Eye detection using gradient histogram matching for cornea localization in refractive eye surgery

The excimer laser, with a gas mixture of argon and fluorine, is widely used in refractive eye surgery. Over the past decade the excimer laser has become the preferred choice for treatment; the ultraviolet laser beam at 193 nm is able to remove microscopic amounts of tissue from the cornea via a photochemical interaction, resulting in a huge improvement in results from refractive eye surgery compared with previous techniques.The use of the excimer laser for ophthalmic surgery introduces a number of hazards, many being non-beam hazards. These non-beam hazards are discussed, and include: fluorine gas, which forms part of the laser active medium, laser plume, high voltage power supply, electromagnetic interference and ozone.It is concluded that the most significant non-beam hazard is fluorine gas. Basic gas law calculations indicate that a fluorine gas leak in an ophthalmic clinic may cause exposure limit values to be exceeded. An incident at an ophthalmic clinic involving a fluorine gas leak highlights the need for a risk assessment to be conducted and contingency plans to be put into place.The excimer laser, with a gas mixture of argon and fluorine, is widely used in refractive eye surgery. Over the past decade the excimer laser has become the preferred choice for treatment; the ultraviolet laser beam at 193 nm is able to remove microscopic amounts of tissue from the cornea via a photochemical interaction, resulting in a huge improvement in results from refractive eye surgery compared with previous techniques.The use of the excimer laser for ophthalmic surgery introduces a number of hazards, many being non-beam hazards. These non-beam hazards are discussed, and include: fluorine gas, which forms part of the laser active medium, laser plume, high voltage power supply, electromagnetic interference and ozone.It is concluded that the most significant non-beam hazard is fluorine gas. Basic gas law calculations indicate that a fluorine gas leak in an ophthalmic clinic may cause exposure limit values to be exceeded. An incident at an ophthalmic clinic involving a fluorine gas leak highlights the n...

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Selective zonal ablations with excimer laser for correction of irregular astigmatism induced by refractive surgery

The popularity of refractive surgery to correct ametropia is increasing, to become among the most commonly performed procedures in medicine. PRK was the first type of surface ablation procedure (refractive eye surgery) used a laser rather than a blade to remove the corneal tissue.Removing of the epithelium in PRK was performed by several techniques including: conventional (mechanical, chemical) or trans-epithelial PRK. Single-step trans-PRK using Amaris excimer laser is a new treatment in which the epithelial removal is using a population-based epithelial profile; this type combines the epithelial and the stromal laser ablation in one step.Many patients complain of halo, glare and blurred vision at night after successful corneal refractive surgery . High order aberrations and changes in contrast sensitivity are expected to be a causes of their complains. Wave-front technology has been developed enough in the last years to have an accurate measurements, diagnoses and treatment of HOAs.

Eye detection is the most important and critical task of diverse applications such as face detection and recognition. However, most eye detection methods do not fully consider detection robustness to people with glasses, illumination variation, head pose change, and eye occlusions. This paper proposes an efficient hybrid eye detection method based on a gray intensity variance filter (VF) and support vector machines (SVMs). Firstly, the VF is used for eliminating most of noneye region images to keep less candidate eye regions. Then accurate two eye regions are determined easily through the trained SVM classifier. Moreover, this paper provides an assessment of the sensitivity of obtained parameters in the SVM classifier on eye detection accuracy. The proposed method was evaluated on different face databases. The experimental results show that the method can improve the performance of eye detection and achieve a higher detection accuracy compared with state-of-the-art methods.

In this paper, we propose an eye detection method that is robust to facial pose changes using gradient directional features of brightness and a particle filter. The rejection function of incorrect eye detection in the proposed method allows for the eye detection again even if the eye is incorrectly detected. In this method, to estimate the boundary between the iris and sclera or eyelid, the gradient intensities are calculated by four directional Prewitt filters in four regions. The likelihood used in the particle filter is obtained by averaging the gradient intensities for the specific direction in the four regions and the upper eyelid area. From experimental results, the average detection rates of both eyes for roll, yaw, and pitch angles of the face are more than 90% by using rejection function for incorrect eye detection. The rejection function produces the 4.4%, 4.5%, and 4.9% increases in average detection rates of both eyes for roll, yaw, and pitch facial angles, respectively. The proposed eye detection method can track both eye in real-time (about 20 ms) and is robust to the facial pose changes.

Focused on the issue that the detection error rate of the current eye detection method is relatively high, and when the AdaBoost algorithm is used to train the classifier, it is easy to appear the phenomenon of weight imbalance. A new eye detection method based on the improved AdaBoost algorithm is proposed. First, the AdaBoost algorithm is applied to the detection of human eyes. Then the reason for the imbalance of weights in training of AdaBoost algorithm is analyzed, and the concept of missing detection rate is introduced to improve the weight updating process of AdaBoost algorithm. The experimental results show that the improved AdaBoost algorithm ensured the sample weight distribution balance and improve the accuracy in the training process; eye detection based on the improved AdaBoost algorithm effectively maintains a high detection rate and inhibits the detection error rate, makes detection more accurate.

Scattered ultraviolet emissions during refractive surgery using a high-frequency, wavefront-optimized excimer laser platform

This paper presents the evaluation of visual features for the proposed two eye detection method applied to thermal images. The use of two eye region is due to its distinctive pattern and to overcome the issue of blurred and noisy characteristic in the thermal image. Comparative performance analysis on three different features which includes Haar, Histogram of Oriented Gradients (HoG) and Local Binary Patterns (LBP) is conducted. The performance of the eyes detection method is measured based on the correct detection of both eyes inside the face image. The experiments were done on the Natural Visible and Infrared Facial Expression Database (NVIE). The method proposed in this paper shows good eye detection accuracy. The best detection accuracy is obtained using the HoG feature.

An innovative method for cascade eye detection using facial geometric features is proposed. The cascade detector is used to detect pairs of eye of candidates. The size similarity, the horizontal symmetry, the horizontal sextant angle, and the scale coefficients extracted from facial geometric feature are integrated to improve eye detection. Both the BioID database and real-time video stream were used in the experiments. Experimental results show that the proposed eye detection method is significantly more accurate than the cascade detector alone without sacrificing overmuch time-efficiency.

This article reviews recent developments in excimer laser refractive corneal surgery. The excimer laser is now used to treat myopia, hyperopia and astigmatism by either surface (photorefractive keratectomy or PRK) or stromal (laser in situ keratomileusis or LASIK) ablation. The refractive outcome of PRK is excellent for low (less than six dioptres) myopia, but it is not without complications. These include initial severe pain, myopic regression, haze, glare, halos and difficulty with vision in reduced light. The refractive outcome for LASIK is similar to that for PRK, but there is negligible pain, much less haze, less regression among highly myopic patients and a more rapid establishment of final unaided visual acuity. Although excimer laser treatment is currently available, some important advances are necessary before the spectacle and contact lens markets are threatened. Control of the healing process is crucial to improve the accuracy of the outcome, reduce regression and eliminate haze. More attention must be paid to the visual outcome and ablation design so that visual functions, such as best corrected visual acuity and contrast sensitivity, are not reduced. It even may be possible, in the future, to custom design aspheric ablations to yield improved best corrected visual acuity.

In order to investigate whether or not checkpoints of features surrounding the eye are suitable for eye tracking, we evaluated the checkpoints using statistical hypothesis testing. By combining the checkpoints of features surrounding the eye, the eye tracking system using the template matching was effective for the eye detection. The parameters of the checkpoints were empirically determined to detect the eye in any individual. The statistical hypothesis testing revealed that the empirical setting values of the checkpoints were significantly different from actual facial features obtained using face images. We investigated suitable parameters of the checkpoints derived from actual facial features obtained with facial images. It was revealed that new checkpoint settings were effective in drastically reducing the possibility of incorrect eye detection, although the correct detection rate was slightly decreased.

Background Dry eye is among the most prevalent complications following refractive surgery, significantly impacting the training and daily lives of recruits. While recent years we have witnessed some advancements in understanding the occurrence and progression of dry eye, the specific effects of refractive surgery on this condition remain unclear. This study aims to investigate the impact of refractive surgery on dry eye among 300 army recruits. Methods A series of examinations specific to dry eye were conducted on the subjects using the OSDI questionnaire and the ocular surface comprehensive analyzer. The correlation between refractive surgery and dry eye was analyzed in conjunction with dry eye symptoms and related data. Additionally, optical coherence tomography (OCT) was employed to observe fundus changes in dry eye patients, comparing those with low to moderate myopia against patients with high myopia prior to surgery. The morphology of the meibomian glands in the upper eyelid was assessed using the Keratograph 5M ocular surface analyzer, where the area of meibomian gland loss was calculated and scored, facilitating an exploration of the relationship between meibomian gland loss and dry eye. Furthermore, the dry eye detection rates of Non-Invasive Break-Up Time (NIBUT), Lipid Layer Thickness Measurement (LTMH), and basal Schirmer secretion (SIT) were calculated, and the diagnostic differences among these three methods for dry eye were analyzed. Results According to the OSDI questionnaire, 117 (39%) patients opted for SMILE, 60 (20%) for F-LASIK, and 123 (41%) for LASIK. Among the recruits, 78 (26%) were diagnosed with dry eye following refractive surgery. Single factor and multiple logistic regression analyses indicated that LASIK may serve as an independent risk factor for the development of dry eye after refractive surgery. Furthermore, the incidence of leopard-pattern fundus was significantly higher in recruits with high myopia compared to those with low to moderate myopia. Keratograph5M assessments revealed that 52.6% of patients exhibited no meibomian gland loss; 45.5% had meibomian gland loss of less than 1/3; 1.9% experienced meibomian gland loss ranging from 1/3 to 2/3; and no patients had meibomian gland loss exceeding 2/3. These results suggest that there is no direct relationship between dry eye and meibomian gland loss following refractive surgery. Additionally, the dry eye detection rate using non-invasive tear break-up time (NIBUT) was 92.6%, while the detection rate for LTMH dry eye was 91.0%. The basal Schirmer test (SIT) yielded a dry eye detection rate of 78.2%, indicating that non-invasive tear assessment methods have a higher detection rate for dry eye. Conclusions The incidence of dry eye among recruits following excimer laser corneal refractive surgery is significantly higher than that observed with other surgical methods, suggesting that it may represent an independent risk factor for dry eye post-refractive surgery. Consequently, we do not recommend the use of laser in situ keratomileusis for refractive surgery.

Dry eye is among the most prevalent complications following refractive surgery, significantly impacting the training and daily lives of recruits. While recent years we have witnessed some advancements in understanding the occurrence and progression of dry eye, the specific effects of refractive surgery on this condition remain unclear. This study aims to investigate the impact of refractive surgery on dry eye among 300 army recruits. A series of examinations specific to dry eye were conducted on the subjects using the OSDI questionnaire and the ocular surface comprehensive analyzer. The correlation between refractive surgery and dry eye was analyzed in conjunction with dry eye symptoms and related data. Additionally, optical coherence tomography (OCT) was employed to observe fundus changes in dry eye patients, comparing those with low to moderate myopia against patients with high myopia prior to surgery. The morphology of the meibomian glands in the upper eyelid was assessed using the Keratograph 5M ocular surface analyzer, where the area of meibomian gland loss was calculated and scored, facilitating an exploration of the relationship between meibomian gland loss and dry eye. Furthermore, the dry eye detection rates of Non-Invasive Break-Up Time (NIBUT), Lipid Layer Thickness Measurement (LTMH), and basal Schirmer secretion (SIT) were calculated, and the diagnostic differences among these three methods for dry eye were analyzed. According to the OSDI questionnaire, 117 (39%) patients opted for SMILE, 60 (20%) for F-LASIK, and 123 (41%) for LASIK. Among the recruits, 78 (26%) were diagnosed with dry eye following refractive surgery. Single factor and multiple logistic regression analyses indicated that LASIK may serve as an independent risk factor for the development of dry eye after refractive surgery. Furthermore, the incidence of leopard-pattern fundus was significantly higher in recruits with high myopia compared to those with low to moderate myopia. Keratograph5M assessments revealed that 52.6% of patients exhibited no meibomian gland loss; 45.5% had meibomian gland loss of less than 1/3; 1.9% experienced meibomian gland loss ranging from 1/3 to 2/3; and no patients had meibomian gland loss exceeding 2/3. These results suggest that there is no direct relationship between dry eye and meibomian gland loss following refractive surgery. Additionally, the dry eye detection rate using non-invasive tear break-up time (NIBUT) was 92.6%, while the detection rate for LTMH dry eye was 91.0%. The basal Schirmer test (SIT) yielded a dry eye detection rate of 78.2%, indicating that non-invasive tear assessment methods have a higher detection rate for dry eye. The incidence of dry eye among recruits following excimer laser corneal refractive surgery is significantly higher than that observed with other surgical methods, suggesting that it may represent an independent risk factor for dry eye post-refractive surgery. Consequently, we do not recommend the use of laser in situ keratomileusis for refractive surgery.

Intraocular lens power calculation after previous laser refractive surgery