Lisa A. Ostrin

Accommodation measurements in a prepresbyopic and presbyopic population

Purpose: To study the efficacy of several subjective and objective methods of accommodation measurement in normal prepresbyopic and presbyopic populations to identify appropriate methods for measuring the outcome of accommodative restorative procedures. Setting: University of Houston, College of Optometry, Houston, Texas, USA. Methods: Thirty‐one normal subjects with a mean age of 43.7 years (range 31 to 53 years) participated. Accommodation was measured monocularly using 3 subjective approaches—the push‐up test, minus lenses to blur, and a focometer—and 2 approaches measured with a Hartinger coincidence refractometer, in which accommodation was stimulated with minus lenses to blur and topical pilocarpine 6%. Results: The push‐up method overestimated accommodative amplitude relative to objective measures in 28 subjects. Two subjective methods, minus lenses to blur and the focometer, produced comparable results, but with lower amplitudes in younger subjects and higher amplitudes in older subjects compared with objective methods. Comparable results were obtained when accommodation was stimulated in 1 of 2 ways and measured with the Hartinger. Pilocarpine elicited stronger accommodative responses than distance blur for subjects with low accommodative amplitudes. Pilocarpine 6% produced stronger responses in subjects with light irides than in those with dark irides. Conclusions: Hartinger‐measured accommodation provides more realistic measurement of accommodative amplitude than the subjective methods tested, especially in the presbyopic population. In presbyopic subjects, the subjective tests resulted in accommodative amplitudes up to 4.0 diopters greater than those measured with objective tests. Measurements of accommodative amplitude are best achieved with objective methods to stimulate and measure accommodation.

Simultaneous Measurements of Refraction and A-Scan Biometry During Accommodation in Humans

Purpose. Accommodation is a dioptric change in power of the crystalline lens resulting from ciliary muscle contraction that leads to an increase in lens surface curvatures and thickness and changes in the position of lens surfaces. Previous studies have used A-scan ultrasound to measure changes in the position of lens surfaces with voluntary accommodation, but have not simultaneously measured the change in refraction. The goal of this study is to simultaneously measure and correlate refractive and biometric changes in the lens during voluntary accommodation in humans. Methods. Refraction was measured off-axis in the right eye and biometry on-axis in the left eye simultaneously during voluntary accommodation in 22 human subjects between the ages of 21 and 30 years (mean ± standard deviation: 25.8 ± 2.3 years). Subjects viewed a distant target and four near targets spanning the full accommodative range available to evaluate refraction and lens surface position at each accommodative state. Results. Maximum objectively measured accommodative amplitude of all subjects was 5.64 ± 0.21 D (mean ± standard error of mean). Biometric and refractive changes during accommodation were linearly correlated. The mean ± standard error of mean decrease in anterior chamber depth was 0.051 ± 0.008 mm/D, increase in lens thickness was 0.067 ± 0.008 mm/D, and increase in anterior segment length was 0.017 ± 0.005 mm/D during accommodation. There was a net anterior movement of the lens center of 0.017 ± 0.005 mm/D. Conclusion. Anterior chamber depth, lens thickness, and anterior segment length change linearly with refraction during accommodation. Per-diopter changes in the lens were greater in the current study compared with previous studies in which only accommodative demand was measured, which overestimates the accommodative response.

Objective accommodation measurement with the Grand Seiko and Hartinger coincidence refractometer.

Purpose. Subjective push-up tests and dynamic retinoscopy are standard clinical accommodation tests. These are inadequate for assessing if accommodation can be restored in presbyopes. Commercially available clinical autorefractors offer potentially reliable methods for objective accommodation measurement. This study evaluated accuracy and reliability of the Grand Seiko WR-5100K autorefractor for objective accommodation measurement in young adults. Methods. Twenty-two subjects, aged 21 to 30 years (mean 25.6 ± 2.26) participated. Three methods were used to stimulate and measure accommodation: (1) subjective push-up test in free space, (2) a near target pushed-up on a near-point rod and the response measured with the WR-5100K and a Hartinger coincidence refractometer (HCR), and (3) a distant target viewed through increasing powered negative trial lenses and the response measured with the WR-5100K and the HCR. Trial lens calibration procedures were also used to test the accuracy of the instruments. Results. Average maximum accommodative amplitude with the subjective push-up test was 7.74 D ± 0.36 D (mean ± SE). For a 5 D stimulus, accommodation of 4.68 D ± 0.10 D (mean ± SE) and 4.13 D ± 0.09 D was measured with the WR-5100K and the HCR, respectively. With a distant target viewed through a −5.00 D trial lens, the WR-5100K measured 4.07 D ± 0.09 D and the HCR measured 4.05 D ± 0.09 D of accommodation. Maximum mean response measured with trial lens-induced accommodation was 5.67 D ± 0.15 D with the WR-5100K and 5.77 D ± 0.18 D with the HCR. Conclusions. The subjective push-up test overestimated accommodative amplitude relative to the objective measures. The WR-5100K showed good agreement in the responses measured for both pushed-up near targets and a distant target viewed through trial lenses with the HCR, a widely used laboratory instrument. The Grand Seiko WR-5100K, a commercially available instrument, has been demonstrated to be well suited for clinical, objective accommodation measurement using a population of normal young adults.

Evaluation of a satisfied bilateral scleral expansion band patient

Purpose: To measure accommodation subjectively and objectively in a satisfied bilateral scleral expansion band patient. Setting: University of Houston, College of Optometry, Houston, Texas, USA. Methods: One bilateral scleral expansion patient (age 50 years), 9 age‐matched normal presbyopic control subjects (age range 48 to 52 years), and 1 normal control subject (age 27 years) participated. The scleral expansion patient had a complete eye examination, corneal topography, and wavefront measurements 19 months postoperatively. Accommodation was measured subjectively with the push‐up technique, minus to blur, and dioptric range of clear vision. Accommodation was determined objectively by measuring the accommodative responses to negative lenses and pilocarpine 6% with a Hartinger coincidence refractometer and to real targets with a dynamic infrared optometer. Results: Distance and near acuity of 20/20 was achieved with +1.00 diopter (D) in the left eye, +0.50 D in the right eye, and a near add of +2.25 D. Corneal topography and ocular aberration measurements revealed no suggestion of optical multifocality. Subjective measurements resulted in accommodative amplitudes of 1.50 to 4.00 D, and objective measurements resulted in amplitudes of 0.25 to 1.33 D. The PowerRefractor showed an accommodative response of 0.50 D to stimuli of 1.00 to 4.00 D and strong pupillary constriction with accommodative effort compared with the control. Conclusions: No increase in accommodative amplitude above normal age‐matched controls was found. Patient satisfaction may have come from the high expectations this patient had for a positive surgery outcome.

The Role of the Iris in Chick Accommodation

PURPOSE Peripheral defocus, higher-order aberrations, and accommodation interact with pupil size to influence retinal image quality and possibly eye growth. Iridectomy (ID) provides a fixed, enlarged pupil. Results from in vitro studies suggest that ID may reduce or eliminate accommodation in the chicken. This paper further investigates the effects of ID on chicken accommodation, eye growth, and refractive development. METHODS Refraction, biometry, and corneal curvature were measured, before, and after topical instillation of nicotine in 43 White-Leghorn chickens that had undergone monocular ID. Intraocular pressure (IOP) was measured, and eyes were imaged with anterior segment optical coherence tomography (OCT) during accommodation. In vitro preparations were used to examine accommodation responses in a lens-scanning instrument. RESULTS Iridectomy induced small but significant decreases in anterior and vitreous chamber depths and an increase in lens thickness (LT). IOP was similar in iridectomized and control eyes from 1 week on. In vivo, nicotine induced similar accommodative changes in iridectomized and control eyes. OCT images revealed a forward displacement of the iris during accommodation in control eyes. Iridectomized and control eyes showed similar increases in LT. In vitro, iridectomized eyes showed minimal nicotine-induced accommodation. CONCLUSIONS Refraction and eye growth were minimally affected by ID in chickens, implying that emmetropization was unaffected and supporting the use of ID as a tool in emmetropization and myopia studies. The greatly attenuated accommodative responses in vitro for iridectomized eyes suggest a role of biomechanical factors in the chick. IOP was unaffected by the surgery, implying that the iris musculature is not essential for maintaining aqueous outflow pathways.

Attenuation of short wavelengths alters sleep and the ipRGC pupil response

Exposure to increasing amounts of artificial light during the night may contribute to the high prevalence of reported sleep dysfunction. Release of the sleep hormone melatonin is mediated by the intrinsically photosensitive retinal ganglion cells (ipRGCs). This study sought to investigate whether melatonin level and sleep quality can be modulated by decreasing night‐time input to the ipRGCs.

Pharmacologically stimulated pupil and accommodative changes in Guinea pigs.

PURPOSE The guinea pig is being used increasingly as a model of human myopia. As accommodation may influence the effects of manipulations used in experimental myopia models, understanding the accommodative ability of guinea pigs is important. Here, nonselective muscarinic agonists were used as pharmacological tools to study guinea pig accommodation. METHODS Measurements were made on 15 pigmented guinea pigs. For in vivo testing, animals were anesthetized and, following baseline measurements, 2% pilocarpine was applied topically. Measurements included A-scan ultrasonography, optical coherence tomography (OCT) imaging, corneal topography, and refraction. In vitro lens scanning experiments were performed using anterior segment preparations, with measurements before and during exposure to carbachol. Anterior segment structures were examined histologically and immunohistochemistry was done to characterize the muscarinic receptor subtypes present. RESULTS In vivo, pilocarpine induced a myopic shift in refractive error coupled to a small, but consistent decrease in anterior chamber depth (ACD), a smaller and more variable increase in lens thickness, and a decrease in pupil size. Lens thickness increases were short-lived (10 minutes), while ACD and pupil size decreased over 20 minutes. Corneal curvature was not significantly affected. Carbachol tested on anterior segment preparations in vitro was without effect on lens back vertex distance, but did stimulate pupil constriction. Immunohistochemistry indicated the presence of muscarinic receptor subtypes 1 to 5 in the iris and ciliary body. CONCLUSIONS The observed pilocarpine-induced changes in ACD, lens thickness, and refraction are consistent with active accommodation in the guinea pig, through cholinergic muscarinic stimulation.

Autonomic drugs and the accommodative system in rhesus monkeys

Accommodation and pupil constriction result from parasympathetic stimulation from the Edinger-Westphal (EW) nucleus of the midbrain resulting in release of acetylcholine at the neuromuscular junctions of the ciliary muscle and iris. Cholinergic and adrenergic drugs can be applied topically to evaluate the effects on the pupil and accommodative system without input from the EW nucleus. This study is directed at characterizing how topical low dose echothiophate, an anti-cholinesterase inhibitor (i.e., an indirect cholinergic agonist), epinephrine, an adrenergic agonist, and timolol maleate, a beta adrenergic antagonist, affect pupil diameter, resting refraction and accommodative amplitude and dynamics in rhesus monkeys. The effects of 0.015% echothiophate, 2% epinephrine, 0.5% timolol maleate and saline on pupil diameter and resting refraction were measured in one eye each of four normal rhesus monkeys for 60-90 min following topical instillation. Pupil diameter was measured with infrared videography and refraction was measured with a Hartinger coincidence refractometer. Effects on static and dynamic EW stimulated accommodation were studied in three iridectomized monkeys (ages 5, 6 and 12 years) with permanent indwelling stimulating electrodes in the EW nucleus. Dynamic accommodative responses were measured with infrared photorefraction for increasing current amplitudes before and during the course of action of the pharmacological agents. Echothiophate caused a significant decrease in pupil diameter of 3.07 +/- 0.65 mm (mean +/- SEM, p < 0.01), and a myopic shift in resting refraction of 1.30 +/- 0.39 D (p < 0.05) 90 min after instillation. Epinephrine caused a 2.76 +/- 0.38 mm (p < 0.01) increase in pupil diameter with no change in resting refraction 60 min after instillation. Timolol maleate resulted in no significant change in either pupil diameter or resting refraction 60 min after instillation. There was no significant change in maximum EW stimulated accommodative amplitude after any agent tested. The amplitude vs. peak velocity relationship for accommodation was significantly different after echothiophate and timolol maleate, and for disaccommodation after echothiophate, epinephrine and timolol maleate. In conclusion, when tested objectively in anesthetized monkeys, epinephrine and timolol maleate did not alter resting refraction or accommodative amplitude, but did have small, significant affects on accommodative dynamics. This suggests that there is an adrenergic component to the accommodative system. Low dose echothiophate had significant effects on pupil diameter and resting refraction, with only small effects on the dynamics of the accommodative response.

Objectively Measured Light Exposure in Emmetropic and Myopic Adults

PURPOSE Light exposure has a close link with numerous aspects of human physiology including circadian rhythm, mood disorders, metabolism, and eye growth. Here, a lightweight wrist-worn device was employed to continuously measure light exposure and activity across seasons and between refractive error groups to assess objectively measured differences and compare with subjectively reported data. METHODS Subjects, aged 21-65 years (n = 55), wore an actigraph device (Actiwatch Spectrum) continuously for 14 days to quantify light exposure, activity, and sleep. Subjects were classified as emmetropic (n = 18) or myopic (n = 37), and answered an activity questionnaire. Additionally, devices were calibrated against a lux meter and UV sensor for indoor and outdoor settings, and used to measure ambient illumination in various environmental conditions. RESULTS Subjects spent 1:52 ± 0:56 hours outside per day, as measured objectively. Subjectively reported measures overestimated objective measures by 0:25 ± 1:19 hours per day (range -1:49 to +4:29 hours, P < .05). Subjects spent 1:04 hours more outdoors in summer and received an increased cumulative light dose compared to winter (P < .005). There were no significant differences in objective measurements of time outdoors between myopic and emmetropic subjects. Ambient illumination measures from the Actiwatch correlated with a lux meter for all locations tested (R = 0.99, P < .001). Ambient illumination was highest in the summer at 176,497 ± 20,310 lux and lowest for indoor artificial light at 142 ± 150 lux. CONCLUSIONS Subjects spent more time outdoors and received an increased light dose in summer, with no differences between refractive error groups in this adult population. Various environmental and seasonal measurements revealed significantly different available light in winter versus summer and indoors versus outdoors. Objective devices such as the Actiwatch can be valuable in studies where quantification of environmental factors is critical.

The Adenosine Receptor Antagonist, 7-Methylxanthine, Alters Emmetropizing Responses in Infant Macaques

Purpose Previous studies suggest that the adenosine receptor antagonist, 7-methylxanthine (7-MX), retards myopia progression. Our aim was to determine whether 7-MX alters the compensating refractive changes produced by defocus in rhesus monkeys. Methods Starting at age 3 weeks, monkeys were reared with −3 diopter (D; n = 10; 7-MX −3D/pl) or +3D (n = 6; 7-MX +3D/pl) spectacles over their treated eyes and zero-powered lenses over their fellow eyes. In addition, they were given 100 mg/kg of 7-MX orally twice daily throughout the lens-rearing period (age 147 ± 4 days). Comparison data were obtained from lens-reared controls (−3D/pl, n = 17; +3D/pl, n = 9) and normal monkeys (n = 37) maintained on a standard diet. Refractive status, corneal power, and axial dimensions were assessed biweekly. Results The −3D/pl and +3D/pl lens-reared controls developed compensating myopic (−2.10 ± 1.07 D) and hyperopic anisometropias (+1.86 ± 0.54 D), respectively. While the 7-MX +3D/pl monkeys developed hyperopic anisometropias (+1.79 ± 1.11 D) that were similar to those observed in +3D/pl controls, the 7-MX −3D/pl animals did not consistently exhibit compensating myopia in their treated eyes and were on average isometropic (+0.35 ± 1.96 D). The median refractive errors for both eyes of the 7-MX −3D/pl (+5.47 D and +4.38 D) and 7-MX +3D/pl (+5.28 and +3.84 D) monkeys were significantly more hyperopic than that for normal monkeys (+2.47 D). These 7-MX–induced hyperopic ametropias were associated with shorter vitreous chambers and thicker choroids. Conclusions In primates, 7-MX reduced the axial myopia produced by hyperopic defocus, augmented hyperopic shifts in response to myopic defocus, and induced hyperopia in control eyes. The results suggest that 7-MX has therapeutic potential in efforts to slow myopia progression.