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- Jóhannesson, Gauti, 1979-
(författare)
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Intraocular pressure : clinical aspects and new measurement methods
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intraocular pressure (IOP) measurement is a routine procedure and a fundament in glaucoma care. Elevated IOP is the main risk factor for glaucoma, and to date, reduction of IOP is the only possible treatment. In a retrospective clinical material, the prevalence of open angle glaucoma was estimated on the west coast of Iceland. IOP measurement and optic nerve head examination were used to capture glaucoma suspects, within the compulsory ophthalmological examination for the prescription of eye glasses. The results were mainly in agreement with a recent prospective study in the same region. This indicated that retrospective data, under certain conditions, may contribute with useful information on the prevalence of glaucoma. However, normal tension glaucoma is underestimated if perimetry and/or fundus photography are not included in the examination. Three studies focused on the measurement of IOP. Goldmann applanation tonometry (GAT) is the standard method. GAT is affected by corneal properties, e.g. central corneal thickness (CCT) and corneal curvature (CC). Refractive surgery changes these properties. This has put focus on how corneal biomechanics translate into tonometric errors and stimulated the development of new methods. As a result, Pascal ® Dynamic Contour Tonometry (PDCT) and Icare® rebound tonometry have been introduced. A method under development by our research group is Applanation Resonance Tonometry (ART). It is based on resonance technology and estimates IOP from continuous measurement of force and contact area. Comparison of PDCT, Icare and GAT in a prospective study showed that the concordance to GAT was close to the limits set by the International Standard Organization (ISO) for PDCT, while Icare was outside the limits. To investigate if laser-assisted subepithelial keratectomy (LASEK) affects tonometry, a study was performed where measurements with GAT, PDCT and ART were obtained before, three and six months after LASEK. The hypothesis was that PDCT and ART would be less affected by LASEK than GAT. The results showed a statistically significant reduction of measured IOP three and six months after LASEK for all tonometry methods. Change in visual acuity and IOP between three and six months suggested a prolonged postoperative process. A servo-controlled prototype (ART servo) was developed. A study was undertaken to assess the agreement of ARTservo and a further developed v manual prototype (ART manual) with GAT. The study design was in accordance with the requirements of the ISO standard for tonometers. ARTmanual fulfilled the precision requirements of the ISO standard. ARTservo did not meet all the requirements of the standard at the highest pressure levels. Four tonometry methods, GAT, PDCT, Icare and ART, were investigated. None of them was independent of both CCT and CC. The inconsistencies in the results emphasize the importance of study design. A meta-analysis comprising healthy eyes (IOP ≤ 21 mmHg) in the three papers, revealed age as an important confounder. In summary, glaucoma prevalence in Iceland was investigated and the results indicated that a retrospective approach can contribute with meaningful information. ART and PDCT had a similar agreement to GAT. ART manual fulfilled the precision requirements set by the ISO-standard, ARTservo and PDCT were close, while Icare was distinctly outside the limits. All tonometry methods were affected by LASEK and no method was completely independent of corneal properties.
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| 2. |
- Rasmuson, Erika, 1981-
(författare)
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Laser treatment in glaucoma : efficacy and safety
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glaucoma is a progressive optic neuropathy and the major cause of irreversible blindness worldwide. Although the pathogenesis of glaucoma is not completely understood, the most important risk factor for development and progression of the disease is an elevated intraocular pressure (IOP). Current glaucoma treatment aims to reduce the IOP in the affected eye. This can be achieved by topical drops, laser therapy or surgery. Laser treatment is used at different stages of the glaucoma disease. Some types of laser procedures are used as first-line treatments or as complement to topical medications or surgery, while other types are used in advanced glaucoma as a last option when other therapies have failed. Although laser therapy has long been used to reduce the IOP in glaucoma, knowledge gaps remain. The aim of this thesis was to evaluate the efficacy and safety, in both a short- and long-term perspective, of two of the most frequently used laser procedures in glaucoma: laser trabeculoplasty (LTP) and transscleral cyclophotocoagulation (TCP).In the first study, a retrospective analysis, the long-term efficacy and safety of TCP was evaluated in 300 eyes of 300 glaucoma patients in northern Sweden. We found an overall substantial IOP reduction of more than 10 mmHg that was maintained at least 2 years in various types of glaucoma. Following TCP, the patients could reduce their treatment with an average of one substance of topical glaucoma medication in the treated eye. No case of phthisis bulbi, the most feared complication of TCP, was reported. However, a general decline in visual acuity (VA) was noted during the two-year follow up period, and the cause of this finding was difficult to assess due to the retrospective nature of the study.The short-term effect of TCP on IOP was further investigated in a prospective study of 58 eyes of 58 glaucoma patients. IOP was measured at baseline before TCP and at five additional time-points up to 24 hours after the treatment. The VA was measured before TCP and at the 24 h examination. The results showed a transient IOP spike with a peak at six hours after TCP in approximately 40% of the eyes. Spikes were more common in eyes with pseudoexfoliation glaucoma.The last two studies of the thesis focused on the short- and long-term efficacy of LTP. One-hundred fifty-two eyes of 122 newly diagnosed glaucoma patients that had been randomized to the multi-treated arm in the Glaucoma Intensive Treatment Study (GITS) were included. All studied eyes were treated with three different IOP-lowering substances and after one week, LTP was performed. We demonstrated that there was an additional IOP-lowering effect of LTP but that this effect was strongly associated with the level of IOP before the laser, where a higher IOP pre-LTP yielded a greater IOP reduction. Eyes with pre-laser IOP ³15 mmHg showed a significant IOP reduction that was maintained during four years of follow-up. However, in eyes with pre-LTP IOP <15 mmHg, the effect of laser treatment was limited.In summary, this thesis investigated the efficacy and safety of TCP both retrospectively in a longer perspective and prospectively during the first 24 hours after treatment. An overall high efficacy without serious complications was shown, but a possible decline in VA must be considered in the long run. Furthermore, the risk of IOP spikes after TCP implies that additional IOP-lowering treatment should be considered during the first 24 hours, especially in eyes with pseudoexfoliation glaucoma or severe glaucoma damage. Finally, LTP may provide a valuable long-lasting IOP-lowering effect despite medical multi-treatment in eyes with a pre-LTP IOP ³15 mmHg.
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| 3. |
- Beckman Rehnman, Jeannette, 1969-
(författare)
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New methods to evaluate the effect of conventional and modified crosslinking treatment for keratoconus
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Today corneal crosslinking with ultraviolet-A photoactivation of riboflavin is an established method to halt the progression of keratoconus. In some cases, when the refractive errors are large and the visual acuity is low, conventional corneal crosslinking may not be sufficient. In these cases it would be desirable with a treatment that both halts the progression and also reduces the refractive errors and improves the quality of vision.Aims: The aims of this thesis were to determine whether mechanical compression of the cornea during corneal crosslinking for keratoconus using a sutured rigid contact lens could improve the optical and visual outcomes of the treatment, and also to find methods to evaluate the effect of different corneal crosslinking treatment regimens.Methods: In a prospective, open, randomized case-control study, 60 eyes of 43 patients with progressive keratoconus, aged 18-28 years, planned for routine corneal crosslinking, and a corresponding age- and sex-matched control group was included. The patients were randomized to conventional corneal crosslinking (CXL; n=30) or corneal crosslinking with mechanical compression of the cornea during the treatment (CRXL; n=30).Biomicroscopy, autorefractometry, best spectacle corrected visual acuity, axial length measurement, Pentacam® HR Scheimpflug photography, pachymetry, intraocular pressure measurements and corneal biomechanical assessments were performed before treatment (baseline) and at 1 month and 6 months after the treatment.One of the articles evaluated and compared the optical and visual outcomes between CXL and CRXL, while the other three articles focused on methods to evaluate treatment effects. In Paper I, the corneal light scattering was manually quantified from Scheimpflug images throughout the corneal thickness at 8 measurements points, 0.0 to 3.0 mm from the corneal centre, in patients treated with CXL. In Paper IV the corneal densitometry (light scattering) was measured with the Pentacam® HR software, in 4 circular zones around the corneal apex and at 3 different depths of the corneal stroma, in both CXL and CRXL treated corneas. Paper III quantified the biomechanical effects of CXL in vivo.Results: Corneal light scattering after CXL showed distinctive spatial and temporal profiles and Applanation Resonance Tonometry (ART) -technology demonstrated an increased corneal hysteresis 1 and 6 months after CXL. When comparing the refractive and structural results after CXL and CRXL, CRXL failed to flatten the cornea, and the treatment did not show any benefits to conventional CXL treatment, some variables even indicated an inferior effect. Accordingly, the increase in corneal densitometry was also less pronounced after CRXL.Conclusions: Analysis of corneal light scattering/densitometry shows tissue changes at the expected treatment location, and may be a relevant variable in evaluating the crosslinking effect. ART -technology is an in vivo method with the potential to assess the increased corneal hysteresis after CXL treatment. By refining the method, ARTmay become a useful tool in the future. Unfortunately, CRXL does not improve the optical and visual outcomes after corneal crosslinking. Possibly, stronger crosslinking would be necessary to stabilize the cornea in a flattened position.
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