Biomedical subjects

W Neil Charman

Publications and source records attributed to W Neil Charman.

20 records · Page 2Linked to original sources

PubMedDate not supplied

Surface roughness after excimer laser ablation using a PMMA model: profilometry and effects on vision.

PURPOSE: To show that the limited quality of surfaces produced by one model of excimer laser systems can degrade visual performance with a polymethylmethacrylate (PMMA) model. METHODS: A range of lenses of different powers was ablated in PMMA sheets using five DOS-based Nidek EC-5000 laser systems (Nidek Technologies, Gamagori, Japan) from different clinics. Surface quality was objectively assessed using profilometry. Contrast sensitivity and visual acuity were measured through the lenses when their powers were neutralized with suitable spectacle trial lenses. RESULTS: Average surface roughness was found to increase with lens power, roughness values being higher for negative lenses than for positive lenses. Losses in visual contrast sensitivity and acuity measured in two subjects were found to follow a similar pattern. Findings are similar to those previously published with other excimer laser systems. CONCLUSIONS: Levels of surface roughness produced by some laser systems may be sufficient to degrade visual performance under some circumstances.

Adult↗

PubMedDate not supplied

Ablation design in relation to spatial frequency, depth-of-focus, and age.

PURPOSE: To consider factors relevant to the design of wavefront-aberration-based customized ablations. METHODS: Review. RESULTS: Ablations that seek to eliminate all wavefront aberrations, both second- and higher-order, may not be optimal for all patients. This is particularly the case for presbyopes. Their main requirement will normally be for extended binocular depth-of-focus to yield adequate distance and near vision with good retinal contrast at lower spatial frequencies, rather than the highest levels of acuity and modulation transfer function at a single distance. For many presbyopes, this can be achieved by aiming for monovision correction or low myopic astigmatism, with reasonable but not necessarily complete correction of higher-order aberrations. This compromise allows a range of everyday tasks to be carried out, including face recognition and reading. CONCLUSION: The targeted correction of wavefront aberration should take into account the visual needs and preferences of the individual patient.

Accommodation, Ocular↗