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Clinical Pearls

Alexander, Larry J.

doi: 10.1097/OPX.0000000000000312

This month, “Clinical Communications,” under the clinical editorship of Editorial Board member Larry J. Alexander, OD, FAAO, includes color image content and optional supplementary digital content, with no cost to our authors.

Each article in this section is followed by a clinical comment by our clinical editor, emphasizing the clinical take-home message. We provide these “Clinical Pearls” of the publication following the article’s title, authors, and abstract. The full text and illustrations are found online with the colored images and any video clips.

Dr. Larry J. Alexander provides all of the clinical comments (“Clinical Pearls”) on each article in “Clinical Communications.” This is all part of our Optometry and Vision Science(OVS) program to enrich the clinical content of OVS and make it very accessible, in color and motion, to clinicians, readers, and authors alike.

Tony Adams, OD, PhD, FAAO

Editor in Chief

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Mathematical Model for Evaluating Soft Contact Lens Fit

Graeme Young

Purpose. To evaluate the effect of varying lens and ocular topography parameters on soft contact lens (SCL) fit, using a novel computer spreadsheet model. Although SCLs are worn by more than 100 million ametropes, the factors governing their fitting characteristics are poorly understood.

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Methods.A spreadsheet-based computer model used a novel ellipto-conical corneal model coupled with population data on corneoscleral topography obtained in a previous clinical study. The model calculated lens edge strain (circumferential elongation) as a predictor of lens tightness. The following parameters were systematically varied: corneal curvature, corneal diameter, corneal shape factor, corneoscleral junction angle, lens base curve (BC), and diameter.

Results.The ellipto-conical corneal model showed closer concordance with actual measurements of corneal sagittal height than a simple elliptical model (limits of agreement, ±0.20 vs. ±0.25 mm; p = 0.0015). For an eye with average ocular parameters wearing a typical SCL design (BC, 8.60; diameter, 14.2 mm), the model calculated an edge strain of 2.7%. For the same SCL, the tightest fit (8.5% strain) was found with the eye showing the combination of smallest, flattest, most aspheric cornea. Conversely, the loosest fitting (−2.6%) was found with the eye showing the combination of largest, steepest, least aspheric cornea. A change in BC of 0.4 mm typically resulted in changes in edge strain of less than 2.5%, whereas a change in diameter of 0.5 mm resulted in a change of less than 2%. Using the typical SCL design and average corneal model, wide variations in corneoscleral junction angle did not critically affect lens fit. More extreme combinations of SCL and ocular parameters resulted in edge strain likely to result in a tight (>6%) or loose fit (<0%).

Conclusions.A novel ellipto-conical corneal model in conjunction with spreadsheet mathematical modeling proved to be a useful tool for attempting to understand the factors governing SCL fit.

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Acquired Pseudoduplication of the Optic Disc in Pathologic Myopia

Seong Joon Ahn, Se Joon Woo, and Jeong-Min Hwang

Purpose.To elucidate the mechanism of acquired pseudoduplication of the optic disc and its associationwith pathologic myopia.

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Methods.The prevalence of pseudoduplication of the optic disc was estimated by reviewing 128 consecutive patients diagnosed as having pathologic myopia between January 2010 and December 2012. The pseudodisc was investigated at the scleral level using enhanced depth imaging spectral-domain optical coherence tomography to elucidate pathologic changes. Fluorescein angiography or indocyanine green angiography was performed to identify the vessel origin.

Results.Among 128 patients with pathologic myopia, 3 patients (2.3%) showed pseudoduplication of the optic disc. Enhanced depth imaging optical coherence tomography showed chorioretinal atrophy and focal scleral excavation in the area showing the pseudodisc. The round scleral excavation gave the underlying visible peribulbar tissue a pinkish appearance, which could be mistaken as the optic disc. Fluorescein angiography or indocyanine green angiography showed that the vessel within the pseudodisc was the short posterior ciliary artery.

Conclusions.Although not a common presentation, scleral excavation associated with pathologic myopia accompanied by a ciliary artery penetrating the excavation's center could make a lesion mimicking pseudoduplication of the optic disc.

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Exome Sequencing Reveals the Likely Involvement of SOX10 in Uveal Melanoma

Debodipta Das, Inderjeet Kaur, Mohammad Javed Ali, Nidhan K. Biswas, Subrata Das, Shantanu Kumar, Santosh G. Honavar, Arindam Maitra, Subhabrata Chakrabarti, and Partha P. Majumder

Purpose. To identify the spectrum of somatic mutations in an Asian Indian patient with uveal melanoma (UM) without metastasis using exome sequencing.

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Case Report.A 49-year-old man from India was diagnosed as having cilio-choroidal (uveal) melanoma (UM), without metastasis, in his right eye with the help of magnetic resonance imaging. This was later confirmed by histopathological evaluation. Two individuals from India with non-neoplastic blind eyes were recruited as controls. The affected eyes from the UM patient and the two control individuals were enucleated, and uveal tissues were collected. DNA was extracted from uveal tissue, and the matched blood sample from each of the three individuals was followed by exome sequencing. Statistical and bioinformatic analyses were done to identify somatic mutations and their putative associations with UM. Thirty-one somatic mutations (25 amino acid altering) in protein-coding (exonic) regions were detected in the UM patient. Of the amino acid–altering somatic mutations, 16 mutations were predicted to be candidate mutations relevant to UM. Somatic mutations, putatively causal for UM, were identified in GNAQ, SF3B1, and SOX10.

Conclusion.Somatic mutations in GNAQ and SF3B1 genes were probable drivers of UM in the Indian patient; these were also reported earlier in some White patients. In addition, a frameshift deletion of 20 base pairs has been identified in SOX10 in the UM patient. Somatic mutations in SOX10, a transcription factor, which acts upstream of microphthalmia-associated transcription factor and synergizes with microphthalmia-associated transcription factor, was identified in some melanoma cell lines. The transcription factor SOX10 was found to have an essential role in melanocyte development and pigmentation. Our finding of the frameshift deletion (p.H387fs) in exon 4 of SOX10in UM provides an important insight and complements earlier findings of mutations in GNAQ and SF3B1 on the genomic basis of UM.

© 2014 American Academy of Optometry