Increase of retinal vessel width in ocular hypertensives with timolol therapy

Review of the association between retinal microvascular characteristics and eye disease

Computerized retinal imaging technologies enable the static and dynamic measurement of a range of retinal microvascular parameters. Large population-based studies have reported associations between these microvascular indices and various ophthalmic diseases including diabetes, age-related macular degeneration, retinal artery embolism, retinal vein occlusion, glaucoma and non-glaucomatous optic neuropathies. Increasingly, sophisticated imaging and analysis techniques have the potential to provide relevant clinical information regarding disease risk and progression; however, further studies are required to verify associations and strengthen the predictive power of these techniques. We summarize the current state of knowledge regarding retinal microvascular characteristics and eye disease.

Opposing effects of atropine and timolol on the color and luminance emmetropization mechanisms in chicks

This study analyzed the luminance and color emmetropization response in chicks treated with the nonselective parasympathetic antagonist atropine and the sympathetic β-receptor blocker timolol. Chicks were binocularly exposed (8h/day) for 4days to one of three illumination conditions: 2Hz sinusoidal luminance flicker, 2Hz sinusoidal blue/yellow color flicker, or steady light (mean 680lux). Atropine experiments involved monocular daily injections of either 20μl of atropine (18nmol) or 20μl of phosphate-buffered saline. Timolol experiments involved monocular daily applications of 2 drops of 0.5% timolol or 2 drops of distilled H2O. Changes in the experimental eye were compared with those in the fellow eye after correction for the effects of saline/water treatments. Atropine caused a reduction in axial length with both luminance flicker (-0.078±0.021mm) and color flicker (-0.054±0.017mm), and a reduction in vitreous chamber depth with luminance flicker (-0.095±0.023mm), evoking a hyperopic shift in refraction (3.40±1.77D). Timolol produced an increase in axial length with luminance flicker (0.045±0.030mm) and a myopic shift in refraction (-4.07±0.92D), while color flicker caused a significant decrease in axial length (-0.046±0.017mm) that was associated with choroidal thinning (-0.046±0.015mm). The opposing effects on growth and refraction seen with atropine and timolol suggest a balancing mechanism between the parasympathetic and β-receptor mediated sympathetic system through stimulation of the retina with luminance and color contrast.

Ocular and retrobulbar blood flow in ocular hypertensives treated with topical timolol, betaxolol and carteolol

The purpose of this study was to evaluate the effect of topical timolol 0.5%, betaxolol 0.5% and carteolol 2% on the blood flow velocity of the central retinal artery (CRA), the posterior ciliary artery (PCA) and the ophthalmic artery (OA) in patients with ocular hypertension. A group of 14 patients with ocular hypertension and a group of 11 normals were studied. The color Doppler was used to measure the peak systolic flow velocity (PSFV) and the end diastolic flow velocity (EDFV) of the CRA, the PCA and the OA in the normals and in the patients. The normals were under no treatment, while the patients were studied before and after treatment with topical timolol 0.5%, betaxolol 0.5% and carteolol 2%. In the systolic phase, there was a significant increase in the flow velocity of the CRA with all three drugs. In the diastolic phase of the CRA, the increase was significant for timolol 0.5% and carteolol 2% but not for betaxolol 0.5%. The flow velocity of the PCA and OA remained unchanged. In this study of 14 patients with ocular hypertension, topical timolol 0.5%, betaxolol 0.5% and carteolol 2% led to a significant increase in the flow velocity of the CRA without creating a steal or decrease in the flow velocity of the PCA.

Effect of topical betablockers on human retinal vessels diameters

PURPOSE

To measure the effect of topical betaxolol 0.5% and timolol 0.5% on retinal vessels diameters by means of photographic enlargement.

METHODS

Thirteen glaucomatous patients (primary open angle glaucoma (POAG) and ocular hypertensive (OH)) were treated twice daily with betaxolol 0.5% for one year. These same patients were subsequently treated with timolol 0.5% during the following year. Fundus photographs were taken with Canon camera 30 degree angle at baseline and two hours after instillation at 3, 6 and 12 months of treatment for each drug. The diameters of the superior and inferior temporal vessels (arteries and veins) were measured at one and two disc radii from the margin of the disc using photographic enlargement (x 66.7) of the right eye and were analysed under double masked fashion during the same session.

RESULTS

A significant increase of the mean arterial diameter (+ 7.4% p = 0.000 paired t) was found after 12 months of betaxolol treatment, while no persistent further difference (+ 1.3% NS) was found after 12 months of timolol treatment. No modification was found in venous diameter.

CONCLUSION

Betaxolol treatment is associated with a beneficial effect on retinal arteries width whereas Timolol does not yield the same amplitude of benefit.