ABSTRACT
Primary congenital glaucoma (PCG) continues to be an important cause of visual impairment in children despite advances in medical and surgical treatment options. The progressive and blinding nature of the disease, together with the long lifespan of the affected population, necessitates a thorough understanding of the pathophysiology of PCG and the development of long-lasting treatment options.
The first part of this review discusses the genetic features and makeup of this disorder, including all currently identified genetic loci (GLC3A, GLC3B, GLC3C and GLC3D) and relevant protein targets important for trabecular and Schlemm canal dysgenesis. These target molecules primarily include CYP1B1, LTBP2, and TEK/Tie2 proteins. Their potential roles in PCG pathogenesis are discussed with the purpose of bringing the readers up to date on the molecular genetics aspect of this disorder. Special emphasis is placed on functional implications of reported genetic mutations in the setting of PCG. The second part of the review focuses on various modifications and refinements to the traditional surgical approaches performed to treat PCG, including advances in goniotomy and trabeculotomy ab externo techniques, glaucoma drainage implant surgery and cyclodiode photocoagulation techniques that ultimately provide safer surgical approaches and more effective intraocular pressure control in the 21st century.
Keywords:
Primary congenital glaucoma, genetics, angle surgery, glaucoma drainage implants
Introduction
Primary congenital glaucoma (PCG) (OMIM 231300) is a potentially blinding ocular disease that occurs secondary to a developmental anomaly of the anterior chamber angle and which results in high intraocular pressure (IOP) with its resultant devastating consequences.1,2 It is an important global cause of pediatric visual impairment and leads to legal blindness, even with treatment.3,4,5 The underlying mechanism in PCG is trabecular dysgenesis with or without varying degrees of associated iridodysgenesis including arrested posterior migration of the peripheral iris tissue and maldeveloped trabecular angle meshwork with or without dysgenesis of the Schlemm’s canal (SC).1 Current evidence suggests that trabecular dysgenesis occurs due to mutations that impair normal trabecular meshwork development.6,7,8 However, the mechanisms through which these genes act to induce trabecular dysgenesis is not, as of yet, clearly elucidated.
Current treatment strategies for PCG revolve around surgical methods that target the abnormal trabecular angle.9 These options include goniotomy and trabeculotomy ab externo, and variations thereof, that are performed as primary procedures in patients with PCG.9,10,11,12 Many patients require more than one surgery and, in some cases, drainage procedures if these angle-based procedures do not lower the IOP to a safe level to halt glaucomatous optic neuropathy.9,13,14 Patients with PCG also frequently require adjunctive topical hypotensive medications in their postoperative course.2,4
The purpose of this review is to provide an update on the genetic basis of PCG and to summarize the current surgical options for treatment of this condition.
Study Limitations
Limitations included identifying and precisely targeting the ciliary body and titrating the laser energy to adequate uptake, especially in varying anterior segment anatomies. Post procedural complications such as inflammation and overtreatment resulting in irreversible hypotony and phthisis are also increasingly more difficult to manage in a pediatric patient.89,92
Most ophthalmologists will reserve TSCPC for patients with a limited visual potential given the adverse effect profile, especially given the potential for retinal detachment (~10%) and irreversible hypotony.88 Additionally, they will reserve this approach for patients who have glaucoma refractory to prior surgeries, elevated pressure with pain in a blind eye, or if surgical/incisional measures are too risky. Rarer complications that can occur with TSCPC involve scleral thinning, especially when too many audible laser sounds are heard. Limiting the area of ablation per session to no more than 180 degrees appears to confer increased safety to the TSCPC procedure, though the procedure may need to be repeated to achieve target IOPs.93
An intraocular procedure that has more recently been utilized in the pediatric population is ECP.93 Using a 19-23-gauge instrument, one can endoscopically visualize the ciliary body processes and treat with photocoagulation directly to the processes.94
Studies reporting results from ECP have been promising, with no sight-threatening complications of severe hypotony, intractable pain, or recalcitrant inflammation.94 At 3 year follow-ups, 50% of patients had a cumulative success rate of 43%.94 Considerations for ECP include whether the patient is phakic or aphakic and risks of introducing potential infection, causing suprachoroidal hemorrhages, or IOP spikes.
Given the propensity for glaucoma surgical procedures to fail over time in the pediatric population, secondary and tertiary surgical procedures have to be considered in these patients. Procedures that will function for the longer life expectancy of the pediatric patient are crucial. The decision to perform another tube surgery versus repeated TSCPC has been shown to be equivocal in the results, despite small powers in numbers of patients to evaluate this.95
Çalışmanın Kısıtlılıkları
Çalışmanın kısıtlılıkları şunlardır: Siliyer cismin tanımlanması ve kesin olarak hedeflenmesi ve lazer enerjisinin, özellikle değişken ön segment anatomisine uyumlu şeklide, uygun doz sağlamak için ayarlanması. Pediyatrik bir hastada, geri dönüşümsüz hipotoni ve fitizise yol açan enflamasyon ve aşırı tedavi gibi işlem sonrası komplikasyonların yönetimi de zordur.89,92
Çoğu göz hekimi, özellikle retina dekolmanı (~%10) ve geri dönüşümsüz hipotoni gibi yan etkiler göz önüne alındığında TSSFK’yi görme potansiyeli sınırlı olan hastalarda tercih edecektir.88 Ayrıca, bu yöntemi cerrahiye refrakter glokomlu hastalar, görmeyen gözde yüksek basınç ve ağrı olan olgular veya cerrahi/insizyon yapmanın çok riskli ise hastalarda kullanmayı seçeceklerdir. TSSFK’de ortaya çıkabilecek nadir komplikasyonlar arasında, özellikle çok fazla lazer sesi duyulduğunda, skleral incelme bulunmaktadır. Seans başına ablasyon alanını en fazla 180 dereceyle sınırlandırmak TSSFK’ye güvenlik kazandırır gibi görünmektedir, ancak hedeflenen GİB değerlerine ulaşmak için işlemin tekrarlanması gerekebilir.93
Pediyatrik popülasyonda daha yakın bir zamanda kullanılmaya başlanan bir diğer intraoküler girişim ESF’dir.94 Siliyer cisim uzantıları 19-23 G boyutunda bir alet kullanarak endoskopik olarak görülebilir ve fotokoagülasyon doğrudan uzantılara uygulanabilir.94
ESF’nin değerlendirildiği çalışmalarda sonuçların umut verici olduğu ve ciddi hipotoni, inatçı ağrı ya da tedaviye yanıt vermeyen enflamasyon gibi görmeyi tehdit eden komplikasyonlar izlenmemiştir.94 Üç yıllık takipte hastaların %50’sinde kümülatif başarı oranının %43 olduğu bulunmuştur.94 ESF ile ilgili akılda bulundurulması gerekenler, hastanın fakik veya afakik olup olmadığı, potansiyel enfeksiyona, suprakoroit kanamalara veya göz içi basıncında ani yükselmelere neden olma riskidir.
Pediyatrik popülasyonda glokom cerrahi girişimlerin zaman içinde başarısız olma eğilimi göz önüne alındığında, bu hastalarda sekonder ve tersiyer cerrahi girişimler yapılması gerekebilir. Pediyatrik hastalarda, daha uzun süre fonksiyonel kalacak yöntemler önem arz etmektedir. TSSFK’yi tekrarlamak veya farklı bir tüp cerrahisi yapmak arasında hangisinin tercih edilmesi gerektiği sonuçlara bakıldığında kesinlik kazanmamıştır ancak bu çalışmalarda dahil edilen hasta sayılarının yeterli olmadığı hatırlanmalıdır.95
Conclusion
PCG continues to be a challenging disease in the 21st century in that long-lasting IOP control is still difficult to achieve and the visual prognosis is somewhat guarded despite state-of-the-art treatment paradigms.3,5 Over the course of five decades, several modifications have been introduced to standard angle surgery procedures to improve IOP outcomes, increase safety of the interventions, and decrease the total number of procedures in PCG. There has been a shift away from trabeculectomy and toward GDIs to decrease the frequency of postoperative hypotony and to ensure long-term IOP control. Currently, aqueous drainage devices as well as laser cyclophotocoagulation are successfully used in current practice to lower IOP in PCG, more frequently as a secondary procedure but in select cases as a primary intervention modality. These procedures can provide a pediatric patient longevity of stable IOP and thus preservation of visual function for a longer period of time. Limitations of current studies that provide evidence of safety and efficacy are the power in numbers of patients as well as duration of follow-up. Comparative studies of various procedures are needed to further investigate efficacy, outcomes, and quality of life outcomes.
Categorizing patients as either PCG or secondary congenital glaucoma and then stratifying those with secondary congenital glaucoma by mechanism, such as trauma-related, aphakic glaucoma, or anterior segment dysgenesis-related glaucoma, could help to better understand outcomes of various procedures in these different patient groups. Additionally, the pediatric patient population is reliant on other social risk factors such as caregivers, economic, education, and distance of travel, all factors that can influence time to diagnosis, time to surgery, and postoperative care. When trying to clinically appreciate the outcomes of this literature review, a case-by-case analysis must also be performed to account for these social risk factors prior to determining a management plan for these patients. A better understanding of PCG as a disease, improved diagnostic capacity, together with advances in surgical procedures will continue to improve the outlook for PCG in the future.
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