Сorneal endothelium after laser activation of trabecular meshwork in patients with primary open-angle glaucoma

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In recent years, laser techniques have been widely used in the treatment of primary open-angle glaucoma (POAG) to improve intraocular fluid outflow by activating the trabecular meshwork. These techniques produce minimal damage to the trabecular tissue while being pathogenically oriented [1, 2]. Selective laser trabeculoplasty is most widely used and effectively reduces intraocular pressure (IOP) with minimal risk of complications (Latina, 1995) [3, 4].

Kurysheva et al. (2012) observed the formation of “voids” in the photographs of corneal endothelium an hour after selective laser trabeculoplasty (SLT). They concluded that apoptosis of endothelial cells was accelerated under the influence of laser

energy [5].

According to K. Ong (2015), K. Atalay (2016), and N. Örnek et al. (2017), changes in the corneal endothelium after a single SLT session in patients with POAG were temporary, and all endothelial cell parameters returned to preoperative values one month after treatment [6–8].

K.E. Leahy et al. (2018) in a study of six cadaver eyes showed that disruption of tight junctions between corneal endothelial cells was observed after SLT, which could have been caused by the release of free radicals [9].

Thus, the investigation of corneal endothelial cells’ state at laser procedures is an urgent scientific problem.

YAG-laser activation of the trabecular meshwork is a new, efficient, and safe technique [10].

It proceeds according to the following mechanism: a “shock wave” is formed above the trabecular surface, which drives the aqueous humor from the anterior chamber and various deposits from the trabecular surface. Therefore, the trabecular slits are “washed” under pressure [1, 2].

Unlike SLT, this technique can be used in patients with POAG regardless of the degree of pigmentation of the drainage zone structures (Fig. 1, 2) [1, 2].

 

Fig. 1. Low degree of anterior chamber angle pigmentation (gonioscopy)

Рис. 1. Слабая степень пигментации структур угла передней камеры (гониоскопия)

 

Fig. 2. High degree of anterior chamber angle pigmentation (gonioscopy)

Рис. 2. Выраженная степень пигментации структур угла передней камеры (гониоскопия)

 

According to T.V. Sokolovskaya et al. (2015), in the long-term postoperative period (follow-up period of up to three years), YAG-laser activation of trabecular meshwork provides a reduction in IOP in 81% of patients with POAG [2]. However, the corneal endothelium state, an important indicator of the laser intervention safety, has to be investigated.

Therefore, we aimed to evaluate the effect of laser radiation in YAG-laser activation of the trabecular meshwork on corneal endothelial cells’ state in patients with POAG.

MATERIALS AND METHODS

We monitored 15 patients (16 eyes, 7 men and 8 women aged 53 to 74 years). The average age of patients was 65.8 ± 5.35 years. The initial stage of POAG was noted in 68.8% patients (11 eyes out of 16), and the developed stage was registered in 31.2% patients (5 eyes out of 16).

Before laser treatment, patients used IOP-lowering drops such as beta-blockers (7 eyes, 43.8%), carbonic anhydrase inhibitors (6 eyes, 37.5%), and prostaglandin analogues (3 eyes, 18.7%).

All patients underwent YAG-laser activation of the trabecular meshwork with the NdYAG laser radiation parameters as follows: laser wavelength of 1064 nm; radiation energy of 0.8–1.2 mJ; spot diameter of 8–10 μm; exposure time of 3 ns; and the number of impacts of 55–70 over 360° at an equal distance from each other. Preoperative preparation included topical local anesthetic instillation (0.4% oxybuprocaine). One hour before surgery, IOP was measured, and confocal microscopy was performed. One hour after the YAG-laser activation of the trabecular meshwork, IOP was measured, eye biomicroscopy and confocal microscopy were performed.

The follow-up time points were at 1 hour, 1 week, 1 month, and 6 months after surgery. In the postoperative period, patients received topical instillations of the non-steroidal anti-inflammatory drug indomethacin (0.1% solution)

for 5 days.

The state of endothelial cells was examined using a ConfoScan 4 confocal microscope (Nidek, Japan) after topical local anesthesia was applied using 0.4% oxybuprocaine solution. The study evaluated the average density parameters of endothelial cells in the central area of the cornea, and we documented pleomorphism and polymegathism.

Statistical analysis was performed using the SPSS software package. The statistical significance of the average indicators was assessed using the Student’s t test.

RESULTS

In our clinical study, no intraoperative complications occurred and there was only one case of reactive hypertension. IOP data at different follow-up time points are shown in Table 1, and confocal microscopy findings are summarized in Table 2. There were no statistically significant differences in the average density of endothelial cells, pleomorphism or polymegathism during follow-up (Fig. 3, 4).

 

Table 1 / Таблица 1

Intraocular pressure level (Maklakov tonometry, mm Hg) after YAG-laser activation of trabecular meshwork in primary open-angle glaucoma patients at different follow-up terms (M ± σ)

Уровень внутриглазного давления (по Маклакову, мм рт. ст.) после YAG-лазерной активации трабекулы у пациентов с первичной открытоугольной глаукомой в разные сроки наблюдения (M ± σ)

Intraocular pressure level, mm Hg	Before YAG-laser activation of the trabecular meshwork	After YAG-laser activation of the trabecular meshwork
		1 h	1 week	1 month	6 months
24.85 ± 5.4	18.5 ± 4.1	20.8 ± 4.9	18.1 ± 2.8	17.9 ± 2.6

 

Table 2 / Таблица 2

Confocal microscopy indices after YAG-laser activation of trabecular meshwork in primary open-angle glaucoma patients at different follow-up terms (M ± σ)

Показатели конфокальной микроскопии после YAG-лазерной активации трабекулы у пациентов с первичной открытоугольной глаукомой в разные сроки наблюдения (M ± σ)

Indices	Before YAG-laser activation of the trabecular meshwork	After YAG-laser activation of the trabecular meshwork
		1 h	1 week	1 month	6 months
Endothelial cell density	2435.8 ± 159.0	2374.5 ± 150.4	2502.2 ± 247.5	2324.7 ± 235.1	2429.1 ± 163.0
Polymegathism	45.7 ± 10.2	49.5 ± 8.7	48.2 ± 9.1	44.9 ± 8.5	45.1 ± 8.8
Pleomorphism	46.8 ± 10.5	43.6 ± 9.7	44.7 ± 7.7	46.3 ± 7.5	45.5 ± 8.1

 

Fig. 3. Confocal microscopy, endothelial cells before YAG-laser activation of trabecular meshwork

Рис. 3. Конфокальная микроскопия, эндотелиальные клетки до YAG-лазерной активации трабекулы

 

Fig. 4. Confocal microscopy, endothelial cells after YAG-laser activation of trabecular meshwork

Рис. 4. Конфокальная микроскопия, эндотелиальные клетки через 6 мес. после YAG-лазерной активации трабекул

 

According to automated perimetry and HRT, there were no adverse changes in the shape or size of the blind spot, no increase in the number of absolute scotomata in the central visual field, no decrease in the neural rim volume, and no increase in the optic disc cup in the patients (Table 3). This indicated that the glaucoma process was stabilized.

 

Table 3 / Таблица 3

Automated perimetry and HRT indices after YAG-laser activation of trabecular meshwork in primary open-angle glaucoma patients at different follow-up terms (M ± σ)

Показатели компьютерной периметрии и HRT до и после YAG-лазерной активации трабекулы у пациентов с первичной открытоугольной глаукомой (M ± σ)

Indices	Before YAG-laser activation of the trabecular meshwork	6 months after YAG-laser activation of the trabecular meshwork
MD, dB	–6.36 ± 2.81	–6.41 ± 2.74
PSD, dB	5.07 ± 2.17	5.05 ± 2.07
Neuroretinal rim area, mm2	1.29 ± 0.37	1.31 ± 0.38
Neuroretinal rim volume, mm3	0.26 ± 0.12	0.30 ± 0.14
Cup to disc ratio	0.59 ± 0.09	0.60 ± 0.09
Mean thickness of the nerve fiber layer, mm	0.17 ± 0.07	0.18 ± 0.09
Note. MD (mean deviation) is the perimetric index characterizing the average deviation of the retinal photosensitivity; PSD (pattern standard deviation) is an integral indicator of local defects.

 

DISCUSSION

Our results suggests that YAG-laser activation of the trabecular meshwork has minimal damaging effects on the corneal endothelial cells due to the low energy parameters of the laser exposure, the very short exposure to the laser impact (3 ns), and a small spot diameter of only 8–10 μm. In contrast, SLT has a much larger spot diameter of 400 μm, which may explain the changes in the corneal endothelial cells in the early period after SLT.

CONCLUSION

Our study shows that the corneal endothelium is not damaged by YAG-laser activation of the trabecular meshwork in POAG patients.

Additional information

There is no conflict of interest.

About the authors

Valeriya N. Yashina

S. Fyodorov Eye Microsurgery Federal State Institution

Author for correspondence.
Email: varlusha92@mail.ru

Postgraduate student

Russian Federation, 127486, Moscow, Beskudnikovskiy bulvar, 59a

Tatyana V. Sokolovskaya

S. Fyodorov Eye Microsurgery Federal State Institution

Email: dr.sokoltv@mail.ru

Ph.D., Leading Research Associate of Glaucoma Surgery Department

Russian Federation, 127486, Moscow, Beskudnikovskiy bulvar, 59a

Pavel L. Volodin

S. Fyodorov Eye Microsurgery Federal State Institution

Email: plvmd@yandex.ru

Med.Sc.D., Head of Retinal Laser Department

Russian Federation, 127486, Moscow, Beskudnikovskiy bulvar, 59a

References

Supplementary files