Objective Measurement of Corneal Light Scattering after Excimer Laser Keratectomy

Braunstein, Richard E.; Jain, Sandeep; McCally, Russell L.; Stark, Walter J.; Connolly, Patrick J.; Azar, Dimitri T.

doi:10.1016/s0161-6420(96)30674-x

Cited by 83 publications

(38 citation statements)

References 19 publications

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“…In addition, patients with complications such as epithelial ingrowths, corneal haze and irregularities were also disqualifi ed. Haze was evaluated subjectively using the slitlamp according to the grading proposed by Braunstein et al [8] .…”

Section: Methodsmentioning

confidence: 99%

Comparison of Forward Shift of Posterior Corneal Surface after Operation between LASIK and LASEK

Kim

Joo

2005

Ophthalmologica

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Purpose: To compare the forward shift of the posterior corneal surface as a function of time after surgery between successful laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK). Methods: Twenty-two eyes from 14 patients who underwent LASIK and 19 eyes from 10 patients who underwent LASEK were reviewed retrospectively. The uncorrected visual acuity, spherical equivalent and pachymetry were obtained before and 1 or 2 weeks and 2, 6, 12, and 24 months after surgery. The change in the elevation of the posterior corneal surface was assessed using the difference map of an Orbscan II (Bausch and Lomb, Salt Lake City, Utah, USA), which was generated from the preoperative and subsequent postoperative elevation map. Results: One or 2 weeks after LASIK and LASEK, the posterior corneal surface had shifted forward by 18.00 and 25.90 µm, respectively (p = 0.008). However, the mean posterior corneal surface reduced by 3.05 µm from 1 or 2 weeks to 2 years in the LASIK group (p = 0.359). In contrast, the mean posterior corneal surface had reduced by 12.40 µm in the LASEK group (p = 0.004). This forward shift did not return to the corneal normal elevation observed prior to surgery in the two groups. Conclusions: Refractive surgery induced a forward shift of the posterior corneal surface early postoperatively in the LASIK and LASEK groups, and this change after LASEK was significantly larger than that observed after LASIK. The posterior corneal surface gradually shifted backwards depending on the time course in both groups, but they did not return to the preoperative levels.

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Section: Methodsmentioning

confidence: 99%

Comparison of Forward Shift of Posterior Corneal Surface after Operation between LASIK and LASEK

Kim

Joo

2005

Ophthalmologica

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“…Previously, the optical quality of cornea was assessed and monitored by standard slit lamp examination i.e. light scattering back to observer and extent of severity was graded subjectively [3][4][5]. This subjective evaluation tends to vary between observers.…”

Section: Introductionmentioning

confidence: 99%

Normal Values of Corneal Optical Densitometry Using Pentacam Scheimpflug Camera

Asrar¹,

Ikram²,

Khan³

et al. 2016

AOVS

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Purpose: The purpose of the study was to illustrate the range of normal values of corneal densitometry using Pentacam Scheimpflug camera. Methodology:Prospective study was conducted at tertiary care Amanat eye hospital. 490 eyes of 490 participants of different age groups were added. All scans were performed in diagnostics room with uniform ambient light, performed by trained ophthalmic technologist. All participants were Pakistani of different ethnic groups. Only one eye of each participant was included to control biasness. T test, One-way ANOVA, pearson correlation coefficient and linear regression model tests were applied for analysis.Results: 490 eyes; 247 right eyes and 243 left eyes were analyzed. Mean age was 41.7±15.27 years (range 20-81 years) with 48.4% male and 51.6% females. based on corneal depth; highest backward scattering of light was observed in anterior (120 µm) layer (20.6±8.52 GSU) than central and posterior layers 13.6±5.17 GSU and 11.7±3.99 GSU respectively. The difference was statistically significant among layers with p< 0.001. Based on corneal surface, minimum backscattering was noted in central 0-6mm zone which increases from central to limbal zone; 0-2mm zone was 13.2±3.81 GSU, 2-6mm zone was 12.6±3.68 GSU, 6-10mm zone was 16.0±8.90 GSU and 10-12mm zone was 22.1±8.26 GSU. The difference was statistically significant with p<0.001. Significant correlation of corneal densitometry and age was observed r= 0.677, p<0.001. Conclusion:Objective assessment of corneal densitometry can be made with Pentacam Scheimpflug. Normative values of corneal density may be used in routine clinical practice and provided a reference for future research.

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“…The small amount of scattered light produced by this tissue has in particular been extensively researched in the literature [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. All previous theories explaining corneal transparency [21][22][23][24][25][26][27] have focused on light propagation in the stromal extracellular matrix.…”

Section: Introductionmentioning

confidence: 99%

“…They can be caused by microstructural alterations, the irregular organization of the extracellular matrix, or by cells [22]. Many studies have attempted to relate form, density, and cell size to the structure of the scattered light [1][2][3][4][5][6][7]17,18]. Mourant et al [12,13] suggest that the cell itself is responsible for scattering at a small angle.…”

Section: Introductionmentioning

confidence: 99%

Measurement of correlation between transmission and scattering during wound healing in hen corneas

Mar

Martínez-García

Blanco–Mezquita

et al. 2009

Journal of Modern Optics

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The aim of this work is to provide experimental data for corneal transparency and scattering to help create a more complete model of corneal transparency. The scattered light in 96 healing hen corneas was measured for three wavelengths by a scatterometer constructed in the Optics Laboratory (The University of Valladolid, Spain). With the help of mirrors and beamsplitters, the light from the three lasers is directed toward the cell containing the sample to be measured. The measured scattered light varies between six orders of magnitude. Corneal transmissivity, mean cosine of a scattering angle, and angular distribution of scattered light were all computed. The total transmitted light remained practically constant over a wide range of light values transmitted in a forward direction (direct transmissivity). The value of the mean cosine of the scattering direction is very close to the unit (g 4 0:98), even in corneas with high opacities. The behavior of g indicates that even damaged corneas evidence extremely small scattering, compared to other biological tissues. The transmission reduction of each cornea is related to an increase in scattered light. In all cases, scattered light is concentrated at very small angles. This behavior is acceptable in corneas that are healthy or which evidence small lesions, but remains in corneas that are severely injured.

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Objective Measurement of Corneal Light Scattering after Excimer Laser Keratectomy

Cited by 83 publications

References 19 publications

Comparison of Forward Shift of Posterior Corneal Surface after Operation between LASIK and LASEK

Comparison of Forward Shift of Posterior Corneal Surface after Operation between LASIK and LASEK

Normal Values of Corneal Optical Densitometry Using Pentacam Scheimpflug Camera

Measurement of correlation between transmission and scattering during wound healing in hen corneas

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