Electrophysiological determination of the refractive state of the eye of the opossum

The refractive state of the eye of the South American opossum Didelphis marsupialis aurita was investigated with electrophysiological techniques. Using adult specimens, trapped from the wild, averaged cortical evoked responses were recorded from the region of projection of the central visual field. Stimuli consisted of a phase reversal of a square wave grating generated on a CRO screen, with luminance of 2.4 cd/m2 and contrast 0.84. The refractive state of the eye was altered by means of trial lenses and the amplitude of the cortical responses thus obtained compared to those obtained with no lens (control values). Refraction "tuning curves" were determined for each animal. The average refractive state was found to be -2.27 D indicating that this species when raised in its habitat shows, at low ambient luminosity, some degree of myopia. Determination of the Contrast Sensitivity Function indicate that induced ametropias lead to a reduction of the cut-off value of the spatial frequency and a loss of contrast sensitivity.     

Influence of exercise on the structure of the anterior chamber of the eye

Purpose

To measure changes in anterior chamber structure before and after exercise in healthy individuals using anterior segment optical coherence tomography (ASOCT).

Methods

Thirty‐two healthy young individuals performed jogging for 20 min. Eye blinking rate was recorded during rest and exercise. The anterior chamber angle (ACA), angle opening distance at 500 μm from the scleral spur (AOD500), trabecular‐iris space area at 500 μm from the scleral spur (TISA500), iris concavity (IC), iris concavity ratio (CR), iris thickness at 750 μm from the scleral spur (IT750), anterior chamber depth (ACD), anterior chamber width (ACW), pupil diameter (PD), intraocular pressure (IOP), blood pressure (BP) and heart rate (HR) were recorded before and after exercise. Anterior chamber angle (ACA), AOD500, TISA500, IC, IT750, ACD, ACW and PD were measured with ASOCT.

Results

Compared with rest, the blinking rate during exercise did not change significantly (13.04 ± 5.80 versus 13.52 ± 5.87 blinks/min, p = 0.645). The average IOP (15.4 ± 2.4 versus 12.4 ± 2.1 mmHg), ACA (35.96 ± 11.35 versus 40.25 ± 12.64 degrees), AOD500 (0.800 ± 0.348 versus 0.942 ± 0.387 mm), TISA500 (0.308 ± 0.155 versus 0.374 ± 0.193 mm²), IC (?0.078 ± 0.148 versus ?0.153 ± 0.159 mm) and CR (?0.027 ± 0.050 versus ?0.054 ± 0.056) changed significantly (all p < 0.001), while the average IT750 (0.463 ± 0.084 versus 0.465 ± 0.086 mm; p = 0.492), ACD (3.171 ± 0.229 versus 3.175 ± 0.238 mm; p = 0.543) and ACW (11.768 ± 0.377 versus 11.755 ± 0.378 mm; p = 0.122) showed no significant change after exercise.

Conclusion

The blinking rate did not change significantly during exercise, while ACA, AOD500 and TISA500 increased after exercise. Exercise also induced or increased IC. These changes in anterior chamber structure were only associated with exercise, but not with the postexercise change in PD or IOP.     

Determination of the location of the fovea on the fundus

PURPOSE: To evaluate whether the distance between optic nerve head and fovea in healthy eyes determined by scanning laser ophthalmoscope may facilitate estimation of the location of the fovea relative to the optic disc in patients with macular disease. METHODS: The angular distance was measured, in horizontal and vertical directions, between the center of the optic nerve head and the fovea in 104 eyes of 104 healthy probands. For additional evaluation of intraindividual variation in 70 of these persons the contralateral eye was measured as well. RESULTS: The distance between the optic disc and the fovea differed vertically more than horizontally (-1.5 +/- 0.9 degrees [-3.65 to +0.65 degrees ] vs. 15.5 +/- 1.1 degrees [13.0-17.9 degrees ]). There was a mean angle between the fovea and the center of the optic disc versus the horizon of -5.6 +/- 3.3 degrees. The intraindividual difference between right and left eyes was markedly lower, with average angles being 0.2 +/- 1.3 degrees vertically and 0.0 +/- 1.1 degrees horizontally. CONCLUSIONS: The distance between the optic nerve head and the fovea does not allow for a meaningful determination of the location of the fovea in eyes in which morphologic changes have occurred. The angle of rotation of the fovea relatively to the center of the optic nerve head is relatively stable. Therefore, the size of a central scotoma can be determined by movement of the blind spot according to the change of the preferred retinal locus (PRL). In addition, the knowledge of the location of the fovea enables determination of the position in the contralateral eye of the same patient.     

On the relevance of the long-time follow-up of the cyclocryotherapy

In spite of the availability of cyclocryodestructive laser therapy there still appears to be an indication for cyclocryotherapy in different kinds of glaucoma. PURPOSE: Cyclocryotherapy very often appears to be the operation of choice in cases of progressive functional visual loss if a patient is not sufficiently helped with the maximum tolerated medical therapy. We investigated long-term IOP effects and possible complications in our group of patients undergoing cyclocryotherapy. PATIENTS: Cyclocryotherapy was performed on 109 eyes of 97 patients from 1988 to 1994. Cyclocryotherapy was performed as follows: 67 of 109 eyes were controlled for IOP for an average of 10 months (3-41 months). We applied cryotherapy six times 3-4 mm behind the limbus for an average duration of 50 to 60 s over half of the circumference. RESULTS: We achieved satisfactory IOP control (IOP K 22 mm Hg) in 40 eyes, however, with 30 additional operations. One eye developed phthisis bulbi, and 3 other eyes became blind because of complications in neovascular glaucomas. Neovascular glaucoma cases responded the least. CONCLUSIONS: Cyclocryotherapy produced a statistically significant IOP reduction in eyes with primary open-angle glaucoma or secondary glaucoma. Close long-term follow-up appears advisable in order to check the eyes for possible increase in IOP or complications of surgery.     

On the relevance of the long-time follow-up of the cyclocryotherapy

In spite of the availability of cyclocryodestructive laser therapy there still appears to be an indication for cyclocryotherapy in different kinds of glaucoma.     

The oculomotor effects of the fractures of the floor of the orbit

PURPOSE: Fractures of the orbit floor have very disabling oculomotor after effects. The objective of this study was to report that close collaboration between the maxillo-facial specialist and ophthalmologist is necessary to avoid oculomotor after effects. METHODS AND PATIENTS: Our study included 10 cases of the fracture of the orbit floor. These cases were recorded between 1992 and 1996. RESULTS: This pathology affected young subjects aged between 20 and 40 years in 70 % of the cases. 80 % of the subjects were males. 90 % of the patients presented a vertical diplopia as a result of a transitory oculomotor deficit. 20 % of the subjects presented a permanent oculomotor deficit at the stage of after effects. All these deficits were of a mechanical origin and, contrary to other authors, we found no deficit with nervous sensory origin. CONCLUSION: Therapeutic success is based on early diagnosis and treatment that requires close collaboration between the maxillo-facial and ophthalmology teams.