Is the tono-pen accurate for measuring intraocular pressure in young children with congenital glaucoma?

PURPOSE: We sought to compare intraocular pressure (IOP) measurements by Perkins tonometer and Tono-Pen in young children with primary congenital glaucoma (PCG). METHODS: This was a retrospective comparative case series. We reviewed the clinical records of all children with primary congenital glaucoma who underwent examinations under general anesthesia at Soroka University Medical Center between January 1999 and July 2002. Our main outcome measures were IOP with Perkins hand-held tonometer and Tono-Pen tonometer. RESULTS: A total of 28 eyes of 16 children were examined under general anesthesia. The mean IOP was 18 +/- 6 mm Hg with the Perkins tonometer and 22 +/- 8 mm Hg with the Tono-Pen. In 18 eyes, IOP was less than 21 mm Hg with the Perkins tonometer; these eyes had already undergone surgical procedures. The other 10 eyes with IOP greater than 21 mm Hg with the Perkins tonometer underwent surgery at the end of the examination under anesthesia. In eyes with IOP greater than 16 mm Hg (Group A, n = 18), a significant difference (P < 0.001) was found between the Perkins and Tono-Pen measurements, even although the values were strongly correlated (r = 0.60). In contrast, in eyes with IOP less than 16 mm Hg (Group B, n = 10) no statistically significant difference (P = 0.28) and good correlation (r = 0.78) were obtained. A difference of 5.8 +/- 3.8 mm Hg and 0.6 +/- 1.7 mm Hg between Perkins and Tono-Pen readings, respectively, was found in Groups A and B. CONCLUSIONS: Tono-Pen readings disagree with Perkins tonometer measurements for measuring IOP in children with PCG who present with IOP greater than 16 mm Hg and tends to overestimate IOP. A further study with a similar population is necessary to confirm these results.

[Primary congenital glaucoma].

Primary congenital glaucoma (PCG) is a rare genetic disease usually diagnosed during the first year of life. It occurs because of developmental anomalies of the chamber angle that prevents drainage of aqueous humor, thereby elevating intraocular pressure. Its incidence is 1 in 10,000 live newborns in Western societies and 1 in 1,200 live newborns in the Arab-Bedouin population of the Negev region in Israel. Most cases of PCG appear to be sporadic. The cytochrome P4501B1 gene located within the GLC3A locus on chromosome 2p21 is mutated in individuals with PCG. The triad of epiphora, photophobia, and blepharospasm is classical for PCG. General anesthesia is usually required for an adequate examination of intraocular pressure, corneal diameter, optic disc, and axial length in young children. Congenital glaucoma is almost always managed surgically, with medical therapy being used only as a temporizing measure before surgery or when surgical intervention has repeatedly failed. At least 50% of eyes with PCG presenting at birth will become legally blind (visual acuity < 6/60). Patients with PCG require follow-up examinations throughout their lives.

High postdialysis urea rebound can predict intradialytic increase in intraocular pressure in dialysis patients with lowered intradialytic hemoconcentration.

BACKGROUND: Intradialytic (ID) decrease in intraocular pressure (IOP) parallel to ultrafiltration-induced hemoconcentration has been recently reported. However, exacerbation of glaucoma in hemodialysis (HD) patients during HD sessions is occasionally observed. Postdialysis urea rebound (PDUR) is induced by the lag in urea removal from the cells to urea removal from the extracellular fluid, which when increased can result in ID drag of water to intracellular compartment. It is our hypothesis that similar lag in urea removal from ocular compartments may also be reflected by PDUR, and may induce drag of water into ocular compartments counteracting the effect of hemoconcentration. Our assumption was, therefore, that PDUR might predict ID increase in IOP. METHODS: IOP, serum urea and hematocrit levels were measured at the start, end and 1 h postdialysis, in 19 chronic HD patients with normal IOP. RESULTS: PDUR was positively correlated with mean (both eyes) ID changes in IOP (MIDIOP) (r = 0.5, p = 0.03) and % MIDIOP (r = 0.55, p = 0.02). ID increase in IOP was observed only in the 7 patients with relatively higher PDUR (> or = 9 mg%), who had also a relatively lower % ID change in Hct (<8%). MIDIOP was negatively correlated with % ID changes in Hct (r = -0.65, p = 0.03) in the 12 patients with PDUR > or = 9 mg, and positively correlated with PDUR (r = 0.57, p = 0.03) in the 14 patients with % ID change in Hct <8%. CONCLUSION: High PDUR may predict susceptibility to ID increase in IOP in patients with lowered ID hemoconcentration.