Biomedical subjects

M Atanassov

Publications and source records attributed to M Atanassov.

4 recordsLinked to original sources

PubMed1998

Learning effect in automatic static perimetry with Dicon TKS 4000 computed perimeter.

To find out the significance of the learning effect in repeated computed perimetry. We performed computed perimetry twice within one week period on 35 eyes (20 patients) with suspected glaucoma and visual acuity > 0.5 (20/40). The program used was with 30 degrees threshold grid. For each quadrant of the visual field were recorded the mean deviation readings. These readings were compared for the initial and the second perimeters for each eye. The mean deviation from the normal readings were significantly higher for the initial perimetric exam for all quadrants (Wilcoxon test for matched pairs, p < 0.05). The visual field defects, if present, were more concentrated and with sharper borders in the second exams. This study suggests that there is a significant learning effect in computed perimetry. A visual field exam, showing defects suspicious for glaucoma, should be repeated within one week and the second one taken for further referral.

Glaucoma↗

PubMed1998

Late post-operative astigmatism after extracapsular cataract extraction and intraocular lens implantation.

The purpose of the study is to establish the amount of surgically induced astigmatism after extracapsular cataract extraction (ECCE) and intraocular lens (IOL) implantation. Eighty three eyes of 79 patients who had ECCE + IOL implantation were examined in the period between the 6th and the 16th month after the operation. The pre- and post-operative auto keratometry readings (K1 and K2) were recorded for each patient. These readings were compared between themselves, as well as with the post-operative cylinder power estimated by an autorefractor (total astigmatism). The mean pre-operative corneal astigmatism (K1-K2) was 1.00 +/- 0.09 Dpt Cyl, and the mean post-operative -1.74 +/- 0.14 Dpt Cyl. The difference is statistically significant. The mean autorefractor cylinder power was 1.70 +/- 0.14 Dpt Cyl. It correlates strong with the post-operative corneal astigmatism. There is a moderate correlation between the degree of the post-operative corneal and total astigmatism. The surgically induced corneal astigmatism is the main component of the total post-operative astigmatism after ECCE + IOL implantation. The total astigmatism is mainly with the rule (vertical plus cylinder) and it does not seem to impair severely the post-operative visual acuity of the patients.

Astigmatism↗

PubMed1998

Influence of stage of glaucoma, age and examination time on reliability parameters in computed perimetry with Dicon TKS 4000.

OBJECTIVE: To evaluate the influence of glaucoma stage, age, and examination time on reliability parameters in computed perimetry with DICON TKS 4000. METHODS: A total of 370 eyes of glaucoma patients were examined in random order with program 9 (30 degrees Threshold grid). They were allocated to 5 groups according to the visual field changes: no changes (112 eyes); mild changes (132 eyes); moderate changes (62 eyes); severe changes (44 eyes); end stage changes (20 eyes). The reliability of each examination was assessed by the rate of false positive responses (FP), fixation losses (FL), and the number of presentations (PR). RESULTS: Fixation losses > or = 20% were observed in 60.8% of the examined eyes. Such a rate of FL occurred more frequently in the initial stages of glaucoma--75% in group 1 vs 10% in group 5. There was a moderate negative correlation between the rate of FL and the stage of glaucoma (r = -0.31, p < 0.001). There was a negative correlation between the examination time and the rate of FL (r = -0.35, p < 0.001). No correlation was found between the age of patients and FL. There was a slight correlation between the stage of glaucoma and FP (r = 0.14, p < 0.01), as well as between examination time and FP (r = 0.28, p < 0.001). There was no correlation between age and FP. The mean examination time for the whole study sample was 9.0 +/- 2.5 min. It correlated positively with PR (r = 0.96) and the stage of disease (r = 0.80). CONCLUSION: FP, FL and PR are dependent on the stage of glaucoma and examination time. The lower frequency of FL in severe stages of glaucoma can be accounted for by the kinetic fixation and the procedure for testing FL (projecting a stimulus in the blind spot).

Adult↗

PubMed1998

A model for quantitative assessment of visual field changes in primary open-angle glaucoma with a computerized perimeter DICON TKS 4000.

PURPOSE: To evaluate the feasibility of using the grading algorithm utilized by the Advanced Glaucoma Intervention Study (AGIS) on a Humphrey Field Analyser with program 9 (76/30 degrees Threshold Grid) of a computerized perimeter DICON TKS 4000 and find whether the obtained score can be used to determine the stage of glaucoma. METHODS: Computerized perimetry was performed on 205 eyes with proven or suspected glaucoma. Visual field changes were assessed first subjectively, and then with the scoring method used in AGIS: the size, depth, and location of the visual field defects, and the nasal step were determined using a stencil and then the final score was calculated. RESULTS: Of 205 eyes examined 79 had perimetric changes. These were allocated subjectively into four groups corresponding to four stages of glaucoma: initial, evoluted, advanced and terminal. The mean scores for each group were calculated. There was a statistically significant correlation between the score and the stage of glaucoma. The mean scores for the first 3 stages differed significantly from each other. For stages 3 and 4 the difference was not statistically significant. CONCLUSION: The AGIS scoring method, developed originally for program 30-2 of the Humphrey Field Analyzer, can be applied with the 30 degrees Threshold Grid program of DICON TKS 4000 Perimeter for objective assessment of the glaucoma stage.

Feasibility Studies↗