Cornea Farinata

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Cornea farinata is a relatively common, asymptomatic corneal degenerative disease characterized by numerous small, fine, dust-like opacities in the pre-Descemet's membrane often bilaterally. The etiology, risk factors, and pathophysiology have been revealed to an extent but more research is needed to completely understand these aspects of this condition. Though mainly diagnosed via slit-lamp examination, confocal microscopy is very helpful in differentiating cornea farinata from similar diseases.

Disease Entity

Cornea Farinata ICD-10 H18.40

Disease

Cornea Farinata, also known as “floury cornea”[1,2], is a relatively common asymptomatic, degenerative, and age-related corneal disease that is characterized by numerous small, fine, and often bilateral dust-like opacities which resemble wheat flour. These opacities have a gray-white or tan-brown color located in the deep central corneal stroma[1–7]. It was first described by Alfred Vogt in 1923[1,2,4,8].

Etiology

The cause of this condition is currently unknown. However, one study reported that it may result from at least six mutations in the steroid sulfatase (STS) gene[9] located on chromosome Xp22.31[10]. Therefore, the etiology may potentially involve metabolic disruption caused by sterylsulfatase enzyme deficiency also associated with pre-Descemet's corneal dystrophy in patients with X-linked ichthyosis (XLI)[7,11-14]. It is also not documented whether this condition has a predilection for expression in either sex, despite being located on a sex chromosome.

Risk Factors

Cornea farinata is a degenerative condition associated with older age as it has rarely been documented in individuals younger than 40 years old[1,2,5,6,15].

Genetic risk factors include any of at least six mutations of the STS gene[9,10]. Though the specific mutations and downstream effects of STS gene variants resulting in cornea farinata have not been discovered, it is thought that different mutations of this gene may result in various distinct phenotypes reflecting a degree of variable expressivity[9,10]. This may be due to varying levels of sterylsulfatase enzyme expression or function depending on the specific STS gene variant. However, the specific details of the genetic and molecular abnormalities involved in the pathogenesis of this condition are yet to be elucidated[2,7,9].

General Pathology

This entity presents with numerous fine, dust-like, cytoplasmic, hyper-reflective, gray-white and tan-brown opacities which are distributed diffusely and evenly in the posterior central corneal stroma, the area also referred to as the pre-Descemet’s membrane [4–6,11–14,16]. There are usually with no accompanying abnormalities or opacities in the Descemet’s membrane, anterior-to-mid-stromal layers, or corneal epithelial or endothelial cell layers[5,6]. The opacities present on slit-lamp microscopy and confocal microscopy are composed of intracytoplasmic vacuoles containing lipofuscin-like inclusions histopathologically and can cause abnormally large stromal keratocytes[2–4].

Pathophysiology

The pathophysiology is largely unknown, but its association with old age[15], a steroid sulfatase (STS) metabolic enzyme deficiency[9,10], and intracytoplasmic lipofuscin-like deposits[4] points towards a degenerative process. STS enzyme deficiencies have also been associated with pre-Descemet's corneal dystrophy in patients with X-linked ichthyosis (XLI)[10], which can present with ocular findings like those found in cornea farinata[7,11-14]. Therefore, it is possible that the ocular findings of Pre-Descemet's corneal dystrophy, associated with XLI, and cornea farinata share common pathophysiologic underpinnings, since STS is localized intracellularly on the endoplasmic reticulum and may be involved in the formation of the intracytoplasmic lipofuscin-like deposits found on histopathology[1–4,6,7,9-14]. However, more research is required to completely understand and confirm the pathophysiology of cornea farinata.

Primary prevention

Due to its degenerative and genetic basis, there is currently no form of primary prevention.

Diagnosis

Cornea farinata is diagnosed clinically via visual examination using slit-lamp microscopy or confocal microscopy. Confocal microscopy provides enhanced detail of the opacities present in this condition[1-3,5,6].

History

Patients do not experience visual, ocular, or otherwise systemic symptoms. A history of ocular or systemic disease is also not significant in this diagnosis[1–3,5].

Physical examination

The fine, dust-like opacities present are best visualized on slit-lamp examination with retro-illumination of the iris[2,3,5,17]. Specific differentiating features of this condition are that no opacities will be observed in the anterior or mid-stroma of the cornea and abnormalities of the Descemet’s membrane and corneal epithelial or endothelial cell layers will not be seen [5,6].

Signs

No other signs besides those listed in the physical examination have been documented.

Symptoms

No significant visual impairment, ocular, or systemic disease has been associated with this condition[2,3,5].

Clinical diagnosis

The diagnosis is clinical and reached visually via thorough slit-lamp examination[5,16].

Diagnostic procedures

Although biomicroscopy is a useful tool for the detection of stromal opacities, confocal microscopy is an especially diagnostic procedure in differentiating corneal farinata from other similar corneal dystrophies and degenerations[5,6].

Laboratory test

Genetic analysis may be performed to screen for STS gene mutations[7,9,10] which, in combination with appropriate physical exam findings, may aid in diagnosis. However, one must be sure to differentiate the combination of pre-Descemet's membrane ocular opacities and STS gene mutations of cornea farinata from pre-Descemet's corneal dystrophy[4-7,9-14].

Differential diagnosis

- Punctate dystrophy

- Deep filiform dystrophy

- Posterior punctiform dystrophy

- Deep blue dot corneal degeneration

- Fleck corneal dystrophy

- Pre-Descemet corneal dystrophy

- Cogan’s microcystic corneal dystrophy

Management

Management is not required for cornea farinata as it is an asymptomatic condition[1-3,5].

General treatment

There is no treatment for this condition.

Medical therapy

There is no medical therapy for this condition.

Medical follow up

No medical follow up is indicated to treat cornea farinata.

Surgery

Surgery is not required or recommended to treat cornea farinata.

Surgical follow up

Surgical follow up is not indicated.

Complications

No complications have been documented in association with cornea farinata.

Prognosis

Those with only corneal farinata and no other co-existing diagnosis are expected to have a good prognosis.

Additional Resources

  1. Kalout P, Pineda R. Cornea Farinata. Encyclopedia of Ophthalmology. Published online 2018:512-513. doi:10.1007/978-3-540-69000-9_953
  2. https://www.aao.org/image/cornea-farinata

References

  1. Kalout P, Pineda R. Cornea Farinata. Encyclopedia of Ophthalmology. Published online 2018:512-513. doi:10.1007/978-3-540-69000-9_953
  2. Yanoff M, Duker JS. Ophthalmology. 4th ed. Elsevier Health Sciences; 2008.
  3. Trattler W, Majmudar P. Cornea Handbook. SLACK Incorporated; 2010.
  4. Durand L, Bouvier R, Burillon C, Mutti P. [Cornea farinata. Report of a case: clinical, histologic and ultrastructural study]. Journal francais d’ophtalmologie. 1990;13(8-9):449-455. Accessed May 18, 2022. https://pubmed.ncbi.nlm.nih.gov/2081857/
  5. Lanza M, Borrelli M, Benusiglio E, Rosa N. In vivo confocal microscopy of an apparent deep stroma corneal dystrophy: a case report. Published online 2009. doi:10.1186/1757-1626-2-9317
  6. Kobayashi A, Ohkubo S, Tagawa S, Uchiyama K, Sugiyama K. In vivo confocal microscopy in the patients with cornea farinata. Cornea. 2003;22(6):578-581. doi:10.1097/00003226-200308000-00019
  7. Haritoglou C, Ugele B, Kenyon KR, Kampik A. Corneal manifestations of X-linked ichthyosis in two brothers. Cornea. 2000;19(6):861-863. doi:10.1097/00003226-200011000-00023
  8. Vogt A. Textbook and Atlas of Slit Lamp Microscopy of the Living Eye. Bonn: Wayenborgh Editions; 1981.
  9. Klintworth GK. The molecular genetics of the corneal dystrophies--current status. Front Biosci. 2003;8. doi:10.2741/1018
  10. Dalla Valle L, Toffolo V, Nardi A, et al. The expression of the human steroid sulfatase-encoding gene is driven by alternative first exons. Journal of Steroid Biochemistry and Molecular Biology. 2007;107(1-2):22-29. doi:10.1016/j.jsbmb.2007.05.004
  11. Hung C, Ayabe RI, Wang C, Frausto RF, Aldave AJ. Pre-Descemet Corneal Dystrophy and X-linked Ichthyosis Associated with Deletion of Xp22.31 Containing the STS Gene. Cornea. 2013;32(9):1283. doi:10.1097/ICO.0B013E318298E176
  12. Shi H, Qi X feng, Liu T tao, et al. In vivo confocal microscopy of pre-Descemet corneal dystrophy associated with X-linked ichthyosis: a case report. BMC Ophthalmol. 2017;17(1). doi:10.1186/S12886-017-0423-5
  13. Chen PL, Tang KP, Liang JB. Pre-Descemet’s corneal dystrophy associated with ichthyosis. Zhonghua Yi Xue Za Zhi (Taipei). 2002;65(8):407-409. Accessed May 23, 2022. https://pubmed.ncbi.nlm.nih.gov/12455812/
  14. Boere PM, Bonnet C, Frausto RF, Fung SSM, Aldave AJ. Multimodal Imaging of Pre-Descemet Corneal Dystrophy Associated With X-Linked Ichthyosis and Deletion of the STS Gene. Cornea. 2020;39(11):1442-1445. doi:10.1097/ICO.0000000000002382
  15. Kotulak JC, Brungardt T. Age-related changes in the cornea. J Am Optom Assoc. 1980;51(8):761-765. Accessed May 18, 2022. https://pubmed.ncbi.nlm.nih.gov/6969271/
  16. Selvan H, Singh A, Tandon R. Deep blue dot corneal degeneration: confocal characteristics. International Ophthalmology. 2019;39(3):667-669. doi:10.1007/S10792-018-0849-7/FIGURES/3
  17. Rapuano CJ, Heng WJ. Color Atlas and Synopsis of Clinical Ophthalmology - Cornea. 2nd ed. (Wills Eye Institute, ed.). Lippincott Williams & Wilkins; 2012.
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