 in OS with refractive error of -4.00DS/+2.00DC at 50 degrees. Slit lamp examination showed mild central corneal thinning in OS , and was essentially normal in OD. Intraocular pressure by Goldmann Applanation Tonometry was 11mmHg in OD and 7 mmHg in OS. Fundus examination was within normal limits. Anterior segment Optical Coherence Tomography (ASOCT) was performed.

In OD (Fig. 1), the anterior curvature map showed a symmetric bow tie pattern and with-the-rule astigmatism (black arrows). The steepK value 44.39 D and the flatK value was 41.69 D (black circle). Kmax was 44.95 D (green arrow). Thinnest pachymetry was 502 microns (cross mark), and posterior elevation at this point was 13 microns. 
In OS (Fig. 2), the anterior curvature map showed asymmetric bow tie with inferior steepening with skewed axis (black arrows). The steepK value was 48.61 D, flatK was 44.46 D (black circle) and Kmax was 52.12 D (green arrow). Thinnest pachymetry was 472 microns (cross mark), and posterior elevation at this point was 53 microns.

Based on the above, a diagnosis of left eye keratoconus was made. The patient was advised corneal cross linking for OS, and close follow-up with serial tomography scans for OD.

Discussion 

Keratoconus is an ectatic corneal disease, characterised by noninflammatory thinning and change in the anterior and posterior corneal curvature. It has usually been believed to be a bilateral but asymmetric disorder, and the Global Consensus on Keratoconus in 2015 concluded that “True unilateral keratoconus does not exist”. However, they also suggest that secondary induced ectasia may be caused by a purely mechanical process in a predisposed cornea, which may be unilateral. This could be due to rubbing of only one eye, which has been noted in some case reports. With the advent of tomographic techniques, the diagnosis of subclinical keratoconus has become much easier in the fellow eye, which means that eyes that would otherwise have been designated as normal, infact have subtle disease already present. 

Some investigators have followed up patients with unilateral keratoconus using tomography, and over a period of 3 to 7 years, these patients have not developed any signs of keratoconus in the fellow eye. They have suggested that it would be difficult to confirm whether these patients have true unilateral keratoconus without further follow up. However, this does raise the question- can we definitively confirm that true unilateral keratoconus is non-existent?

Our patient had all the tomographic signs of keratoconus in the left eye, and right eye tomography was within normal limits at presentation. We can say with some certainty that this is unilateral keratoconus, at least at presentation. However, given his young age, it would be difficult for us to predict the occurrence of ectatic changes in his right eye over the next few years. Serial tomography, every 6 months or so, is the best way to monitor these changes and confirm or rule out the presence of true unilateral keratoconus. 

ReadWise 

1. Gomes JA, Tan D, Rapuano CJ, Belin MW, Ambrósio R Jr, Guell JL, Malecaze F, Nishida K, Sangwan VS; Group of Panelists for the Global Delphi Panel of Keratoconus and Ectatic Diseases. Global consensus on keratoconus and ectatic diseases. Cornea. 2015 Apr;34(4):359-69

2. Imbornoni LM, Padmanabhan P, Belin MW, Deepa M. Long-Term Tomographic Evaluation of Unilateral Keratoconus. Cornea. 2017 Nov;36(11):1316-1324 

Correspondence 
Dr Prabhat Nangia
DNB, FICO, FMRF, FAICO
Consultant  
Department of Cornea and ocular surface
Suraj eye Institute
Email – drpn@surajeye.org

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