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Glaucoma

Glaucoma Associated with Aniridia

Congenital aniridia is a rare disease with complete or partial absence of the iris. The prevalence is 1 in 64,000 to 96,000 people, and it was classified as a designated intractable disease in Japan in 20171).

The cause is loss-of-function mutations in the PAX6 gene on chromosome 11p13. PAX6 is a master control gene for eye development, and haploinsufficiency leads to the disease. Biallelic abnormalities are lethal in utero1). Inheritance is autosomal dominant in two-thirds of cases, and sporadic in one-third. 60–90% are bilateral, with a slight male predominance.

Glaucoma is considered an acquired complication of aniridia, occurring in 50–75% due to angle dysgenesis1). Onset in infancy is rare; it progressively develops after adolescence. The Japanese Glaucoma Guidelines (5th edition) classify it as “3-iii Aniridia” under secondary childhood glaucoma. Management follows the treatment principles of primary congenital glaucoma (PCG), but angle dysgenesis specific to aniridia requires special consideration in treatment strategy.

Aniridia is a pan-ocular disease accompanied by various ocular and systemic complications in addition to glaucoma, and frequently includes macular hypoplasia, aniridia-associated keratopathy (AAK), cataract, and nystagmus. In sporadic cases, deletion of the WT1 gene adjacent to the PAX6 gene can cause WAGR syndrome, requiring attention for Wilms tumor (nephroblastoma).

Q If diagnosed with aniridia, will I definitely develop glaucoma?
A

Glaucoma occurs in 50–75% of cases, but not all patients develop it. Onset in infancy is rare, and progressive intraocular pressure elevation often becomes apparent after adolescence, so lifelong regular intraocular pressure monitoring is important.

The main complaint in aniridia is often horizontal nystagmus observed from early infancy due to associated macular hypoplasia. Because the iris is absent, the amount of light entering the eye cannot be regulated, causing severe photophobia (glare). Poor fixation is also observed, and the condition is often detected relatively early in life.

Symptoms related to glaucoma are as follows:

  • Symptoms due to elevated intraocular pressure: Often progresses asymptomatically. Since open-angle type is common, subjective pain is rare.
  • Visual field defects and vision loss: In advanced cases, visual field narrowing or vision loss may be detected in adulthood.
  • Visual prognosis: Generally poor, often around 0.1. Macular hypoplasia is the major factor for vision loss.

Clinical Findings (Findings Confirmed by Physician Examination)

Section titled “Clinical Findings (Findings Confirmed by Physician Examination)”

Slit-lamp microscopy reveals varying degrees of iris dysplasia, from partial iris atrophy to complete iris absence1). In cases of severe absence, the lens equator and Zinn’s zonules may be visible.

Glaucoma-related findings:

  • Elevated intraocular pressure: High intraocular pressure exceeding 21 mmHg. Corneal thickness may differ from normal (tendency to thicken), making estimation of true intraocular pressure difficult.
  • Optic disc findings: Increased cup-to-disc ratio (C/D ratio), thinning of the rim. In infants, a C/D ratio of 0.3 or more raises suspicion of glaucoma.
  • Gonioscopic findings: Abnormalities of the iris root are observed. The iris stroma extends anteriorly over the trabecular meshwork, covering the angle as the disease progresses.
  • Corneal findings: Haab’s striae (breaks in Descemet’s membrane), corneal edema due to high intraocular pressure. In neonates, a corneal diameter of 11 mm or more is abnormal.

Main ocular complications:

Macular hypoplasia

Frequency: Occurs in nearly all cases.

Impact on visual prognosis: The most significant factor for reduced visual acuity. Presents with absence of the foveal pit and abnormal macular vascular pattern.

Corneal disease (AAK)

Frequency: Develops progressively.

Characteristics: Conjunctival tissue invades the cornea due to limbal stem cell deficiency. Leads to pannus formation and corneal opacity.

Cataract

Frequency: Occurs in about 80% of cases1).

Characteristics: Develops in 50–85% of patients by age 20. Surgery is challenging due to fragile zonules of Zinn.

Nystagmus

Frequency: Seen in all cases.

Characteristics: Mainly horizontal nystagmus. Often the chief complaint in early infancy. Affects visual development.

Association with long-term prognosis of glaucoma:

In a case series of 306 patients, no patient with glaucoma had visual acuity better than 20/60 (0.33)15). In another study of 30 patients, 10 (30%) had glaucoma, which was the main cause of vision loss. Among them, 2 patients (6%) became blind16). Visual field and optic nerve damage due to glaucoma is irreversible, and early detection and appropriate intraocular pressure management are directly linked to maintaining visual function.

Extraocular findings: WAGR syndrome (11p13 deletion syndrome) includes Wilms tumor, genitourinary abnormalities, and intellectual disability. PAX6 is also expressed in the central nervous system, pancreatic islets of Langerhans, and olfactory epithelium; associated conditions include agenesis of the corpus callosum, epilepsy, higher brain dysfunction, anosmia, and glucose intolerance1).

PAX6 is expressed from the early eye and is a master control gene for eye development, regulating various transcription factors. Abnormalities in PAX6 cause congenital anomalies throughout the eye (aniridia, Peters anomaly, macular hypoplasia, optic nerve hypoplasia, etc.).

The types of genetic mutations and associated diseases are shown below.

GeneChromosomeAssociated Disease
PAX611p13Aniridia, macular hypoplasia, Peters anomaly
WT111p13 (adjacent to PAX6)Wilms tumor
PITX24q25Axenfeld-Rieger syndrome type 1
FOXC16p25Axenfeld-Rieger syndrome type 3

PAX6 mutations are often premature truncated codon (PTC) types such as nonsense and frameshift, and missense mutations have also been reported1). Sequencing detects some mutation in nearly 85% of isolated aniridia cases2).

In a large registry study, genetic diagnosis was obtained in 56.5% of glaucoma associated with non-acquired ocular developmental anomalies, and PAX6 is shown to be one of the major causative genes10).

PAX6 and WT1 (the causative gene for Wilms tumor) are adjacent on 11p13, and chromosomal deletions that delete both result in aniridia complicated by Wilms tumor (WAGR syndrome: Wilms tumor, Aniridia, Genitourinary abnormalities, mental Retardation).

  • About one-third of aniridia cases are part of WAGR syndrome2)
  • About 30% of sporadic cases develop Wilms tumor by age 5
  • 1.4% of Wilms tumor patients have congenital aniridia
  • Degree of angle dysgenesis: The more the iris stroma extends anteriorly onto the trabecular meshwork, the higher the risk
  • Age: Progressively develops after adolescence with growth. Intraocular pressure monitoring from childhood is essential.
  • History of cataract surgery: There is a risk of increased intraocular pressure or worsening of glaucoma after surgery2).
Q If WAGR syndrome is suspected, what tests should be performed?
A

Chromosomal microarray (CMA) or FISH testing is recommended to detect deletions in the 11p13 region including PAX6 and the adjacent WT1 gene. If a WT1 gene deletion is confirmed, the risk of Wilms tumor is high, so regular abdominal ultrasound examinations until age 6 are necessary. Testing should be performed under genetic counseling2).

Clinical diagnosis is easy by confirming iris defects with slit-lamp microscopy. The diagnostic criteria established by the Ministry of Health, Labour and Welfare research group are classified into the following categories1):

  • Definite: A symptoms (either binocular visual impairment or photophobia) + B1 (iris dysplasia) + E (PAX6 gene mutation or 11p13 deletion) + C (exclusion of differential diagnoses)
  • Probable: (1) A + B1 + F (family history), (2) A + B1 + B2 (foveal hypoplasia), or (3) A + B1 + B3 (keratopathy), with C excluded.
  • Possible: A + B1 met, but C cannot be completely excluded.

Severity classification is based on corrected visual acuity and visual field constriction1).

SeverityCriteria
Grade IUnilateral involvement, fellow eye normal
Grade IIBilateral involvement, best corrected visual acuity in the better eye ≥ 0.3
Grade IIIBilateral involvement, best corrected visual acuity in the better eye ≥ 0.1 and < 0.3
Grade IVBilateral involvement, best corrected visual acuity in the better eye < 0.1

If grades I–III are accompanied by visual field constriction due to secondary glaucoma, the severity shifts up one grade1). Grade III or higher qualifies for medical expense subsidies for designated intractable diseases.

The diagnostic criteria for childhood glaucoma are as follows: glaucoma is diagnosed when two or more of the following items are met.

  • Intraocular pressure > 21 mmHg (including under general anesthesia)
  • Progression of cup-to-disc ratio increase, asymmetry ≥ 0.2 between eyes, rim thinning
  • Corneal findings: Haab striae, corneal diameter ≥ 11 mm in newborns, ≥ 12 mm in infants under 1 year
  • Progression of myopia due to axial elongation
  • Reproducibility of glaucomatous visual field defects

In aniridia, corneal thickness may differ from normal (tendency to thicken, thinning in aphakic eyes), and caution is needed when interpreting intraocular pressure values. There is no interchangeability between different tonometers.

  • Gonioscopy and ultrasound biomicroscopy (UBM): Assessment of the extent of residual iris tissue and angle abnormalities. Also useful for confirming anterior displacement of the ciliary body6)
  • OCT (optical coherence tomography): Evaluates glaucomatous thinning of the retinal nerve fiber layer. Macular OCT can also determine the degree of macular hypoplasia.
  • Visual field testing: Dynamic perimetry is used because it is difficult in children under 5 years of age. Perform regularly once the patient is old enough for accurate visual field assessment.
  • Refraction and axial length measurement: Progression of myopia and axial elongation are findings suggestive of glaucoma progression.
  • Abdominal ultrasound: Screening for Wilms tumor. In sporadic cases, perform regularly until 6 years of age.
  • Genetic testing: Detect mutations by PAX6 sequencing, MLPA, and CMA. Important for confirming WAGR syndrome2)

Diseases that may be confused with aniridia are listed below1). These are disease groups that should be excluded as criterion C (differential diagnosis) of the diagnostic criteria.

  • Iris coloboma: Iris defect due to incomplete closure of the optic fissure, typically localized inferiorly. May be accompanied by choroidal coloboma. It is distinguished from aniridia by the diffuse iris defect in aniridia.
  • Axenfeld-Rieger anomaly: Characterized by iris adhesion to the posterior embryotoxon (anterior displacement and thickening of Schwalbe’s line), often with corectopia. Caused by PITX2/FOXC1 mutations, not PAX6 mutations.
  • Traumatic or postoperative iris defect: Can be differentiated by history of trauma or surgery.
  • Iris atrophy due to prior herpesvirus infection: Often unilateral; check for history of infection and decreased corneal sensation. Iris atrophy due to herpes zoster or herpes simplex is often segmental.
  • Iridocorneal endothelial (ICE) syndrome: Unilateral iris atrophy common in adult women. Progressive corneal endothelial abnormality leads to iris deformation and adhesion.

Treatment for high intraocular pressure and glaucoma in aniridia is strongly recommended (evidence strength C)2). Treatment is considered stepwise in the following order.

① Medication Therapy

First step: Intraocular pressure reduction using eye drops or oral medication.

Medications used: Beta-blockers, carbonic anhydrase inhibitors (CAIs), prostaglandin analogs.

② Outflow Reconstruction Surgery

Second step: When medication therapy is insufficient.

Procedures: Goniotomy, trabeculotomy. Indication depends on the degree of angle dysgenesis.

③ Filtration Surgery / Tube

Third step: When outflow reconstruction is difficult or ineffective.

Procedures: Trabeculectomy, long tube surgery (Ahmed/Baerveldt).

④ Cyclophotocoagulation

Last resort: When all other treatments are ineffective.

Caution: High risk of phthisis bulbi (loss of eye function); ciliary body hypoplasia has been reported in aniridia.

Intraocular pressure (IOP) control with eye drops or oral medication is the first-line treatment. A long-term observational study of 60 cases reported that 31 developed glaucoma, and in 12 of these, IOP was managed with medication alone3).

The main medications used are as follows:

  • Beta-blockers (e.g., timolol): Caution for bradycardia and bronchospasm in children. Start with a low concentration.
  • Carbonic anhydrase inhibitors (CAI): Topical eye drops (dorzolamide, brinzolamide) or systemic administration (oral acetazolamide).
  • Prostaglandin analogs (e.g., latanoprost): Effective, but may be less effective in children compared to adults.
  • Alpha-2 adrenergic agonists (brimonidine): Contraindicated in children under 2 years of age. Risk of serious neuropsychiatric symptoms such as coma2)7).

In cases with corneal epithelial stem cell deficiency (AAK) or when worsening of AAK is a concern, consider using preservative-free formulations7).

Outflow Reconstruction Surgery (Goniotomy/Trabeculotomy)

Section titled “Outflow Reconstruction Surgery (Goniotomy/Trabeculotomy)”

Goniotomy has been reported effective for controlling high IOP and glaucoma4), and outflow reconstruction surgery can be recommended as an initial procedure2). Trabeculotomy has also been reported effective as an initial surgery5). However, note the following:

  • In cases where residual iris tissue covers the trabecular meshwork, trabeculotomy may be ineffective.
  • Due to the absence of iris tissue, there is a risk of damaging the zonules of Zinn during trabeculotomy, which may affect lens development.
  • The degree of angle abnormality in aniridia varies greatly among individuals; surgical indication should be based on detailed angle evaluation using gonioscopy and UBM6).

This is selected when outflow reconstruction is difficult or unsuccessful. There are reports of achieving intraocular pressure control11), but the following issues exist.

  • Outcomes are generally poor in children, with postoperative phthisis bulbi reported in about 1/4 of cases8)
  • There are reports of malignant glaucoma occurring after surgery
  • The use of antimetabolites (e.g., mitomycin C) should be carefully considered due to the risk of worsening AAK

Long-tube surgery (glaucoma implant surgery)

Section titled “Long-tube surgery (glaucoma implant surgery)”

Baerveldt glaucoma implant and Ahmed glaucoma implant are available. This is selected when trabeculectomy is ineffective or when filtration surgery is expected to have poor outcomes due to angle pathology2).

A meta-analysis of Ahmed and Baerveldt implants for pediatric glaucoma (32 studies, 1,221 eyes) showed a decrease in mean preoperative IOP from 31.8 mmHg to 16.5 mmHg (95% CI: 15.5–17.6) at 12 months. Success rates were 87% (95% CI: 0.83–0.91) at 12 months and 77% (95% CI: 0.71–0.83) at 24 months, but declined to 37% (95% CI: 0.32–0.42) at 120 months in the long term9).

Arroyave et al. (2003) summarized the use of GDD for glaucoma associated with aniridia and reported a certain degree of IOP-lowering effect14). Recent reviews also indicate that glaucoma drainage devices are a major option when outflow reconstruction or filtration surgery is insufficient13). In Japan, there are case reports of effective Baerveldt implant use12). In aniridic eyes, due to the absence of the iris, it is recommended to insert the tube tip tangentially rather than toward the center of the cornea7). In phakic eyes, attention must be paid not only to the corneal endothelium but also to contact with the lens.

This is a last resort when all surgical treatments are ineffective2).

  • Cyclocryotherapy leads to phthisis bulbi in many cases, and cataract development is frequent, making postoperative visual function maintenance difficult
  • In aniridia, ciliary body hypoplasia has been confirmed by UBM6), and the risk of phthisis bulbi is higher compared to healthy eyes8)
  • Select only when the utility is high despite the risk of complications such as phthisis bulbi that lead to poor visual prognosis
  • Photophobia: Tinted glasses and artificial iris soft contact lenses (SCL) are recommended (CQ6: strong recommendation)2)
  • Low vision care: Based on refractive correction, recommend visual aids such as magnifiers, low-vision glasses, and magnifying reading devices (CQ5: Strong recommendation)2). Educational support through enlarged textbooks and consultation with schools for the visually impaired is also important.
  • Cataract surgery: Cataracts develop in 50–85% of patients by age 20. The risk of intraoperative complications is high due to fragile zonules of Zinn. Postoperative worsening of glaucoma and anterior fibrosis syndrome also require attention (CQ3: Weak recommendation)2).
  • Corneal stromal opacity: Full-thickness corneal transplantation has a high rate of rejection, and long-term visual prognosis is often poor due to glaucoma and graft failure (CQ1: Weak recommendation against performing)2). However, for severe corneal stromal opacity, corneal transplantation combined with limbal transplantation or Boston keratoprosthesis may be considered.

Long-term intraocular pressure management and follow-up

Section titled “Long-term intraocular pressure management and follow-up”

In the management of glaucoma associated with aniridia, lifelong regular intraocular pressure monitoring is essential. Follow-up should be performed with attention to the following points.

  • Childhood: In infants, note that even eye drops may result in a relatively high dose compared to body weight and surface area; use the lowest concentration possible. Intraocular pressure measurement under general anesthesia may be necessary.
  • School age to adolescence: This is a period when glaucoma tends to become progressively apparent. Once visual field testing becomes possible, regularly assess for glaucomatous visual field defects.
  • After surgery: Meta-analysis of tube shunt surgery shows a success rate of 87% at 12 months, decreasing to 37% at 120 months9), so the need for additional surgery in the long term should be kept in mind.
  • Multidisciplinary collaboration: Collaboration with pediatrics (Wilms tumor screening), genetics (genetic counseling), and educational support (low-vision classes, schools for the visually impaired) is important. Many patients can attend regular classes but require support such as enlarged textbooks.
Q If glaucoma surgery becomes necessary, which surgical procedure is chosen?
A

First, medication therapy is attempted; if insufficient, outflow reconstruction surgeries such as goniotomy or trabeculotomy are considered. If these are difficult or ineffective, trabeculectomy is performed, followed by long-tube surgery (Ahmed or Baerveldt implant). Only when intraocular pressure control cannot be achieved with any treatment is cyclophotocoagulation considered as a last resort 2).

Q Can glaucoma eye drops worsen the cornea?
A

Aniridia may be complicated by aniridia-associated keratopathy (AAK). Long-term use of eye drops containing preservatives (such as benzalkonium chloride) can worsen corneal epithelial damage, so the use of preservative-free formulations is recommended 7).

6. Pathophysiology and Detailed Pathogenesis

Section titled “6. Pathophysiology and Detailed Pathogenesis”

PAX6 encodes a transcription factor that regulates gene expression and is a master control gene expressed from the early eye. It is involved in optic cup formation, lens differentiation, and development of the corneal epithelium and retina. PAX6 haploinsufficiency affects not only the iris but also the macula, corneal limbal stem cells, optic nerve, and the entire eye.

PAX6 is also expressed in the central nervous system, pancreatic islets of Langerhans, and olfactory epithelium, and hypoplasia of these tissues leads to various extraocular complications 1).

Angle Dysgenesis and Pathogenesis of Glaucoma

Section titled “Angle Dysgenesis and Pathogenesis of Glaucoma”

Pathologically, smooth muscle is absent except for the iris root, and angle development is incomplete. The pathogenesis of glaucoma progresses stepwise as follows 3):

  1. Congenital angle dysgenesis due to PAX6 mutation
  2. Remaining iris stroma (iris root tissue) extends anteriorly over the trabecular meshwork
  3. Gradually covers the trabecular meshwork, obstructing aqueous outflow
  4. Elevated intraocular pressure → glaucomatous optic neuropathy

This progressive angle change was reported by Grant and Walton in 1974 3), and in recent years has been confirmed by UBM as anterior displacement of the ciliary body 6). Depending on the degree of angle dysgenesis, both open-angle and closed-angle types can occur.

Pathology of Aniridia-Associated Keratopathy (AAK)

Section titled “Pathology of Aniridia-Associated Keratopathy (AAK)”

PAX6 mutations also affect corneal limbal stem cells, leading to dysfunction of corneal epithelial stem cells.

  • Dysfunction of corneal epithelial stromal cells → Bowman’s layer abnormality
  • Formation of vascularized pannus (invasion of conjunctival tissue into the cornea)
  • Progressive corneal opacity → decreased vision

AAK often develops and progresses with growth even if normal in early childhood1). There are two types of keratopathy: congenital central corneal opacity (CCO) and AAK, and it has been reported that the rate of glaucoma complication is higher in cases with CCO than in those with AAK16). Antimetabolites and preservative-containing eye drops used for glaucoma treatment carry a risk of worsening AAK, affecting the choice of treatment strategy. Since corneal and glaucoma management interact with each other, an integrated evaluation of both is required.

As an anatomical finding specific to aniridia, hypoplasia of the ciliary body has been reported on UBM6). This finding increases the risk of eyeball perforation during cyclophotocoagulation and also suggests that the amount of aqueous humor produced by the ciliary body may be less than normal.


7. Latest research and future perspectives (reports under investigation)

Section titled “7. Latest research and future perspectives (reports under investigation)”

Chen and Walton (1999) reported that based on the natural course of progressive angle changes in aniridia, prophylactic goniotomy performed before the onset of ocular hypertension or glaucoma may prevent the development of glaucoma4). However, this is a descriptive study without a control group, and the evidence is limited2).

Future prospective studies are awaited regarding the effectiveness of prophylactic surgical intervention.

Corneal reconstruction using stem cell transplantation

Section titled “Corneal reconstruction using stem cell transplantation”

For the treatment of limbal stem cell deficiency (LSCD), allogeneic limbal transplantation and cultured oral mucosal epithelial transplantation are being considered. Clinical practice guidelines weakly recommend surgical treatment, and it is reported that ocular surface reconstruction can be achieved with a certain probability 2). In cases complicated by corneal stromal opacity, combined corneal transplantation may be useful.

Large-scale registry studies are revealing the genetic profile of childhood and early-onset glaucoma 10). Correlation analysis between PAX6 mutation types (e.g., PTC type, missense type) and glaucoma risk/severity is expected to lead to personalized medicine based on risk stratification.


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