A study recently published in International Ophthalmology evaluated the ocular effects of methylphenidate used in children and adolescents diagnosed with attention-deficit hyperactivity disorder (ADHD).
Give me some background.
ADHD is a neurodevelopmental disorder most frequently identified in childhood and characterized by:
- Age-inappropriate inattention
- Impulsivity
- Hyperactivity symptoms
As a pharmacologic therapy for ADHD, methylphenidate group drugs have been shown to reduce clinical symptoms of inattention and hyperactivity in 70% of children with ADHD.
- How: Increasing dopamine levels by blocking the reuptake to presynaptic neurons of dopamine in the prefrontal cortex and striatum.
In addition: Previous animal models have demonstrated that methylphenidate, which can affect dopamine and catecholamine levels, may cause pathological changes in retinal and corneal tissues.
Let’s get to the study.
In this prospective study, investigators categorized children diagnosed with ADHD and health controls into three groups:
- Group 1:
- 30 children (mean age: 10.53) with ADHD receiving methylphenidate therapy for at least 1 year
- Group 2:
- 32 children (mean age: 9.21) newly diagnosed with ADHD not using methylphenidate
- Group 3 (control group):
- 35 healthy children (mean age: 11.03)
And what was evaluated across these groups?
Key parameters of ocular health, including:
- Morphology and number of corneal endothelial cells (CECs)
- Corneal thickness
- Choroidal thickness (CT)
- Retinal thickness (RT)
- Ganglion cell layer (GCL)
- Retinal nerve fiber layer (RNFL)
Findings?
No statistically significant differences were observed between the three groups in terms of (p > 0.05):
- Age
- Visual acuity (VA)
- Refraction values
However: Significant differences were reported in endothelial cell counts and hexagonality values between Groups 1 and 2 (p = 0.041 and p = 0.031, respectively):
- Group 1:
- Endothelial cell density: 2981.13
- Percentage of hexagonal cells: 71.00%
- Group 2:
- Endothelial cell density: 3118.78
- Percentage of hexagonal cells: 67.12%
Note: Hexagonality refers to the variability in hexagonal CEC shape over time. In a normal health cornea, 70-80% of CECs have a hexagonal shape.
Tell me more.
There were no significant changes among the three groups in terms of (p > 0.05):
- Central CT
- Central RT
- Mean RNFL values
GCL values were higher in Groups 1 and 3 than Group 2, with Group 1 having the highest measurement (p = 0.0001 and p = 0.02, respectively):
- Group 1:
- GCL value: 97.14μm
- Group 2:
- GCL value: 85.73μm
- Group 3:
- GCL value: 93.30μm
Note: The difference in GCL value between Groups 1 and 3 was not significant (p = 0.551).
Expert opinion?
In accordance with previous studies, patients with ADHD who received methylphenidate—compared to untreated and newly diagnosed patients—had higher GCL values.
“The underlying mechanism is hypothesized to be attributed to the neurodevelopmental effects of the drug,” the study authors explained.
Limitations?
These included:
- The small number of patients
- Different gender distribution between the groups
- A lack of pre-drug data in patients taking methylphenidate
- Pre- and post-treatment follow-up may have yielded more reliable information concerning the positive and adverse effects of methylphenidate by permitting more accurate evaluation of changes in RNFL, GCL, and CEC counts
Take home.
These findings indicate that CEC counts were lower in children diagnosed with ADHD receiving methylphenidate therapy than those not receiving treatment and health controls.
Further: GCL measurements were lower in the children diagnosed with ADHD and not using medication compared to those using methylphenidate and the control group.