Amphiregulin and ocular axial length

Intravitreal panitumumab and myopic macular degeneration

BACKGROUND

In experimental studies, intravitreally applied antibodies against epidermal growth factor (EGF), EGF family members (amphiregulin, neuregulin-1, betacellulin, epigen, epiregulin) and against the EGF receptor (EGFR) were associated with a reduction in lens-induced axial elongation and decrease in physiological eye elongation in guinea pigs and in non-human primates. Here, we investigated the intraocular tolerability and safety of a fully human monoclonal IgG2-antibody against EGFR, already in clinical use in oncology, as a potential future therapeutic approach for axial elongation in adult eyes with pathological myopia.

METHODS

The clinical, monocentre, open-label, multiple-dose, phase-1 study included patients with myopic macular degeneration of stage 4, who received intravitreal injections of panitumumab in various doses and in intervals ranging between 2.1 months and 6.3 months.

RESULTS

The study included 11 patients (age:66.8±6.3 years), receiving panitumumab injections in doses of 0.6 mg (4 eyes; 1×1 injection, 3×2 injections), 1.2 mg (4 eyes; 1×1 injection, 2×2 injections, 1×3 injections) and 1.8 mg (3 eyes; 1×1 injection, 2×2 injections), respectively. None of the participants showed treatment-emergent systemic adverse events or intraocular inflammatory reactions. Best-corrected visual acuity (1.62±0.47 logarithm of the minimal angle of resolution (logMAR) vs 1.28±0.59 logMAR; p=0.08) and intraocular pressure (13.8±2.4 mm Hg vs 14.3±2.6 mm Hg; p=0.20) remained unchanged. In nine patients with a follow-up of >3 months (mean:6.7±2.7 months), axial length did not change significantly (30.73±1.03 mm vs 30.77±1.19 mm; p=0.56).

CONCLUSIONS

In this open-labelled, phase-1 study with a mean follow-up of 6.7 months, panitumumab repeatedly administered intravitreally up to a dose of 1.8 mg was not associated with intraocular or systemic adverse effects. During the study period, axial length remained unchanged.

TRIAL REGISTRATION NUMBER

DRKS00027302.

Inhibitory Effect of Jinkui Shenqi Pills on Glucocorticoid-Enhanced Axial Length Elongation in Experimentally Myopic Guinea Pigs

OBJECTIVE

To explore the underlying mechanism of inhibition by Jinkui Shenqi Pills (JKSQP) on glucocorticoid-enhanced axial length elongation in experimental lens-induced myopia (LIM) guinea pigs.

METHODS

Sixty 2-week old male guinea pigs were randomly divided into 4 groups with 15 guinea pigs in each group, according to the random numbers generated by SPSS software: control, LIM, saline and JKSQP groups. The control group includes animals with no treatment, while the guinea pigs in the other 3 groups received lens-induced myopization on the right eyes throughout the experiment (for 8 weeks). The saline and JKSQP groups were given daily intraperitoneal injections of 10 mg/kg hydrocortisone for 2 consecutive weeks at the same time, and then orally administered either saline or JKSQP [13.5 g/(kg•d) for 6 consecutive weeks. Body weight, anal temperature and animal appearance were observed and recorded to evaluate the GC-associated symptoms. The ocular parameters, including refraction and axial length, were measured by streak retinoscopy and A-scan ultrasonography, respectively. The levels of plasma hormones associated with the hypothalamic-pituitary-adrenal axis (HPAA), including free triiodothyronine, free thyroxine, estradiol and testosterone, were measured by radioimmunoassay, and cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate were measured by enzyme-linked immunosorbent assay. In addition, the mRNA and protein expressions of retinal amphiregulin (AREG) was measured by quantitative real-time polymerase chain reaction and Western blotting, respectively.

RESULTS

JKSQP effectively increased body weight and anal temperature, improved animal appearance and suppressed axial length elongation in glucocorticoid-enhanced myopic guinea pigs with normalization of 4 HPAA-associated plasma hormones (all P<0.05). The plasma level of cAMP was significantly increased, whereas the plasma level of cGMP and the mRNA and protein expressions of retinal AREG were decreased after treatment with JKSQP (all P<0.05).

CONCLUSION

JKSQP exhibited a significant inhibitory effect on axial length elongation with decreased expression of AREG in the retina, and normalized 4 HPAA-associated plasma hormones and the expression of cAMP and cGMP in GC-enhanced myopic guinea pigs.

Reduction of experimental ocular axial elongation by neuregulin-1 antibody

Background

Since the mechanisms underlying myopic axial elongation have remained unclear, we examined the effect of neuregulin-1 (NRG-1), an epidermal growth factor family member, on myopic axial elongation.

Methods

The guinea pigs aged two to three weeks were subjected to bilateral negative lens-induced axial elongation and received weekly intravitreal injections into their right eyes of NRG-1 antibody (doses: 5 μg, n = 8; 10 μg, n = 8, 20 μg, n = 9) or of NRG-1 (doses: 0.05 μg, n = 8; 0.01 μg, n = 9; 0.2 μg, n = 8), underwent only bilateral negative lens-induced axial elongation (myopia control group, n = 10), or underwent no intervention (control group, n = 10). The contralateral eyes received corresponding intravitreal phosphate-buffered solution injections. One week after the last injection, the guinea pigs were sacrificed, the eyeballs were removed, the thicknesses of the retina and sclera were histologically examined, the expression of NRG-1 and downstream signal transduction pathway members (ERK1/2 and PI3K/AKT) and the mRNA expression of NRG-1 in the retina was assessed.

Results

The inter-eye difference in axial length at study end increased (p < 0.001) from the normal control group (-0.02 ± 0.09 mm) and the myopia control group (-0.01 ± 0.09 mm) to the low-dose NRG-1 antibody group (-0.11 ± 0.05 mm), medium-dose NRG-1 antibody group (-0.17 ± 0.07 mm), and high-dose NRG-1 antibody group (-0.28 ± 0.06 mm). The relative expression of NRG-1, ERK1/2, and PI3K/AKT in the retina decreased in a dose-dependent manner from the myopia control group to the NRG-1 antibody groups and the normal control group. The relative NRG-1 mRNA expression in the retina was higher (p < 0.01) in the myopic control group than in the NRG-1 antibody groups and normal control group. Scleral and retinal thickness decreased from the normal control group to the NRG-1 antibody groups to the myopic control group. After intraocular injection of NRG-1 protein, there was a slight dose-dependent increase in the difference in axial length between the right and left eye, however not statistically significantly, from the normal control group (-0.02 ± 0.09 mm) to the high-dose NRG-1 protein group (0.03 ± 0.03 mm; p = 0.12).

Conclusion

Intravitreal NRG-1 antibody application was dose-dependently and time-dependently associated with a reduction in negative lens-induced axial elongation in young guinea pigs.

Myopia: Histology, clinical features, and potential implications for the etiology of axial elongation

Myopic axial elongation is associated with various non-pathological changes. These include a decrease in photoreceptor cell and retinal pigment epithelium (RPE) cell density and retinal layer thickness, mainly in the retro-equatorial to equatorial regions; choroidal and scleral thinning pronounced at the posterior pole and least marked at the ora serrata; and a shift in Bruch's membrane opening (BMO) occurring in moderately myopic eyes and typically in the temporal/inferior direction. The BMO shift leads to an overhang of Bruch's membrane (BM) into the nasal intrapapillary compartment and BM absence in the temporal region (i.e., parapapillary gamma zone), optic disc ovalization due to shortening of the ophthalmoscopically visible horizontal disc diameter, fovea-optic disc distance elongation, reduction in angle kappa, and straightening/stretching of the papillomacular retinal blood vessels and retinal nerve fibers. Highly myopic eyes additionally show an enlargement of all layers of the optic nerve canal, elongation and thinning of the lamina cribrosa, peripapillary scleral flange (i.e., parapapillary delta zone) and peripapillary choroidal border tissue, and development of circular parapapillary beta, gamma, and delta zone. Pathological features of high myopia include development of macular linear RPE defects (lacquer cracks), which widen to round RPE defects (patchy atrophies) with central BM defects, macular neovascularization, myopic macular retinoschisis, and glaucomatous/glaucoma-like and non-glaucomatous optic neuropathy. BM thickness is unrelated to axial length. Including the change in eye shape from a sphere in emmetropia to a prolate (rotational) ellipsoid in myopia, the features may be explained by a primary BM enlargement in the retro-equatorial/equatorial region leading to axial elongation.

Comparison of the accuracy of axial length measurement by different imaging methods in Sprague Dawley rats

Background

Obtaining accurate axial length (AL) is very important for the establishment of animal models of myopia. The purpose of this study is to compare the accuracy of Quantel A-B scan, OD-1 A scan, and vernier caliper in measuring AL in Sprague Dawley (SD) rats.

Methods

In total, 60 5-week-old SD rats were divided into female rat group (n = 30) and male rat group (n = 30). Quantel A-B scan and OD-1 A scan were, respectively, used to measure the AL of both eyes of each living rat, and vernier caliper was used to measure the anterior-posterior diameter of each rat's eyeball. Besides, the correlation between refractive error (RE) and AL measured by different instruments was evaluated, and the accuracy of the three measurement methods was compared according to gender and left/right eyes.

Results

There were significant differences in AL and diopter of SD rats at the same age (p < 0.05). the AL of male rats was greater than that of female rats, while diopter (D) was the opposite; There was no significant difference in AL and D between left and right eyes in the same SD rats (p > 0.05); There were statistical differences among the three measurement methods (p < 0.05), AL measured by vernier caliper was the largest, followed by Quantel A-B scan, OD-1 A scan; Difference in AL between male and female was not statistically significant between the results obtained by Quantel A-B scan and vernier caliper (p > 0.05), but there were statistically significant differences between the other two measurement methods (p < 0.05).

Conclusion

Sex is the influencing factor of AL and RE. Imaging measurement can accurately measure the AL in living small rodents. Compared with OD-1 A scan, Quantel A-B scan may be more accurate.

Intraocular Amphiregulin antibody and axial elongation in nonhuman primates

Purpose

To examine the effect of intraocularly applied amphiregulin antibody on physiological axial elongation in young nonhuman primates.

Methods

The experimental study included six male 12-months-old macaque nonhuman primates (body weight:2.46 ± 0.25kg;range:2.20-2.90kg). In the experimental group (n=3 animals), three intravitreal injections of amphiregulin antibody (100μg/50μl) were applied to the left eyes at intervals of 4-6 weeks, and injections of phosphate buffered solution (50μl) were applied to the right eyes. Three other animals were assigned to a blank control group.

Results

During the study period of 23.6 weeks, axial length in the experimental group did not change in the left eyes (18.91 ± 0.37mm to 18.94 ± 0.67mm;P=0.90), while it linearly increased in the right eyes (18.87 ± 0.38mm to 19.24 ± 0.53mm;P=0.056) and in the control group (left eyes:19.15 ± 0.22mm to 19.48 ± 0.22mm;P=0.009; right eyes:19.17 ± 0.15 mm to 19.46 ± 0.23 mm;P=0.024). The interocular difference in axial elongation increased in the experimental group from -0.11 ± 0.12mm at 4 weeks after baseline to -0.34 ± 0.15mm at the study end, while in the control group, the interocular side difference did not change significantly (from 0.01 ± 0.10 mm to 0.03 ± 0.08 mm;P=0.38). The difference in the interocular difference in axial elongation between the two groups was significant at 8 weeks (P=0.01), 15 weeks (P=0.007), and at study end (P=0.02). The interocular difference in axial length correlated with the interocular difference in vitreous cavity length (standardized regression coefficient beta:0.85;P<0.001). The interocular axial length difference was inversely associated with the interocular refractive error difference (beta:-0.49;P<0.001).

Conclusions

Intraocularly applied amphiregulin antibody (100μg) reduced the physiological ocular axial elongation in juvenile nonhuman primates.

Safety and tolerability of intravitreal cetuximab in young and adult rabbits

To assess safety and tolerability of intraocularly applied cetuximab as epidermal growth factor receptor antibody, we conducted the experimental study which consisted of groups of adult rabbits (body weight: 2.4 kg) and young rabbits (body weight: 1.6 kg). All animals received three intravitreal injections of 0.5 mg cetuximab (Erbitux) (0.10 mL; 5 mg cetuximab/mL) into their right eyes in 4-week intervals, while the contralateral eyes received intravitreal injections of Ringer's solution. All animals underwent regular ophthalmological examinations at baseline and two-week intervals. Four weeks after the last injection, the animals were sacrificed, and the eyes were enucleated, fixed and examined by light microscopy. The study included 10 adult rabbits (age: 18 weeks; range: 17–19 weeks) and 8 young rabbits (age: 8 weeks; range: 7–10 weeks). Biometric measurements of axial length, anterior chamber depth and lens thickness and intraocular pressure readings did not differ significantly (all P > 0.05, Bonferroni corrected) between the right (study) eyes and the left (control) eyes, neither in the young nor in the adult rabbit group. Signs of intraocular inflammation or fundus peculiarities were not detected. Thickness of the outer nuclear layer, inner nuclear layer, combined outer and inner nuclear layer and outer plexiform layer, and total retina, measured at the posterior pole, posterior pole/equator midpoint, equator, and ora serrata region, did not vary significantly between study eyes and control eyes (all P > 0.05, Bonferroni corrected). The results suggest that repeated intravitreal application of cetuximab did not result in any detected intraocular toxic or destructive effect in young and adult rabbits, concurring with the notion of an intraocular tolerability of cetuximab.

Epiregulin, epigen and betacellulin antibodies and axial elongation in young guinea pigs with lens-induced myopization

Background

To examine an effect of intravitreally applied antibodies against epidermal growth factor family members, namely epiregulin, epigen and betacellulin, on ocular axial elongation.

Methods

The experimental study included 30 guinea pigs (age:3–4 weeks) which underwent bilateral lens-induced myopization and received three intraocular injections of 20 µg of epiregulin antibody, epigen antibody and betacellulin antibody in weekly intervals into their right eyes, and of phosphate-buffered saline into their left eyes. Seven days after the last injection, the animals were sacrificed. Axial length was measured by sonographic biometry.

Results

At baseline, right eyes and left eyes did not differ (all P > 0.10) in axial length in neither group, nor did the interocular difference in axial length vary between the groups (P = 0.19). During the study period, right and left eyes elongated (P < 0.001) from 8.08 ± 0.07 mm to 8.59 ± 0.06 mm and from 8.08 ± 0.07 mm to 8.66 ± 0.07 mm, respectively. The interocular difference (left eye minus right eye) in axial elongation increased significantly in all three groups (epiregulin-antibody:from 0.03 ± 0.06 mm at one week after baseline to 0.16 ± 0.08 mm at three weeks after baseline;P = 0.001); epigen-antibody group:from -0.01 ± 0.06 mm to 0.06 ± 0.08 mm;P = 0.02; betacellulin antibody group:from -0.05 ± 0.05 mm to 0.02 ± 0.04 mm;P = 0.004). Correspondingly, interocular difference in axial length increased from -0.02 ± 0.04 mm to 0.13 ± 0.06 mm in the epiregulin-antibody group (P < 0.001), and from 0.01 ± 0.05 mm to 0.07 ± 0.05 mm in the epigen-antibody group (P = 0.045). In the betacellulin-antibody group the increase (0.01 ± 0.04 mm to 0.03 ± 0.03 mm) was not significant (P = 0.24).

Conclusions

The EGF family members epiregulin, epigen and betacellulin may be associated with axial elongation in young guinea pigs, with the effect decreasing from epiregulin to epigen and to betacellulin.

Dynamic Changes of AREG in the Sclera during the Development of Form-Deprivation Myopia in Guinea Pigs

PURPOSE

To investigate amphiregulin (AREG) expression in the sclera during the development of form-deprivation myopia (FDM) and after the recovery of FDM in guinea pigs.

METHODS

Sixty-four 2-week-old guinea pigs were randomly divided into the control and FDM groups. The right eyes of animals in FDM group were covered for 2 weeks (2 W) and 4 weeks (4 W), or were covered for 4 weeks and then uncovered for the subsequent 2 weeks (6 W). The diopters and axial lengths (AL) in the right eyes of guinea pigs were measured. Reverse transcription polymerase chain reaction (RT-PCR), immunofluorescence, and western blotting assays were used to detect the relative mRNA and protein expressions of AREG in the sclera of guinea pigs.

RESULTS

Before masking (0 W), the refraction and AL in the right eyes of guinea pigs in the control and FDM groups did not differ significantly (both p > .05). Myopic shift was induced in guinea pigs with the diopters gradually decreased and AL increased in the FDM group. While no significant difference was found in control group at different time points, the relative AREG mRNA and protein expression levels in the FDM group were significantly increased in 2 W and 4 W and then decreased after 4 weeks of covering followed by uncovering for 2 weeks (all p < .05).

CONCLUSIONS

AREG was expressed in the sclera of guinea pigs. Moreover, the expression levels of AREG increased during the development of FDM and downregulated after recovery of FDM. Therefore, AREG may be involved in the regulation of scleral remodeling in myopia.

Visually induced changes in cytokine production in the chick choroid

Postnatal ocular growth is regulated by a vision-dependent mechanism that acts to minimize refractive error through coordinated growth of the ocular tissues. Of great interest is the identification of the chemical signals that control visually guided ocular growth. Here, we provide evidence that the pro-inflammatory cytokine, interleukin-6 (IL-6), may play a pivotal role in the control of ocular growth using a chicken model of myopia. Microarray, real-time RT-qPCR, and ELISA analyses identified IL-6 upregulation in the choroids of chick eyes under two visual conditions that introduce myopic defocus and slow the rate of ocular elongation (recovery from induced myopia and compensation for positive lenses). Intraocular administration of atropine, an agent known to slow ocular elongation, also resulted in an increase in choroidal IL-6 gene expression. Nitric oxide appears to directly or indirectly upregulate choroidal IL-6 gene expression, as administration of the non-specific nitric oxide synthase inhibitor, L-NAME, inhibited choroidal IL-6 gene expression, and application of a nitric oxide donor stimulated IL-6 gene and protein expression in isolated chick choroids. Considering the pleiotropic nature of IL-6 and its involvement in many biological processes, these results suggest that IL-6 may mediate many aspects of the choroidal response in the control of ocular growth.

Intravitreal application of epidermal growth factor in non-exudative age-related macular degeneration

PURPOSE

To assess the safety of intravitreally applied epidermal growth factor (EGF).

METHODS

The clinical interventional, prospective, single-centre, case series study included patients with age-related macular degeneration-related geographic atrophy (GA), in whom the eye with the worse best-corrected visual acuity (BCVA) underwent a single, or repeated, intravitreal injection of EGF (0.75 µg in 50 µL). At baseline and afterwards, the eyes underwent ophthalmological examinations.

RESULTS

The study included seven patients (mean age:70.0±12.2 years (range: 54-86 years), with five patients receiving a single injection and two patients receiving two intravitreal injections in an interval of 4 weeks. Mean duration of follow-up was 97±97 days (median:35 days; range: 7-240 days). Mean BCVA was lower at baseline than at study end (1.41±0.44 logMAR vs 0.97±0.12 logMAR; p=0.03). Mean size of the GA lesions did not differ significantly between baseline and study end (29 212±22 887 pixels vs 29 300±22 905 pixels; p=0.59) nor did the mean perimetric mean defect (-10.3±5.9 dB vs 12.0±8.8 dB; p=0.35) or the electroretinographical b-wave amplitude (44.53±31.7 µV vs 64.5±25.5 µV; p=0.12). After a second injection 4 weeks after the first injection, one of two patients developed a cystoid macular oedema in association with an induced incomplete posterior vitreous detachment. It persisted for 3 weeks. Visual acuity in this eye improved from 1.0 logMAR at baseline to 0.80 logMAR at study end.

CONCLUSIONS

Except for one eye with temporary, self-resolving cystoid macular oedema, single and repeated intravitreal applications of EGF (0.75 µg) in patients with GA did not lead to intraocular inflammations or any observed intraocular side effect.

TRIAL REGISTRATION NUMBER

ISRCTN12733334.

Intraocular epidermal growth factor concentration, axial length, and high axial myopia

Purpose

Various molecules such as dopamine have been found to be associated with axial elongation in experimental studies. Here, we examined whether intraocular EGF is associated with axial length in myopic patients.

Methods

The hospital-based investigation included patients of European descent without optic nerve, retinal, or macular diseases except for myopic maculopathy. Using aqueous humor samples collected during surgery, the EGF concentration was examined applying a cytometric bead array. High myopia was defined by an axial length of ≥ 27.0 mm.

Results

The study included a non-highly myopic group of 11 patients (mean age, 72.9 ± 10.8 years; mean axial length, 24.3 ± 1.1 mm) and a highly myopic group of three patients (age, 81.11 ± 12.3 years; axial length, 29.5 ± 1.3 mm), with one of them having pathologic myopic maculopathy. In multivariable linear regression analysis, higher EGF concentration was correlated with the highly myopic versus non-highly myopic group (beta, 1.24; non-standardized correlation coefficient B, 6.24; 95% confidence interval (CI), 0.10,12.4;P = 0.047) after adjusting for axial length. The amount of intraocular EGF was significantly higher in the highly myopic group than in the non-highly myopic group (89.1 ± 40.8 pg versus 34.1 ± 13.2 pg; P = 0.005), and it was highest in the eye with myopic maculopathy (135 pg).

Conclusions

The intraocular amount of EGF is higher in highly myopic versus non-highly myopic eyes.

IMI 2021 Yearly Digest

Purpose

The International Myopia Institute (IMI) Yearly Digest highlights new research considered to be of importance since the publication of the first series of IMI white papers.

Methods

A literature search was conducted for articles on myopia between 2019 and mid-2020 to inform definitions and classifications, experimental models, genetics, interventions, clinical trials, and clinical management. Conference abstracts from key meetings in the same period were also considered.

Results

One thousand articles on myopia have been published between 2019 and mid-2020. Key advances include the use of the definition of premyopia in studies currently under way to test interventions in myopia, new definitions in the field of pathologic myopia, the role of new pharmacologic treatments in experimental models such as intraocular pressure-lowering latanoprost, a large meta-analysis of refractive error identifying 336 new genetic loci, new clinical interventions such as the defocus incorporated multisegment spectacles and combination therapy with low-dose atropine and orthokeratology (OK), normative standards in refractive error, the ethical dilemma of a placebo control group when myopia control treatments are established, reporting the physical metric of myopia reduction versus a percentage reduction, comparison of the risk of pediatric OK wear with risk of vision impairment in myopia, the justification of preventing myopic and axial length increase versus quality of life, and future vision loss.

Conclusions

Large amounts of research in myopia have been published since the IMI 2019 white papers were released. The yearly digest serves to highlight the latest research and advances in myopia.

Compatibility of intravitreally applied epidermal growth factor and amphiregulin

Introduction

To examine the compatibility of intravitreally injected epidermal growth factor (EGF) and amphiregulin as EGF family member.

Methods

Four rabbits (age: 4 months; body weight: 2.5 kg) received three intravitreal injections of EGF (100 ng) uniocularly in monthly intervals and underwent ocular photography, tonometry, biometry, and optical coherence tomography. After sacrificing the rabbits, the globes were histomorphometrically examined. In a second study part, eyes of 22 guinea pigs (age: 2–3 weeks) received two intravitreal administrations of amphiregulin (10 ng) or phosphate buffered solution (PBS) in 10-day interval, or were left untouched. Ten days after the second injection, the guinea pigs were sacrificed, the enucleated eyes underwent histological and immune-histological examinations.

Results

The rabbit eyes with EGF injections versus the contralateral untouched eyes did not show significant differences in intraocular pressure (7.5 ± 2.4 mmHg vs. 6.8 ± 2.2 mmHg; P = 0.66), retinal thickness (158 ± 5 µm vs. 158 ± 3 µm; P = 1.0), cell counts in the retinal ganglion cell layer (3.3 ± 1.7 cells/150 µm vs. 3.0 ± 1.4 cells/150 µm; P = 0.83), inner nuclear layer (46.4 ± 23.2 cells/150 µm vs. 39.6 ± 6.4 cells/150 µm; P = 0.61), and outer nuclear layer (215 ± 108 cells/150 µm vs. 202 ± 47 cells/150 µm; P = 0.83), or any apoptotic retinal cells. The guinea pig eyes injected with amphiregulin versus eyes with PBS injections did not differ (P = 0.72) in the degree of microglial activation, and both groups did not differ from untouched eyes in number of apoptotic retinal cells and retinal gliosis.

Conclusions

Intravitreal applications of EGF (100 ng) in rabbits nor intravitreal applications of amphiregulin (10 ng) in guinea pigs led to intraocular specific inflammation or any observed intraocular destructive effect. The findings support the notion of a compatibility of intraocular applied EGF and amphiregulin.

Optic nerve head anatomy in myopia and glaucoma, including parapapillary zones alpha, beta, gamma and delta: Histology and clinical features

The optic nerve head can morphologically be differentiated into the optic disc with the lamina cribrosa as its basis, and the parapapillary region with zones alpha (irregular pigmentation due to irregularities of the retinal pigment epithelium (RPE) and peripheral location), beta zone (complete RPE loss while Bruch's membrane (BM) is present), gamma zone (absence of BM), and delta zone (elongated and thinned peripapillary scleral flange) within gamma zone and located at the peripapillary ring. Alpha zone is present in almost all eyes. Beta zone is associated with glaucoma and may develop due to a IOP rise-dependent parapapillary up-piling of RPE. Gamma zone may develop due to a shift of the non-enlarged BM opening (BMO) in moderate myopia, while in highly myopic eyes, the BMO enlarges and a circular gamma zone and delta zone develop. The ophthalmoscopic shape and size of the optic disc is markedly influenced by a myopic shift of BMO, usually into the temporal direction, leading to a BM overhanging into the intrapapillary compartment at the nasal disc border, a secondary lack of BM in the temporal parapapillary region (leading to gamma zone in non-highly myopic eyes), and an ocular optic nerve canal running obliquely from centrally posteriorly to nasally anteriorly. In highly myopic eyes (cut-off for high myopia at approximately -8 diopters or an axial length of 26.5 mm), the optic disc area enlarges, the lamina cribrosa thus enlarges in area and decreases in thickness, and the BMO increases, leading to a circular gamma zone and delta zone in highly myopic eyes.

Highlights from the 2019 International Myopia Summit on 'controversies in myopia'

Myopia is an emerging public health issue with potentially significant economic and social impact, especially in East Asia. However, many uncertainties about myopia and its clinical management remain. The International Myopia Summit workgroup was convened by the Singapore Eye Research Institute, the WHO Regional Office for the Western Pacific and the International Agency for the Prevention of Blindness in 2019. The aim of this workgroup was to summarise available evidence, identify gaps or unmet needs and provide consensus on future directions for clinical research in myopia. In this review, among the many 'controversies in myopia' discussed, we highlight three main areas of consensus. First, development of interventions for the prevention of axial elongation and pathologic myopia is needed, which may require a multifaceted approach targeting the Bruch's membrane, choroid and/or sclera. Second, clinical myopia management requires co-operation between optometrists and ophthalmologists to provide patients with holistic care and a tailored approach that balances risks and benefits of treatment by using optical and pharmacological interventions. Third, current diagnostic technologies to detect myopic complications may be improved through collaboration between clinicians, researchers and industry. There is an unmet need to develop new imaging modalities for both structural and functional analyses and to establish normative databases for myopic eyes. In conclusion, the workgroup's call to action advocated for a paradigm shift towards a collaborative approach in the holistic clinical management of myopia.

Myopia: Anatomic Changes and Consequences for Its Etiology

The process of emmetropization is the adjustment of the length of the optical axis to the given optical properties of the cornea and lens after the end of the second year of life. Up to the end of the second year of life, the eye grows spherically. Axial elongation in the process of emmetropization after the second year of life is associated with a thinning of the retina and a reduced density of retinal pigment epithelium (RPE) cells in the equatorial and retroequatorial region, and a thinning of the choroid and sclera, starting at the equator and being most marked at the posterior pole. In contrast, retinal thickness and RPE density in the macular region and thickness of Bruch membrane (BM) in any region are independent of axial length. It led to the hypothesis that axial elongation occurs by the production of additional BM in the equatorial and retroequatorial region leading to a decreased RPE density and retinal thinning in that region and a more tube-like than spherical enlargement of the globe, without compromise in the density of the macular RPE cells and in macular retinal thickness. The increased disc-fovea distance in axially myopic eyes is caused by the development and enlargement of parapapillary, BM-free, gamma zone, whereas the length of macular BM, and indirectly macular RPE cell density, and macular retinal thickness, remain constant.

Ocular size and shape in lens-induced Myopization in young Guinea pigs

Background

Lens-induced myopization in guinea pigs has been used as model for the process of myopization in humans. It has not been explored yet whether the change in globe shape in eyes undergoing myopization is similar in experimental myopia in guinea pigs and in clinical myopia in patients.

Methods

The study included 70 guinea pigs (age:2–3 weeks) equally divided into a study group with lens-induced myopization for 5 weeks, and a control group wearing goggles with no refractive power. The globe diameters were measured using a microcaliper after enucleation.

Results

The horizontal globe diameter (9.19 ± 0.15 mm versus 9.15 ± 0.18 mm; P = 0.25) and vertical globe diameter (9.02 ± 0.11 mm versus 8.99 ± 0.14 mm; P = 0.29) did not differ significantly between the study group and control group. The sagittal diameter was significantly longer in the study group (8.96 ± 0.15 mm versus 8.84 ± 0.14 mm; P = 0.001). While the vertical and horizontal globe diameters were correlated with each other in a ratio of approximately 1:1 (non-standardized regression coefficient B:0.94;95% confidence interval (CI):0.73,1.15), the steepness of the regression lines of the associations of both diameters with the sagittal diameter were flatter (horizontal to sagittal diameter: B: 0.64; 95% CI: 0.44,0.83; vertical to sagittal diameter:B:0.55;95% CI:0.41,0.69). Correspondingly, the ratios of horizontal-to-sagittal globe diameter and of vertical-to-sagittal globe diameter decreased (P < 0.001) with longer sagittal diameter.

Conclusions

For each mm axial elongation in young guinea pigs the horizontal globe diameter increased by 0.64 mm (95%CI:0.44,0.83) and the vertical diameter by 0.55 mm (95% CI:0.41,0.69), indicating that the globe enlargement occurred predominantly in the sagittal direction. Axial elongation in guinea pigs led to a similar relative change in ocular shape as in humans.