title: A clinical and optical evaluation of a modified lens for irregular corneae.
abstract: BACKGROUND
  Correction of high regular and irregular astigmatism with rigid gas-permeable contact lenses can result in discomfort, compromised corneal physiology and fluctuations in visual acuity due to excessive lens movement. Using a non-probability sample, this study explored the optical, clinical and subjective performance of a modified countersunk piggyback lens (MCL) for the management of high regular and irregular corneal astigmatic refractive conditions, as the first phase for a larger randomised control study of the efficacy of the custom piggyback MCL system.
  
  
  METHODS
  The sample was a single group of 10 patients (n = 17 eyes) selected primarily on the basis of a history of failure with conventional management regimes. The objective clinical and optical performance of the MCL used in the management of high degrees of regular and irregular corneal astigmatic conditions was assessed, including measures of visual performance and ocular health. Subjective performance of the MCL was evaluated by patient feedback.
  
  
  RESULTS
  Objective and subjective measures were analysed using appropriate statistical analyses. There was a significant improvement in the uncorrected vision and visual acuity (VA) with the MCL, as well as a significant improvement in refractive status. There was no statistically significant increase in adverse ocular responses with the MCL. Statistical analysis of the subjective responses indicated a strong acceptance of the MCL by all subjects, thus supporting the objective analysis indicating the superior performance of the MCL over prior conventional treatment regimens.
  
  
  CONCLUSIONS
  The custom piggyback MCL performed successfully in the management of a range of high regular and irregular astigmatic conditions, which have been unsuccessfully managed with a range of conventional optical corrections. Despite the additional cost and handling implications of the two-lens system, the MCL was well accepted by all subjects due to its superior optical and clinical performance.
authors.affiliation: School of Physiotherapy, Sports Science and Optometry, University of KwaZulu-Natal, Durban, South Africa. mehtam@ukzn.ac.za
authors.forename: M
authors.initials: M
authors.lastname: Mehta
authors.forename: Anil
authors.initials: A
authors.lastname: Bhagwanjee
authors.forename: Owen
authors.initials: O
authors.lastname: Hilliar
mesh_terms: D001251:Astigmatism / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D003262:Contact Lenses, Extended-Wear; D003315:Cornea / Q000473:pathology*; D005500:Follow-Up Studies; D006801:Humans; D017060:Patient Satisfaction; D011474:Prosthesis Design; D012029:Refraction, Ocular; D016896:Treatment Outcome; D014792:Visual Acuity