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Background
The Agency for Health Care Policy and Research (AHCPR) panel concluded that laser capsulotomy should not be scheduled at the time cataract surgery is performed because one can not predict whether a cataract surgery patient will develop posterior capsular opacification or the time at which any such opacification will occur. For similar reasons, manual removal of the posterior capsule, performed with a needle or hook (called corneo-scleral section), should not be routinely performed at the time of initial cataract surgery.
The AHCPR panel also concluded that neodymium:yttrium-aluminum-garnet (Nd:YAG) laser capsulotomy should not be performed prophylactically or scheduled routinely at particular times after cataract surgery.
The eye examination should confirm the diagnosis of posterior capsular opacification and exclude other ocular causes of functional impairment. The panel concurred with the finding of the literature review that there is yet no objective method of relating the degree of capsular opacification to the severity of functional impairment.
The panel also concluded that posterior capsular opacification rarely occurs within 3 months of surgery, and that it is uncommon for posterior capsular opacification to occur within the first 6 months of surgery. Therefore, any cases of Nd:YAG laser capsulotomy occurring within 6 months of cataract surgery should be reviewed, to ensure that Nd:YAG laser capsulotomy is reasonable and medically necessary.
In a single center retrospective study, Delaney and colleagues (2002) determined the effectiveness of Nd:YAG vitreolysis and pars plana vitrectomy in the treatment of vitreous floaters. A total of 31 patients (42 eyes) who underwent 54 procedures (Nd:YAG vitreolysis or pars plana vitrectomy) for the treatment of vitreous floaters were included in the study. Main outcome measures were percentage symptomatic improvement following treatment and incidence of post-operative complications. Statistical analysis was performed using the Fisher exact test. Posterior vitreous detachment was the primary cause of floaters in all 42 eyes with co-existing vitreous veils in 3 eyes and asteroid hyalosis in 2 eyes. Thirty-nine of 42 eyes received Nd:YAG vitreolysis; 38 % found Nd:YAG vitreolysis moderately improved their symptoms while 62 % found no improvement. After an average of 14.7 months follow-up, no post-operative complications were recorded. Fifteen eyes underwent a pars plana vitrectomy, 1 with combined phaco-emulsification and posterior chamber implantation and 11 following unsuccessful laser vitreolysis. Pars plana vitrectomy resulted in full resolution of symptoms in 93 % of eyes. One patient developed a post-operative retinal detachment which was successfully treated. The authors concluded that patients' symptoms from vitreous floaters are often under-estimated resulting in no intervention. This paper showed Nd:YAG vitreolysis to be a safe but only moderately effective primary treatment conferring clinical benefit in 1/3 of patients.
Kirwan and Cahill (2011) reported on a case of successful drainage of a large pre-macular hemorrhage using laser photo-disruption of the posterior hyaloid membrane. A 47-year old man presented acutely to the authors' emergency department complaining of a 24-hr history of sudden onset, painless and persistent loss of vision in his left eye. Immediately before noticing this loss of vision, he had been vomiting violently from excessive alcohol intake. The left visual acuity was counting fingers. Dilated fundoscopy of the left eye revealed a large pre-macular hemorrhage that was 14 disc diameters in size. Clotting investigations were normal. A diagnosis of valsalva retinopathy was made and the patient elected to receive a prompt Nd:YAG laser posterior hyaloidotomy as an outpatient. At 1 week follow-up, the hemorrhage had drained completely into the vitreous space revealing a healthy macula and the visual acuity had improved to 6/12 unaided. At 6-month follow-up the left visual acuity stabilized at 6/9 unaided. The authors concluded that Nd:YAG laser posterior hyaloidotomy is an useful outpatient procedure for successful clearance of large pre-macular hemorrhages that offers patients rapid recovery of visual acuity and the avoidance of more invasive intra-ocular surgery. The findings of this case study (with short-term follow-up) needs to be validated by well-designed studies.
In a prospective, randomized, controlled trial, Scott et al (2011) tested the hypothesis that Nd:YAG laser peripheral iridotomy (LPI) significantly reduces the incidence of conversion from pigment dispersion syndrome (PDS) with ocular hypertension (OHT) to pigmentary glaucoma (PG). A total of 116 eyes of 116 patients with PDS and OHT were used in this analysis. Patients were assigned randomly either to Nd:YAG LPI or to a control group (no laser). The primary outcome measure was conversion to PG within 3 years, based on full-threshold visual field (VF) analysis using the Ocular Hypertension Treatment Study criteria. Secondary outcome measures were whether eyes required topical anti-glaucoma medications during the study period and the time to conversion or medication. Fifty-seven patients were randomized to undergo laser treatment and 59 were randomized to no laser (controls). Age, gender, spherical equivalent refraction, and intra-ocular pressure at baseline were similar between groups. Outcome data were available for 105 (90 %) of recruited subjects, 52 in the laser treatment group and 53 in the no laser treatment group. Patients were followed-up for a median of 35.9 months (range of 10 to 36 months) in the laser arm and 35.9 months (range of 1 to 36 months) in the control arm. Eight eyes (15 %) in the laser group and 3 eyes (6 %) in the control group converted to glaucoma in the study period. The proportion of eyes started on medical treatment was similar in the 2 groups: 8 eyes (15 %) in the laser group and 9 eyes (17 %) in the control group. Survival analyses showed no evidence of any difference in time to VF progression or commencement of topical therapy between the 2 groups. Cataract extraction was performed on 1 patient in the laser group and in 1 patient in the control group during the study period (laser eye at 18 months; control eye at 34 months). The authors concluded that the findings of this study suggested that there was no benefit of Nd:YAG LPI in preventing progression from PDS with OHT to PG within 3 years of follow-up.
Ascaso and colleagues (2012) reported on the case of a 65-year old male who underwent intra-vitreal triamcinolone acetonide (IVTA) injection for treating a clinically significant macular edema (CSME) due to background diabetic retinopathy in his left eye. On the first post-operative day, visual acuity dropped from 20/80 to hand movements. Slit-lamp examination showed the drug between the posterior capsule of the lens and the anterior hyaloid face. Two weeks later, visual acuity and the milky fluid seemed unchanged. Neodymium:yttrium-aluminum-garnet laser anterior hyaloidotomy was performed. One week later, slit-lamp examination of the retrolental space revealed the complete disappearance of triamcinolone and intra-ocular pressure remained stable. After a follow-up period of 2 months, visual acuity increased to 20/50 with the lens remaining clear. The authors concluded that Nd:YAG laser anterior hyaloidotomy is an effective, simple, useful and minimally invasive outpatient procedure in patients with persistent entrapment of triamcinolone behind the crystalline lens, allowing the drug to clear without trauma to the lens. The findings of this case study (with short-term follow-up) needs to be validated by well-designed studies.
Ramani et al (2009) examined the morphologic changes in the anterior segment of primary angle closure suspects (PACS) who underwent laser peripheral iridotomy (LPI) for a period of 2 years. Primary angle closure suspects (n = 82 eyes) of Asian Indian origin underwent A-scan biometry and ultrasound biomicroscopy. Anterior chamber depth, anterior chamber angle (ACA), axial length, lens thickness, relative lens position, central corneal thickness, angle opening distance 500, trabecular-ciliary process distance, iris-ciliary process distance, and iris thickness were measured before LPI and after LPI at 1 week, 6 months, 1 year, 1.5 years, and 2 years. Variation in the parameters measured over a period of 2 years was analyzed. Fifteen eyes out of 52 eyes developed into primary angle closure (PAC) with synechial changes. Uni-variate analysis for the predictive factors of PAC showed no significant association for age, sex, narrow angle, ultrasound biomicroscopy parameters, and vertical cup-disc ratio. When analyzed as continuous variables, decreasing ACA was significant risk factor (95 % confidence interval [CI]: 0.703, 0.989, p = 0.037). Iris-ciliary process distance, ACA, lens thickness, and angle opening distance 500 were the parameters that varied significantly (p < 0.05) between "before LPI group" and "after LPI groups". None of the subjects developed increased intra-ocular pressure (IOP) after laser iridotomy. The authors concluded that in this hospital-based study on the course of PACS subjects after LPI, as many as 28 % progressed to PAC. Decreasing ACA was the predictive factor for the progression of PACS to PAC. There was no increase in IOP, history, or symptoms of acute attack of glaucoma among the study subjects after LPI.
In a case-series study, Lin and colleagues (2011) evaluated the long-term changes in anterior segment morphology by using ultrasound biomicroscopy (UBM) following LPI in eyes with PAC. A total of 54 eyes with PAC of 31 consecutive patients were enrolled. Routine ophthalmic and UBM examination were performed at visit-1 (before LPI), 2 weeks, 6, and 12 months after LPI. The parameters of anterior chamber were measured by UBM and calculated. Results of each follow-up time were analyzed using repeated measures analysis of variance. Parameters of UBM measurement at 750 µm anterior to the sclera spur and at 500 µm counterpart were compared using paired student t-test. Compared to before LPI, anterior chamber depth (ACD) was deepened by approximate 0.10 mm after LPI, however, it was not statistically significant (F = 3.50, p > 0.05). Angle opening distance (AOD), trabecular-iris angle (TIA), angle recess area (ARA) and trabecular-ciliary process distance (TCPD) were significantly increased at 2 weeks, 6 and 12 months after LPI compared with respective baseline [AOD750: (165.0 ± 70.3), (185.8 ± 68.5), (196.1 ± 77.7) µm versus (66.2 ± 51.6) µm, F = 92.60; TIA750: 14.1° ± 6.3°, 15.5° ± 6.2°, 16.4° ± 5.9° versus 6.4° ± 4.9°, F = 92.60; ARA: (0.058 ± 0.024), (0.065 ± 0.023), (0.068 ± 0.026) mm(2) versus (0.025 ± 0.017) mm(2), F = 92.60; TCPD: (647.1 ± 113.0), (701.8 ± 93.4), (670.1 ± 95.4) µm versus (571.0 ± 97.2) µm, F = 34.00; p < 0.05]. The parameters of UMB measurement at 750 µm were significantly increased more than that at 500 µm anterior to the sclera spur (AOD: t = 5.90, TIA750: t = 2.70, p < 0.05; ARA: t = 2.00, p = 0.05). The authors concluded that LPI can significantly widen the peripheral anterior angle in eyes with PAC lasting for at least 1 year after LPI. Parameters detected by UBM at 750 µm anterior to the sclera spur appear to be more sensitive in evaluating the alternation of peripheral angle structure.
The American Academy of Ophthalmology’s Preferred practice pattern guidelines on “ Primary angle closure” (AAO, 2010) stated that patients with PAC may have elevated IOP as a result of a chronic compromise of aqueous outflow due to appositional or synechial angle closure, or damage to the trabecular meshwork from previous intermittent acute angle-closure crisis. Iridotomy is indicated for eyes with PAC or primary angle-closure glaucoma (PACG).
A Medscape review on “Glaucoma, angle closure, chronic treatment & management” (Tham, 2012) stated that “Laser iridotomy is indicated for all stages of chronic angle-closure glaucoma (CACG). Laser iridotomy involves the creation of a hole in the peripheral iris by laser. The hole provides an alternative pathway for aqueous to flow from the posterior chamber into the anterior chamber, bypassing the pupil. Therefore, iridotomy will eliminate pupillary block and prevent forward bowing of the iris as a result of the pressure difference between the two chambers. Iridotomy will open those areas of the angle not involved by PAS (peripheral anterior synechiae) and prevent further synechial closure”.
Thomas and Walland (2012) noted that PACG and its precursors represent both a significant proportion of world glaucoma blindness and a currently insurmountable burden of treatment. In contrast to primary open-angle glaucoma, preventive interventions in primary angle closure disease (PACD) can sometimes be definitive. These investigators have synthesized data from randomized controlled trials (RCT's) -- and where this is not available -- principles grounded in known biology, biological plausibility, logic, preferred practice and personal experience to develop detailed and explicit clinical algorithms for the management of the spectrum of PACD. Laser iridotomy is the mainstay of first-line intervention and is usually required for all PACD with the exception of some PACS. Laser iridotomy is a necessary but not always sufficient step and uncertainty arises where a patent iridotomy has not alleviated the angle closure profile or achieved clinically desired end points. The crucial step-wise considerations after iridotomy are: whether the angle is open or closed; whether the IOP can be medically controlled; the extent of PAS and the presence of visually significant cataract. These lead to further interventions that include iridoplasty, cataract surgery, trabeculectomy or phacotrabeculectomy. Such subsequent interventions are based on an arbitrary threshold (180 degrees) for angle opening and extent of PAS following iridotomy and other initial procedures.
Furthermore, an UpToDate review on “Angle-closure glaucoma” (Weizer, 2013) states that “Laser peripheral iridotomy is the first step in treatment of patients with chronic angle closure glaucoma, to relieve any pupillary block component. The intraocular pressure may remain elevated, however, if scarring has already damaged the drainage angle. In this case, the remaining glaucoma is treated medically and surgically much as in open-angle glaucoma …. Patients with signs and symptoms suggesting an acute attack of angle-closure glaucoma require emergency treatment by an ophthalmologist …. We recommend emergency use of topical ophthalmic medications to reduce intraocular pressure (Grade 1C). These drugs may include a beta-blocker, an alpha agonist, and an agent to produce miosis. We also suggest systemic medication to decrease intraocular pressure, which may include oral or IV acetazolamide, IV mannitol, oral glycerol, or isosorbide (Grade 2C). Once the acute attack is controlled, definitive treatment for angle-closure glaucoma is a laser peripheral iridotomy to provide a small drainage hole through the iris”.
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