The binocular accommodative response in uncorrected ametropia

PURPOSE

To measure the changes in astigmatism and in the degree of anisometropia when ametropes respond to accommodative stimulation.

METHODS

The accommodative responses of ametropes were binocularly measured with an improved photorefractometer (PR-1100), which objectively measured binocular refraction in all meridians simultaneously, when a visual fixation target was shown in natural space at 5 and 0.5 m.

RESULTS

(1) Changes of astigmatism and anisometropia occur during binocular accommodation. (2) Changes of astigmatism mainly result from lag of accommodation in the horizontal meridian. (3) Changes of anisometropia result from the effort to focus. (4) The interaction of both eyes is suggested as the cause of the changes of astigmatism and anisometropia with accommodation. (5) In the majority of strong anisometropes (nonoverlapping group in this paper), the magnitude of anisometropia decreases (approaching isometropia) with accommodation.

CONCLUSION

Changes in astigmatism and anisometropia can occur during accommodation, and these interactions of both eyes with accommodation may contribute to the development and maintenance of binocular function.

[Measurement of apparent accommodation with a 20/20 near vision optotype]

PURPOSE

The value of apparent accommodation varies with methods of measurement. To discuss the details of apparent accommodation, it is appropriate to measure it with the smallest possible near vision optotype. In the present study, we used a 20/20 near vision optotype for the measurement of apparent accommodation.

SUBJECTS AND METHODS

Forty-six eyes of thirty-eight patients (45-84 years old) who had undergone cataract surgery and intraocular lens implantation, and had at least 20/20 best corrected visual acuity at near and far distances, were used in this study. After the eyes were corrected by glasses to gain the best corrected long distance visual acuity, they were forced to watch a 20/20 near vision optotype. Then we gradually added plus lenses until they could recognize the optotype. The value of apparent accommodation was recorded by subtracting the value of plus lens by which the eye could first recognize the 20/20 near vision optotype from three diopters.

RESULTS

The value of apparent accommodation was 0.00-3.00 D (medium 0.50 D). Two eyes had three diopters of apparent accommodation.

CONCLUSION

In the present study with correction of astigmatism and small near vision optotype, most eyes showed smaller apparent accommodation than those in previous studies. Despite that, patients with three diopters of apparent accommodation do exist. To analyze high quality visual functions, we should use the smallest possible near vision optotype for the measurement of apparent accommodation.

The Influence of Corneal Thickness and Curvature on the Difference Between Intraocular Pressure Measurements Obtained with a Non-contact Tonometer and Those with a Goldmann Applanation Tonometer

Purpose: The influence of corneal thickness and curvature on the difference between intraocular pressure (IOP) measurements obtained with a non-contact tonometer (NCT) and those with a Goldmann applanation tonometer (GAT) was studied.Methods: The corneal thickness and curvature were obtained in 230 eyes of 115 subjects. The correlation between them and ratios of measurement with NCT to that with GAT ([NCT/GAT]) were examined.Results: [NCT/GAT] and corneal thickness showed a significant positive correlation (r = 0.556, P <.01), but, the correlation between [NCT/GAT] and the radius of corneal curvature was not statistically significant (r = -0.035, P =.30).Conclusion: The thick cornea has more influence on the measurement with NCT than GAT, because IOP is measured with NCT over a wider applanation area. The corneas with steeper curvature also cause higher corneal rigidity and produce more overestimation of NCT measurement, while they have stronger capillary attraction of the precorneal tear film for the GAT tip and also produce overestimation of GAT measurement. As a result, [NCT/GAT] was believed to be not influenced by the corneal curvature.

[The influence of corneal thickness and curvature on the difference between intraocular pressure measurements obtained with a non-contact tonometer and those with a Goldmann applanation tonometer]

PURPOSE

The influence of corneal thickness and curvature on the difference between intraocular pressure (IOP) measurements obtained with a non-contact tonometer (NCT) and those with a Goldmann applanation tonometer (GAT) was studied.

METHODS

The corneal thickness and curvature were obtained in 230 eyes of 115 subjects. The correlation between them and ratios of measurement with NCT to that with GAT ([NCT/GAT]) were examined.

RESULTS

[NCT/GAT] and corneal thickness showed a significant positive correlation (r = 0.556, p < 0.01), but, the correlation between [NCT/GAT] and the radius of corneal curvature was not statistically significant (r = -0.035, p = 0.30).

CONCLUSION

The thick cornea has more influence on the measurement with NCT than GAT, because IOP is measured with NCT over a wider applanation area. The corneas with steeper curvature also cause higher corneal rigidity and produce more overestimation of NCT measurement, while they have stronger capillary attraction of the precorneal tear film for the GAT tip and also produce overestimation of GAT measurement. As a result, [NCT/GAT] was believed to be not influenced by the corneal curvature.

Accommodation causes with-the-rule astigmatism in emmetropes

PURPOSE

To measure the changes in astigmatism when bilateral emmetropes accommodate.

METHODS

Bilateral emmetropes accommodative responses were measured with an improved photorefractometer PR-1100, which measured binocular refraction in all meridians simultaneously as a fixation target was shown in natural space.

RESULTS

The accommodative responses in the vertical meridian are greater than those in the horizontal meridian. In the horizontal meridian, the accommodative responses are less than the accommodative stimulus.

CONCLUSIONS

When accommodating the majority of bilateral emmetropes show with-the-rule astigmatism and lag of accommodation in the horizontal meridian.

[High-speed recording of fluorescein fundus angiography using an argon laser as the illumination source]

We constructed a new fluorescein fundus angiography system using a speedy and sensitive fundus camera and an argon laser apparatus as the illumination source. The system consists of a fluorescein fundus camera, a high-speed camera, a digital recorder, an argon laser apparatus, and a cathode ray tube(CRT)monitor. The frame speed was 200 frames/s. It was possible to record high speed fluorescein angiography with lower illumination by using an argon laser as the illumination source. This system allowed us to measure the rate of blood flow in the retinal vessels because it easily detected the dye front in the retinal vessels.

[Equivalent ultrasonic velocity for intraocular lens implanted eyes in A-mode biometry]

With the standard ultrasonic velocity in commercially available instruments, there is a large difference of the ultrasonic velocity between the ocular medium and the implanted intraocular lens (IOL). If the PMMA or silicon IOL-implanted eye is assessed by using the ultrasonic velocity of the phakic or aphakic eye (1,550 m/s or 1,532 m/s), the error induced by the mismatch of the velocity is considerable. Therefore, we estimated the axial length error of pseudophakic eyes in ultrasonic biometry, and also derived theoretically the overall average sound speed (equivalent ultrasonic velocity, EUV) in IOL-implanted eyes. We found that the EUV (VE) can be estimated from the equation, VE = LV1V2/ T(V1-V2)+LV2], where L is the axial length of the eye, V1 the ultrasonic velocity of aqueous and vitreous body, V2 the ultrasonic velocity of the IOL, and T the central thickness of the IOL. The EUV for a PMMA IOL-implanted eye is approximately 1,560 m/s, and the EUV for a silicon IOL-implanted eye is approximately 1,500 m/s in an eye of standard length (24 mm) and an IOL of standard central thickness (1 mm). However, the EUV is a function of the axial length of the eye (L), the central thickness of the IOL (T), and the sound velocity in the implanted IOL (V2), and thus the EUV can not be applied for all cases. To perform more accurate ultrasonic biometry in pseudophakic eyes, we should rectify the apparent axial length assessed by the aphakic sound speed (1,532 m/s) with the central thickness of the implanted IOL.

[A portable automatic infrared refractor]

In order to measure refractive errors in infants who cannot be measured by the conventional refractor, we have devised a portable automatic infrared refractor. This device has four unique advantages. The first is that an examiner can measure refractive states at any position. The second is an auto-start system. The third is that this device enables the patient to look at an external fixation object through the half-mirror of the handipiece. The fourth is its portability. From the measurements on 44 infant subjects, a good correlation between this device and the conventional refractor was obtained. The specifications are: minimal pupil diameter, 2.9 mm; measurement range: spherical power +/- 20 D, cylindrical power +/- 7 D. We believe that this device has wide applicability in clinical examination. For example, we can use this device for measurements of refractive states during cataract surgery.

Rapid determination of intraocular lens tilt and decentration through the undilated pupil

The apparent optical axis of an implanted intraocular lens (IOL) can be located by alignment of the examiner's hand light with the third and fourth Purkinje images from the front and back surfaces of the IOL. Tilt of the IOL can be estimated (or measured with an arc perimeter) by the angle between the apparent optical axis and the patient's line of sight (actual tilt approximately 0.85 x apparent tilt). Decentration of the IOL is easily detected, equal to the distance of the IOL optical axis from the center of the pupil. This simple technique can be used through the natural pupil with posterior chamber IOLs, providing the optical axis of the malpositioned IOL still passes through the pupil.

Centering corneal surgical procedures

Currently used methods for centering corneal surgical procedures emphasize the visual axis of the eye but do not define it properly. We obtained the best optical result by centering the surgical procedure on the line of sight and entrance pupil of the eye, not on the visual axis. We found an error of 0.5 to 0.8 mm in currently used methods of marking the visual axis, which arose from the use of the corneal light reflex as a sighting point or from inadvertent monocular sighting in techniques requiring binocular sighting. Proper centering requires the patient to fixate on a point that is coaxial with the surgeon's sighting eye, and the cornea is marked at the point in line with the center of the patient's entrance pupil, ignoring the corneal light reflex.

Depth distortion during slitlamp biomicroscopy of the fundus

The apparent depth of an optic nerve cup or apparent height of a fundus lesion changes with the optics used by an examiner. With slit-lamp biomicroscopy of the fundus, both the auxiliary fundus lens and the biomicroscope contribute to differences in magnification that produces distortion of the object. It is important to understand these differences so that inaccurate conclusions are not drawn and inappropriate therapy will not be instituted when the examiner uses different instruments for making serial observations or uses an unfamiliar instrument.

Visual-evoked potentials elicited by laser speckle patterns. Studies on the characteristics and assessment of visual function in patients with ocular media opacities

Visual-evoked potentials (VEPs) were recorded using a laser speckle pattern. Stimulation with a speckle pattern was elicited either by pattern appearance-disappearance or by pattern shift. The VEPs obtained by this method were similar in properties to the previous pattern VEPs that were obtained either by pattern appearance-disappearance or by pattern reversal. Patients in whom dense and diffuse ocular media opacity defied measurement by the interferometric visual acuity method were studied to test if the speckle pattern generated by diffusion from lens opacity itself could act as a stimulus for obtaining VEPs. It is concluded that the present method enables one to obtain a reliable VEP and to assess the visual function of the retino-cortical system, even in patients with mature cataracts.