PHARAO laser source flight model: design and performances.

In this paper, we describe the design and the main performances of the PHARAO laser source flight model. PHARAO is a laser cooled cesium clock specially designed for operation in space and the laser source is one of the main sub-systems. The flight model presented in this work is the first remote-controlled laser system designed for spaceborne cold atom manipulation. The main challenges arise from mechanical compatibility with space constraints, which impose a high level of compactness, a low electric power consumption, a wide range of operating temperature, and a vacuum environment. We describe the main functions of the laser source and give an overview of the main technologies developed for this instrument. We present some results of the qualification process. The characteristics of the laser source flight model, and their impact on the clock performances, have been verified in operational conditions.

[Fixation disparity with the Pola pointing test: not representative for eye position under natural viewing conditions]. / Fixationsdisparation am Pola-Zeigertest: nicht repräsentativ für die Augenstellung unter natürlichen Sehbedingungen.

BACKGROUND: According to certain findings obtained with the Zeiss Polatest, H.J. Haase defined a "Fixation Disparity Type One". In this diagnosis, the "Zeigertest" is particularly important. The Zeigertest consists of a central ring presented to both eyes for fixation, a vertical clock hand presented to the right eye and two markings at the six and twelve o'clock positions presented to the left eye. All parts are surrounded by a binocularly visible frame. Subjects with a "Fixation Disparity Type One" see a misalignment between the clock hand and the peripheral markings. We investigated (1) whether the perceived misalignment correlated with an objective deviation of the eyes from orthovergence and (2) whether subjects with a "Fixation Disparity Type One" had a deviation of the eyes from orthovergence when looking at a natural, i.e., fully fusionable object. SUBJECTS AND METHODS: Out of 303 medical students, 10 subjects with a "Fixation Disparity Type One" were selected and asked to indicate the perceived alignment or misalignment in the Zeigertest with a laser pointer. Two subjects without fixation disparity served as controls. The position of both eyes was recorded using the search coil technique. One of the 10 subjects with "Fixation Disparity Type One" had to be excluded due to excessive blinking. Experiment 1: In the beginning all parts of the Zeigertest were presented to both eyes (natural viewing condition). Then, the object for one of the eyes was switched off leaving the frame as the only fusional stimulus. The outcome variable was a refixation movement of the other eye. This experiment is similar to the unilateral cover test. Experiment 2: In the beginning all parts of the Zeigertest were presented to both eyes (natural viewing condition). Then, the original Zeigertest was switched on (clock hand presented only to the right eye, peripheral markings only to the left eye). The outcome variable was a change of vergence. RESULTS: Experiment 1: A significant refixation movement did not occur in any of the subjects. Experiment 2. In all 9 subjects with "Fixation Disparity Type One" the vergence changed significantly between 2.4 and 14.9 arcmin. The change of vergence correlated significantly with the angle of the perceived misalignment between clock hand and peripheral markings. CONCLUSION: A fixation disparity ascertained at the Zeigertest does not indicate a fixation disparity under natural viewing conditions.

Effect of surgical technique on the increase in intraocular pressure after cataract extraction.

BACKGROUND AND OBJECTIVE: A prospective study was performed to determine the influence of surgical technique on the increase in intraocular pressure (IOP) after cataract surgery. PATIENTS AND METHODS: Three groups of 30 patients each underwent either extracapsular cataract extraction with sclerocorneal suture (ECCE), phacoemulsification with sclerocorneal suture (PS), or phacoemulsification with a sutureless scleral tunnel (PT). RESULTS: Each group experienced a significant increase in IOP 5 to 7 hours after surgery: 20.2 +/- 7.9 mm Hg for ECCE, 11.2 +/- 8.3 mm Hg for PS, and 4.7 +/- 8.7 mm Hg for PT. The differences in the increases among the three groups were significant. CONCLUSION: PT [corrected] produces the lowest postoperative increase in IOP and should be considered for patients with glaucomatous damage.

Pattern electroretinogram and computerized optic nerve-head analysis in ocular hypertension--interim results after 2.5 years.

Evidence exists that both the pattern electroretinogram (PERG) as a parameter of ganglion-cell function and computerized morphometric disc analysis (ONHA) predict subsequent glaucomatous visual field defects in ocular hypertensive eyes. Since November 1991 we have conducted a prospective longitudinal study to evaluate the suitability of PERG and ONHA for detecting incipient glaucoma damage. Inclusion criteria were: an intraocular pressure of > or = 25 mmHG (at least two measurements taken on different days) or, in eyes with additional risk factors, > or = 23 mmHG; a normal Octopus visual field (mean defect < or = 2 dB, no local defect); and no definite glaucomatous disc cupping. After a mean follow-up period of 14.6 +/- 8.8 (range 1-33) months and with a mean intraocular pressure of 24.4 (range 18-42) mmHg, none of the 66 patients (115 eyes) converted to glaucoma. Furthermore, PERG and ONHA do not agree in their estimation of the glaucoma risk at this stage.

Intraocular pressure rise after phacoemulsification with posterior chamber lens implantation: effect of prophylactic medication, wound closure, and surgeon's experience.

AIMS: A prospective clinical trial was carried out to evaluate the effect of prophylactic medication, the technique of wound closure, and the surgeon's experience on the intraocular pressure rise after cataract extraction. METHODS: In 100 eyes, the intraocular pressure was measured before as well as 2-4, 5-7, and 22-24 hours after phacoemulsification and posterior chamber lens implantation. Each of 25 patients received either 1% topical apraclonidine, 0.5% topical levobunolol, 500 mg oral acetazolamide, or placebo. Forty four eyes were operated with sclerocorneal sutureless tunnel and 56 eyes with corneoscleral incision and suture. Sixty three operations were performed by experienced surgeons (more than 300 intraocular operations) and 37 by inexperienced surgeons (less than 200 intraocular operations). RESULTS: The pressure increase from baseline to the maximum 5-7 hours after surgery did not differ significantly (p = 0.8499) for apraclonidine (9.5 mm Hg), levobunolol (7.2 mm Hg), acetazolamide (7.8 mm Hg), and placebo (8.6 mm Hg). The increase was significantly (p = 0.0095) lower in eyes with corneoscleral tunnel (5.5 mm Hg) than in eyes with corneoscleral suture (10.5 mm Hg) and significantly (p = 0.0156) lower for experienced (6.6 mm Hg) than for inexperienced surgeons (11.2 mm Hg). CONCLUSIONS: The intraocular pressure rise after phacoemulsification and posterior chamber lens implantation depends strongly on the technique of wound closure and the surgeon's experience. Compared with these two factors, the effect of prophylactic medication can be neglected.

[Psychometric function of stereo disparity in normal persons]. / Die psychometrische Funktion des querdisparaten Tiefensehens bei Normalpersonen.

UNLABELLED: The accuracy and efficiency of threshold estimation depend on a priori knowledge of the shape of the psychometric function. Such knowledge is available for contrast detection and visual acuity, but not for disparity detection. METHODS: We studied the psychometric function for disparity detection in 26 visually normal, untrained observers by measuring detection rates over a wide range of disparities. In a two-alternative forced-choice (2AFC) task the subject had to decide whether the right or left of two vertical bars, differing in depth, was closer to them. An S-shaped Weibull function was fitted to each subjects's data using the maximum-likelihood procedure. RESULTS: In 21 of the 26 subjects the psychometric function rose with increasing disparities up to a level of about 100%. Five of the 26 subjects only reached hit rates clearly below 100% (66% to 82%), even at disparities well above the threshold. The mean slpe of the S-shaped psychometric function of disparity detection was much lower (1.2 Weibull units) than that known for visual acuity and contrast detection (about 3.0 Weibull units). The slope differed widely among subjects, but was not related to stereo acuity. CONCLUSION: For accurate and efficient estimation of stereo acuity, the shallow slope of the psychometric function requires more than 100 single trials around the threshold if a 2AFC procedure is used. In addition, several disparities well above the threshold must be presented in order to detect subjects who do not reach a hit rate of 100% at any disparity. Otherwise, stereo acuity would be underestimated in these subjects.

[Increased intraocular pressure after cataract extraction--effect of surgical technique, surgical procedure and preventive drug administration. A prospective, randomized double-blind study]. / Intrakularer Druckanstieg nach Kataraktextraktion--Einfluss von Operationstechnik, Operationserfahrung und medikamentöser Prophylaxe. Eine prospektive, randomisierte Doppelblindstudie.

BACKGROUND: We performed a double-masked, randomized and prospective study to compare the effect of surgical technique, surgeon's experience, and prophylactic medication on the intraocular pressure rise after cataract extraction. PATIENTS AND METHODS: Intraocular pressure of 120 patients was measured the day before, as well as two to four, five to seven and 22 to 24 hours after uncomplicated cataract extraction. 47 patients were operated with phacoemulsification and sclerocorneal sutureless tunnel (phaco/tunnel). 61 patients with phacoemulsification and corneoscleral incision and suture (phaco/suture), and 12 patients with extracapsular technique (ECCE). 48 operations were done by inexperienced surgeons (less than 200 intraocular operations), 72 by experienced surgeons (300-2000 intraocular operations). Patients were treated with either levobunolol, acetazolamide, apraclonidine, or placebo. Each treatment group contained 30 patients. RESULTS: In all groups, the mean intraocular pressure increased to a maximum at five to seven hours after surgery. The pressure rise was significantly higher in the ECCE group (20.6 mm Hg) than in the phaco/suture group (10.5 mm Hg) and in the phaco/tunnel group (5.4 mm Hg, p always < 0.05). Eyes operated by inexperienced surgeons had a significantly (p < 0.005) greater pressure rise (12.9 mm Hg) than eyes operated by experienced surgeons (7.1 mm Hg). Treatment had no significant (p = 0.41) effect on the intraocular pressure rise. CONCLUSION: The intraocular pressure rise after cataract extraction strongly depends on the surgical technique and to a lesser extent, on the surgeon's experience. At least for phacoemulsification, the effect of the prophylactic medication used in this study is small and appears to be clinically irrelevant.

[The Freiburg Stereotest. On assessment of stereovision in automobile driver examination]. / Der Freiburger Stereotest. Zur Beurteilung des Stereosehens bei Führerscheinbewerbern.

BACKGROUND: The "Freiburg Stereotest" is a new instrument where disparate pictures are generated by a computer and displayed on one single high resolution video monitor. In the present work, the Freiburg Stereotest was used to check the stereo qualification for certain categories of driver's licence. For this purpose, a determination of the smallest detectable disparity is not reasonable. Rather, it should be checked whether or not a certain disparity, usually well above threshold, is recognized with a sufficient reliability. We have chosen a disparity of 100 arcsec; this value is considered to be an acceptable requirement for certain categories of driver's licence. SUBJECTS AND METHODS: 6 strabismic subjects were examined binocularly and 10 normal subjects were examined both binocularly and monocularly. Two targets ("busses"), side by side and different in depth by a disparity of 100 arcsec, were presented 78 times and, in a two-alternative forced-choice procedure, a minimum of 66 hits was required to pass the test. Monocular cues were excluded by a systematic variation of the lateral distance between the two targets. RESULTS: The strabismic subjects and the monocularly occluded normal subjects reached random scores only. With both eyes open, 8 of the 10 normal subjects reached scores near 100%, while 2 of them passed the test only when the lateral distance between the two targets was 15 minarc or less. For a lateral distance between the two targets of more than 15 minarc, these 2 subjects showed a learning effect. CONCLUSIONS: The Freiburg Stereotest allows to determine with statistical significance whether or not a proband can recognize a certain disparity which may be required for a driver's licence.