Reasons for not performing keratorefractive surgery in patients seeking refractive surgery in a hospital-based cohort in "Yemen"

Bamashmus, Mahfouth A.; Saleh, Mahmoud F.; Awadalla, Mohamed A.

doi:10.4103/0974-9233.71605

Cited by 21 publications

(23 citation statements)

References 28 publications

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“…Additionally, the model does not account for physiologic corneal thickness variation [21]. For example, healthy patients with corneas too thin to be considered candidates for photorefractive surgery (< 450 µm, [40]) have predicted water content values of ~70%, a level not theoretically possible while the cornea is still attached to the eye. Additional inaccuracies plague the utility of the linear fit which predicts a dehydrated cornea thickness of ~127 µm [39] where the generally accepted thickness is >200 µm [38].…”

Section: Corneal Tissue Water Contentmentioning

confidence: 99%

THz and mm-Wave Sensing of Corneal Tissue Water Content: Electromagnetic Modeling and Analysis

Taylor

Garritano

Sung

et al. 2015

IEEE Trans. THz Sci. Technol.

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Terahertz (THz) spectral properties of human cornea are explored as a function of central corneal thickness (CCT) and corneal water content, and the clinical utility of THz-based corneal water content sensing is discussed. Three candidate corneal tissue water content (CTWC) perturbations, based on corneal physiology, are investigated that affect the axial water distribution and total thickness. The THz frequency reflectivity properties of the three CTWC perturbations were simulated and explored with varying system center frequency and bandwidths (Q-factors). The modeling showed that at effective optical path lengths on the order of a wavelength the cornea presents a lossy etalon bordered by air at the anterior and the aqueous humor at the posterior. The simulated standing wave peak-to-valley ratio is pronounced at lower frequencies and its effect on acquired data can be modulated by adjusting the bandwidth of the sensing system. These observations are supported with experimental spectroscopic data. The results suggest that a priori knowledge of corneal thickness can be utilized for accurate assessments of corneal tissue water content. The physiologic variation of corneal thickness with respect to the wavelengths spanned by the THz band is extremely limited compared to all other structures in the body making CTWC sensing unique amongst all proposed applications of THz medical imaging.

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Section: Corneal Tissue Water Contentmentioning

confidence: 99%

THz and mm-Wave Sensing of Corneal Tissue Water Content: Electromagnetic Modeling and Analysis

Taylor

Garritano

Sung

et al. 2015

IEEE Trans. THz Sci. Technol.

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“…Candidates for refractive surgery were screened using pachymetry, biomicroscopy and topography (TMS‐2) and 1660 of 2,091 (79 per cent) met the criteria for LASIK or photo refractive keratectomy and 431 were poor candidates, 17.9 per cent with keratoconus and 10.4 per cent with suspect or forme fruste representing 28.3 per cent of the 431 poor candidates . Of the initial sample of 2,091, 5.8 per cent were classified as poor candidates because of keratoconus or forme fruste . This 5.8% figure from 2010 represents 25 times the upper range estimate for keratoconus reported prior to 1966.…”

Section: Increasing Prevalence or Better Detection?mentioning

confidence: 99%

Screening for keratoconus suspects among candidates for refractive surgery

McMonnies

2014

Clinical and Experimental Optometry

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This review examines methods for estimating the risk of post‐surgical ectasia in candidates for refractive surgery by establishing a diagnosis of keratoconus suspect as a contraindication for proceeding with surgery. Notwithstanding the desirability of achieving 100 per cent sensitivity, any associated reduction in specificity and increased numbers of false positives might deny some candidates the opportunity to proceed with refractive surgery. The introduction of a model for the risk of ectasia involving both pre‐ and post‐surgical findings has been followed by a plethora of attempts to achieve the same purpose based on topographic and/or tomographic evaluation before surgery. The desirability of being able to depend on objective assessment using one type of instrument needs to be weighed against the possibility that subjective assessments may contribute significantly to screening success. For example, consideration of ethnicity, family history of keratoconus, a history of atopy or ocular allergies in particular, a history of significant exposure to corneal trauma associated with abnormal rubbing habits or with vocational, leisure or geographically increased exposure to ultraviolet radiation or with contact lens wear trauma or a history of significant exposure to activities which elevate intraocular pressure may improve screening success. To the extent that these factors could contribute to increased risk of the development of keratoconus, they may be useful in estimating the risk of post‐surgical ectasia. If any combination of these factors helps to explain the development of keratoconus in normal or even thicker than normal corneas, they may have more significance for those corneas, which have been thinned surgically.

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“…Progressive ectasia, corneal thinning, and scarring are the hallmarks of KC, known to affect both males and females [1]. Prevalence has been increasing steadily, going from 1:2000 back in the 1980s to 1:350 in the 2000s worldwide [3][4][5][6], perhaps due to technological advancements and better diagnostics.…”

Section: Introductionmentioning

confidence: 99%

Gonadotropins in Keratoconus: The Unexpected Suspects

Karamichos

Barrientez

Nicholas

et al. 2019

Cells

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Keratoconus (KC) is the most common ectatic corneal disease with a significant visual acuity burden. The actual burden is intangible given that KC can disrupt daily activities (reading, driving, and various career paths). Despite decades of research and clinical studies, the etiology, onset, and pathobiology of KC remain a mystery. The purpose of this study was to investigate the role of gonadotropins in KC. We recruited 86 KC patients (63 males, 23 female), and 45 healthy controls (22 male, 23 female). Plasma samples were collected and analyzed using an enzyme-linked immunosorbent assay. Corneal stromal cells from KC and healthy controls, and human epithelial corneal cells, were also investigated for gonadotropin-related markers. Our results show significant alterations of LH/FSH in KCs, compared to healthy controls. Our data also reveals, for the first time, the existence of gonadotropins and their receptors in KC. Our study is the first to demonstrate the role of LH/FSH in KCs, and expand the list of organs known to express gonadotropins, or their receptors, to include the human cornea. Our findings suggest that the human cornea is capable of responding to gonadotropins, and propose an intriguing mechanism for the onset and/or progression of KC.

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Reasons for not performing keratorefractive surgery in patients seeking refractive surgery in a hospital-based cohort in "Yemen"

Cited by 21 publications

References 28 publications

THz and mm-Wave Sensing of Corneal Tissue Water Content: Electromagnetic Modeling and Analysis

THz and mm-Wave Sensing of Corneal Tissue Water Content: Electromagnetic Modeling and Analysis

Screening for keratoconus suspects among candidates for refractive surgery

Gonadotropins in Keratoconus: The Unexpected Suspects

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