Macular corneal dystrophy with keratoconus – Case report and review of literature

Renu Hashia; Debapriya Chatterjee

doi:10.4103/ijo.IJO_2155_22

CASE REPORT

Year : 2023 | Volume : 3 | Issue : 2 | Page : 288-291

Macular corneal dystrophy with keratoconus – Case report and review of literature

Renu Hashia, Debapriya Chatterjee
Department of Ophthalmology, Acharya Shri Chander College of Medical Sciences, Sidhra, Jammu and Kashmir, India

Date of Submission	29-Aug-2022
Date of Acceptance	15-Mar-2023
Date of Web Publication	28-Apr-2023

Correspondence Address:
Debapriya Chatterjee
Department of Ophthalmology, Acharya Shri Chander College of Medical Sciences and Hospital, Bye Pass Road, Sidhra, Jammu and Kashmir - 180 017
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijo.IJO_2155_22

Abstract

We report a case of macular corneal dystrophy with suspected keratoconus on clinical examination in a 20-year-old female. On Scheimpflug imaging, anterior sagittal and posterior sagittal maps were suggestive of keratoconus. Anterior segment optical coherence tomography showed focal areas of hyperreflectivity in the anterior stroma with diffuse thinning. We report this case to illustrate that high astigmatism and thinning, commonly present in macular dystrophy, may have features suggestive of keratoconus. Corneal haze precludes an accurate assessment of the posterior corneal curvature.

Keywords: Astigmatism, keratoconus, macular corneal dystrophy, thinning

How to cite this article:
Hashia R, Chatterjee D. Macular corneal dystrophy with keratoconus – Case report and review of literature. Indian J Ophthalmol Case Rep 2023;3:288-91

How to cite this URL:
Hashia R, Chatterjee D. Macular corneal dystrophy with keratoconus – Case report and review of literature. Indian J Ophthalmol Case Rep [serial online] 2023 [cited 2023 Jun 2];3:288-91. Available from: https://www.ijoreports.in/text.asp?2023/3/2/288/374942

Corneal dystrophies are a group of rare inherited disorders that are bilateral, symmetric, slowly progressive, and unrelated to environmental or systemic factors. Multiple reports of the association of different dystrophies with various systemic disorders challenge this traditional definition. Ocular associations are less commonly reported. Most reports are on the association of keratoconus (KC) with Fuch's endothelial dystrophy, posterior polymorphous dystrophy, and granular dystrophy.^[1] Myopia and astigmatism are reported with macular dystrophy and posterior polymorphous dystrophy.^[2]

We present a case of macular corneal dystrophy (MCD) with clinical features indicative of KC.

Case Report

A 20-year-old female patient presented to our outpatient department with bilateral vision loss for the past 7 years. There was no significant systemic, ocular, or medication history. There were no other affected family members. Her parents were not consanguineous. Her physical examination was unremarkable. At the first visit, uncorrected visual acuity was 20/125 right eye (RE) and 20/200 left eye (LE). The best spectacle-corrected acuity was 20/40 in both eyes. Manifest refraction was +0.75/−4.50×5 RE, ±/−4.50×175 LE. Pupillary reactions were normal. On slit-lamp examination, focal breadcrumb-like opacities with indistinct borders were seen centrally in the anterior stroma. Diffuse haziness was present in the corneal stroma, extending to the periphery but was more marked centrally [Figure 1]. The corneas appeared thin and steep. Intraocular pressures were 10 and 12 mmHg in RE and LE, respectively. Even though the media was hazy, fundus examination was possible and within normal limits. We could not perform retinoscopy due to the dull glow, but we noted a scissoring reflex. The patient was clinically diagnosed with MCD and suspected KC. Corneal topography with Scheimpflug imaging Allegro Oculyzer (Wavelight, GmbH,Erlangen, Germany) showed RE flat keratometry (Kf) 45.6, steep keratometry (Ks) 49.6, maximum keratometry (Kmax) 51.2, thinnest pachymetry 329 μm, LE flat K 46, steep K 50.3, Kmax 51.4, and thinnest pachymetry 361 μm. Posterior curvature maps also showed steepening. However, the front and back surface elevation maps were normal [Figure 2]a. Anterior segment optical coherence tomography (Topcon Corporation, Tokyo, Japan) showed localized areas of hyperreflectivity in the anterior stroma at a thickness of 65–70 μm. The epithelium over the deposits was normal. There was diffuse thinning of the cornea (≈400 μm) [Figure 2]b.

Figure 1: Slit-lamp images of RE and LE, diffuse illumination, broad slit beam, and slit section demonstrating the presence of ill-defined macules with significant haze and thin and steep cornea. LE = left eye, RE = right eye

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Figure 2: (a) Pentacam images showing inferior steepening on the anterior sagittal curvature but normal elevation maps. (b) AS-OCT images showing localized hyperreflectivity in the anterior stroma and diffuse haze with thinning of the cornea. AS-OCT = anterior segment optical coherence tomography

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Given the patient's age and refractive needs, we ordered a scleral lens trial. She improved to 20/20 in both eyes with mini-scleral lenses.

Genetic testing was also carried out, which detected a mutation on exon-3 of the carbohydrate sulfotransferase-6 (CHST6) gene. This variant, reported as c. 487dup, is causative of MCD.

Discussion

MCD is an autosomal recessive corneal stromal dystrophy, which falls in category 1 of the International Committee for the Classification of Corneal Dystrophies (IC3D) system. The pathogenic gene is CHST6 located on chromosome 16q23.1. CHST-6 transfers the sulfate group from 3′-adenosine 5′-phosphate to keratin sulfate. Gene mutation changes the enzyme function, resulting in keratin sulfation disorders leading to MCD.^[3]

KC, on the other hand, can present with an autosomal recessive or dominant inheritance pattern. Studies in various fields, such as genetics, genomics, small biomolecule analysis, and gene expression analysis, suggest that the disease may be multifactorial.^[4] Several types of collagen are reduced in KC epithelium and stroma. It is postulated that the altered activity of lysyl oxidase, which plays a critical role in the synthesis of connective tissue, weakens the covalent bonds between collagen fibrils. The genetics of KC are complex and mapped to multiple genes. Loukovitis et al.^[5] carried out a literature search exploring possible genetic relationships with comorbidities in KC. Systemic associations of KC in conditions such as atopic diathesis, Down syndrome, Marfan syndrome, Ehlers–Danlos syndrome, and so on are known. Ocular associations with granular dystrophy, Fuch's dystrophy, Leber's hereditary optic neuropathy, and Leber's congenital amaurosis have also been reported. One of the linked loci for KC, 16q22.3-q23.1, also houses the CHST6 gene that is involved in the pathogenesis of MCD.

The first report in the literature documenting MCD with keratoconus (KCN) was on two siblings from Tehran, Iran.^[6] The authors postulated that there might be biochemical similarities, with both conditions having decreased levels of keratin sulfate and Increased ratio of dermatan to keratan sulphate. X-ray diffraction studies have shown that collagen fibrils in MCD are typical in diameter, but with decreased interfibrillary spacing. In contrast, fibril diameter is normal, but collagen fibrils are lost in the KC. Two later case reports from Kuwait and Tehran reported the same association [Table 1].^[7],[8]

Table 1: Previously published case studies

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Our case is of a 20-year-old female presenting with clinical features of MCD and signs suggestive of KC. Scheimpflug imaging showed steepening of anterior sagittal curvature and steepening on the posterior curvature map; however, the front and back elevation maps did not corroborate the findings. Anterior segment optical coherence tomography showed diffuse thinning of the cornea. Corneal thinning associated with macular dystrophy and astigmatism gave rise to this KC-like picture on the anterior curvature maps.

In a later article, Dudakova et al.^[9] analyzed phenotypic similarities between MCD and KC in six eyes of three probands. Scheimpflug imaging demonstrated a pattern consistent with KC on anterior sagittal mapping. However, examination of the posterior elevation, posterior sagittal curvature, pachymetry, and corneal thickness spatial profiles (CTSP) showed diffuse thinning without focal ectasia. They suggested that corneal thinning and astigmatism are phenotypic features of both KC and MCD; hence, evaluation of the anterior corneal surface in isolation can give indices that spuriously suggest the presence of KC. Correlation with posterior corneal maps and pachymetry maps is required in such situations.

Measurement of corneal thickness and keratometric indices by Pentacam has been reported to be influenced by corneal haze, as shown in a cross-sectional study on Post collagen cross-linking (post-CXL) eyes by Shetty et al.^[10] As management decisions in MCD would be influenced by the coexistence of KC, due caution should be exercised in interpreting these results.

Conclusion

The association of KC with MCD has been reported multiple times, raising the possibility that this may be due to more than mere chance. However, imaging these eyes in the presence of significant haze remains a concern.

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

Nil.

Conflicts of interest

There are no conflicts of interest.

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