APHAKIC GLAUCOMA

 

Aphakic glaucoma was probably recognized for the first time by Bowman in 1865 (Bowman, W. 1865, Quoted by Duke Elder: System of Ophthalmology, 11, 722, Henry Kimpton, London, 1969).

Aphakic glaucoma is now quite rare in the adult population as most patients undergo cataract surgeries where the capsular bag and posterior capsule are left intact. In such cases intraocular lenses (IOL) are also implanted routinely. These pseudophakic procedures have significantly reduced the numbers of patients developing glaucoma after cataract surgery. Implanting an IOL probably protects the anterior segment from some “chemical poison” originating in the posterior segment. (Levin AV. Aphakic glaucoma: a never-ending story? Br J Ophthalmol. 2007 Dec;91(12):1574-5. doi: 10.1136/bjo.2007.121020)

This scenario was not so common about 30 years back when intra-capsular cataract extraction (ICCE) was done in camp surgeries on a mass scale. Such patients were left aphakic and had higher prevalence of aphakic glaucoma. Even the later use of anterior chamber IOLs such as the Choyce Mark VIII did not significantly reduce the number of patients developing glaucoma. The advent of extra-capsular cataract extraction (ECCE) and phacoemulsification has decreased appreciably the incidence of this condition in adult populations. Aphakia increases the risk for suprachoroidal hemorrhage. 

VISUAL FIELD CONSIDERATIONS IN APHAKIA:

Assessment of the visual fields in aphakic glaucoma patients is difficult due to the refractive aberrations in these patients. Contact lenses, both soft and rigid types, can be used in these patients. These lenses reduce the chance of a "lens artifact" affecting the visual field report. Conversely, they increase the total field size visible to the patient, have better blind spot size and plotting and less distortion secondary to prismatic effects.

PEDIATRIC APHAKIC GLAUCOMA:

Currently pediatric cataract surgery is usually associated with aphakic glaucoma. In pediatric patients the posterior capsule is partially or completely removed. This is so since primary posterior capsulotomy is often done in pediatric patients, or the entire lens with its capsules removed in lensectomy procedures. These aphakic children are at increased risk of developing aphakic glaucoma.

Aphakic or pseudophakic glaucoma is the 2nd most common type of childhood glaucoma (after primary congenital glaucoma). The prevalence of pediatric aphakic glaucoma ranges from 4-to-41%.

The factors associated with increased risk of glaucoma following cataract surgery includes surgery in the first year of life, microphthalmia and coexistence of persistence of fetal vasculature.

Scheie and Ewing have defined “early” aphakic glaucoma as that occurring within the first 6 postoperative weeks and “late” aphakic glaucoma as occurring at any later time. (Scheie HG, Ewing MQ. Aphakic glaucoma. Transactions of the Ophthalmological Societies of the United Kingdom. 1978 Apr;98(1):111-117. PMID: 373170.)

The number of patients developing aphakic glaucoma ranges widely, depending upon the time period of the study.

A study to evaluate glaucoma related adverse events in the Infant Aphakia Treatment Study found 9% of 114 patients developing aphakic glaucoma, while 4% were glaucoma suspects. (Beck AD, Freedman SF, Lynn MJ, et al. Glaucoma-Related Adverse Events in the Infant Aphakia Treatment Study: 1-Year Results. Arch Ophthalmol. 2012;130(3):300–305). 

But, a study from Ireland reported 33% patients operated for congenital cataract developing glaucoma in the first year of follow-up. (Kirwan C, Lanigan B, O'Keefe M. Glaucoma in aphakic and pseudophakic eyes following surgery for congenital cataract in the first year of life. Acta Ophthalmol. 2010 Feb;88(1):53-9).

A study by Agarwal et al (1981) from India reported 26.7% eyes developing aphakic glaucoma. Kessing and Rasmussen (1977) had found 1.8% eyes undergoing “microsurgery for senile cataract” developing aphakic glaucoma.

The incidence of aphakic glaucoma increases with the duration of follow-up. It can occur weeks to years after surgery.

A number of factors have been identified with the development of aphakic glaucoma in pediatric patients. These include:

Onset and mechanism of glaucoma= The onset of glaucoma often shows a bimodal pattern of distribution. Aphakic glaucoma with an angle-closure mechanism frequently occurs within the first few months after surgery and open-angle glaucoma has a later onset (average 7.4 years). The longer the patients are followed after cataract surgery, the longer the time for onset of open-angle glaucoma. Children who have undergone cataract surgery have a continuing risk to develop glaucoma throughout their lives.

Timing and role of cataract surgery in glaucoma development= Cataract surgery within the first year of life has been identified as a risk factor for glaucoma. Early extraction of congenital cataracts is considered to be important to achieve good visual and functional results. However, early surgery increases the risk for glaucoma. Vishwanath et al (Vishwanath M, Cheong-Leen R, Taylor D, Russel-Eggit I, Rahi J . Is early surgery for congenital cataract a risk factor for glaucoma? Br J Opthalmol 2004; 88: 905–910) and also Koc (Koc, F., Kargi, S., Biglan, A. et al. The aetiology in paediatric aphakic glaucoma. Eye 20, 1360–1365 (2006)) have recommended delaying cataract surgery until the infant is 4 weeks old in bilateral cases, for a full-term child.

Microcornea= The prevalence of microcornea among aphakic glaucoma patients is as high as 88.5% to 94%. Smaller eyes and eyes with reduced corneal diameter have a predisposition for angle closure. Koc et al found abnormally thick corneas in a number of their patients. This could account for the misleadingly high IOP in some patients. Microphthalmia is a significant risk factor for aphakic glaucoma (Bruce Shields).

Possible mechanisms for delayed-onset open-angle glaucoma= The surgical removal of it early in life can alter normal development of the filtration angle. Studies have found that there is a relative arrest in the normal development of the filtration angle and the trabecular meshwork in the eyes of aphakic children. (Levin AV)

Barotrauma to the immature angle= In support of this theory is the higher frequency of aphakic glaucoma in children who have their surgery at younger ages. Arguing against this theory is the seemingly equal rate of aphakic glaucoma following pars plana lensectomy.

Goniodysgenesis= Some eyes with aphakic glaucoma have an angle appearance which resembles the angle seen in congenital/infantile glaucoma. Such eyes may even respond to goniotomy. This suggests that these eyes seem to have multiple isolated pathologies such as cataract and glaucoma.

Role of the vitreous= In aphakic patients there is often vitreous disturbance and it enters the angle. It is speculated that the exposure of the angle to vitreous causes permanent changes there, affecting aqueous outflow.

Chemical factors= Rupture of the posterior capsule exposes the anterior segment to certain chemicals which could cause changes in the aqueous outflow pathways. Certain vitreous excitatory amino acids and other factors have been speculated, but there needs to be more research done in this area.

Genetic factors= Aphakic glaucoma in children has been found to have familial tendency. It is often bilateral too, raising the possibility of genetic factors responsible for this condition. Many genes are known to be involved in both cataract and glaucoma, PAX6 being perhaps a paradigm. The complex interaction of gene mutations and polymorphisms continues to be unravelled.

MANAGEMENT OF APHAKIC GLAUCOMA

Aphakic glaucoma is a challenging condition to manage. Depending upon the severity of the condition, it has been managed by medical, laser, surgical and other modalities. Open-angle glaucoma can be attempted by conservative means but angle-closure glaucoma or glaucoma associated with angle anomalies needs surgical intervention.

Medically a number of medications such as miotics, phenylephrine and atropine eyedrops (Agarwal H C, Sood N N, Dayal Y. Aphakic glaucoma. Indian J Ophthalmol 1981;29:221-5.) The advent of newer anti-glaucoma agents has widened our armamentarium to manage aphakic glaucoma.

Laser procedures mentioned in the literature include Argon Laser Trabeculoplasty (ALT) (Agarwal and Sood) and Argon laser photocoagulation of ciliary processes (Lee P. Argon Laser Photocoagulation of the Ciliary Processes in Cases of Aphakic Glaucoma. Arch Ophthalmol. 1979;97(11):2135–2138. doi:10.1001/archopht.1979.01020020453008).

Surgical treatments include goniotomy, cyclodialysis, trabeculotomy and trabeculectomy. Angle procedures have been found to be successful in more than half the patients in one study (Bothun ED, Guo Y, Christiansen SP, Summers CG, Anderson JS, Wright MM, Kramarevsky NY, Lawrence MG. Outcome of angle surgery in children with aphakic glaucoma. J AAPOS. 2010 Jun;14(3):235-9. doi: 10.1016/j.jaapos.2010.01.005. Epub 2010 Mar 11. PMID: 20226703.).

Cyclocryotherapy has also been used for management of aphakic glaucoma. A study to evaluate the role of this modality was performed in 96 eyes of 96 patients of aphakic open-angle glaucoma (AO), aphakic angle-closure glaucoma (ACL). IOP was lowered to less than 21 mmHg in 76% of eyes with AO, 68% of eyes with ACL. Glaucomatous field loss was arrested in 71% of patients with AO and 65% of patients with ACL. (Caprioli J, Strang SL, Spaeth GL, Poryzees EH. Cyclocryotherapy in the treatment of advanced glaucoma. Ophthalmology. 1985 Jul;92(7):947-54. doi: 10.1016/s0161-6420(85)33951-9. PMID: 2410846.)

Perhaps the most commonly performed surgical intervention in aphakic glaucoma currently, is the Ahmed Valve Implantation (Kirwan C, O’Keefe M, Lanigan B & Mahmood U (2005): Ahmed valve drainage implant surgery in the management of pediatric aphakic glaucoma. Br J Ophthalmol 89: 855–858). The advantage of the pediatric sized Ahmed valve has made this technique a procedure of choice in the management of aphakic glaucoma in pediatric patients. In adults also aphakic glaucoma is often intractable and Ahmed Valve has been used with positive outcomes. (Wang, H., Chen, H., Qi, Y. et al. Surgical results of Ahmed valve implantation combined with intravitreal triamcinolone acetonide injection for preventing choroidal detachment. BMC Ophthalmol 15, 13 (2015))