Daniel S. Mojon

Adaptive local thresholding by verification-based multithreshold probing with application to vessel detection in retinal images

In this paper, we propose a general framework of adaptive local thresholding based on a verification-based multithreshold probing scheme. Object hypotheses are generated by binarization using hypothetic thresholds and accepted/rejected by a verification procedure. The application-dependent verification procedure can be designed to fully utilize all relevant informations about the objects of interest. In this sense, our approach is regarded as knowledge-guided adaptive thresholding, in contrast to most algorithms known from the literature. We apply our general framework to detect vessels in retinal images. An experimental evaluation demonstrates superior performance over global thresholding and a vessel detection method recently reported in the literature. Due to its simplicity and general nature, our novel approach is expected to be applicable to a variety of other applications.

High prevalence of glaucoma in patients with sleep apnea syndrome.

OBJECTIVE To determine the prevalence of glaucoma in sleep apnea syndrome (SAS), an entity characterized by repetitive upper airway obstructions during sleep, inducing hypoxia and sleep disruption with the risk of cardiovascular and neurologic sequelae. DESIGN Cross-sectional study. PARTICIPANTS A total of 114 white patients consecutively referred for polysomnographic evaluation of suspected SAS. INTERVENTION Complete ophthalmologic examination, including computerized perimetry and simultaneous stereoscopic optic disc photographs. MAIN OUTCOME MEASURES Spearman rank correlations between the respiratory disturbance index during night sleep (RDI), a value used to diagnose and grade SAS, and visual acuity, intraocular pressure (IOP), visual field indices, presence or absence of glaucomatous optic disc changes, and diagnosis of glaucoma. Each correlation was controlled for age and body mass index. To compare proportions of patients harboring glaucoma, the binomial test was used. RESULTS Sixty-nine (60.5%) of the 114 patients had an RDI > or =10, which indicates SAS. Three patients had primary open-angle glaucoma, and two had normal-tension glaucoma. All patients with glaucoma had SAS. The observed prevalence of glaucoma in patients with SAS (5 of 69, 7.2%) was significantly higher than expected in a white population (2%) (P = 0.01). The RDI correlated positively with IOP (P = 0.025), visual field loss variance (P = 0.03), glaucomatous optic disc changes (P = 0.001), and diagnosis of glaucoma (P = 0.01). CONCLUSIONS Patients with SAS constitute a high-risk population for glaucoma and should therefore be screened for glaucoma.

Central corneal thickness measurements in patients with normal tension glaucoma, primary open angle glaucoma, pseudoexfoliation glaucoma, or ocular hypertension

BACKGROUND/AIMS Recent studies have revealed patients with ocular hypertension to have thicker than normal central corneas and those with normal tension glaucoma to have thinner than normal ones, as determined by ultrasonic pachymetry. Since corneal thickness measurements and applanation tonometric estimates of intraocular pressure (IOP) correlate positively, monitoring of the former parameter have served as the basis for adjusting readings pertaining to the latter, with the consequence that many patients have had to be reclassified. With a view to validating these pachymetric studies, the central corneal thickness was determined in patients with normal tension glaucoma, primary open angle glaucoma, pseudoexfoliation glaucoma, or ocular hypertension, as well as that of normal subjects, using optical low coherence reflectometry, which is a new and more precise method than ultrasonic pachymetry. METHODS 34 patients with normal tension glaucoma, 20 with primary open angle glaucoma, 13 with pseudoexfoliation glaucoma, and 12 with ocular hypertension, together with 21 control subjects, were included in this observational, concurrent case-control study. One eye per individual was randomly selected for investigation. IOP was measured by Goldmann applanation tonometry and central corneal thickness by optical low coherence reflectometry. RESULTS Central corneal thickness was significantly higher (p ⩽0.001) in patients with ocular hypertension than in normal individuals or in subjects with either normal tension glaucoma, primary open angle glaucoma, or pseudoexfoliation glaucoma, there being no significant differences between the latter four groups. Patients with ocular hypertension were also significantly younger (p ⩽0.003) than those within any of the three glaucomatous groups. CONCLUSION This study confirms that a significant number of patients with ocular hypertension have normal IOPs after the appropriate adjustments have been made for deviations from normal in their central corneal thickness. The accurate measurement of this latter parameter is important not only for individual patient care, in permitting more precise estimations of IOP, but also for clinical studies, in assuring a more reliable classification of subjects.

Normal-tension glaucoma is associated with sleep apnea syndrome

Introduction: In normal-tension glaucoma, optic nerve damage occurs without elevated intraocular pressures, hence vascular and pathogenic mechanisms other than intraocular pressure effects have been postulated. However, the exact cause(s) remain unknown. We have looked for an association between normal-tension glaucoma and sleep apnea syndrome, a disease characterized by repetitive upper airway obstructions during sleep, inducing hypoxia and sleep disruption with the risk of late cardiovascular and neurological sequelae. Methods: We performed overnight polysomnography in 16 consecutive Caucasian patients with normal-tension glaucoma. The respiratory disturbance index (RDI) during night sleep was used to diagnose and grade obstructive sleep apnea. Patients with an RDI of 10 or more were diagnosed as having obstructive sleep apnea. Results: We observed the following prevalences of obstructive sleep apnea in normal-tension glaucoma patients: 0% (0 of 2) for the group of patients younger than 45 years, 50% (3 of 6) for the age group 45–64 years, and 63% (5 of 8) for the group older than 64 years. Prevalences in the middle and older age group were significantly higher than in a historic control group (p < 0.025 for both, binomial test). Conclusion: Normal-tension glaucoma patients constitute a high-risk population for sleep apnea syndrome. Therefore, they should be screened for sleep apnea syndrome, and, if necessary, be treated to avoid late cardiovascular and neurological sequelae.

Primary open-angle glaucoma is associated with sleep apnea syndrome.

Introduction: The etiology of primary open-angle glaucoma remains unclear. Various risk factors, including vascular abnormalities, have been associated with this disease. Sleep-associated diseases, like sleep apnea syndrome, might also represent a risk factor. Sleep apnea syndrome is characterized by repetitive upper airway obstructions during sleep, inducing hypoxia and sleep disruption with the risk of cardiovascular and neurological sequelae. In this study, we determined the prevalence of sleep apnea syndrome in primary open-angle glaucoma patients. Methods: Overnight transcutaneous finger oximetry was performed in 30 consecutive patients having primary open-angle glaucoma. We assessed the oximetry disturbance index during night sleep, a parameter used to diagnose sleep apnea syndrome and to grade its severity. Results: Sleep apnea syndrome was more prevalent among primary open-angle glaucoma patients compared to normal historic controls of the same age and sex distribution (χ2 = 9.35, d.f. = 3, p < 0.025). The oximetry disturbance index grade was significantly larger in the primary open-angle glaucoma group compared to normal controls (U = 3,352, p = 0.01). According to the oximetry disturbance index, 20% (6/30) of primary open-angle glaucoma patients had sleep apnea syndrome. Conclusion: Primary open-angle glaucoma is associated with sleep apnea syndrome. Early recognition and treatment of sleep apnea syndrome are important to avoid cardiovascular and neurological complications.

Eyelid, conjunctival, and corneal findings in sleep apnea syndrome

OBJECTIVE To determine the prevalence of eyelid, conjunctival, and corneal findings in patients with sleep apnea syndrome (SAS). DESIGN Case series. PARTICIPANTS Seventy-two white patients referred for evaluation of suspected SAS. INTERVENTION Complete examination of eyelids, conjunctiva, and cornea, including videokeratography. MAIN OUTCOME MEASURES Spearman rank correlations were determined between the respiratory disturbance index (RDI) during night sleep, a value used to diagnose and grade SAS, and tear film break-up time, eyelid distraction distance, presence or absence of ocular irritation symptoms, blepharoptosis, floppy eyelids, lacrimal gland prolapse, keratoconus, and endothelial dystrophy. Each correlation was controlled for age and body mass index. RESULTS According to the RDI, 44 (61 %) of the 72 patients had SAS. The RDI correlated positively with the eyelid distraction distance (P = 0.05), presence or absence of floppy eyelids (P = 0.01), and lacrimal gland prolapse (P = 0.01), and correlated negatively with tear film break-up time (P = 0.02). None of our patients with floppy eyelids had corneal abnormalities. One patient with SAS had bilateral keratoconus; another had bilateral Fuch endothelial dystrophy. CONCLUSIONS Sleep apnea syndrome was significantly associated with reduced tear film break-up time, floppy eyelids, and lacrimal gland prolapse. However, ocular irritation symptoms and corneal involvement were rare among patients with SAS. These findings do not confirm previous studies that reported a high prevalence of corneal involvement in floppy eyelid syndrome.

Optic neuropathy associated with sleep apnea syndrome

OBJECTIVE The study aimed to determine ocular abnormalities in sleep apnea syndrome (SAS), an entity characterized by repetitive upper airway obstructions during sleep, inducing hypoxia and sleep disruption with the risk of cardiovascular and neurologic sequelae. DESIGN The study design was a case series. PARTICIPANTS Nine patients referred for evaluation of suspected SAS participated. INTERVENTION Complete ophthalmologic examination, including computerized perimetry, was performed. MAIN OUTCOME MEASURES Correlations between the respiratory disturbance index (RDI) during night sleep, a value used to diagnose and to grade SAS, and visual field indices using the Spearman rank correlation coefficient (r(s)) were measured. RESULTS One patient was excluded from the statistical analysis because of optic nerve drusen with constricted visual fields, another because of tilted discs with corresponding temporal visual field defects. All three patients with severe SAS and one patient with moderate SAS had relative nasal arcuate visual field defects; two patients with severe SAS also had paracentral relative defects. One patient with normal polysomnographic result and two patients with mild or moderate SAS had normal visual fields. The RDI correlated positively with the mean visual field defect (r(s) = 0.81, P < 0.05) and with the visual field loss variance (r(s) = 0.78, P < 0.05). The clinical ophthalmologic examination results were normal in all seven patients. In two of the three patients with severe SAS treated with continuous positive airway pressure (CPAP), visual field defects remained stable over 18 months. The patient with optic nerve drusen also had severe SAS and was, therefore, treated with CPAP. His constricted visual fields improved dramatically after treatment. CONCLUSIONS Visual fields of patients with SAS showed defects consistent with an optic neuropathy. The CPAP therapy seems to stabilize or even reverse visual field defects.

Strabismus and employment: the opinion of headhunters

Purpose:  The aim of this study was to determine the influence of strabismus on an individual’s ability to find employment based on the opinion of Swiss headhunters.

Normal Isopter Position in the Peripheral Visual Field in Goldmann Kinetic Perimetry

Purpose: Often in young patients the question arises if a disease state has contracted their peripheral boundary of the visual field. Since the ‘hill of vision’ is steeper in the periphery, kinetic perimetry is more sensitive in detecting peripheral visual field abnormalities than static perimetry. In order to be able with kinetic perimetry to detect mild peripheral visual field constrictions, we determined the normal position of 4 isopters in the peripheral visual field. Subjects and Methods: Intraindividual sensitivity variations of the isopters in the peripheral visual field were determined in 3 normal subjects by one perimetrist. Then, in 22 subjects (19–42 years old) the position of the isopters V4e, III4e, I4e and I3e has been determined by one perimetrist. Visual fields were registered using a Goldmann kinetic perimeter. Results: The intraindividual sensitivity variations (measured as 1 standard deviation) for the isopter V4e was 0.98° and for the isopter I4e 1.13°. To visualize the normal isopter positions in the peripheral visual field, the average positions ± 2 standard deviations were plotted for the isopters V4e, III4e, I4e and I3e. Conclusion: In this study, we determined the normal position of 4 isopters frequently used to plot the peripheral visual field. The plots have been printed in a scale of 1:4 in order to facilitate its use. Photocopying the figures on transparencies by scaling them with a factor 4 will allow to superpose the transparencies on individual Goldmann kinetic visual fields in order to easily determine whether the individual isopters are inside or outside the normal range.

Impact of Low Vision on Well-Being in 10 European Countries

Background: Because of the growing life expectancy in developed countries and the exponential increase in vision loss with increasing age, a growing number of elderly persons will eventually suffer from visual impairment and blindness. This paper describes the association between self-reported vision and well-being in individuals aged 50 years and older and their families. Methods: Using binary logistic regressions on data from the 2004 Survey of Health, Ageing and Retirement in Europe (SHARE), we analysed the association between self-reported corrected vision in general, corrected distance vision and corrected reading vision on 11 variables capturing emotional well-being, future hopes and perspectives, and concentration on daily activities. Results: For 22,486 individuals from 10 European countries, aged 64.23 ± 10.52 years, lower vision was associated with a highly significant negative impact on all measured aspects of well-being. Conclusions: These data from a large population base in Europe provide evidence that persons with low vision have a higher probability of concentration problems during reading and entertainment; losing interest and enjoyment in their activities; feeling fatigued, irritable, sad, and tearful; having less hope for the future; and wishing for death. Effective measures of early detection, prevention, rehabilitation, education and research, as well as a holistic view of a patient, could help counter these problems, thereby improving mental and physical health and reducing the economic impact of low vision.