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  • 1.
    Fredriksson, Anneli
    et al.
    Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå.
    Behndig, Anders
    Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå.
    Eccentric small-zone ray tracing wavefront aberrometry for refraction in keratoconus2016In: Acta Ophthalmologica, ISSN 1755-375X, E-ISSN 1755-3768, Vol. 94, no 7, p. 679-684Article in journal (Refereed)
    Abstract [en]

    PURPOSE: To compare objective refraction using small-zone eccentric laser ray tracing (LRT) wavefront aberrometry to standard autorefraction in keratoconus (KC), and whether the visual acuities achieved with these refractions differ from corresponding values in healthy eyes.

    METHODS: Twenty-nine eyes of 29 patients with KC and 29 eyes of 29 healthy controls were included in this prospective unmasked case-control study. The uncorrected (UCVA) and spectacle-corrected (SCVA) Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuities based on refractions derived from LRT in central and four eccentric zones were compared to those achieved with standard autorefraction. The spherical equivalent (M) and two astigmatic power vectors (C0 and C45) were calculated for all refractions. Pentacam HR(®) was used to generate keratometry readings of the corresponding zones.

    RESULTS: In KC, the refraction from the upper nasal zone rendered a higher SCVA than the standard autorefraction more often than in the controls (p < 0.001). There were no significant variation in M between the different LRT measurement points in the control group, but central data provided the best SCVA. The UCVA:s and SCVA:s were worse in KC, and the KC eyes showed inferior myopia and superior hyperopia. Multiple refractions rendered similar SCVA:s in KC. Pentacam HR(®) showed higher keratometry readings infero-temporally, but also lower readings supero-nasally, compared to controls.

    CONCLUSION: In KC, eccentric LRT measurements gave better SCVA than standard autorefraction more often than in healthy eyes. Eccentric LRT may become a valuable tool in the demanding task of subjective refraction in KC.

  • 2.
    Fredriksson, Anneli
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
    Behndig, Anders
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
    Measurement centration and zone diameter in anterior, posterior and total corneal astigmatism in keratoconus2017In: Acta Ophthalmologica, ISSN 1755-375X, E-ISSN 1755-3768, Vol. 95, no 8, p. 826-833Article in journal (Refereed)
    Abstract [en]

    Purpose To investigate the central and paracentral astigmatism and the significance of centration and measurement zone diameter compared to a 3-mm pupil-centred measurement zone in keratoconus and in healthy eyes.

    Methods Twenty-eight right eyes from 28 KC patients with an inferotemporal cone were selected according to specified criteria based on Oculus Pentacam HR (R) measurements and were matched with healthy control eyes. The flat (K1) and steep (K2) keratometry readings were registered from the Total Corneal Refractive Power' (TCRP) display as well as the anterior and posterior corneal astigmatism displays (ACA and PCA, respectively). Astigmatic power vectors KP0 and KP45 were calculated and analysed for a 6-mm and two 3-mm zones centred on the corneal apex and the pupil, and for 8 paracentral 3-mm zones.

    Results The astigmatism was generally higher in KC. Many astigmatic values in KC differed between the 3-mm pupil-centred and the 3- and 6-mm apex-centred zones in KC. In the controls, no corresponding differences between measurement zones were seen, apart from PCA, which differed. The magnitude and direction of KP0 and KP45 varied greatly between the paracentral measurements in KC.

    Conclusion Centration and measurement zone diameter have great impacts on the astigmatic values in KC. A small pupil-centred measurement zone should be considered when evaluating the astigmatism in KC.

  • 3.
    Fredriksson, Anneli
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
    Näslund, Sofie
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
    Behndig, Anders
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
    A prospective evaluation of photorefractive intrastromal cross-linking for the treatment of low-grade myopia2019In: Acta Ophthalmologica, ISSN 1755-375X, E-ISSN 1755-3768Article in journal (Refereed)
    Abstract [en]

    Purpose: To evaluate photorefractive intrastromal cross‐linking (PiXL) treatment for low‐grade myopia, comparing three treatment protocols.

    Methods: Healthy individuals, 25.6 ± 3.6 years of age, with low‐grade myopia underwent epi‐on PiXL with either: 4‐mm zone treated in high oxygen environment (4 mm‐HIGH; n = 15), 4‐mm/room air (4‐mm LOW; n = 6), or 6‐mm/high oxygen (6‐mm HIGH; n = 6). Efficacy was determined by change in uncorrected visual acuity (UCVA), manifest refractive spherical equivalent (MRSE) and corneal curvature (Kmean) over a 12‐month follow‐up. Safety was determined by best spectacle corrected visual acuity (BSCVA), corneal endothelial cell loss and registration of side‐effects.

    Results: Twenty‐seven subjects were included. Due to insufficient effect with the 4‐mm LOW treatment and an unacceptable degree of initial light sensitivity/ocular irritation in the 6‐mm HIGH group, the inclusions to these treatments were stopped after inclusion of 6 patients in each group. The 4‐mm HIGH treatment showed a significantly larger improvement in UCVA (−0.45 ± 0.27 LogMAR) and MRSE (+0.99 ± 0.44 D) at 1, 6 and 12 months compared with the 4‐mm LOW treatment (p < 0.05). At 12 months posttreatment, endothelial cell count and BSCVA were unaltered. More initial side‐effects were noted with the 6‐mm HIGH treatment, compared with the 4‐mm HIGH treatment (p < 0.05).

    Conclusion: Epi‐on PiXL may become a safe and effective non‐ablative treatment for low‐grade myopia. The effect is augmented by high oxygen environment and remains stable for 12 months. The initial ocular irritation is acceptable with a 4‐mm treatment zone. The present results justify further clinical studies on PiXL, including refinements of the technique and long‐term results.

  • 4.
    Nordström, Maria
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
    Schiller, Maria
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
    Fredriksson, Anneli
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
    Behndig, Anders
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
    Refractive improvements and safety with topography-guided corneal crosslinking for keratoconus: 1-year results2017In: British Journal of Ophthalmology, ISSN 0007-1161, E-ISSN 1468-2079, Vol. 101, no 7, p. 920-925Article in journal (Refereed)
    Abstract [en]

    PURPOSE: To assess the refractive improvements and the corneal endothelial safety of an individualised topography-guided regimen for corneal crosslinking in progressive keratoconus.

    METHODS: An open-label prospective randomised clinical trial was performed at the Department of Clinical Sciences, Ophthalmology, Umeå University Hospital, Umeå, Sweden. Thirty-seven patients (50 eyes) with progressive keratoconus planned for corneal crosslinking were included. The patients were randomised to topography-guided crosslinking (photorefractive intrastromal crosslinking (PiXL); n=25) or uniform 9 mm crosslinking (corneal collagen crosslinking (CXL); n=25). Visual acuity, refraction, keratometry (K1, K2 and Kmax) and corneal endothelial morphometry were assessed preoperatively and at 1, 3, 6 and 12 months postoperatively. The PiXL treatment involved an asymmetrical treatment zone centred on the area of maximum corneal steepness with treatment energies ranging from 7.2 to 15.0 J/cm(2); the CXL treatment was a uniform 9 mm 5.4 J/cm(2) pulsed crosslinking. The main outcome measures were changes in refractive errors and corneal endothelial cell density.

    RESULTS: The spherical refractive errors decreased (p<0.05) and the visual acuity improved (p<0.01) at 3, 6 and 12 months after PiXL, but not after CXL. The between-groups differences, however, were not significant. K2 and Kmax decreased at 3, 6 and 12 months after PiXL (p<0.01), but not after CXL (p<0.01 when comparing the two treatments). No corneal endothelial cell loss was seen after either treatment.

    CONCLUSIONS: Individualised topography-based crosslinking treatment centred on the ectatic cone has the potential to improve the corneal shape in keratoconus with decreased spherical refractive errors and improved visual acuity, without damage to the corneal endothelium.

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