|Year : 1983 | Volume
| Issue : 2 | Page : 57-60
Static perimetry in glaucoma-an evaluation
Bakulesh M Khamar
M & J Institute of Ophthalmology, B.J. Medical College. Ahmedabad, India
Bakulesh M Khamar
M & J Institute of Ophthalmology, B. J. Medical College, Ahmedabad. 380 016 (Gujarat)
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Khamar BM. Static perimetry in glaucoma-an evaluation. Indian J Ophthalmol 1983;31:57-60
Static perimetry is the method of testing the threshold luminosity level of a given point.
Its usefulness in glaucoma lies in early detection of glaucoma, finding out scotomas missed by kinetic and noticing changes in scotomas in follow-up examinations.,, Inspite of its preciseness and ability to detect earliest and smallest field defects, it is not so popular due to cost of modern perimeters and time involved in charting the fields.
In this paper an attempt has been made to evaluate the results of static and kinetic perimetry to determine limitations of kinetic perimetry in scotoma detections compared to static perimetry.
| Materials and methods|| |
For the purpose of this study analysis of 36 patients in whom static and kinetic perimetry was performed for glaucoma are analysed.
1. Selection of Cases
Established or suspected cases of glaucoma were included in this study. All the patients were highly educated and motivated. Cases with any opacity in the media or lesion in the fundus were excluded. Vision was corrected in all cases before recording fields.
2. Field Charting:
Goldman's perimeter was used. Back ground illumination was adjusted to 31.5 apostits with photometer, rheostat control filter combination and sliding occluder of bulb.
Perimetry was carried out after 10 minutes of adapttion to perimetric environment.
(i) Kinetic Perimetry: This was done with different stimulus value and outline of fields were noted. (Quantitative Kinetic perimetry). Attempt was made to chart scotomas with various stimulus including suprathreshold stimulus in between two isopters.
(ii) Static Perimetry: Meridional static perimetry was performed in all cases. Selection of meridians were done from the results of scotomas of Kinetic perimetry at the site of Scotomas.
In absence of such clues they were performed at 45. 135. 225. 315' meridians as suggested by Aulhorn & Harms.' They were performed 2° apart in absence of scotomas & 1° apart at the sites of scotomas.
| Observations|| |
Of the 38 fields which showed defects with static and Kinetic perimetry. 10 fields had 22 paracentral scotomas detected with static perimetry alone.
[Table - 1] shows the site of scotoma which were not detected with kinetic perimetry. It also shows that majority of scotomas (16 of 22 i.e. 72.73°,,) were situated between 6° to I5° and 10 of them extended on either side.
[Table - 2] shows that scotomas not detected with kinetic perimertry had more co-orelation with the extent of scotoma rather than with the depth of scotoma. Fifteen scotomas out of 22 had extent less than 5° with depth ranging from 0.4 to absolute and only one with a extent of 16° to 20°. While depth of scotoma is considered it does not show much corelation. 8 with 0.4 log unit and 6 with more than I log unit.
But when depth and extent of scotoma are taken together it clearly shows that as extent of scotoma increases, depth decreases.
All scotomas not detected with kinetic perimetry were of less than 30° in circular extent i.e. did not extend to meridians on either side.
No Angioscotomas were detected in this study.
| Discussion|| |
Drance was the first person to show importance of static perimetry in early diagnosis of glaucoma. Portney showed importance of static perimetry in glaucoma by detecting field defects missed by kinetic. The difference between two is that Drance performed kinetic with tangent screen and was able to chart the field defects with projection perimeter missed by tangent screen and revealed by static. While Portney demonstrated it when missed by projection perimeter of Goldmann.
Portney suggested that because small space for central 30 o on field chart Goldmann's perimeter and smaller area occupied. more central the defect is, more likely it is to be missed. From Table f it is seen that in this series scotornas missed were situated central to 5 o in 8 (36.36°.) cases. Though majority were situated in central 15°, they were missed in 3 cases when situated at the outer periphery i.e 16°-30° of central 30° of field.
Depth of the scotoma missed has a greater value in diagnosis and treatment of glaucoma when compared with extent. The smaller and shallower scotomas are of least significance compared to big scotomas of considerable depth.
In Kinetic perimetry depth of scotoma is measured by charting scotomas with various test objects of different stimulus value. Relative scotomas can not be charted with bright objects but can be charted with objects of low stimulus value. In static perimetry relative scotomas do not reach the base line but absolute scotomas reach the base line. This is the reason why it is easy to plot small relative scotomas precisely with static perimetry compared to Kinetic perimetry.
From [Table - 2], it is clear that extent of scotomas is inversely proportionate to depth of scotoma, But you can have a range of depth as scotomas become smaller and smaller.
Drance has suggested that scotomas less than 0.5 log unit depth should be considered insignificant and so by that standard only 14 scotomas were of significant depth.
When results in thus series are compared with that of Portney, we find that scotomas missed were large in size and of considerable depth in his series.
It is also observed that in this series scotomas were of less than 30 o in circular extent i.e did not extend to the meridians on either side were of 45° to 125° in are length in Portney's series.
Exact cause can not be given for this. Probably this because of-1 Perimetry in this series was performed by Ophthalmologist and not perimetrist.
2. It was done prospectively to evaluate both techniques with a knowledge regarding advantages and pitfalls of each technique.
This results suggest that if one is precise performing Kinetic Perimetry then - scotomas of signficance are rarely missed.
| Summary|| |
Static perimetry in glaucoma is evaluated by analysing the scotomas which were detected by static but missed by kinetic perimetry.
Majority of the scotomas missed are within 15° from center and are small in radial length. The depth of scotoma missed is inversely proportionate to radial length.
| References|| |
Drance S. M., 1967, Canad. Jour. Ophthalmol. 2 : 249.
Portney, G. L., 1978, Ophthalmology 85 : 287
Khamar. B. M., 1981, Proceedings 40th A.I.O.S. Conference (Under publication)
Aulhorn E and Harms, H. 1967, ACTA XX Congress Ophthalmol.. pp 151
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]
[Table - 1], [Table - 2]