[Intraocular pressure, ocular blood flow, and corneal biomechanics changes after LASIK surgery for myopia]

AIM

to study changes in intraocular pressure (IOP), volumetric ocular blood flow (OBF) rate, and biomechanical properties of the cornea after excimer laser ablation in patients with myopia of different degrees.

MATERIAL AND METHODS

A total of 16 patients (32 eyes) with myopia ranging from 2.75 to 9.0 D were examined before and after LASIK. Ocular Blood Flow Analyzer (OBFA) was used to measure IOP and OBF as well as pulse amplitude and volume. Ocular Response Analyzer (ORA) was also employed to provide the following data: Goldmann-equivalent IOP, corneal compensated IOP, corneal hysteresis, and corneal resistance factor. The eyes were then divided into two groups: group 1 - 15 eyes with less than 70-µm deep ablation of the cornea and group 2 - 17 eyes with more than 70-µm deep ablation.

RESULTS

Group 1 demonstrated a statistically reliable decrease in IOP values provided by either method and biomechanical parameters of the cornea (p<0.005), but no difference in pre- and postoperative OBF, or pulse amplitude, or pulse volume (p>0.05). In group 2, all the parameters changed reliably, except for the pulse volume (p>0.05). In particular, a decrease was recorded for IOP (with no dependence to the method of measurement; p<0.001), pulse amplitude (p<0.01), corneal hysteresis (p<0.001), and corneal resistance factor (p<0.001); an increase - for OBF (p<0.05).

CONCLUSION

One should allow for possible mismeasurement of IOP and OBF as well as biomechanical parameters of the cornea in post-LASIK patients, keeping in mind that the extent of error depends on the depth of ablation. Shallow ablation (no more than 70-µm deep) has no statistically significant effect on OBF readings, while IOP seems to decrease considerably. In deep ablation (more than 70-µm deep), both parameters are reliably lower than at baseline.

[Electrophysiological parameters of the retina in idiopathic macular hole]

AIM

To investigate the nature and range of electrophysiological disturbances in idiopathic macular hole (IMH) and establish their relationship with structural parameters of the retina.

MATERIAL AND METHODS

The study included 249 patients (280 eyes) with IMH. All of them underwent ganzfeld and multifocal electroretinography (ERG), optical coherence tomography, and evaluation of retinal electrical sensitivity and analyzer lability. The results were then compared to those of non-IMH patients (196 paired eyes) and controls (25 people, 49 eyes).

RESULTS

Multifocal ERG findings prove that IMH is always associated with significant changes in bioelectrical potential of the central retina. In 62% of cases its decreased density and extended latency were registered in not only the fovea, but also the para- and perifovea. In 8% of cases the changes involved everything within a 30-degree area of the central retina. In 30% of cases the maximum bioelectric potential was found to have shifted from the centre to para- and perifovea, its amplitude and density being supernormal for these regions (shift phenomenon). A weak correlation between electrophysiological parameters and retinal thickness around the hole has been also established.

CONCLUSION

Of all methods used to assess retinal function in IMH, multifocal ERG is the most informative. In 100% of cases foveal biopotential is sharply reduced in density and disfigured. In 70% of cases these changes spread outside the fovea.

[Tomography findings in optic nerve head and retina in differential diagnosis between normal-tension glaucoma and ischemic optic neuropathies]

AIM

to determine tomography findings in optic nerve head (ONH) and retinal nerve fiber layer (RFNL) that may be valuable for differential diagnosis between normal-tension glaucoma (NTG) and ischemic optic neuropathy (ION) outcome.

MATERIAL AND METHODS

Group 1 consisted of 17 patients (32 eyes) with NTG, group 2--17 patients (24 eyes) with ION outcome. The control group included 22 patients (22 eyes) with no sighs of optic neuropathy. Optic nerve head and retina assessment included scanning laser ophthalmoscopy (HRT 111) and optical coherence tomography (Stratus OCT 3000). Statistical analyses were performed using Statistica 10 software suite.

RESULTS

Statistically significant changes in HRT parameters, namely, the mean RNFL thickness, retinal height variation along the contour line, and RB discriminant function, were observed in both study groups as compared to the controls. NTG patients also showed lower rim indices, larger cups, smaller values of the FSM discriminant function, and lower GPS (glaucoma probability score) than both ION patients and the controls. OCT findings included a statistically significant decrease in RNFL thickness in both study groups as compared to the controls. As for the difference between the groups, it was unreliable. Quadrant comparisons of RNFL thicknesses revealed that lower quadrant RNFL thinning was more significant in NTG patients, while temporal quadrant RNFL thinning--in ION patients.

CONCLUSION

Both conditions are associated with a similar degree of RNFL thinning, as confirmed by OCT, however, HRT changes are much more pronounced in NTG than in ION patients.

[Ocular blood flow and carotid artery malfunction]

AIM

to evaluate ocular hemodynamics and informativity of estimated individual normal range of intraocular pressure (IOP).

MATERIALS AND METHODS

A total of 12 patients (22 eyes) with carotid artery malfunction were examined. Ocular blood flow (OBF) and IOP were measured with Ocular Blood Flow Analyzer. Actual OBF was then compared with what is considered normal for a given axial length (AL). Individual normal range of IOP was calculated according to an original formula (described in previous publications). Doppler imaging of ocular vessels enabled blood flow velocity measurement. Morphological parameters and functional status of the retina and optic nerve were judged on automated perimetry (Octopus 900) and optical coherence tomography (Cirrus HD-OCT) findings. Statistical analyses were performed using Statistica 10 software.

RESULTS

Generally, OBF showed no correlation with the grade of carotid artery stenosis (p < 0.05), however, was significantly reduced as compared to its AL-dependent norm in patients with greater than 85% narrowing of the internal carotid artery, which can cause misestimating of their individual normal range of IOP. A negative relationship was established between the blood flow velocity in short posterior ciliary arteries and the grade of internal carotid artery stenosis (p < 0.005). Ocular blood flow deficit relative to the AL-dependent norm correlated with ophthalmic artery resistance index.

CONCLUSION

OBF-based estimation of individual normal range of IOP is inexpedient in patients with greater than 80% carotid artery stenosis due to its possible influence on ocular hemodynamics. In most cases of less than 80% carotid artery stenosis OBF is adequate or slightly reduced as compared to its AL-dependent norm and thus, has no significant impact on estimated individual normal range of IOP.

[Effects of blood flow properties on ocular hemodynamics]

AIM

to study the effects of blood rheology on ocular blood flow (OBF) parameters and estimated individual normal range of intraocular pressure (IOP).

MATERIAL AND METHODS

A total of 15 patients (15 eyes) taking warfarin were enrolled. Volumetric parameters and linear velocity of OBF under warfarin treatment and after its cessation were obtained by means of flowmetry (Paradigm's Blood Flow Analyzer) and color Doppler flow mapping (Voluson 730), respectively. On the basis of flowmetry results an individual normal range of IOP was calculated in all patients.

RESULTS

Pulsatile OBF does not appear to correlate with warfarin-induced changes in blood rheology (p = 0.09), however, depends on IOP fluctuations (p = 0.02). Resistance index of retinal vessels is found to rise significantly with increasing blood viscosity (p < 0.05).

CONCLUSION

The use of warfarin, an indirect thrombin inhibitor, has no effect on estimated individual normal range of IOP, which is crucial for glaucoma diagnosis and monitoring.

[A case of bilateral cystoid macular edema (Irvine-Gass) after bilateral multifocal intraocular lens implantation]

OBJECTIVE

To evaluate clinical outcomes of cystoid macular edema (CME) developed after phacoemulsification with multifocal intraocular lens (IOL) implantation.

MATERIAL AND METHODS

The article reports a favorable outcome of bilateral CME in a 66-year-old after bilateral phacoemulsification with Rayner M-flex Multifocal IOLs implantation. Optical coherent tomography (OCT) and multifocal electroretinography (mfERG) were used for follow-up.

RESULTS

In the first eye CME developed 3 weeks after the surgery and required 1.5 years of treatment. In the fellow eye CME manifested 2 weeks after the surgery and resolved in six months under the treatment. The follow-up period was 5 and 2 years correspondingly.

CONCLUSION

It is shown that retinal OCT is useful for distinguishing clinical forms of CME and is able to confirm positive effects of the treatment, whereas mfERG provides the opportunity to assess subtle mechanisms of retinal function recovery, which may take several years.