Some aspects of the mechanics of accommodation

A minimal model for the mechanics of accommodation is presented. The main components of the model are ciliary muscle, zonular system, elastic lens, and elastic choroid. Using estimates for physical properties of as many of the components as possible, the model can be made consistent with most available evidence. One exception is that ciliary muscle is required to be stronger than suggested in earlier physiological work.     

Biological and physical aspects of intraocular pressure

A thorough understanding of intraocular pressure homeostasis is the biological foundation for the development of new strategies to treat patients with elevated intraocular pressure or glaucoma. However, investigations on the physiology of intraocular pressure homeostasis are also important to gain more comprehensive insights into the pathogenesis of glaucoma and other diseases with associated alterations of intraocular pressure. The present review intends to give alternative insights into the biological and physical aspects of intraocular pressure regulation. The pressure-volume as well as the hydraulic model of intraocular pressure and also the relationship between ciliary blood flow and aqueous humor production, which has moved into the centre of interest because of its possible clinical relevance for glaucoma patients, will be explained. The authors Have attempted to interrelate the different aspects of intraocular pressure genesis and regulation in a comprehensive but understandable way.     

The intraocular pressure: clinical aspects.

Only a few conclusions can be mentioned: The IO pressure of the normal eye is not fixed, but shows spontaneous variations of pulsatory, respiratory, vasomotoric and diurnal type. The highest and lowest point of a 1 minute tracing can differ for 8 mm Hg. Very short acting tonometers are, therefore, less reliable than those with slower reactions, which will average some of the quicker oscillations. Normal limits of diurnal variations are 5 mm Hg with peaks below 25 mm Hg and differences between right and left eye of less than 4 mm Hg. The range of pressure of an eye is more important than a definite value which is true for the moment only. Factors which influence the IO pressure in healthy subjects are discussed in detail, such as age, sex, eye muscles, sports, muscular spasmus, child birth, position of the body, real or simulated tonometry, and mental stress. Difficulties in tonometry are discussed. In applananation tonometry, +/- 2.5 mm Hg must be accepted as the possible error of clinical results. This is not caused by any lack in the construction of the instrument, but by the combination of interobserver variation in reading the instrument, spontaneous pressure changea and an individually different decrease of pressure in consequence of repeated measurements. It is concluded that the rigidity of the living eye cannot be measured with a satisfactory degree of exactness. For the clinical purpose of early diagnosis, the diurnal tension curve combined with the tonography test of the author are the best methods. Early normalization of intraocular pressure is the safest means to prevent damage of the optic nerve. In spite of the individual variations of pressure and the inaccuracies of any single tonometry, the present methods of tonometry are clinically sufficient to form an opinion about the diagnosis and also about the success of our treatment, the aim of which is to normalize the pressure through the 24 hours below 20 mm Hg.     

Thyrotropin releasing hormone increases intraocular pressure. Mechanism of action

Intravenous injections of 1-100 micrograms thyrotropin releasing hormone (TRH) in rabbits elevated intraocular pressure (IOP). The 2-5 mm Hg increase of IOP lasted for less than 2 hr. No change of pupil size was observed. This IOP elevation was not due to a direct effect of TRH on ocular tissues since intravitreal injections of 0.1 and 1 micrograms TRH did not change IOP. Concentrations of thyroid stimulating hormone (TSH), triiodothyronine (T-3), epinephrine (Epi) and norepinephrine (NE) in the plasma were elevated at 30 min after an i.v. injection of 10 micrograms TRH. Plasma levels of prolactin and thyroxine were not changed. Bolus i.v. injections of 0.1-1 micrograms TSH and 0.1-1 micrograms T-3, which would produce an equivalent increase of relevant hormones in the circulation, did not increase IOP. However, similar i.v. injections of 10-100 ng Epi and 100 ng NE caused a 1.5-3 mm Hg IOP elevation for 15-30 min. Thus, the IOP elevation following TRH administration probably is caused by the increase of circulating endogenous catecholamines and not by the stimulation of the TSH-thyroid hormone axis. Heart rate, but not blood pressure, was increased with 10 micrograms TRH. After unilateral transection of the cervical sympathetic trunk, the IOP elevation in the decentralized eye was larger than that in the intact eye. Topical treatment of 0.1% or 1% timolol in the decentralized eye inhibited the IOP elevations in both eyes, but 0.1% prazosin was not effective. Topical 1% atropine and atropine given subcutaneously at 0.6 mg/kg decreased the bilateral IOP elevations. These observations indicate that beta-adrenergic and muscarinic mechanisms, not an alpha-1-adrenergic mechanism, are involved.     

葛根素滴眼液降眼压作用及其在眼房水中的药物浓度

目的观察葛根素滴眼液对家兔高眼压模型的作用和测定房水中葛根素药物浓度。方法兔眼球结膜注射地塞米松形成慢性高眼压模型,兔耳缘静脉注射葡萄糖形成急性高眼压模型,先后滴用10g·L1葛根素滴眼液,观察其降低或抑制高眼压作用;兔眼滴用葛根素滴眼液后。定时抽取房水．用反相高效液相色谱法测定房水中药物浓度。结果10g·L1葛根素滴眼液能降低慢性高眼压兔的眼压;能抑制急性眼压升高;药物滴入兔眼后．能被眼组织吸收进入房水,其高峰浓度（Cmax）为0.963mg·L-1,高峰时间（tmax）为2．0h,半衰期（t1/2β）为8．32h。结论10g·L1葛根素滴眼液通过滴眼用药．能降低地噻米松引起兔眼高压,并能抑制由快速注射葡萄糖引起的眼压升高;药物能被吸收进入房水中．半衰期为8．32h,为该药临床应用提供了依据。     

Single intraocular pressure measurements and diurnal intraocular pressure profiles

PURPOSE: To evaluate the probability of a single intraocular pressure measurement to be the highest measurement within a diurnal intraocular pressure profile. DESIGN: Hospital-based clinical, observational study. METHODS: The study included 3,025 day-and-night intraocular pressure profiles measured on 1,072 eyes of 547 Caucasian glaucoma patients or glaucoma suspects. Applanation tonometry was performed at 7 am, noon, 5 pm, 9 pm, and midnight. RESULTS: Intraocular pressure measurements were highest at 7 am, noon, 5 pm, 9 pm, and midnight, respectively, in 20.4%, 17.8%, 21.3% 13.9%, and 26.7% of the profiles, respectively. The measurement taken at 7 am was significantly (P < .001) closest to the maximal value of the profile. CONCLUSIONS: Any single intraocular pressure measurement taken between 7 am and 9 pm has a higher than 75% chance to miss the highest point of a diurnal curve. Intraocular pressure may be measured at different times of the day to have the best chance of observing the maximal value.     

The duration of action of pilocarpine Ocusert on intraocular pressure in man.

A study of the duration of intraocular pressure reduction of Ocusert P 20 and P 40 revealed that both agents were active in this regard at the end of a week. The side effects of this new mode of medication were less than with conventional Pilocarpine drops.     

Intravitreal human chorionic gonadotropin decreases intraocular pressure in rabbits: mechanism of action

Intravitreal injection of purified human chorionic gonadotropin (hCG) in rabbits decreased intraocular pressure (IOP). A dose-dependent decrease in IOP was observed with intravitreal hCG concentrations at 30 nM and 100 nM. The onset of this effect was later than 10 hr following the injection and it lasted for more than 24 hrs. The purified beta-subunit of hCG caused a similar decrease in IOP with a short duration. The threshold intravitreal concentration was 10 nM. Unlike the intact hCG, the hCG beta-subunit was inactive as a gonadotropic agent to activate the adenylate cyclase in the rat testis. Intravitreal injection of rabbit luteinizing hormone, which was active as a gonadotropic agent, had no effect on IOP in 4 intravitreal concentrations ranging from 1 nM to 30 nM. These observations indicate that the mechanism of IOP decrease by intravitreal hCG is not related to its gonadotropic action. The IOP decrease in rabbits due to intravitreal hCG or its beta-subunit is probably related to a contaminant or an immune reaction.     

The action of Berberin-drops on the intraocular pressure (IOP) (author's transl)]

A double-blind trial was performed on 12 patients with chronic open angle glaucoma with Berberin and Placebo drops. There was no evidence for the hypothesis that Berberin or Placebo cause changes in the bio-regulation of the IOP. The statistical analysis was done by a new procedure (Kannemann 1976). The authors tried to propose generally valid rules for the planning of trials which are supposed to prove or disaprove the connection between various eye-drops and IOP-changes.     

Self-measurement of intraocular pressure

OBJECTIVE: To study Draeger's self-tonometer handling and accuracy. MATERIALS AND METHODS: This microprocessor-controled applanation tonometer enables the patient to perform frequent measurements himself. Two studies were carried out. In a first patient series of 22 participants we analyzed patient-acceptance with regard to tonometer handling, in a second group of 10 normal eyes, 30 average readings obtained using the Draeger tonometer were compared to the results from Goldmann applanation tonometry. RESULTS: In the first group of 22 patients, 8 participants considered that the new tonometer was easy to handle, 7 reported moderately difficult and 6 difficult handling. One patient did not succeed in measuring at all. The results of the second group showed a statistically non significant mean difference of 0.3mmHg with a standard deviation of nearly 2 mmHg. 80.1% of measurements were within +/-2mmHg. The correlation coefficent was 0.73. CONCLUSIONS: Handling the self-tonometer is quite simple and provides close and reliable readings. Thus, in addition to early detection, self-tonometry offers the possibility of improved management and follow-up of glaucoma.     

七氟烷吸入麻醉对大鼠青光眼造模眼眼压的影响

目的研究吸入麻醉药七氟烷对磁性微球前房注射诱导实验性大鼠青光眼造模眼和正常眼眼压(IOP)的影响。方法雄性8～10周挪威褐鼠6只,进行2周清醒状态下IOP测量训练后,采用磁性微球前房注射方法诱导实验性青光眼,右眼为青光眼造模眼,左眼为自身对照眼,研究吸入麻醉药七氟烷麻醉对造模眼和对照眼IOP的影响。结果七氟烷可明显降低造模眼和对照眼的IOP,麻醉平稳后造模眼IOP最大降低幅度为52.6%(t=20.61),对照眼最大降低幅度为37.5%(t=4.98),造模眼降低的程度明显大于对照眼。造模眼IOP在大鼠苏醒后仍低于基础值,差异有统计学意义,而对照眼IOP在苏醒后即恢复至接近基础值。结论七氟烷吸入麻醉可以显著降低大鼠IOP,其中青光眼造模眼的下降幅度更为显著,持续时间更长。该结果提示在对先天性青光眼患儿使用七氟烷全身麻醉下检查时,应充分考虑到该药物降低IOP的作用。