Dr.Dhrubojyoti Sarker, Dr.Rajiv Kumar Gupta,Dr. TIRTHAJIT MAITRA
Introduction-
Selective laser trabeculplasty (SLT, Lumenis, Yokneam, Israel) was approved by the United States Food and Drug Administration in 2001 for the treatment of open-angle glaucomas . With the previous procedures like argon laser trabeculoplasty (ALT) which had a few unavoidable shortcomings significant post laser IOP spike (more than 10 mm of Hg) as shown by Rosenblatt and Luntz[1], AC reaction, synicheae formation. To conquer these drawbacks Latina and Park[2] experimented using Q-switched Nd:YAG and frequency-doubled Nd:YAG lasers, and found selective photocoagulation of pigmented TM without involving the non-pigmented TM. The technical advancement resulted in fewer side effects. Bejng a safe and highly effective procedure SLT controls its adverse effects.
Like every invasive maneuvers the laser treatment is not free of iatrogenic phenomenon. Beside minimal IOP spike, iritis, ocular irritation. SLT could be attributable for transient visual blurring that resulted from altered corneal architecture. The study emphasizes this effects of laser. Although permanent corneal changes after SLT are extremely rare with only two reported cases [3]. in the literature of corneal edema, haze, and thinning occurring within 24–48h post laser. These cases resulted in irreversible corneal scarring, thinning, and a myopic shift in refractive error.Therefore, like any other treatment SLT induces inflammatory reaction which can lead to ac reaction and cylcitis, both of them resolved by steroids and cycloplegics but things that could not be medically treated yet troublesome are in the forefront of this study
Study design- prospective interventional study
Material and method-
the patients were selected from the regular and follow up cases who visited the outdoor general ophthalmology and specialized glaucoma clinic. The subjects were recruited for this study in a tertiary care eye center of eastern India between May 2017 to April 2018. This study adhered to the tenets of the Declaration of Helsinki. Informed patient consent and approval by the Institutional Review committee were obtained before commencing the study. All the patients were examined and evaluated by general ophthalmologist and laser procedure performed by glaucoma specialist. The 31 cases were included from whom
we collected the ocular and systemic history, special emphasis given to age, duration of ocular morbidity, family history of glaucoma, chronic administration of oral or any per enteral medication (steroids,) previous ocular surgeries, general health and lifestyle characteristics. The anti-glaucoma therapy currently being used were also enquired about. Onset,duration, progression of thedisease. How the previous managements helped out the patient, consistency and temporal variation of the condition were asked for. We also asked the patients for their previous clinical and treatment records which were evaluated and proper documentation done.
On the examination protocol we followed a comprehensive approach for the sake of satisfactory and targeted treatment and emphasized on the corneal examination. The 32 eyes from 21 cases examined. Baseline visual acuity(both eyes), anterior segment evaluation by slit lamp bio microscopy performed, followed by applanation tonometry of both eyes. Indirect gonioscopy performed and angle information documented by Speath classification system. Stereoscopic examination of optic disc and retinal nerve fiberlayer photography done. Vertical cup disc ratio documented.
Humphreys visual fields analysis(VFA)(Carl Zeiss Meditec AG, Berlin, Germany) 24-2 SITA protocol was performed on every eyes for establishing the diagnosis of glaucoma. These investigations helped out to delineate ˚the cases of glaucoma and 21 cases were diagnosed to be suffering from actual glaucoma which are adhered to the diagnostic criteria.Corneal examination was crucial and performed by expert. We evaluated cornea from two aspects. The thickness was measured by AS-OCT and central corneal thickness(CCT) was measured followed by specular microscopy for gross assessment of endothelium.pre laser CCT and ECC measured in all the eyes.
Performing SLT-
The laser procedure was performed on the cases who fulfilled the following inclusion criteria- open angles cases, on glaucoma medications sine last 3 years, unhindered detoriation of field and/or disc on serial follow up, pigmentary and psuedoexfoliation cases, patients not opting for trabeculectomy, and patients in whom serial follow up may not be possible. We excluded- pediatric and juvenile cases, who had history of active or old history of uveitis, irregular appositional angle closure, haziness or opacity in cornea, advance glaucoma with significant optic neuropathy.
The subjects were prepared after obtaining informed consent Baseline IOP was measured and one drop of 1% pilocarpine nitrate instilled in the eye followed by a single session of SLT performed by one surgeon using a Q-switched Nd:YAG laser (Ellex Medical Lasers, Adelaide, SA, Australia) for 360˚ in all patients. An initial energy of 0.8mJ was used for 3 nseconds creating a 400 µm spot size with titration in energy until bubble formation was just visible in the trabecular meshwork. Subjects with bilateral disease were offered treatment of both eyes in the same session.A Latina SLT gonio laser lens was used for treatment. In the treated eyes, a single drop of 1% Brimonidine was instilled immediately post SLT and a Dexamethasone 0.1% and moxifloxacin 0.5% combination eye drop was used four daily for 1 day and subsequently continued for 2–3 days if anterior chamber reaction was seen on the day following SLT. Patients were for followed-up 1 day, 1 week, and 1 month following SLT session. We asked Patients to continue the same pre-SLT topical anti-glaucoma medication regime throughout the duration of the study.
The endothelial cell count was calculated using non-contact specular microscopy (Noncon ROBO-CA by Konan Medical USA Inc., Irvine, CA, USA), and the central corneal thickness (CCT) is measured by AS-OCT scan. Thesemeasurements were taken on the pre laser visit and the subsequent follow up sessions as the schedule prepared.The central corneal endothelium was photographed using a non-contact specular microscope. After fixing the patient’s head was stabilized on the specular microscope. The microscope was aligned and focused on the center of the cornea by aspecialist. The automatic function of the machine captured the central endothelium (field size of 0.25×0.40mm, resolution of 100lines/mm). The endothelial cell density was assessed and defined as the number of cells per mm2. Adequacy of tear film was ensured before each scan and the repeatability of measurements was confirmed.
Statistical analysis-
An ANOVAtest with nested design was performed to assess for differences between each time point before and following SLT for the following outcome measures: endothelial cell count, CCT, and IOP. The ANOVA was used to account for using both eyes from patients in the same sample. The total laser energy was calculated by multiplying the number of laser shots with the energy level used for treatment in each case. A Friedman test with Dunn’s Multiple Comparison was used to compare for difference between the corneal parameters of the treated V/S the untreated fellow eyes in the 11 eyes with unilateral SLT treatment.
Result-
The study comprises of the 21 patients from whom 32 eyes were subjected to laser management. There were 12 male and 9 female patients. Mean age of presentation 48.71± 7.23 years. It was seen that both eyes were involved eually.14 and 8 eyes had been diagnosed with POAG and NTG. This study also highlighted the prevalence of an underdiagnosed entity normal tension glaucoma( in this zone of eastern India).cases were treated with single session laser and same post laser medication prescribed to all of them. Mean glaucoma medications were being used were 1.47.We found no significant correlations between the number of anti-glaucoma medications and the number of SLT laser applications and the corneal parameters (all P=0.6). The mean number of SLT laser applications was 156.8±43.4 with mean energy of 1.16±0.07mJ. The mean total laser energy used was 169.21±35.3mJ
The endothelial cell count was found to be affected by the laser episodes. The mean baseline value was 2378/ mm² which was decreased up to decreased by 4.7% to 2267±351cells/mm2 at 1 week and increased up to 2354.0±342cells/mm2 on 4-week post SLT. We came acrossstatistically significant relation between baseline and 1st week value and between 1st week and 4rth week value. Although total energy applied, duration of treatment, baseline IOP had no significant correlation with the final outcome parameters like endothelia; count and central corneal thickness.
Similarly, the assessment of CCT was measured from baseline and it was found from baseline value of 538± 37.1 µm, it reduced to 532.04±34 µm after 4 weeks andthen final value found as 529.3± 36.7 µm. There was a small but statistically significant positive correlation between the total laser energy applied and CCT. It was the CCT value of baseline and 4rt week findings. Selective laser treatment was also proven to be superiorly efficacious as it helped to reduce IOP to such an extent of to reach the target range. The baseline pre-treatment IOP was 18.6±3.8mmHg. on the 1st day, 1 week, and 1-month post SLT IOP’s were 13.0±2.5 (27% reduction), 11.5±3.6 (11% reduction), and 9.12±2.7mmHg (21% reduction), respectively. multiple regression analysis showed significant differences between these IOPs at all-time intervals.
During the early and late monthly follow ups all cornea were found to be clear. AC reaction was present but minimal in 4 eyes. As we prescribed post laser steroid drops which helped to control such iatrogenic inflammation.
Discussion-
selective laser trabeculoplasty has become a novel therapeutic approach towards complicated open angle glaucoma cases. It is a fast, repeatable, affordable modality that has evolved to be a boon for several patients of resistantand medically non-compliant glaucoma. The study was an endeavor to delineate the adverse outcomes associated with the SLT. It is well known that argon laser was introducedfirst in the field of laser therapy in order to control the excess aqueous production by photo ablating the trabecular meshwork. Works started from 1970 began a new era and promising results followed, In a paper by Wise and Witter in 1979,argon laser trabeculoplasty (ALT) wasreported as an alternative to more invasive filtering surgery with minimalrisks and high success rates[4].teh efficacy of ALT also established after “Glaucmoa laser trial”, which was a multicenter, randomized clinicaltrial that compared initial treatmentof primary open-angle glaucoma withALT versus 0.5 percent timolol.[5] At twoyears, eyes initially treated with ALT hadan IOP 2 mm Hg lower than eyes initiallytreated with timolol.
ALT was able to treat glaucoma by reducing IOP but associated with a few drawbacks, like some researchers like STRUMAR J et al [6]have found ALT being responsible for widespread tissue destruction and persistent inflammation which can lead to a membrane formation over TM. This study was an visionary approach to understand the underlying pathology, the study was further supportedby Barkana Y et al [7] who demonstrated that bleb encapsulation could be resulted from ALT.
Studies began to emerge using the Nd:YAG laser. This laser, when compared to argon gas laser had the advantage of smaller size, longer operating life, and high electrical to optical efficiency.[8] Kwasniewska and associates[9], in a 1993 report, evaluated 106 eyes treated with trabeculoplasty using a continuous wave Nd:YAG laser. Success was defined as reduction in IOP to 22 mm Hg or less without further laser or surgical intervention.employing Nd:YAG laser to make aqueous outflow to flow smoothly is brought forth by three mecahnisms, the theories are – mechanical, cellular and repopulation. It isestablished from Rodrigdes et al[10] who accepted Wise and Witters theory of TM beam splitting by Photocoaglution and photoablation.
Studies are done to understand basic pathophysiological phenomenon like TM disruption and its immediate and delayed effect on cornea and angle. Especially the trabecular cell damage that release a sufficient amount of nuclear and cytoplasmic tissue debris, along with it clusters of melanin pigment granules, fibrinous material, macrophages, and focal edema of corneal endothelial cells. Our studyemphasizes on the local biological modifications and it is well documented that immediate post laser inflammation would definitely setting up a nuance that may not be a concern for Ophthalmologist but instant patient’s visual satisfaction might be hampered. Changes that we came across are reversible, Parshley and associates [11] examined the effect of ALT on anterior segment organ cultures on stromelysin, a metalloproteinase that is thought to degrade trabecular proteoglycans.
On comparison to ALT, SLT is less damaging to the non-pigmented TM. The nanosecond pulse technologyof SLT that delivers only 1% of the energy used in ALT. [12], therefore the adverse reactions are mild and transient and reversible also. We encountered post SLT AC reaction, IOP elevation, eye pain, non-specific conjunctivitis, corneal edema, blurred vision, and, rarely, the appearance of corneal keratitis or scarring as mentioned in various studies. [13-15]. The study conducted by Lee JWY et al [16] had shown the similar findings on a large cohort of 111 eyes with longer follow up session, the study emphasizes properly on the trendof endothelial count and similarly on the central corneal thickness. First 1week follow up showed up to 5% reduction in endothelial count. Which got normalized by 1 month.
This study also found that parameters came into normal range by 1 month which was contradictory to the White et al [17] who established that with 180˚ SLT subtle endothelial changes do occur and it was reversible by 6 weeks. these two studies agreed at the point of transient inflammation that the endothelium or cellular edema separating the endothelial cells from the Descemet’s membrane impairing their count on specular microscopy. According to our notionTransient corneal oedema was an inevitable issue in a few trials because of using alcohol in SLT lens clearing agent athat caould be a reson for keratopathy also. Our SLT lens was rinsed with normal saline after disinfection which could avert cross infection also.
Corneal thickness of baseline value of 538± 37.1 µm which was graduated up to529.3± 36.7 µm. on the 4rth week follow up. This architecturalchangesattributed to all layers of the corneal stroma in response to thermal coagulation subsequently followed by replenishing of keratocytes to the treated area during the healing process.Tanaka T et al [15] postulated the theory of lamellar dysregulation and trivial injury to Na-K ATPase pump mechanism to delineate the post laser corneal changes. Though the keratocytes got replenished and stromal healing occurred but it took at least 1 month. The laser energy that eventually induce endothelial an the cornealoedema could revert back by 1st week. It is beyond the normal corneal imaging to draw definite conclusion of what is the real ultrastructuralchanges in corneal lamellae after laser.
We were able to achieve good IOP control. It is a well-documented fact that IOP elevations above 5 mm Hg range from 0 to 37.5 percent. [16,17,18]. In our study 8 cases (38.09%) had IOP spike beyond baseline after 6 hours of treatment.
Conclusion-
the load of blindness from glaucoma is rising. Treatment of the chronic progressive neuropathy is a crucial factor which depends on patient’s ocular morbidity status, regularity in follow up and economic acceptability. SLT is a newer and novel modality that is repeatable, cost effective and pathophysiology oriented. Transientcorneal and anguler nuances might troublesome for the patients.
Financial disclosure-nil
Conflict of interest -nil
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