Higher-order wavefront aberrations in retinitis pigmentosa

Relationship Between Foveal Cone Structure and Visual Acuity Measured With Adaptive Optics Scanning Laser Ophthalmoscopy in Retinal Degeneration

Purpose

To evaluate foveal function in patients with inherited retinal degenerations (IRD) by measuring visual acuity (VA) after correction of higher-order aberrations.

Methods

Adaptive optics scanning laser ophthalmoscopy (AOSLO) was used to image cones in 4 healthy subjects and 15 patients with IRD. The 840-nm scanning laser delivered an "E" optotype to measure AOSLO-mediated VA (AOSLO-VA). Cone spacing was measured at the preferred retinal locus by two independent graders and the percentage of cones below the average density of 47 age-similar healthy subjects was computed. Cone spacing was correlated with best-corrected VA measured with the Early Treatment of Diabetic Retinopathy Study protocol (ETDRS-VA), AOSLO-VA, and foveal sensitivity.

Results

ETDRS-VA significantly correlated with AOSLO-VA (ρ = 0.79, 95% confidence interval [CI] 0.5-0.9). Cone spacing correlated with AOSLO-VA (ρ = 0.54, 95% CI 0.02-0.7), and negatively correlated with ETDRS letters read (ρ = -0.64, 95% CI -0.8 to -0.2). AOSLO-VA remained ≥20/20 until cones decreased to 40.2% (CI 31.1-45.5) below normal. Similarly, ETDRS-VA remained ≥20/20 until cones were 42.0% (95% CI 36.5-46.1) below normal. Cone spacing z scores negatively correlated with foveal sensitivity (ρ = -0.79, 95% CI -0.9 to -0.4) and foveal sensitivity was ≥35 dB until cones were 43.1% (95% CI 39.3-46.6) below average.

Conclusions

VA and foveal cone spacing were weakly correlated until cones were reduced by 40% to 43% below normal. The relationship suggests that VA is an insensitive measure of foveal cone survival; cone spacing may be a more sensitive measure of cone loss.

Wavefront aberrations and retinal image quality in different lenticular opacity types and densities

To investigate wavefront aberrations in the entire eye and in the internal optics (lens) and retinal image qualities according to different lenticular opacity types and densities. Forty-one eyes with nuclear cataract, 33 eyes with cortical cataract, and 29 eyes with posterior subcapsular cataract were examined. In each group, wavefront aberrations in the entire eye and in the internal optics and retinal image quality were measured using a raytracing aberrometer. Eyes with cortical cataracts showed significantly higher coma-like aberrations compared to the other two groups in both entire eye and internal optic aberrations (P = 0.012 and P = 0.007, respectively). Eyes with nuclear cataract had lower spherical-like aberrations than the other two groups in both entire eye and internal optics aberrations (P < 0.001 and P < 0.001, respectively). In the nuclear cataract group, nuclear lens density was negatively correlated with internal spherical aberrations (r = −0.527, P = 0.005). Wavefront technology is useful for objective and quantitative analysis of retinal image quality deterioration in eyes with different early lenticular opacity types and densities. Understanding the wavefront optical properties of different crystalline lens opacities may help ophthalmic surgeons determine the optimal time to perform cataract surgery.

Effects of optical blur reduction on equivalent intrinsic blur

PURPOSE

To determine the effect of optical blur reduction on equivalent intrinsic blur, an estimate of the blur within the visual system, by comparing optical and equivalent intrinsic blur before and after adaptive optics (AO) correction of wavefront error.

METHODS

Twelve visually normal subjects (mean [±SD] age, 31 [±12] years) participated in this study. Equivalent intrinsic blur (σint) was derived using a previously described model. Optical blur (σopt) caused by high-order aberrations was quantified by Shack-Hartmann aberrometry and minimized using AO correction of wavefront error.

RESULTS

σopt and σint were significantly reduced and visual acuity was significantly improved after AO correction (p ≤ 0.004). Reductions in σopt and σint were linearly dependent on the values before AO correction (r ≥ 0.94, p ≤ 0.002). The reduction in σint was greater than the reduction in σopt, although it was marginally significant (p = 0.05). σint after AO correlated significantly with σint before AO (r = 0.92, p < 0.001), and the two parameters were related linearly with a slope of 0.46.

CONCLUSIONS

Reduction in equivalent intrinsic blur was greater than the reduction in optical blur after AO correction of wavefront error. This finding implies that visual acuity in subjects with high equivalent intrinsic blur can be improved beyond that expected from the reduction in optical blur alone.

Effect of aberrations and scatter on image resolution assessed by adaptive optics retinal section imaging

The effect of increased high-order wavefront aberrations on image resolution was investigated, and the performance of adaptive optics (AO) for correcting wavefront error in the presence of increased light scatter was assessed in a model eye. An AO section imaging system provided an oblique view of a model retina and incorporated a wavefront sensor and deformable mirror for measurement and compensation of wavefront aberrations. Image resolution was quantified by the width of a Lorentzian curve fitted to a laser line image. Wavefront aberrations were significantly reduced with AO, resulting in improvement of image resolution. In the model eye, image resolution was degraded with increased high-order wavefront aberrations (horizontal coma and spherical) and improved with AO correction of wavefront error in the presence of increased light scatter. The findings of the current study suggest that AO imaging systems can potentially improve image resolution in aging eyes with increased aberrations and scatter.

A Method for Differentiating Ocular Higher-Order Aberrations From Light Scatter Applied to Retinitis Pigmentosa

PURPOSE

The purpose of this study is to report a method for differentiating ocular higher-order aberrations and intraocular light scatter based on a deconvolution technique.

METHODS

An optical system was used to image a laser slit on the retina and also to perform Shack-Hartmann wavefront sensing. From the laser slit image, the line spread function, incorporating both ocular higher-order aberrations and light scatter, was derived. The laser slit image was deconvolved with a point spread function obtained from the Shack-Hartmann image. The area under the line spread function that was derived from the laser slit image after deconvolution provided a measurement of intraocular light scatter. The deconvolution technique was applied to images obtained in a group of 13 patients (mean age +/- 1 standard deviation: 42 +/- 12 years) with retinitis pigmentosa (RP), a retinal disease in which, by clinical examination, changes in the lens of the eye can be manifested. Measurements were compared with those obtained from 20 visually normal control subjects (mean age +/- 1 standard deviation: 43 +/- 17 years).

RESULTS

Combined higher-order aberrations and light scatter, measured as the area under the line spread function derived from the laser slit image, were increased significantly in the patients with RP as compared with the control subjects (p = 0.004). Ocular higher-order aberrations obtained from the Shack-Hartmann images were higher in the patients with RP than in the control subjects (p = 0.05). Intraocular light scatter derived from the deconvolved laser slit image was significantly higher in the patients with RP than in the control subjects (p = 0.009). Minimizing the contribution of ocular higher-order aberrations by deconvolution reduced the area under the line spread function in the control subjects and patients with RP, denoting an improvement in retinal image quality.

CONCLUSIONS

A method for differentiating ocular higher-order aberrations and intraocular light scatter based on deconvolution was developed that may be useful for determining the level of improvement in retinal image quality that can be anticipated by the application of adaptive optics to aging and diseased human eyes.