Pentacam® Corneal Tomography for Screening of Refractive Surgery Candidates: A Review of the Literature, Part I

Corneal tomography and Scheimpflug imaging are frequently used to analyze the corneal surface, especially in the field of cataract and refractive surgery. The Pentacam system is one of the most commonly used commercially available systems for this purpose. Through a rotating Scheimpflug camera, the system is capable of creating a three-dimensional map of the cornea. These advances in tomography have simultaneously enhanced the ability of clinicians to screen surgical candidates and detect subtle corneal changes in diseases such as keratoconus. However, there remains a need to enhance diagnosis in order to recognize mild and early forms of corneal ectasia. As iatrogenic ectasia and keratoconus are dreaded complications of refractive surgery, it is imperative to screen patients appropriately prior to surgery. The Pentacam is one of many systems utilized in the screening process, but the literature has not identified specific protocol nor parameters that are capable of carrying out this process appropriately. Post-operative keratoconus continues to occur despite the advances in technology seen in corneal imaging. Therefore, clear indices for screening are required in order to diagnose early forms of keratoconus and other corneal diseases that may exclude the seemingly asymptomatic patient from undergoing refractive surgery. This article aims to summarize the indices available on the Pentacam system and to identify the most accurate parameters for screening of the refractive surgery candidate

Keratoconus in Down’s syndrome

Keratoconus is a primary cause of visual impairment in young people in the UK. Corneal cross-linking is a recently-introduced treatment for halting progression of keratoconus, which is more effective in early cases. It has long been observed that keratoconus is significantly more prevalent in those with Down’s syndrome (DS) when compared to the general population. Moreover, young people with Down’s syndrome are less able to report early symptoms of keratoconus, often presenting late to eye clinics when cross-linking is no longer possible. A cohort of children and young people with DS were examined with the aim of discovering optometric correlates of keratoconus and to establish the utility of these parameters as risk factors for identifying keratoconus in primary care. An abnormal retinoscopy reflex was found to be the earliest indicator of keratoconus, showing greater potential as a screening test than either refractive error or objective vision measurement. The cornea of individuals with DS is known to be thinner and steeper than usual. Despite this, the high prevalence of keratoconus in DS has long been attributed to eye-rubbing, despite the inherent difference in baseline shape. The current work revealed no relationship between eye rubbing and the development of keratoconus in DS eyes. In vivo biomechanical analysis demonstrated an increased deformation tendency in DS eyes vs. controls, largely accounted for by the decreased corneal thickness in the test group. These results suggest that the high prevalence of keratoconus in DS originates from biomechanical weakness, permitting the loss of regular corneal shape in the absence of eye rubbing. However, ultrastructural analysis of the cornea of the Tc1 mouse model of DS revealed an unaltered collagen and proteoglycan structure. Topographical examination of ‘cone’ morphology in individuals with and without DS demonstrated a similar phenotype at all stages of the disorder, indicating that people with DS and keratoconus may be a useful cohort for future genetic studies into keratoconus as a whole

Queensland University of Technology: Handbook 1994

The Queensland University of Technology handbook gives an outline of the faculties and subject offerings available that were offered by QUT