Biomedical subjects

H G Lemij

Publications and source records attributed to H G Lemij.

28 records · Page 2Linked to original sources

PubMed1997

Improved reproducibility of measurements with the nerve fiber analyzer.

PURPOSE: This study was undertaken to assess and improve the repeatability and reproducibility of nerve fiber layer (NFL) measurements using the Nerve Fiber Analyzer (NFA I), a scanning laser polarimeter. METHODS: The repeatability of two subsequent measurements was determined in 100 healthy eyes. Four methods of image evaluation were performed. Polarimetric measurements of retinal NFL were obtained along a peripapillary band at the superior and inferior poles of the optic disk and analyzed in a one-pixel band of absolute retardation values (method 1) and relative to the nasal segment (method 2). Method 3 used measurements obtained in a 10-pixel band along the same peripapillary band. Method 4 comprised measurements in selected areas outside the peripapillary band, which did not contain blood vessels. The repeatability (r) and relative reliability coefficient (Rel) were assessed as indices of agreement of repeated measurements. In addition, the reproducibility (R) from day to day for methods 3 and 4 was assessed by taking 10 images on 10 consecutive days from each of 10 subjects. RESULTS: The 95% critical value for r in the superior and inferior segments improved from about 30% for methods 1 and 2, to 23% for method 3, and to 11% for method 4. For the superior and inferior segments, the fourth method of image evaluation yielded a Rel of 98%, as compared with 54% in method 1, 80% in method 2, and 87% in method 3. The 95% critical value for R was 23% for method 3 but only 15% for method 4. CONCLUSIONS: The improved reproducibility of measurements has made the NFA I a promising device. An improved reproducibility (smaller limit for detecting change) does not necessarily indicate good sensitivity and specificity for any instrument. The role of the scanning laser polarimeter in clinical practice requires further study.

Humans↗

PubMed1996

Measurement by nerve fiber analyzer of retinal nerve fiber layer thickness in normal subjects and patients with ocular hypertension.

PURPOSE: To measure retinal nerve fiber layer (NFL) thickness in normal subjects and patients with ocular hypertension and examine the relationship between age and normal NFL thickness. METHODS: Nerve fiber layer thickness was determined by scanning laser polarimetry in 210 normal subjects and 100 patients with ocular hypertension. Relative ratios for the superior and inferior NFLs were calculated by dividing the NFL values of the respective regions by the nasal value. RESULTS: Mean superior NFL in normal subjects measured 2.5 (95% confidence interval [CI], 1.3 to 3.7), and mean inferior NFL, 2.4 (95% CI, 1.2 to 3.6). Regression analysis showed a gradual decrease in NFL thickness with increasing age. In the patients with ocular hypertension, mean superior and inferior NFL were significantly lower compared with those of normal subjects: superior, 1.6 (95% CI, 0.4 to 2.8) and inferior, 1.6 (95% CI, 1.0 to 2.2). Of the patients with ocular hypertension, 58 of 100 (58%) had an abnormal NFL parameter. CONCLUSIONS: Normograms we obtained for NFL as determined by scanning laser polarimetry may serve as reference points for future studies. Patients with ocular hypertension had a significantly lower NFL thickness, although there was some overlap in resulting measurements with those of normal subjects. The Nerve Fiber Analyzer may be useful for individual follow-up of people at risk for glaucoma; however, its role as a screening instrument requires further study.

Adult↗

PubMed1995

Conjugacy of eyelid movements in vertical eye saccades.

PURPOSE: To examine the conjugacy of lid saccades in normal subjects. METHODS: Saccades of both upper eyelids were recorded simultaneously by means of small, lightweight, magnetic search coils, fixed on each lid. Subjects then made vertical eye saccades between fixed targets. The associated eye saccades were recorded simultaneously by means of magnetic search coils. The authors further examined whether the position of the lid coils affected the recordings. RESULTS: Lid saccades were not as conjugate as their associated eye saccades. Nonconjugacy of lid saccades averaged approximately 8% of the target amplitude, irrespective of saccadic direction. By contrast, nonconjugacy of the associated eye saccades averaged approximately 1% of the target amplitude. Coil position significantly (P < 0.05) affected the recordings. CONCLUSIONS: Lid saccades are not as conjugate as their associated eye saccades. Coil position is critical for the recordings of lid saccades.

Adult↗

PubMed1995

Conjugacy of saccades in deep amblyopia.

PURPOSE: To determine the degree of conjugacy of saccades in humans with one deeply amblyopic eye, to assess whether Hering's law requires good binocular visual acuity. METHODS: By means of magnetic search coils, horizontal saccades were recorded accurately in 11 subjects with unilateral, deep amblyopia. The recordings were compared to those made in 11 normal subjects. In addition, three subjects with amblyopia were submitted to artificial anisometropia, which called for nonconjugate adaptation of their saccades. RESULTS: The saccades of most subjects with amblyopia were nonconjugate. These nonconjugacies often were larger in one direction than in the opposite one. The magnitude of the nonconjugacies varied inconsistently with the size of the saccades. In addition, the amblyopic eye often showed conspicuous drift. The saccades adapted nonconjugately to the imposed anisometropia. CONCLUSIONS: In deep amblyopia, the two eyes often make saccades that are unequal in size. The amblyopic eye does not move aimlessly, roughly following the movements of the normal fellow eye. Instead, the saccades of the amblyopic eye appear to reflect a deliberate oculomotor strategy, bringing visual targets to presumed retinal points of preference.

Adaptation, Ocular↗

PubMed1994

The lax eyelid syndrome.

The floppy eyelid syndrome (FES) was first described in middle aged, obese men. In later descriptions, age and sex were not specifically mentioned. Associations of FES with various other syndromes have been described. The authors question whether all these cases represent the same, single, syndrome. They suggest that a clinical picture similar to FES may occur in lax upper eyelids of any cause. Four such cases are reported here. The authors therefore coin the more general term 'lax eyelid syndrome'. They suggest using the term 'floppy eyelid syndrome' uniquely for patients with the classic signs and symptoms.

Aged↗

PubMed1992

Nonconjugate adaptation of human saccades to anisometropic spectacles: meridian-specificity.

Recently it has been demonstrated that saccades become different in size in the two eyes if a subject is adapted to anisometropic spectacles, which provide visual images of different magnitude to the two eyes. These nonconjugate adaptations adequately meet the requirements of those spectacles and, once acquired, they persist (with some reduction) even during monocular viewing. We now demonstrate that such nonconjugate adaptations of saccades can be meridian-specific, if there is a pressure for such meridian-specificity. This pressure was provided by means of a cylindrical spectacle-lens. Adaptations along a vertical, horizontal or oblique meridian did not transfer to the orthogonal meridian. These results demonstrate a capability of saccadic adaptation to deal with calibration problems restricted not only to one eye, but even to one specific plane of muscular action. Our results also suggest that the meridian-specific adaptations of oblique saccades take place at a stage before the decomposition of motor commands into separate horizontal and vertical components. The meridian-specific nonconjugacies were also expressed in smooth-pursuit eye movements. Post-saccadic drift adapted only along the horizontal meridian.

Adaptation, Ocular↗

PubMed1992

Blepharoptosis induced by prolonged hard contact lens wear.

PURPOSE: The authors attempt to establish a relation between hard contact lens wear and upper eyelid ptosis. METHODS: This study consists of two parts. In the first part, the authors compare the unilateral or bilateral ptosis that developed during hard contact lens wear in 17 patients with the involutional ptosis that developed in another group of 73 patients. In the second part, the authors compare both upper and lower eyelid position in 46 patients who had been wearing hard contact lenses for at least 10 years with the position of 50 matched controls who had never worn contact lenses. RESULTS: The ptosis that had developed in the 17 patients who wore hard contact lenses was clinically similar to that caused by involutional levator disinsertion. The second part of the study shows that the prolonged wearers of hard contact lenses had upper eyelids that were lower by approximately 0.5 mm when compared with control subjects. This difference is statistically significant. According to standard criteria, there were at least 10 ptotic eyelids in the contact lens group versus 1 in the control group. CONCLUSION: The study findings suggest that prolonged hard contact lens wear may induce a lower position of the upper eyelid and eventually lead to ptosis through levator disinsertion.

Adolescent↗

PubMed1991

Long-term nonconjugate adaptation of human saccades to anisometropic spectacles.

It is generally believed that saccades follow Hering's law in the sense that they are equally large in the two eyes. We demonstrated that saccades are different in size in the two eyes in 8 habitual wearers of anisometropic spectacles, which have lenses of different refractive powers, and therefore supply each eye with a differently sized visual image. The eye provided with the larger visual image made larger saccades than its fellow eye. This nonconjugate adaptation was almost complete for both horizontal and vertical saccades. Post-saccadic drift was also asymmetrically adapted: it reduced any fixation-disparity present at saccadic offset. The nonconjugate adaptation was also expressed in smooth-pursuit eye movements. In addition, these nonconjugate adaptations were present during monocular viewing, which shows that they were hard-programmed.

Adaptation, Ocular↗

PubMed1991

Short-term nonconjugate adaptation of human saccades to anisometropic spectacles.

It has been demonstrated before that the long-term wearing of anisometropic spectacles may induce nonconjugate adaptations of saccades. Saccades then become different in size in the two eyes. We examined the time-course and the limits of such adaptations of horizontal and vertical saccades during the short-term (1-6 hr) wearing of anisometropic spectacles. After only 1 hr of conditioning to 2 D of anisometropia, the nonconjugate size-adaptations were almost complete along the horizontal meridian. For progressively larger anisometropias (up to 8 D) the adaptative nonconjugacies after 1 hr became also systematically larger. An anisometropia larger than 6 D did not further increase the rate of adaptation during the first 6 hr of conditioning, which suggests that about 6 D of difference in spectacle correction, causing size differences of about 12%, may be the upper limit of the nonconjugate adaptive range of the saccadic subsystem. Post-saccadic drift of horizontal saccades was also adequately changed. In addition, nonconjugate adaptations had developed in smooth-pursuit eye movements. All of these plastic changes persisted during monocular viewing, indicating that the basic programming of these eye movements was changed.

Adaptation, Ocular↗

PubMed1989

Differences in accuracy of human saccades between stationary and jumping targets.

Saccades have traditionally been studied in response to suddenly changing visual stimuli, such as jumping targets. In every-day life, however, most targets are stationary. We studied saccades made in either target condition. Saccadic accuracy was two- to five-fold better with stationary targets than with jumping targets. In addition, both the number of secondary saccades and the total time required to foveate the target were decreased with stationary targets in comparison to jumping targets. We also found that with an illuminated background the total time required to foveate the target was shorter than when the background was dark.

Adult↗